AMPEROMETRI

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NONAQUEOUS TITRATIONS OF SOME METAL CHELATES , ,\. _' l'

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AMPEROHETRIC NOHAQUE?J ~ITRATIONS 0; THE .

THENOYLTRIFLUOROACETONATES OF SOHE METALS WITH

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SODIUM DIETHYLDITHIOCARBAHATE AS TI~T

by

. 1

DORCAS MAY-LING FUNG

f A thesis submit ted , , Graduate Studies 'and Research in

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.fulfil1men~ of the re~uir~ents

d~gre'é of Mas ter 1 '.

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artiB.l

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From the Analytical Chemistry Laboraiory • "

under the direction of Dr. G. C. B. Ca~e.

Department of Chemistry ~ .

McGill University • Montreal, Que~ec

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eanada

"ooRCAS MA Y -LING FUNG' 1978 "

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March, 1978

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~~erometry was

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to thè chelate-exchange titration of

metal-thenoyltrifluoroacatone c plexes with sodium diethyldithiocarbamate fi

as' the titrant, in ethano1 and 1:1 (v/v) ethapol-benzene solventa.

The metals studied we e Cu(II), Pb, Cd, Ni and Zn, at a

1 -5 1 ~ concentration level of 10 M; dfterminations of_binary and ternary

~ . ~ mixtures of them were a1so inv~stigated. Both A.C. and ~. C. po1arography

1 ~ 1 using a dr'o~ping mercury' worki~g electrode, and D. t. voltammetq using a

1 • 1

rote:ting platinum working elec,trode were emp10yed for the ampel"ometric 1 1

1 titrations. \ ;," 1

, rl single metals w+re determined vith a precision and accuracy

of 1%. The fo1lowing binary and ternary metal mixtures were aIso

determined with a precision of 1% and accuracy of 1-5% depending on the

systems: Cu-Pb~ Cu-Ni, ~b-~n, Cd-Zn, Cu-Zn and Cu-Pb-Zn. The effect of ;'

, 1

excess thenoyltrifluoroacetone,on the accuracy of the tltrations was also ;'

studied up to a mo1ar ratio of 10:1 for M(TTA)2/HTTA, and found to have

no significant effect:

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Résume

L'ampèr~m~trie fut employé dans

---' chélate pour les complexes métalliques du ~ . . le diéthyldithiocarbaméte de sodium, dans

benzene l:ICv/v) • ., " '.-

, r.

1·

~ l~~' dosage par l'échange de

\1 . . th~noyl~Fifluoroacétone par

~!~~~nol et dans l'éthanol-'-.,

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Le Cu(II), Pb, Cd, Ni et Zn furent étudies il une concentration

" -5 de fO Mi le dosage des mélanges binaires 'et ternaires,de ces métaux fut

,

i ' 1 d ...", aussi exam ne. Les osages amperometr1ques furent effectués par " l' ,.. , l' ,

" ,

,( polarographie en CA et en CD à l'aide d'une/électrode à gou~te de

mercure ou par voltamétrie ~n CD à l'aide d'une 'électrode rotative de

platine. , ,

Les métaux fure~t dosés ~ndividue1lement avec une précision

et une exactitude de 1%. Les systèmes binaires suivant furent do~éJ:

Cu-Pb, Cu-Ni, Pb-Zn, Cd-Zn, et Cu-Zn, ainsi que le système ternaire:

Cu-Pb-Zn. 1 La précision fut de 1% et l'exactitude de 1 il 5% selon

ies cas. \L'exactitude des dosages en présence d'un excedent de

thénoyltrifluoroacetone fut vérifié jusqu'au rapport molaire de 10:1

" ,pour M(TTA)2/(H~TA), et aucun effet significatif ne fut mesuré.

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ACKNOWLEDGEMENT

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1 would like to express my sincere ~hanks to Dr. G.C:B. Cave,

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my research director., for his continuous guidance, assistan~e and r

1 inyaluable training during the investigat~on and the preparat~on of thiâ .

,thesis.

1 thank the National Research Council of Canada for fina~cial

support.

1 also want to' thanlt FY co~leagues and friends who have been

1 helpful and und ers tanding in many ways.

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Finally, l sr, deep~y gratefûl,to my parents for their support,

patience and encouragement during ai! these years.

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AB S TRACT \.---.

ACKNOWLED &MENTS /'

TiBLE, OF C?NTENTS ./ ,

LIST OF ABLES

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TABLE OF CONTE TS , l ,

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" ~ LIST OF

i./ "" 'l, LIST OF

\' LIST OF \ :

\ CHAP,;R ,I \

~::::~ C~TER IV

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INTRODUi

STATEMiT OF

'PRELIMINARY SUR

1 ,\1 ' , 1 PROBLEM AND PLAN ~F RES~R HI

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EXPERIMENTAL 1

A) APPARATUS

1) Cambridge General-Pu Rose'Polarogra [p-.C. polarograms using il dropping me electrode (DNE) ,

h ~or \

2) Cambridge General-Purpose Polarogra h ~nd ~ ambridge Univector Polarograph Unit fa,r

, .. polarograms 1

3) Cambri Geheral-Purpose P61arogr , D. C. polaro ams using a rotating p

!ectrode (R~ "

4) Bé~B Spectrophotometer

5) Leeds and Northrup Potentiometer

6) Beckman pH meter'

7) G1assware-..

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/ B) REAGENTS

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2)

3)

4)

5)

6)

7)

8D

, ,1 hy1ammonium ch10ridè

"" " hy1ammonium hydroxide \ . \,

ch10ride 'tl., \ , 1 (HTTA)

diethyldithiocarbamate

rd metal ~p~utions

t;eagents

1) St ndar,dization of sod:f,'um diethyl ithio­

1 1,

)

ca bamate (NaDDe)

a) Sp~ctrophotometric of NaDDC

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b Amperometric stand J11zation f NaDDe using a DME / \

! ' c Amperometric ~tand r~~zation of NaDDe

us ing a RPE i 1 l tration of metkl~\Tit systems sing a DME 1 ~ 1 <\

i i ) Single metal 6yst s using D C.

, , 1 polarography;' , 1·

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36

3~ ." II

36 !

37

37

38

38

40

40

40

40

43

44

46

46

62

62

62

69

69

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vi) . Effect of exc~~s HTTA' réagent oJo

the accuracy of ampel"ometric titrations of rnetal-'1'TA complexes ih ethanol-benzene mixtures, with a standard solution of NaDDC

" )lr ethanol 69

b) Single rnetal systems usIng A.C. 1l 176 polarography ,

'" i) Cu(TTA)2 76

11) Zn(TTA) 2 76 .. j. ': Hi) Pb (TTA) 2 81

} Iv) Cd (TTA) 2 81 0

V') Ni (TTA),2 81 /

c) Binary Metal sy:stems 87

(' ~ l

"i) CU(.JrA)2 + Pb(TTA)2 87 c

i ii) Cu (TTA) 2 + Ni (TTA) 2 9t Hi) Pb(TTA) 2 + ?n(TTA) 2 94

,iv) Cd(TTA)2 + Zn(TTA)2 100

'\) Pb (TTA) 2 -+ Cd(TTA) 2 103

vi) Cu (TTA) 2 + ~n (TTA) 2 ' Ib3

3) Procedure fot' the titration of metal-TTA uys t,ems us~ng 1 a RPE 105 ..

a) Single metal ~ystems 105 1" \

i) Cu (TTA)2 105

il) Pb (TTA) 2 106

iii) Cd (TTA) 2' Ni{TTA) 2 and Zn{TTÀ)'2 Hf , 1

, . b~ Bina~y metal systems III

1 i

i) Cu(T~TA)2 + N{CTTA)2 111 i ! il) c, Cu (TTA) 2 '+ Pb (TTA) 2' 118 1

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iii) r Cu(TTA)2 + Zn(TTA) 2 118

Iv) Cd (~TA)2 + Zn(TTA) 2 121 1 .~, C.

c) f'ernary metal sys tern l" 0 123

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" CHAPTER V DISCUSSION

A) Prob1ems in nonaqueous vo1tammetry 127

B) Theoretica1'consideration of the CU1;rent-: ,,, voltage curves If ' '- /0 131

, 1 .. C) Titrations' "'t1- 141 "

~

APPENDICES 143''). .. 1

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CLAIMS TO ORIGINAL RESEARCH 164

SUGGESTIONS FOR FURTHER WORK ' 1 165

/ REFERENCES 166

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LIST oF' TABLES )

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TABLE l, ~f{

5 or' -~--,/f----~ - __ 1,1

. ' 1 Polarographically reducihle fu~ctional_ gro~ _______ -.0-

TABLE 2

TABLE 3

TABLE 5

TABLE 6

Standard solutions of metals, /

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Miscellaneous reagents 1

Accuracy and precision of the standardization of , so,dium ~iethyldifhioc~rbamate (NaDDC) in ethanol with

a standard solution of copper in ethanol, by using spectrophotometric and,amperometric procedUres

Accuracy and preci~ion of amperometric titrations of single metal-TTA complexes 'in ethanol and ethanol­benzene mixtures, with a standard solution of NaDDC in ethanol, uSibg D.C. polarography

"t" •

l'he effect of excess HTTA' reagent on the accuracy of amperometric' titrations of metal-TTA complexes with--

- ~

& standard solution~ of NaDDC in ethanol, by uaing. D. C. polarography ~

TABLE 7 'Accuracy and pred~ion oJ dmperometric titrations' of single metal-TTA complexes in ethanol and ethanol-

,,"< b'enzene mixtures 'with a standard solution of NaDDC in e~thanol' using A. C. polarography

TABLE fl

TABLE 9

TABLE 10

, TABLE 11

AccuraCy and precisiono~f amperometric titr~tions' of binary metal-TTA complexes in ethano,1 ând ethanol­benzene"lIlixture$" rith ,a standard solution of NaDDC in ethanol ' i :,f () . ,> •

\

Accuracy and preèision of amperomé'tric titrations of single metal-TTA complexes with a standard solution of NaDDC in ethanol

Accuracy and precision of amperometric titrations of binary metfl-TT.t\ ,~omplexes wit;h a standard solution' of NaDDC in ethanol ,'...- ,

Accuracy and precision of amperometric titrations of" ' ternary metal-tTA complexes with a standard splutlon of NaDDe in -ethanol '

vii ... . . '

39

41

47

74

75'

86

104

114

122

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TABLE).2 Resi'stance of the polsrographic cell for severa!. _. ",, 1." solvents, and supporting electrolyte, measured acros~ : ~~e terminaIs Çlf thé wôrking elec trode (DMÉ or RPE)

~{'p~'~~~"--__ ~~~-;;-~an~~~~~~~~~e~l~ec~~tr~o~d~e~~~~, :'fi~~~~~~=======r~~===-========~It== TABLE 13 Half-wave potentials of Cu. " Zn " .' obtained in waCer aJ;ld in eth'anol wirlh a DME and

O.lM, O.2M Licl a~ sûppo~ting. electrolyte "

-::-----']:'AiLE-......;1~4L Half-wave potentia1s for, the diethyldithiocarbamates o u. ~ Ni' and Zn in two solvent mf~cures, , .~'v~~~~~~ __ ~~~ ob tained with a DME ""J,.

TABLE 15 Results for the s tapdardizat,lon of ~tal solutions in ethanol with a stanllard soluU.on of NaDDC in ethanol by :using ",.an .ampe~ometric proced~te ,

'" ~ J'~ \ t ,

<r---...~_of n -;Values for the polarograp,llic waves of some chelat ng . . tal complexes in ethanol and 1: l (v/v) ethanol-benzene mixture w

.~ O.lM LiC! as 1 the supporting ele,s..trcrlyte

. -- ' ---------- -

'1'''-

154 '

163

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<:V ---~ ---...- • 'jr . ----- ~~~--------------------------,-

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FIGUIŒ î

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LIST OF FIGURES

/

-D.C.po1arograms o~

é) a) 8/'"Quino1:lnOfl!,'/

fi>

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b) 2-.Nl,~roso-l-naphtho1

c) Dipheny1thiocarbazone- -------------- ----

, /

------------------- d)- 1~21Pyridylazo-2-naph~hol (HPAN)

, \

(

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e) a-Benzoinoxime

f) Dimethylglyoxime (DMG)

g) Salicylaldoxime

1 ~) 2-Thenoy1trifluoroacetone (HTTA)

i) Sodium diethyldithiocarbamate (NaDDC) cr ~ ~;

FIGURE 2 D·F!POlarOgram~ of Cu(N03)2~ Pb(N03)~' Cd(N03)2'

_____ ---'N"-'i...,C .... l"12r-· 6H 2 0 and Zn (NO 3) 2 •

FIGURE 3 D. C. polaro$!8IDs of Cu(DDC) 2' Pb(bDC)2' C~(DDC) 2'

, Ni(DPC1~and !n(llDC)2. 0

Page

16

,F .20

20

22

22

26

28 , --------~~'-*-:" FIG~ 4 An 1mperometric tit:ration graph- of a solution of 1]

-:;'iO-~_,~_f metal+pA.N-;i~h a -8o~tion of lO-~ N~DC ,in,...rkt-hanOl as t'itrant. .

• ':\,0 1 --30'

ogr8IDS of Cu(TTA)2' Pb(TTA)2' !

~- A>;-ând ili{TTA~i' -----=::-= _==---=--- - '---,- J

- FIGURE 6--_--a)_::_ Sa-tural:-edcalomel eJ;ectrode---fseE~-~---'--- -- -- ---"'- -

- .32------ 1 ____ _

49

tration _ 8sse1Jlb1y using a DME workifg elec~:_~de_-__ ~ __ ---

/ c) Co1d trap for benzene vapor 51

~'> • Modified burette tip for the Koch microburette /

51 -------=-----

-Jf __________________________ ------------~i~x--------~~-------.. --------

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Page

" FIGURE 7 a) Rotating platinum.electrode (RPE) 53

'b) Titration ass~b,ly using a RPE working electrode 53

FIGURE 8 Visible spectrum of Cu(DDC) 2 in ethano1

FIGURE 9" Typicaf titFation graph of the spectrophotometric

titration of Cu(N01)2 in ethanol, by an ethanol ,>

,1

solutiort i of NaDDC

FIGURE 10 a) , ..

Polarograms of Cu(NO~)<2' NaDDC and Cu(DDC)2 "-

alone and of a titrated solution of 2xlO-5M

-5 . Cu(N0

3) 2 in the, ptese~ce of 10 M excess NaDDC,

with NaDDC in et~ano1 as tiyral}t· f , /. --;-":JI

b) Typical amperometric titratidn ~I)ph for the " t·

standar~ization of NaDDC in et'hQn01 with a

solution of Cu (N03) 2 in ethanol

, '

FIGURE Il a) Voltantiograms o~ Cu(DDC) 2 ànd NaDDC ~~d,ne\ and

, -5

b)

! 1 r

FIGURE \ 12 a}

.of a titrated solution of 10 M Cu(N03

)2 in

. -5 the presence, of 10 M excess NaDDC, with NaDDC

as titrant ~­

Typical ,amperometric titration graph for the

sta~dard12ation if NaDDC in ethanol, with a

standar4 ~olution of Çu(N03)2 in ethano1

Polarograms of Cu(TTA) 2' \ NaDDC, and Cu(DDC) 2

. ." '-5 at~n.e, and of a solution .2~10 M in Cu (TTA) '2

after titTs,Üon with NaDDe in ethanol and

containing lO-~M NaDDC in excess 1

x

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55

57

1·-

59

59

61

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----,... --------..- -- ,-

FIGURE 12 '!» Typical amperometric titration graphs fot"the

chelate-ex change tltration of Çu(TTA)2 in -- , ethanol, with a 8t~ndard solution of NaDDC in f lr ~:

ethanoi"

FIGURE 13 a) Polal;pgrams'of Pq(TTA)2' NaDDC, and Pb(DDC)2

f • -5· alone, and of a .solution 2xl0 M~in Pb(fTA)2 '1 1

after titration ~ith NaDDC in ethanol and , ". -5

containing'10 M NaDDC in excess

b) Typica1 amperometric titration graphs for the '. ,

chelate-exchange titration of Pb(TTA)2 in.

etha~l, with a standard solution of NaDDC in

~thano1 ! FIGURE 14 a) Po1arograms of Cd(TTA)2' NaDDC, and Cd(DDC)2

alone, and of a solution ix10-SM in Cd (TTA) 2

a,fter titration with NaDDC in ethanol and . . , 5'

containing 10- M ~aDDC!/ in excess , , ,

b) /Typiçal amperometric titration graphe for the

ch~bte-exchange, titrat~on of Cd (TTA) 2 in '/ . ,", .....

1

FIGURE 15 a) Po1arograms of Ni(TTA)2' and of a solution

1

-5 2x10 M in Ni(TTA)2. after titration with NaDDC . -5 ~

in ethanol anW containing 10 rM NaDDC in excesi' ,

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J~' 6/V . "qi.

66

66

68

68

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FIGURE 15 b) , 1

Typical amperometric trtration graphs for the ,

chelate-exchan~e titration of Ni(TTA)2 in 1 i lethapol, with a standard' solution of NaDDC in

ethano~

FIGURE 16 a) Polarograms of Zn(TTA)2' NaDDC, anp Zn(DDC)2 -5 .

alone,'and,of a solution 2xlO M in Zn(TTA)2

after titration with NaDDC in athano1 and . -5 '

containing 10 M NaDDe in excess ,

b) Typical amperometric titration graph for the , -~ ~

che:lBte-exchange tUration Itbf Zn (T'l'A) 2 in) • li,

ethanol, with a standa~~ solution Qt~pDDa4~n "~

ethanol

, ,

FIGURE 17 A.C.po+arograms of CU(DDC)~and NaDDC alone, and of

a titl'ated solution of Cu(~A) 2 ~i~h NaDD~. in

ethanol as titrant , , '"

Page. 1.

71

.: / 73

'73 \

78

r"

FIGURE 18 A.C.polarograms of Zn(DDC)2 ald NaDDC alone, and of '<,' 'li

J~" 'a titrated solution of" Zn(TTA) 2 with NaDDC in " .. ,

78 <, •

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80

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----------------------~ '" 1

FIGURE 20 ça-) A. C. polarograms 01 Pb (TTA) 2 Jo NaDDC, and

Pb(DDC) 2 alon~~)-rand ;- • ~ ;. ~ of'

of a titrated solution of

"

Pb (TTA) 2 wit1i lfaDDC in ethanol as t~trant

h) Typical amp~rome~,ric titration graphs fot: the

"'" chelatk-excnari~e titration of Pb(TTA) 2 in " ,"' ....

eth'anol wl~h a standard solution of NaDDC in

ethanol by usfng A.C. polarography

. FIGURE ,21 a) A.C., po1arogra~~ Cd(DDC) 2 and NaDDC alone,

, 1-

and 01 a titrated solu~io~~f Cd(T:A)2 with

NaDDC in ethanol as titrant

b) Typ~cal amperoml7tri~ titration graph for the ,

chelate-exchange titration of Cd(TTA)2 in

ethanol with a standard solution of NaDDC in - ,

ethanol by using A.C. polarography

I! ,FIGURE 22 a) D. C. polarograms of a mixture of Cu(TTA) 2 and

Pb (TTA) 2 before and after titration with NaDDC

in ethanol as tit~pt

-, '

b) Typical amperolQ~tic titration graph of the

mixture of Cu(~TA) 2 and Pb (TTA) 2 in ethanol, r

" ! with a standard solution of NaDDC in ethanol

FIGURE 23 a) D.C.po~ar~gr~s or a mixture of Cu(TTA)2 and

N~(TTA) 2 b~fore and after tit~ation with NaDDC

in 'ethanol as titrant fi

, " xiii

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. Page

\ 83

83 '

85

tir 85

89

89

93

,

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1 FIGURE

F23 b) Typical,amperometdc titration graph of -the

mixture of Cu(~TA) 2 ~and Ni(TTA) 2 in eth~nol!

with a standaId solution of NaDDC in ethanol '""" ';.:

FIGURE 24 a) 'p. C. and A, .. é. pOlardg,rams of' a mtxit~re of J p~ ~~1 ~.~ > -

Zn(TrA)2 and Pb(TTA)2' rifter titration 'with \ ,

NaDDC, and D.C.po1arogram of the mixture

before titratiQn

b) , TYPtca,~ amp~rometric titration graph of the

p mixture of" ~n(TTA) 2 and P,b {TIA) 2 with a

standard solution of NaDDC by using A.C.

a ~oL~raphy , -

F~GURE 25 Red'dual current tor., an A. C. polarogram of a

"'sô'tution of D.lM Lié1 in ethanol and in 1:1 (v/v)

FIGURE 26

i ~I

1

- 1

i , l' i

, ethano1-beqzene mixture, using a 'D~"

a) D.C. and A.C. polarogram of a mi~ture of

b)

l'

Zn (TTA) 2 and Cd(TTA) 2 after Ùtration vith

NaDDC, and D.C. po1arogram of the mixture

before titt:atijn r Typica1 amperometdc titration graph' of the

mixture of Zn(TTA) 2 and Cd(TTA) 2 w~th a

stanqard soÎution of NaDDC by using A.c.1 1

pO larog r aphy

,

.rage l'

(

93 ! ~: t~< ,1

, 1

97

1 , ,

97

99,

102

t " , "

c

FIGURE 27 a) vdi~~mmograills at va:dous ~tages of '!-~< ~-

5' , titration of 10- M Cu (TTÀ) 2 with N~~,C in

FIGURE 28 .,.....

\ ethanol as tftrant

b) Typical amperometr1c 'titrat1on graphs o'f

a)

b)

;'

Cu~'ITA) 2 with a standard solution of NaDDC

in éthanol

Volt~gram of a titrated solution of

Pb\TTA) 2 Wit~ '. aDDe tittant and' containing as , "

excess NaDDC ,

Typical amperom titration graphs of

! ~b(TTA)2 WH)' ~ andard solution! of NaDDC ;'

in ethanol \ '~ tt, '

FIGURE 29 a) Voltammogram o~ta titratéd solution of

"

. /

Cd (TTA) 2 with NaDDC as titrant and containing

excess NaDDC

b) Typical amperometric titration graph of )

, Cd (TTA) 2 W1t~ ~~a standard sa lu tion of NaDDC -% ....

in ethanol' "~

-;-: -------.. Il FIGURE '~o' a) VoltannnograIl! of a titrated solution of a

t

f ; , , \

),

. l "t.

m~ture of Cu (TTA) 2 and N:~~TA) 2 wi.th NaDDC

id'ethanol as titrant an~ containing exqess

r, NaDDC

b) Typical amperometric titration,graph o~

.mixture of Cu (TTA) 2 a~d Ni (T'1:.Al2 with a

standard S()lU~~Oï 'Of NaDDC' in e/thanol

xv

Pag~

1108

JI.

, 108

110

110

113

113

117

117 '

'"r; '.' i· '

" e l

\

(

~ .. , '

C . ' ! \.J~ .

" ."

i ;-,

• , (

-

(

l '

FIGURE 31 Typica1 amperometric titrati~n graphs of a

FIGURE 32

FIGURE 33

FIGURE 34 - .. }.. .. . .

. -5 ~ixtU're of Cu(TTA22. and Pb(TTA)2 t eac~ lO'~M,

with a standard solu tion of NaDDC in ethan 1 .1' "

, 1

Typié~l amperomet,tic titration graphs of 'g -5\

mixt:ur~ of Cu (TTA) 2 and Zn(TTA) 2 each 10 z:t,

with a standard solution aI NaDDe in ethanol

Typica1 amperometric titration graphs of a li?

" , mixture of Cu(TTA)'2' Pb (TTA) 2 anp Zn(T~A) 2' each

-5 10 M,- with a standard solution ,of NaDDC in

etl\anol

a)

b)

1

D.e.polaragrams pf Pb(N03)2' 1

beforej-titration,

1

~nd after titration with NaDDC in ethanol as

titrant,

Typical

1 , '5 and having 10- M NaDDC in :excess

1 1 •

ampetometric :titration 8ra~h of the r 1

1

~. Pb (NO ) with a sta,ndard solution o~ ~-, _ _ 3 2 \ NaDDC

~";'. \1 ~. " ,in ethanol

r

FIGURE 35' a) D.C:pO'laragrams of Cd(N03

)2' before titration,

r

and after titrati6n with NaDDClin et anol as

\ -5 ~itrant ~ and having 10 M NaDDC in e cess

b) Typicd! amperometric titration graph of the

Cd(N03)'2 with a standard solution of NaDDe in

ethanol

xvi

-- \/

Page ·f '

. 120

120 ., . '

125

147

147

149

149

(.

(

o .:::

-~.,,, 1/

f , r

f

, ' ~ .' !

, , '

'"" FIGURE 36 a) D. C. po1ar~;rams of NiC12 '6H20, before"

"

FIGURE 31 - *1

titration and after titration with NaDDC in

J! '-5 .ethano1 as titran~, and having 10 M NaDDC in

excess , Typical amperometr,ic -titration graph of the - ~-(, , r\. Niqf2.6H

ZO with a s tanda~.9 ~oluti4n of 'Na~DC

,"

• in ethanol'

a) ,D.C.polarograms of Zn(N03)2' before titration

. and after titration with-NaDDC in ethanol as 1 ri " • .

-5 -titrant, and having 10 M Na~DC in ~xcess , b) , Typical amperométtic tÙration graph _!lf the

Zn(N03

)2 with, a standard solution of,NaDDC in

ethano1

FIGURE 38 A pl~t -of log id:i versus E to -test for

reversibi1ity of the anodic wave of NaDDC' ln 1 1')

etl1aJo1 .

, f

. xvii·

Page

151

151

153

'153

,162

J

1 !

J , ,

~:

.. f

'1 , ! "1 ., '

f

! 1 , 1

1

c

APPENDIX l

APPENDI~ 2

,~

APPENDIX 3

,

. APPENDIX 4

( :APPENDIX 5

1 1

, , ,

r. ,

(

t, '. , ;

, . ..

r- i - ,--~ - .

1- "... (

'{

\ Standardization 0 M tal Solu ions, ~ing

Standard sOlulion of NaDDC in Ethan ];-

Care and Pretreatm n of the

ElectrFde ~ Preparation of the

" . 1 •

Polarographic De te 1 1 a1 Cd(DDC)_2 in Eth nel and Ethan -B nz~, ••

lM J tur;,~s ,

P lepa.k~tion of the' Calibratio:n

Spectropho~ometric Determination

the ;'

f u(DDC) 2' 1 1 , ~ ,

1'~s~ for Reversibility of thé Ele

.at thE7- DME, of the chelating Ag-efr.t ~ -Chélates use/d in the Presen Work

~ 1. 1 ,

-

xvii! ~ ".

ons

•

\

..

Page

157

"

159

1

, ,

Il '

l (

, ' ... , '

'. ,

"' 1

(

( 1 "-

1

1

l'

l,

; 1

1

/

..

Et4NCl

Et4N'OH

HTTA

NaDDC

DMG

HPAN

DME

RPE

SCE

HDz 1

EtOH

! 1 ,1

, ! -r .-1

LIST OF ABBREVIATIONS , J.. ~,

~.

"

,

te~raethrlammonium chloride '. ~ ~... 1

tet;~ethy±~onium hydroxide

2-thenoy l t rifluoroacetone

$odium diethyldithiocarbamate

dimethylgl'yoxime

1-2-py~azo-2-naphtho;:, ,

droppiIl;~ Mercury ele(ctrode

rotating platinum electrode' "';" ';t ..,'r "1} ~,

saturated {calomel elec~rode

isobutyl methyl ketoné': ", . ., , ,.

1

,

di pheny 1 thiqtar~azone (di.-thizrne) (

ethanol

benzene ::"" ..

r

,/~ -\

, 1 ., ,

... -;:

xix

, 1

,

. " . "

, '.... ~

1 "

(

,"

1·

;:\ C '.

1 'l,

{'

"

(

1. INTRODUCTION • -<, .0'

"

.... Solvent extraëtion of metals by chelating- agents ,;ls a wi~ely ,

used anatytical technique Jor the separafrô1\ and concentrad~~n of minute

amount of metal contained'in a sample !g~. .;; 'Z'"

extensive (1-~.

The ~iterat~re and mono-c '

graphs in this area a~e very !.

Arter the extraction, the metal chelates in the n{snaqueous }

" layer are usually determined by one of the fol1owing techni~ues: (1)

dir.ect colorimetrie détermination of the nonaqueous layelj,;f"(2) evaporation ~ 11 dl

1 ,;. :1'

of the nonaqueoüs layer ,followed by decomposition of thé m~tt~l chelates; "

··and the metai then det~~irted b'Sr some conventional method; (3)' re-l

extraction of the metal into an aqueous phase and determination by an

e1ectrochemical method; or. (4) radiometric tecnniques. r Î

Direct titra tion of the metal chelates in .the

1 "r 0 ' layer by a~standard solution of another chelating agent in a

solv1pt offe'tos another direc~~ lN,!lY. of det~rtnini_ng the m~tal This {

method was proposed and d~veloped by IGrey and Cave (7), who caU d it

" ,chelate-:-exchange titrimetry. They titrated metal;.!~-q.~il1olinates .. dithizo~e. and metal dlthizonates-with sodium ~.

They -fol1owed the course of the titrÇl.ti~n 'by speclt~,~photometry, in which

the absorbance of the meta! chelate formed or reacted during the titration

was measured. Formation • Î

were also determined:

1

,. of the chelates and'fuixed chelates

-­"

"

,,,

\ '

(

"~'

~'

" .

..

."

J

o .. \

~

MX2 + HY

MXY + HY

KI .. MXY

K2 = MY

2

,J

1

-," ';'

+HX

+HX

. (

whère M is the metal, and HX and H'!V are the chelating agents.

This method was e~tended by d'Amboise(8)-Who studied the o

"

titration of 2-thenoyltr~fluoroacetonates (H17A) of some metals, using

l-2-pyridylazo-2-naphthol (HPAN) a~ the titrant. Barroso (9) studied the

1 . 1 effect of mixed solvents on the Cu(TTA)2 + HPAN system.

The present work is another exteRsio~ of chelate-exchange

titrimetry. lt i~ an exp]oratory study of the poss!bility of ~mploying ~I'

voltammerric techniques to follow the chelate-exchange titration, and

hence the quantitative determination of

extJacted . nonaqueous phase. . '; .

- ," the metal chelates in the ,. ,

->.

Kopanica and Stara (10) applied polarography to det~rmine the

end poirtt in chelometric titrati~ns 3f sorne metais ~ith triethyl~netetr ~

Î

hexa-acetic acid (TIRA). 'The diffusion current either of thé.métal, the

metal complex, or the excess complexing agent .was followed. The .'

were carried ou t in an aqueous medium. \

Use ,of electroche~icàl methods for ~he determination of an

f'

extracted metal ~sually have prescribed the prior re-ext~action of the

"

~.

~

metal into an aqueous phase, in order tO~àvoid the"low ~lectrlconducti~it [ i

of thv~~na~u~èus sOlvents. \ .,

terna mi~ture' as 'a solvent 1·

/

Fujunaga et ~1, (11) proposed thè use of a

in polarographic analysis: the organic

, ?c-_.

" 1

J ' 1

• ...J -

..

.'

----3

o

---.:-==----:~~ -'. - ---~---fl

(

(

---was diluted with an aqueous solution containing the supporting-electrolyte /

and another mediating liqui~ to produce a homogeneous phase.

'" Th~present :ÏdY \~ropo:es the use of benz~;~ as the ol;"ganic

°soIv=e-=-nCC;t~w"'h""1~ch ex tracts tne--~.Çhelates, after which the organic phase . \ ---------

~ ,

~esulting mixture is then ti rated directly by anQ~r chelating agent

ls diluted with ethanOlfcontjining the suppor~i~ectrolyte. The

in Ethanol. The titration i monitored by measuring the diffusion current

. either of the initial m.ta~ ·Jh';;'~te. or he';"Cha~ Metal che1a~;:- ~~ ~ the exeess ehelating agent •. Jhe ehoiee dependf 0 on the nature of the .

sys..tem. 1

1 l 'W 0

The procedure doesfnot require re-extraction or evap·oration.

Therefore the time requi~ed 10F an analysis is shortened. The possibility )

ofi determinin~binary or 't;Î~ mixtures of metal ionsqby this procedure

was "also investiga ted. A / ......-------- - . 0 1"

1

/

o ---~---------------

/

" ' 0'

i ' _ ........ -..-.---".. ..... ~ -- - .--,.-.......--..-...-_._--_.

r ' i !

, '

1

---------------------------~

/

. , :.

( 1_~

,-, ;

(

l' '.

"

J 4

II. STATEMENT OF THE PROBLEM AND l'LAN OF RESEARCH t.

The purp?se 'of, this work i8 to inves tiga te and develop analyticai ' ~

procedures for the amperometric titration of metal chelates in organi~

solvents, by ùsing another chelating agent as the titrant:

/.... 1 ,MXn + nHY = MY + nHX

n

Thè intended application of these procedures to analytical chemistry ;1s " ~;' l,

the quantitative determination of metais in an organic phase, after<th~ir

separa~1on by a sOlvent-ex/raction step.

•

, .. , ,

~ __ . .TlLe~tudy inv~lved two- aspects: (1) po1atography of organic

compounds, specifical1y che1ating agents and ~etal chelates, and (2)

polarography 1n organic solvents. 1

1

Since the introduction of polarography as an analytica1

technique, there ha.s been a considerable application of it to organic . '

'analysis (5, 12-18, 42, 44). Functional.groups shown in Table 1 (16) ..

Many of the counnon1y_.us..ed_~telLContail)."polarographical1y 'l ~~ ..

reduèible functiona1 groups. The~efore, they woq1d be ~xpected ta give '. , .. ,

p1larographiC waves which might be used in the present work-: Sorne of the

work :a1ready, reported in this ar~8Tncludes: polafographic reduction of ,,"

/8-qui~plinol, by Stock (19); porarographic characteri~tics and controiled-

potential electroreduction of dimethylglyoxtmé, by Spritze~ and Meites ft - '" <6 ::t" { '.

(20); ~he an~ic waves of dia1ky~Jthio~arbàmate~ by Halls ,"·To\mShend and

I~ 1

o ,

o

!<

1·,

','

~ ", " . ~~~

1

~

Ji/ t, " . , ~f ,

C

,. ~,

/

/" '/'

-J-

.. J/'t

5

"

/

Table 1 Polarographically Reducible Functional Groups 1

C6HSC = 0 CHa CX -NO

n 2

C6H

SC = C C = N- C

6H

SX -NO,

f

,-.

C6H

SC 1 ~ .

-C =N C6HS

CX -NHOH 1 - 1

C = C - C = ç' -N II: N- -ONO , l'

C = C - C = d C = C - C = 0 -0-0- ~ 0 = C - CX -ON02

o = C - C = 0 -s-s-I ·-NO -~-

Heterocyclic ~ouble bon~ Polynuclear aromatic ring system <

Il , .

/

7 . - ~, ,

"

'II

/

(

(1

\ , \ .,

,(

/

/

/

- 6

Z~man (2~); thr polarographic .behavior of, thenoyl trifluoroacetone etc.,

by Elving et al (22).

,The metal chelates titrated in the final syst~s of the present 1

work were those of diethyldithiocarbamate and thenoyltrifluoroacetone. -_ .... -

Diethyldithiocarbamate forms stable complexes with many metals, and it

was found ta give an'an~dic wave which did not Interfere with the wave af

1 the metai complex of thenoyltrifluoraacetone which was the chosen analyte.

'The literature cited above mainly covers polarographi'c behavior

in an aqu~ous solution or in a mixture of an aqueous and a nona~ueo~s . ' Il.

solvent. In going from an aqueou's to a completely nonaqueous solvent,

sev~ral parameters are affected. The solubility of the supporting

electrolyte, purity of the solvent, polarographic inertness of the solvent

"'~ith reference to 'bo~h oxida~ion fact~to be considered. 1

,1 ,1 The <:<Ymmonly use'd organic solvents fall into one of the" ,.

-,' ~ , ',,"

following groups: (1) solvents such as alcphols, ethers, polyethers, j , /

l' ~-ketones and esters, (2) nitrogen-containing solvents such as amines, ..

, ,

... '-- . diamines, polyamines, ethano.lamines i pyridi~e, hydrazine, nitz:iles and ----------,...-- ,

, , amides such as formamide and'acetamide, (3) solvents which , the lower aci

are acids, fo example, acetic aciç and form~c acid and (4) mlscellaneous l ' . , ~

sol'-l~nts such as hydr~carb9~s and the~~ deri~atlves. The literature on

polar?grap~y- n orga~ic solvents ls extenstve (23-33). ~

(A)

The study in the present work are:

Titration f metal 8-quinolinates in ethanol-~~nzene. wlth radium

JiethYldit. iocsrbamate disaolved in ethanol as the titrant.

... ,l' "

/

/ Q

(.

/

t

(

( "

" ;'

.. / .' 7 ...

l' ... "-

" ,

(B), Titration of metal-PAN* complexes in ethanol-benzene, with sodium 1

- l ", titrant. diethyldithiocarbamate in"ethanol as

(C) Titration of metal-TrA* complexes in ethanol-benzene, with sodium

diethyldithiocarbamate dissolved in ethanol as titrant.

These systems ~ere chosen because:

""- (J); The chelating agents are in wide analytical use because they forro

stable cO~Plexes with many met~ls. f • f "',1

A.;~ > .:t

(2) Sodiury diethyldithiocarbamate Itself has an anodic wave,. a~~

therefore "­'-'~rving

'-...

leaves a large cathodic potential range available,for , , ' 1 - ~'

the reduction waves of the metai chelates. -,( ~~

(~) Some m~~ 8-quinolinates and metal-PAN complexes are eolored while

their corre 'diethyldithiocarbamate has no absorption in the

visible region, , allowing a vieuai de~ection of t~e titrat~on.

(4) Sydkem C h&s been studied b d t Amboise(8), using a spectro-

photometrie technique. compare. the two

analytical techn~ques in the chelate-exchange system: , ,.

An et;hrnol-benzene mixture was eh'o,sen as the BoIvent because

both benzene and ethanol can be readily obtained in a pure form. They

are arao polarograpbically inert over a brge pd~erntia1 rans.e. Benzene 1 ,

1 - I b-ca~ ~e used to extract the meta chelates. Ethanol 1s misei le with ~

ben.te \ d Us sddit~n ~ us_fu1 r~r dis,olving inorganie ,a1ts: n..;.i~y \ .

Hst of abbreviation 18 on pag~ xix •. ~

the' anion of 1-2-pyridybzo-2-naphthol,' and Tl'A 1a the anion of oyltrifluoroacetone •. Henceforth. the abbrevlations will be used,

for co~venienee •.

, .

III

, , 1

/

. ,

. " >.

(

(

(:

III

j f"

8

1/

'. ,

,1

{' ,

" the s~pporting electr01ytes used ta minimize the migration current,of e j' -; 1

-..1"­i' -

species being reduced at the working el~ctrode. , 1 The fo1lowing factors were also studied during the course of

deJ;erm;lning the precision and' accuracy of the tit};a,t:lo}'t: .~~ - .. 1

/

(1) E.ffect of the supporting electrolyte, s'peéifically !ts nature and , ," concentration. ..

(2) Effect of buffering, or pH of the system.

.' '('3) .Effect of the solvent ratlio. Pure ethanol, 2:1 ethanol-benze~e,

1:1 ~thano1-benzene, and 1:2 ethanol-benzene sb1vent mi~tures were

(4)

studied for some systems. \.

Effect of excess initial cheiat~ng agent. For example, in sys tem ,

.' C, the effeet of an excess of HTTA'on the precision \ 7, '.' 1 .the titration.

1 . / \.; and accuracy ot: j

, rr

, 1

A mercury pool ~lec'trode was used as the reference e!ectrode in

some of ~the systems during the preliminary 'survey. However, a' 'saturated )0 1 ; 1

1 1. . calome! electrode.(SCE) was used in the final titration systems.

-' ~, "'1

A dropping mercury e!ectrod~ (DME) was uèed !pitia11y as the j'-~o- ~ ,.~l '4f!I'"

for obtaining D. C. poiarogram~' (if the\netal chelates and . i " '" carbamate. In some systems, an A.C.sensitive component

improved resolution and sensi Finally, the use of a rotating . 1

platinum electrode (RPE) was alsof'4.hvestiga

]'

The end po~nt w~s obtained from \.,r- .'

graphs either by visual detection, or by a least-square

j"

/l

1

'1 1

/,

(

'l

! 1

'.

, ,/

<-' .

1

'"

1

r

9

" ); -J, '.

Single-meta} systems were studied., In addition, by usin~

amperometry in certJin systems, and a combination of amperomel::ry and , J

spectrophotometry in others, the inv~stigation was extended to Qinary 1

and ternary metal m,ixtures. ~ /' ~

" . AlI voltammograms were recorded and titrations were carried

out at room 't~mp~ratùre 1 ~

• 1

"

-e 1 '

\ 1 -,

+ 0 1 (25-0.5 le) .

('

~

/ /

,

7

\

II·

r

J,

J

, , l, : 1

". i '

1 ~ 1

1 b

r j

t

J

(

" 1

(

\

C', ,

_._~. \, 1

"f

J,.O 1

Ill. PRELIMINARY SURVEY ('

The polarographic b,havior was studied of several che~ating tl

agents that ~re extensively used for the solvent extraction of metals (3).

" In addition, t~eir chelat'es of sev:eral metals were similarly studied, as . )

well as nitrates ,or chlorides of· these metais. The solvents were

ethanol 1 ~~.

and ethanol-benzene mixtures. The polarograms were recarded at

25°C ~IO.5°C. The purpose of the study was to select one or two chelat­

ing agents and metai chelates that had convenient'polarograms, for late~

detailed studies.

r The chelating agenl-s studied were: '~-quinolinol (oxine) ~ diphenylthioçarbazone (dithizoné), sodi~m diethYldithioca~bamate. J.-

l'

thenoyltrifluoroacetone, 1-2-pyridyla:to~2-naphtho'l, 2-nitroso-l-naphthol, 1

• • ) , f a-benzoinoxime (cupron , dimethylglyoxime, and salicylaldoxime. Their (

polarograms are shown in Figure 1 a-i (see p. 15).

Next, polarogramt:i of Cu, Zn, Cd, Pb and Ni nitrates or,

chlorides were ob tained in e th,anol, and in e'thanol-ben:tene mixtures. l,· q;

They are shown in Figure 2 a-e. These are metais of ànalytical interest,

since the'quantitative determination and separation of,one fram the 1 1

o~hers a~e often neceèsary,. . f .( The diethylditbiocarbamates of Cu', Zn, Cd, Pb aq.d Ni were'

stt,tdied next. They were obtained by mixing in a 1: 2 molar ratio a . " ~ ,

standard solution o'f the met,al. in ethano!, with a standard solution of ( • D

sodium diethyIdithiocàr:bamate in eth~nol. Theit-, pqlarograms ',are shown

in Figure 3 a-e (see p. 27.)

r In addition the polaiogra~ of the 1~2-pyridylaz~~naphthol

complexes of those mixtures w~re also recorded. ,/

. (

, /

/ 1 ,

/

1

. ,

/

(

(

(

.. , 11

Il

Some of' the waves obtained w;eI)e found to'be irreversible (for

the determination of th~ reversibility of the waves, see Appéndix 5). \

,Therefore, "starting potential" will hé used instead of l''half-wave 1

~ '1 potential" in the following descriptions.

As a result 'of this preliminary screening process, the meta!

chelates of oxine, sodium,diethy~dith~ocarbamate, 2-thenoyltrifluoro­

'acetone and' 1-2-pyrfdylazo-2-naphthol wer~-c~osen for further study.

The sodium diethyldithiocarbamate was tentatively chosen as the titrant

1 for the proposed amperometric titrations. The following systems were

investigate~ with respe~t to the chelate-exchange reactions that occurred

in them:

-CA). Reaction of the oxlnates of Cu, Zn, Cd, Pb and Ni wUh sodium

diethyldith1o~arbamate in an ethano~-pe,z~ne ~lxture. The extent 1 l_

of the reaction \l1as followèd by measu;ing the anodic curr1ent of the

diethYldithloca~bamate.~ ft was found that the reaction either

proceeded very S~oWly,. ï eise the metai oxinates were 50 stable

,-

that ~e oxinate ion cannat be replaced by the diethylditpiocarbamate

!Qn. This ~ystJm 'waal therefore abandoned.

(B) Reaction Of the CU/Pb, Ca, Zn and Ni chelates of 1-2-pyrt!dylazo-2-k, "

naphth~l,' ,with sodium 1iethyldithiOCB:r~amate ~n an (eth,a~ol-ben.zene

mixture. The reactio~ was observed t~ proceed rapidly, as evidenced

by the change of col~~ in the reaction mixture as the, titrant was

addèd,' (the metal chelates of 1~2-pytidylazo-2-napllthol are -highly . 1

coloréd while some metal~dietb;ldithioJarbamates are colorIess).

"

/ .

, ~ ...

\

, 1

(

~ ( 1 •• ,

" 1 ]2

Unfortunately, however, the reduct,ion 'wave of 1-2-pyridylazo-

2-naphthol occurred in the region where the metal chelates were

also reduced. Since in a normal

, chelattn~ resgent in the organic

would not be a very practical procedure to use, The amou ~

chelate can in thi~ case be determined by ~asuring the e

titrant added', Le., by measuring the anodic current of the \

f

diethyldithiocarbamate. However, this method would nat be selective,

in that only the total metai concentration would be determined, .

whéreas a PifPose of 'the present work was ta titrate sequent~ally

two or more metal chelates, A titration graph ois shown fn Figure 4."

Study on this system'was discontinued at this point. Neverthe-

less, instead of an amperometric titration, a spectrophotometric

titration of this chelatE!:-exchange ,reac,tion may be feasible. r

(C) Re~ction of Cu,' Pb, Cd, Zn:an~ Ni 2-theftoYltrifluor~acetorates 1

-(M";TTA) with' sodium dlethyldithiocarbamate (NaDDC). Polarograms of

metal-TTA complexes are shown in Fi~ure 5 à-e. The titrat10ns were ,,' 1

followed either py measuring ehe decrease in the polarographic 1 ( l "ï '

current of the metal-TTA complex, or use the-incre~se in tne current

of~the metal-DDC complex, or the increase in thé anodic current of

i h ,l' NADDC w en this titrant was added,in excess. ,

~ DME was used as the warking electrode fot~ost systems. <;,

H~wever. for c,e:rt~in systems, the RPE was used. In both cases, a

satu~ated calomel electrode (SCE) was used as the reference eleet-i

rode.

, ) , "

, ;

, , ,

(

(

c.

1 r '

';

13 , 1

'~.

The reaction rates of the metal-TTA complexefo with NaDDC were

found to be faàt~ , ~--Moreover, the~e was little or no cur~ature

of the ',titration graphs, showing that therè .... a

r re1atively large equilibrium constant for the exchange reaetion.

,-

Therefore this pa.rticular syste$,- namely metabJI'TA complexes with

, :tjaDDC as titrant, appeared promising for the practical application 'f

of amperometry. Consequently, .it was s tudied in d~tail, p{lrti~ularly "

an investigation o~ the accuraey and precision ofi'the procedure. 1 - fi':"

: ( . 2-Thenoyltrifluoroacetone was introduced as an analytie~l

ographie ana~ysis. He studied both the spectrophotometrie and the

polarographic beh~vior, as weIl as the dissociation equilibr~a of r . solutions of various pH values. the reagent in buffered

~t forms.chelates with many meta!s and it is a valuable reagent

for the solven~ extraction of many meta! ions. A summary of RTTA

extraction ~oe~ficients in b~nzene was giy~n ~~ P9skan~er and

Foreman (34).

1 Most metals form stable complexes with NaDDC. T}le reagen.t was

first introduced-by Delepine (43) for the determination of copper.

r -

- f

,

,- j

• !

'.

/

/ t'f ... t

/

(

-.

: /

1 !

1· 1

14

\

Sodium diethyIdithiocarbamate ia one of the best known organic

reagenti ~hiC~ for:m c~elate~ with m,~a,n .. :-y-meta1,~ (36). It forma \!

co,lored complexes with severa1 meta1 ion8,- for examp1e bismuth, . 1. c,'

copper, coba1 t, nickel and iron. Hulanicki (45) reviewed the, 1

complexation reactions of diethyldithiocarbaptate,' and also the , ~ .. ~

c01Dposition and stability of its V,arious metaI complexes. Bode

/':(_ (35) publis~ed works on extraction of me~als using NaDDC. J. . "t \ '

Stary

: and K~atzer (37) determined the, extraction const:aÎtts- and ~... Jf ~ ~"'! ....

1 ... r st'abf.1ity order of some meta1 diethyldithiocarbamates.

~:<

also the·',

, l" .

Halls. ~ownsÎend and Zuma~ (46, 4 7) ::~udied the pola.ro.graphic

, behavior, of some sulfur-containing comp.ounds inciuding the .mono- . r •

alkyidithiocarbamâtes and ~U.alkyldithiocarbainates and their heavy

metai .cQmplexes. Polarographic determinations of sorne metal-DDC ,', ...... \ "" ... ~

, were done in a 1: 1 methanol-ben'zene mixture (48),'

.1

o

""

4',

Il -,. ... ,

l'

o

\

.. ,

/

, 1

Q. / ..

.1

, a.

·b.

(.

\ ,1 ", i

\

C· 'r_

-.~ . . ..

.. 1

15 '

l ' p

, 1

1

FIG.l I~ 1

D. C. polarograms

8-Quinolinol', initial pH':' 7.2 . , l "

2-nitroso-l-naphthol, initial pH: 1 ".0

\

• 1 .... -.F' ...

• 0 S;upporting ':,. ,0 "\M Et_4 Ne,l " lec~trolyte , \ '

Sol_vent (' E"thanol

Electrode D.M.E.

/

/

\ .

\ .. 9 '

\ \

o'

\ \ ,

-i'~,,<

/

, 1

\ "

1·

\ "

" -1 '.

~

f.'

J '

. , " .. .'j,

> •

.\ "

, i , .

-. , ' . \

\ .

'1

r 1 - - - - , -~ _.,

1 ~

'')

f "\ -J ..

>6 ____ -/

0. r' ,1 o~FIG. '::1' :

'" (d) :'

1 OH "

. , ...... Z w l 5 !X 0. 0:: 0: J

~u

1

i· " 1

.';l '. ;:,. i'"

" l if/. , ~~ '1 0

~

ï'

1 ' , , ~

0 OA 0·5 0.8 ~'

" ,(." ~, ~,

/- }/

( ,/

.. Cb' ,OH' . NO' ./

"

,1

\ ; , .. • ,s

l 5 J.L (), r

~

.. 1

-l' D 0.6 b.8

..- ,

, 1 1

1

.. , -,---

1

16 "

0 ,. /

1.0 1.2. 1.4 1.6

-E \ . (VOL.,TS)

.' .....

:"-' -'

1.0 1,2, '.4 1.6

. .~ E (VOLTS)

1.8

'--- . ,

2.0

."5 SC E " .

')

D

.' , .

''/ s SICE

'"

\ ')

.-

1· ...-

, i .

1"1,

) 1

-',

(

c.

d.

r '

1

--'

/

17

'FIG.l

D. C, olarograms

lO-3M Diphenyl th' ocarbaz.one, ini tia~ pH: 6.8

lO-3M l-2-Pyridy azq-2-naphthol, initial pH: 7.0

Supporti g : ,O.lM Et4NCl electrol te

Solvent Ethanol

Electrod : D.M.E.

- • 1

, - , /r

1

"

, ,

,1

....

.'

r " \-

, ),

, \

(

1 : ,"-r t !

',î

l ,

f ( ~ ,

r i

J

" ; 1

FIG. CC)

, H H ON-N, u -"0 0 r. +-ra u

0

C=S ( }N=N/

-'

l ~ [-La 1 ••

"

0.2 bA 0.6 0.8 1

Cd)! , Il HO \,:' ,

r- Cf=N z w rr: 0::' l 8 5 [-La.

18

.,

1.0 ' 1.2 '·4 1.6 1·8 2.0

~ E "( VOLT S ) \15 ,5 CE,

Il

. '

o~~~~~ __ ~ __ ~~~~~ __ ~~~ 0.4 0.6 0·8 ~y 1.0 1·2,' '·4 1.6 . 1.

'-

/ , -- - E (VOL..TS) vS SC"E

• '.,

'" . J,

.

, "

III :::<

, '

" ( f,

. i

, ~-{.~~- .... _---- _ ... _-_ .

. /

. 1

c ;

r'

f 1 f

i / . ~ ~ ,

If

~

1 1 ,

, .. • C 1

)

J

f

,1 ------------~-~-~-----"'

FIG.l

D. ~. po~arOgram8 e. lO-3M ~-Bprizoinoxime, iri:itiaJ, pH: '7.0

f. lO-3foi Dimethylglyo~ime't initial pH: 7. a ( 1 . .

1 1/

li

~ Supporting electrolyte

Solvent

Electrode

1/

Ethanol

D.M.E.

~

1 If (

"

'.

,1

.ç

' r

1 r

/

,1

(

. ,

"

, I( " , i

~

1

F tG. Ce)'

. ( .

20

. 1

~I

Il

• ...

o~~~====~~====~~~~~~ 0.2. 0.4 O· 6 0:8 '.0 1.1, 1.4 ,.6 1-8 2..0

/ - E ,( YO \.. T S) vS SC E

/ (f) , . ( .. - - -- - - - - ---- -- -_.

- -----------------1- c~-c- c-c~ Z Il fi ' '3 ~ HON NOH 0::: :,) . ' ..

<...:> I,5/-la,

0 O-i, 0·4 0·6 0-$ 1.0 ,.2, -, ..... '·6 •. 8 2.0

11 . - 1 -

; - E ( VOLTS) \/5 SC E~ \ {

(-

, '

1

(

/

...

--------_ .. _. -',---+--

21

FIG .1-

,D. C. pola~Qgrams

h.

g. "10-3M Salicylaldoxime, initial

10-3M 2i~The~OYl trifluoroaceton_~, , ~,

l

, uppo;rting: O.IM Et4NCl ellectrolyte

f

sàlvent '~~. Ethanol

\EI~ct~~de : D.M.E. 1

\

/

il'

" l,

.. ; .....

initial'pH: 7.8 r

·è

l,

/

{,

. {

'"

(

(

f r f

~

i ' : ( t t i

..

\ 1

0 1

~, ,2,

lJJ 0: 0:: ::>

,f'l)

,

0

()

~CH=NOH

~H f

-;-

0..2 0.4 0·6 0.8 /

Il Ch)

~H C-C~C-CF3· 6 Il, ,0

. f5 ,p.a

1 {

O. 0·4 0·6 0·8 1

..

- 22

- , "

, .' ----t-.. - .. ---- /

, { _. i ".

~ , 1

. {

.. -.'

1.0 1.2 1.4 1.6 1.8 2.0 r

- E ("Olr~) " SC E

- r

..,

- E ' ( VO LT 5) 'oJ S S'GE ..

1_-__ .-_' _-----"----~-~~I'

1 1

(

l'

\

(

(" t

(

Il

23 "

FIq .l~ /

',:D, C. polarogram , ,

i. 'lO-'M Sodium diethyl~.ithioc.a~bamate. initial pH: a.o

Supporting C.lM E~4NCl êlectroly,te

Solvent Ethanol

Electrode D.M.E. 1 .

{. ,"

1

1 1

! 1

" ~.

, ,r

, ,

,1

~-

,,)...

24 ,-

,-ç,

( FIG. 1 ~ . ;,

CI ) r / 1

0

C2HS \ #S + N-C Na t

CzH5/ \ 5 G -1:5 0 , r:. t-'0 5f.La. u'

'f -/, ( , ( ~, \ / ,1 r , '

C 0 0'.8 1.8

/' ' r

0.2 0.4- 0.6 - 1.0 J.2 /1.4 1.6 2n f

/ ' ,

-E ( VOLIS) vI St:E

'.

J 1

"

1 -

..... {..~'1. ~~ ~ ... ;"','_~ __ ,,, ~ ... _ ... -~ / ~ --~----,- -

t[, " t /

/ /

//

/ 25

Il C,

'/ /

/

-.

:/ FIG.2

r

/' D, C. polarograms .- -

a. IO-3M Cu(N03 )2 " "

, ,

.,' b . (lO-3M Pb(NO j )2 ~ c. Ç'lo-3M ,1" Cd(NO j )2 \, '1\ ,~ lo-3M -~ ~ d,. Nün2 • 6H2û " ~',

. • l:;~ IO-3M Zn(N03)2 " ' 'e. If, J. '( l'

! 1

( Supporting O.lM Et4NCI electrolyte

Q, , 1

Initial pH 8.0 i'

, Solvent Ethanol

Electrod~ D .M.E: -1 ?~ " <-'. "

)" r 1

, J

. , ' l , /

{ i • i i, l ! » •

r " 1

-< '-

i ,r

( 1-

"

, 't

J (

, (

/ dl

( '0

". ( .

, (

1

i~

• ; .

f Î t~ f ~

\

'1

l,

26

FIG. 2

, 1

. '.

J2J.1.o. , ,.

1

Il

l-Z l.JJ 1,1,(Tr 0: 0:: ::> U ...

,1

cl b c d f e

O--~~--~~~--~----~----~~--0.2 Q.4 0.6' O.a 1.0 1.2 I~, 1.6 1.8, 2..0

1/ """7 E (VOLTS) vs S C ~

1 •

/

'-~.

(

\ ..

. /

. ; Ir ; 1

J 1 • g

l: '

l ~ ( \ ~

t \-, i,

1

27

,FIG.3 .....

D. C. polarograma

a. lO-3M Cu(Joc ') 2

b. lO-'M Pb(~PC)2 <

c. lO-3M Cd(DDC) 2

d. lcr3M Ni(D,DC)2

e. lO-3M· Zn(DDC) 2

SUPITorting : O.Hl Et4NCl electrolyt'e ~

Solvent

Electrode ,-

Initial pH Il .

\ .

: Ethanol

:1 D.M.E.

: 8.0

- 1

'/

, .,

.-

1 0

1

1 (

•

r 1

, ~ -..

-i , t \ 1

l, ~

~ f ~

t ! 1 , i, ,

Je

i ~ i,

1

( ,1

c

~

C'

\

1

Il

~ z W 0:: cr :::> u

.' . ,··~t--- -- ---_.~~ - -- ~ - :;;

, '-il;, ,r

28

~

1 , ~.

FIG. ~

,/ ~ ... '".

o

.'"

e 1 •

O~~--~~~4--U~~~----~--~~--~~~ 0.2. \ 0.4 0.6 1.0 1.2 I~ l,? 1.8' lP

- E- (VOLTS) vs·SCE

1 . 1. II>

l' ,

,-",

, , 1 .-

t' '~-l , ' , " <: ........

~ 1 "

1 -'. l "

" 1 ~ ~

(

Il

/

'. , -, le 1

"'~ r

~ i ~ , i~

, r, (

'" c

o " ---p._------29

\

FIG.4 "

, ,

.. J;~ ...

, J

!

, 1

1 !I An amp-eromet i~.: tftra}ion grapll of a' solution

of 10-5M 0 metal-PAN wi th a . \ of 10-2M ,;

NaDDC in ethanol as titrant.' measured

at -O. V (v.s. 'Sc'È) l,

'" ! , J' 'Supporting ': 0.1101 ,LiCI ~

electr'ôlyte . .". .......

Solvant Ethanol

Electrode D .M.E'. 1

" 1 l ,.

-'

~'

1 ~ ,.-:.. , 1

"-l', <.';" 1

q ,l'-: ~

;$ , ~. ; i

" , ..

'*'

.. r

... 1 ;1 i' f;l .... r '.j'

-' '4

"""."" -:Ir

. {

1

! ' /

\

\ \

\ \ \ 1

\ \

\

- l, I~

\ -' .

"

" ,

il

,1

'1

\

-1 -

-.

:. "

\'

~

,)

1 1

a '1 1

, . ;

1 • ,;

, ,

,,'

'il I, \ ~.

"1 , \

r'

=; I._-,~ .. ,.,._ .. "

(

1"

C' '! .

.'

,>

--

~

1-" Z W 0::' cr :> u

/

.. ,/'

1 !

- ,

f,

"-

JG. 4

'"

/

/

Q.I..fL?-.'

ft

~

. _1

\

...

ML

.,;.

li

t

30

'fJ

rf,

" ,J -R-' . ,

.p

..

)

'X 0.1

1·

Of TITRANT

,'1

'i

,.r _1

l' ,

1

1':-

"

i~\

~ ..

ML

[.

1-,

/

,

1.

. ,

'" ". Î J

, !~

1

"'

- .1 ' ,

. -. - ~~- ~_ .......... _ .... ' ,

/

J

~

31 1

" ~

( v

1

1 FIG.~

i v D. C~ polarograms

" . ~. , 10.,.3M CU( TTA) 2 ",-

" a.

i

1 b. lO-3M Pb(TTA)2

1 1 0 lO-3M Cd(TTA)2 [,

c. , ~

~

d. lO-3M Ni ('TTA) 2

lO-3M Zn(TTA)2 ir

-

e. ,-, ,

C' Supporting • O.lM Et4~Cl ,( • electr~lyte "

/ -il

Solvent Ethanol " ;,

,~

Electrode D.M.E. ,.-

" ) ~~, .,

,! "

l, Ini tial pH 8.,0 ) , ,,, ,l , I .... ~.

r~1 1

i 1 ~~~ ~

. 1

;A l" ..... J

1 {;l

! '~J; ;

/ 1 '1 ' 1";

" , .. f '* ~ ~ ~~ ;:' .-

1

,

t .' . ~ \ i:, ~

f " r' 'k

~.' /

~ r S" /

( t , " r

1

' r .,

l .. L,

(

(

, .

, .

/

t­Z W 0: 0:: :::)

U

32

FIG. '5

" .---'----

/ 1

- 1

O~--~--~--'---~--~--~--~------~~ O.l 0.4.0 0.6 OlS- 1.0 1.2 l4 1:6 1.8 2..0

\\ '.

'>,

\ - E ( VOLTS) 'II" s I S C E '\-

/

, \ ,

,

/

o

1 1" l '

) , , ,

.. -(

(

(

- ...... ~ .... __ I! .. _---

33

IV. EXPERIMENTAL -....

(A) Apparatus 1

1. Cambr1d~e General'Purpose POlarOgta~ for D.C.polar~grams using a

2.

DME ,

For D.C.polarograms, a Cambridge General Purpose Polarograph

with a convent~onal DME and an Ht~ll wai use~. AliBaturated calomel

elect~ode (SCE) as shown in Figure 6a (see ~48) was used ~~_the reference

el~ctr~de. lt has a lower resistance as compared to th, commercial

fiber-tip ~CE. In addition, it has ~ large area for the metal-1 _ ,

solution interface so that tne current densi~y and hence any polar-

ization effects are minimized. The contact·between the working r /

electrode (DME) and the reference (SCE) was through an aqueous

saturated solution of tit~aethY1ammOnium chlor!de (~t4NCl) in one

side of the H-cell, the agar plug (ssturated w~th Et4NCI solution)

1 and t~e glass: .frit. The current was me~sured by a 'Sargent-Welch

-2/311/~ , recor~e~. The value of m t at the potential of ~he ~CE waB

, 2/3 -1/2 ' ---2.0 mg sec • Linde nitrogen pre-saturated with the yapor of

the particu1ar solvent mixture being used in ~he Bample solution wa~~

bubbled thr~Ugh the solution ti remoye the ~xYgen before ana1y~is.

Cambridge General PurpoBe Polarograp~ and Cambridge univrct~r

Polarograph Unit (C659051) for A. C. po1arograms •. ~- ~

added

_ 0 '7 "

For A.C.polarograms a Cambridge1fiivector~POlarOgraPh 'Unit /, l' D' / " • ,

to the circuit between the Cambr géGen,ra1 Purpose Polaro-

grap~ and 1 tne electrodes. . \

.' , '

Il

/

{ . , ~"

c l ~ j,

v'

.' ,

l

1 r

t , , H 'p j'

.' '{

f t b l,

Î ~

J

1

(

c

fI) 1

(

....

Il

34 /

1

3 • Camb ridge General Purpos.e Polarograph for D. C. polarograms using a "

RPE. 1

\ r

Jn systems where a' J.ŒE was usedas the working elect,-1"ode, a .

Sa~g~nt-Welch synchronous motor (S76485) which rotates,at a constant J ~ 1

speed of 600 rpm was used. The RPE was a commercial one supplied by

Sargent-Welch (830420), nam~ly a bulb tYf~ with a p~ece of platinum

wire extendin~ Smm from ~he side of the bulb at r~ght angle to'the Il .1 /

axis of rotafion. The inside of the Èulb was filled with Mercury, 1

/ and the cpntact wss provided by a piece of wire dipping into the

Mercury (see,Figure 7a). The ce Il was a 25-ml borosilicate gl~s

, besker with-a 100se1y 'fitted cover with four holes. One hole was , 7

-- '- l ' - , 1 for the RPE, on~ for, the salt bridge, one for the burette tip and the

fourt~ for the passage of nitrogen., A Cambridgr General,Purpose

Polarograph was used 'to supp1y the voltage rang:, and the rest of

the instrumentation was the,~am~ as' in Section IV.A.l. 'The titration

assembly is shown in Figure 7b' (sec: p. 52.) ,

The nitrogen inlet tube was ve~ti~ally adjustable (see Figure

7b). For d'é-aeration Qf the ~olution, the tube was positioned below

the solution and the burette tip w~s r,place1 b! another tube leading

to the cold trap (sée Figure 6c) for the condensation of the benzene

vapor. During the titration, the burett~ tlp ~as put back and the

nitrogen inlet tube was adjust,ed ta a position above the solution t_o 1 1

allow a slow stream of nitrogen to pass over the solution.

il

.1

i. 1

, ,

r '

l'

, , .

(/~

(

, , ,

.. ,-'-

- . .....,...:---~, ( ,)

-,l'

35

, 4. Beckman DB Speetrophotometer

5.

" A Beekman model DB speçtrophpmeter wfth a,tungsten lamp was . \

~sed for the measurement of the absorption spe~tra of the,metal 1

chelates in some o~ the systemS. fi

Leeds and Northrup Potentiometer. (eat. No. 8687)1 (

A Leeds and Northrup potentiometer was used to measure the 1

v?ltag,e applied acrob the two elecfrodes of the polarographic cell.

6. Beckman pH Meter

A Be~kman Zeromatie II pH meter/was used to measure the pH of 1 1

the solution. A commercial glass electrode (Beekman 39000) and ,

SCE (Fi~her Scientifie Ca~. no. 13-639-51) were used as indicator

and reference electrodes. 1

7. . Glassware JI f/"

....

1 AlI volumetrie gla~sware wa~ calibrated at 25°C with the 1

solvent used. . . -,- The glassware was cleaned with the norinal procedure,' namely it

was, allowed ta ,stand in.hot cle~ing solution (sodium dichromate and

cone. sulfur1e acid) fbr 10-1'5 minutes, rinsed with tap water,' 1 then

with distilled deiori1zed water t and finall)' wi,th absolute ethanol ~,

" and allowed to

1

were Pyrex c18ss A np. 71&0 type.'

(

' .... ,.

1-

I!I

'f

, i

,J 1

l,

'l~

~ - r

' .. I~

-J...~

(

. , " t

{" :.~ , I\\,. }

fi ,

t c'

36

(B) Resgents ( I! ~

1. Benzene "-B~nzène supplied by American Chemicals Ltd. Spectrograde was ~ 1

used. A ga~ chromatogram waS run to establish its purity. It was -(

used without further purification •

Due to the toxie nature of this solvent, 'aIl titrations were

carried out in a well-ventilated room. The nitrogen that was pas~ed

over the henzene-alcohol solution being titrated contained some - '

benzene vapor. Therefore it was led directly into a cold trap (shown

in Figure 6c) to condense almost all of the vapor before the

nitrogen stream was ventilated to the atmosphere near' a fume-hood.

2. Ethanol

3.

'1 '

Absolute ethyl alcohol supplied by Consolidated Alcoho1s

Limited was used Wit~~ut further purif!~n. polar~grams of the

purif1ed supporting electrolyte (LiCl) using pur1fied (distilled) - -

ethanol and non-purified ~thanol as solvents showed no detedtable

difference. Where ethanol i8 mentioned ln the present work includ1ng

the Tah~es and FigUres,"absol~te ~t~anol 1s to he understood~

TetraethYlammonium chloride '

Tetraethylammonium chloride monohydra~e from Aldrich Chemlcal

Co~pany was'used.

ethanol (38). ,

\

1

It was purifi~d ~y recrystallisation twice from

\

. l '

tJ

J !

i .'

l' l :

(

i li< •

1 ( ! J

4.

37

Tetraethylammonium hydroxide o '

Tetraethy1ammo~ium hydroxide, 10% in water, fro'IEas.m~n Kodak

Co. w,s us~d without further purification.

'5. Lithium chloride

6.

Fisher Scientific Certified lithium chloride ~as purifled by

recrysta1islng It twlce from ethanol, then drylng the product for

several hours at 130°C (38). - 1

2-Thenoyltxifluoroacetone 1/

Fisher Sçientific Certified 2-thenoy1trifluoroacetone was ~sed. -.1 '

lIt has the chemical formulae:

Cl H S ç-C=Ç-CF3

r 6 OH'. Keto Enol

I~' Is a pale stra'W-yellO\ol solld with a melting p'oint 42.5-

43.2°C, easily solublé'in such organic so1verlts as benzene and

methanol.,

,S-diketones are usually purifled ~y vacuum su~1tmation or by -)

J/

/

recrystalisation from. benzene. However, in the present work, ~it "as ..,

found that' the polàrograms Il of tn~ purified pr~ducté were -similar at ' 1 [ ,,-

a given pH,' and the stock solutioJs of HTTA in ethanol were foundlto , i be stable. Thus, identical polarograms were o~tained in a freshly

1 . ~

prepared r stock solution and in those that vere allowed to stand for'

several days.

1

",

1 •

Î.

J ., ,

"

1:­

!

, ~ ,

l , t ,

f

t , r

1 (

(

(

\

38

7. Sodium Diethyldithiocarbamate

8.

l'

Fisher Certified sodium diethyldithiocarbamate was us~d.

has the formula:

+ Nd

It 1

The reagent was p~~-;ied by recrystallisation twiee f~om ethanol,

the crystals were filteJed onto a fritted-glass fil~ert then dried

in a vacuum de~ieeator ovez. Drierite"" for one wJek. The aasay ~f ~he

, PjrifiJd produet was carried out by a- gravimetric determination of

1

the DDC radical, by precip~tation with eup,rie ion Ç49).

A standard NaDDC solution was made by dissob',.ing a weighed '" }. 1

amount of the purified NaDDC in ethanol and diluting to the desired

volume. 'NaDDC solutions in ethanol were found not to be stable for

more th an 48 hours -(49) '. Thereforé' fresh solutions vere made every

1 day for use in the titration procedures carried out in the present

work.

1 Standard metal solutions

A summary of the source and standardisation of the standard.

me~al solutions is given in Table 2. '-----

!

A weighed amount of the metal vas dissolved in 10 ml of 1:11

, nitric acid, and beated until,the'meta1 was disso~ved. The solution

was then ev~porated to m~ist dryness, and the residue was .dis'solved

,~n ethanol and diluted to the required volume. '. '

. / -1

,,' , " }

:t,

1 J

1 "

I},

l

Il

f

t,,'

, !

c'.

- ~_ .. _""""~---

39

~ Table 2~ Standard Sôlutihns of Metals

Reagent Source

Cu metal Baker Analysed reagept , 1

Pb meta! Fisher, L-24

Cd meta! B.D.H'. Analar

Zn meta! B.D.H. Analar

NiC!2· 6H20 B .» . H. Analar • J

*Cu assay: 1 99.9%.

**See Appendix 1 for the 2roéedure.

1 .

,1

1

Method of Standardization

Primary standard (*)

Titration with NaDDC (**)

Ti tration with NaDDC (**)

! Titt:.ation w~th-NaDDC (**)

-Gravimetrie, dimethyl-g!yoxime

l',

, "

1· ,

. . '

! .... 1

1

t -,

(

1--

40 , ,

'/

9. General reagents

(C)

1.

"

Other re~gents used in t,~ 'present work

They were used without fur~her 'purification.

are listéd in Table 3.

Procedures

, .. Standardizati6n of sodium diethyl~ithiocar~amate

(

A Cu (N03) 2 solution in ethan~l prepared as described in i Spectrophotometric Section IV.B.a was used as a primary standard.

and amperometric titration procedures were used for the standard-1

ization of the NaDDC solution.

a. , ~

Procedure for the spectrophotometric standardizat10n of Na&1C. .. .CoPper f,orms a c'omplex with d;i.ethyldithiocarbamate which i5

soluble -in chloroform t carbon tetrachloride and ethanol. Bode

(35) f~und, that this chelatE; has the tormula Cu(DDC) 2' and hS,s

an absorption, spect:r:um in carbon tetrachlorid with a maximum at

1 .. 435nm. The absorption spectrum in ethanol r ethanol~benzene '/ \, !

( /

mixture was found in the present work be' the saine "(Figure 8, p. 5,4).

The NaDDC solution was the tit ante '~aliqu9t of the ,

stan~ard copper solQtion to be itrated wss transferred ta a ~ 1 (

IOO-ml flaak, and diluted 50 ml ~lth ethanol. The solution

was s~jtred by ~a2ne c bar through the titration. Constant c~. 1

ri. increm.ents of~ Utr t were adaed from a microburette. 1 Âfter

each ~~dition,' a weIl as for the initial solution, a portion of •

transferred to a cl~n, dry, l-cm spectrophotometric

,. , " , . , ! "/ ,', .,-, '-

1.

(

l'

-, , 1 ~

\ j ,-i., ~l î\ Î" ( ~

. ,

( • ~ .

1

1

! 1 i , ~ , j'

t

t '" o

i t . ; ( t . J I.:I~

- ..... _----- ----

0

Table 1

3. Mis tellaneous Reagents

Reagent

Dimethylg1yoxime

~-Nitros(j-l­naphthol

Salicy1aldoxime

aïBenzoinoxime 1

HP AN

Dithizone'

8-Quinolino~ ,

~a:OH

LiOH

Source

B.D.H. Ana1ar

-B.D.H. Certified chemical

B.D.H. Certif1ed chemicai

Fisher B-268

Baker 1 Analyse'd reagent

(B.D.H. 1 Certified chemica1

B.D.H. Ana1ar ,

Fisher S-318

Fisher' L-127

Baker Analyeed reagent

41 ~

'" l, "

\)

," .,

(

-,Ufi,e in the Present Work

Studyof,its potarographlc behavi~r, and gravimetric,determination of Ni.

Study of its polarographic behavior.

• 1 Stud~ of its polarographic behavior.

1

Study of 'its po1arographic b~havior.

Study of its po1arographi~ behavior. /

Study of its po1arographic behavior.

Study of its po1arographic behavior.

_ pH adj us tmen t of the sys tems •

( pJl adjustment of the systems. '

P~eparation of standard solutions of met81s. 1

, 1

"

HC104, EO-62% " Anachemia Pretreatment of the RfE. _--.....--_____ ·I~ __ ~-----i11

, .

'" , "

\

",

"0'

{r .. \

"-<J I-r: !,. :r~ " " . ,

:t' .1 '.

\

\ J ,

i i

1 , .

(

~ ç ( { ,

J

-"

42

spectroPhot~meter uslng ethknol in the reference celle The

portion take~ out for spectrophotometric measurement was then'

returned to the tltration flssk after each measurement. After the

next addition of titran~, th~ portion of the ceU was mixed with the

solution before the absorbance was measurld and the celi rlnsed

... ' with th-e soluti9n in the flask. Severai increm~qt8 were , added

beyond the end po~nt (p. 56). J' • 3

The titrant was quite concent!ated (5xlO- ~) compared with

-- the , -5 tltrated, copper solutiôn (10 M,), 50 that the total voltJllle

of titrant added was smaii (0.25 ml in 50 ml), which made a j.

volume correcti~n unnecessary.

-A plot of the absorbance of the titrated solution at 435nm -"' l ' against the volume of titrant added gave the titration graphe

On extrapolating the two stiaight-line portion of the graph, the .2-----J.-~-

intercept gave the equ,Uralence pof;nt: Drawing the best straight .. ~ line from tpe experimental points by visual inspection was fdûnd

to be satisfactory. A typ'lcal titration graph Is' shown in 'j,

Figure 9 (see p. Si]). 1 lk

. Two breaks w~re observed in the titr,ation gl;aph. The first

one was located at about a 1:'1 molar ratio of' copper: NaDDC, and

the second at a 1: 2 molar ratio. • Grey (7)

• f

found the saJ~ results. i the 1:1 Grey attributed the firet break ta tbe formation of

Il . complex of copper with DDC, and the second to the Cu(DDC)2' In

'the ~regent work, this second oreak was taken as the equivalence

, 'point for the titration. 1

$'

! '

" , '0

~ .

'1

....

(

;f. l'

(

, , r

,-

43

o

b. Procedure for the amperometriê standardization of NaDDC us~ng a

DME

Copper nitrate in O.LM LiCl in ethanol gave-a reduction wave

which started at -O.20V versus SCE at a dropping mercury electr9de,

while that ,~f Cu(DDC)2 started a~ ~O.40V (see Figure lOa~ :' 58)._

Therefore, the titration Of~U(N03)2 with N~DDC could be'followed

by measuring the decrdase ~in the diffusion c~rrent of ,CU,NO~) 2' . • ( ,..,.

Beyond the end yoint of the titra~iont an anodic current d~e to 1

the excess NaDDC occurred in this region and could be measured.

The slope of these two lines changed at-the end point. This

poin.t indicated the equivalence point.

An aliquot of the standard copper solutio~ to -be titrated

was transfe~red to the sample compartment of the polarographit.

H-cell. The solution was chen d~lutedlto 25 ml by the' ad~itian 1

ofVO.LM LiCI in ethanol, and a pre-determ~ned amount*-of

saturated LiOH in: ethanol. The mixture-LiCI-LiOij was found to

have'some buffering action on the system, and the pH before and . -- 1 .

after the titration~wasrfound to remain the same. 1

The DME was assembled. .The Koch microburette was rinsed , 1

then fi lIed with the standard'solution of NaDDC in ethanol. Its i

tip was then positioned so that it was under the level of the 1

~An,aliquot of the,solution ta be titrated was tr~nsf~rred ta a lOO-ml beaker, diluted to 25 ml with O.IM LiCI in ethapol, and the pH ~easured The pH was then adjustéd to t~' re~ire~ value ~y,~ijding a saturated solution of LiOH in ethanol. The ount of LiOH add~d was noted, and used for the amperometric- dete ina ions. 1

"

Il, ,,~ .. __ ~ _______ D ______ _

:

,,'

l' '.

"

~.

1: ~;

"'7"'-·,....·/1'

r ..

(

Il .

. .

, ,

./

/

44 •

s.olution to .be titrat·ed. Linde nitrogen pre-saturated w tlJ.···the

soivent was bubbled through othe solution for 15 ~inutes. ~efore .

the analysis.* . J { ·1 .• rÎ.e voltage was set at the :required value, and the ~rrent

measured. ~ncrements of titrant were th~n added, and,th~ current ., • '\ J

was measured after each addit~o~. Equilibrium was assumJd to be

attained when a constant current value was obtai~ed for a

,period of two minutes. (D

The reaction was obs~rv~9-to he almost

instantan~'ous • t

• A plot of the current at a iixed applied voltage gave the . ~ . 'titration grs,ph (Figure ,lOb). Extrapolation of the two straight

,: r>· ,

~nes gave an intercept whi~h ~~s the-equivalen~ point. "

" c. Pr~cepure for the amperometric,standardization of NaDDe using ~

RPE ;:

For the volt~ge range of +O.80V ta O.OOV versus SCE,

CU(N03)2 did not show'ariy reduction wave at a pH greater;thatt,?,

using a RPE. However, NaDDC gave an oxidation 'Wave which started ~

at O.OOV and reached its maximum value ~t +O.20V. 'therlore, the ~ II

"course ot.the titration of Cu(N03) 2 by NaDDe .. JI ' , ,

o

"

f'

ti could be f llowed by

f

. " n ~ ~ •• . , . 't~

. \

Il

.f ,

, '.'

',01 , '.

l~,

,~ ~~: -:('î ...!~ ~'.

(-

c

(, "

/ )

45

l ' measuring the limiting current of tbe NaDDC wave.

, Since'the copper-DDC complexes also gave oxidation waves but

at a more/positive potential than that of NaDDC, the rllnge of t,

voltage over which the diffusion current of NaDDC could be ! •

uieasured was limited to +0. 2,OV to +O. 40V versus SCE (see

Figure lIa 1 p. 60).

Pretreafment of the rotating platinum electrode is discussed "

in Appendix 2. The é.lec~rode was stored in conc. nitric J 8cid

~hen not in use. Before uset" it was shorted, against a SeE in an

ai~free O .. lM HCI0'4 solution until the current was zero.

This l'clean electrode" was then placed in the test solution, and

the applied potential was adj us ted to -O. 20V versus SeE' until

the cathodic current decayed to zero. The p~tential was then

moyed to +0.05\7 Jersus seE 'until the current decayed to zero

again.

,An aliquot of thé copper solution to be titrated was

transferred to a: 50-ml beaker. It was then diluted to 25 ml by , , , ~

, O~l.M LiCl in ethanol. The pH was adjusted to 8.0 by adding " ~

saturatel LiOH in' ethanol. IAfter the salt bridge, n~!rogen' in-,. ,

let tube, ,rotating electrode and the microburette were assemble~ , ..

~... ,7

nitrogen was bubbled through the sol.ution for fiVè minutes. J

The potential was adjuâted to the dedred voltage. The ". ,. ,

soluti0l! ~a8 allowed to attain ~qU_11ibrium for 5-10 minu~es.

Incremènts of the titrant were added, the equilibrium_ , ' 1 ...

current of the 8Y8 tem being recorded after each incrëment.

,1

. ,

.'/ ;;1

, ,

/

" e

c'

Il

, '-

/

46

-S~veral increments were &1so added beyond the end point.

Nitrogen was allowed to flow' above the solution during the

titration.

A plot Jf the current at a fixed voltagé against the volume ~

of titrant added gave the .titration grà;h '(Figure llb). The

intercept produced by the manual extrapolation of the two

straight-line portions indicated the equivalence, point •. ~ r( •

Good agreement was obtained between the molarity of 'th~

NaDDC found by the three titration procedures ~nd the molarity

calculated from the weight of NaDDe used. The precision was

satisfactory. Results are shown in Table 4. 1

The amperometrib method using either a DME o'r a RPE was

adopted for aIl future standardization of NaDDC t by using the

primary-standard copper nitrate solution ..

2. Procedure for the titration of metal-TTA s~stems using a DMF!

a. Single metal system using D. C. polarography

A solution of the metal cOlÎlPlixes M(TTA) 2 was prepare~ by'

mixing in a 1:'2 molar r~tio a lo-2i-r standard metal nitrate pl '-"" l '

chloride solutionl and a lO-~ BTTA standard solution. The titra-

tion proêedure was descri~ed in Section IV. C .lb • . Ti tration of Cu (TTA) 2' Pb (TTA) 2' Cd (l'TA) 2' Ni (TTAf2 and

, ZnCFA)2i'with standard NaDDC in ethanol were carried out. Vadous

,>

pH values,. and ethanol-benzene mixtures were used •

j ..

<. " 1

Il

/

.11'.

. dl

, ' ... I~

, ",~ ,'!,. .,

f)

, , ---

1

_ .. p.

(.

/

47

1 1

Table 4. Accuracy and Precis ion of the Standardization of Sodium Diethyldithiocarbamate (NaDDC) in Ethanol with a Standard \ Solution of Copper iri Ethanol, br Using SpectrophotoOletric

, 1>

and 'Amperometric Procedures r'

Kolarity of standard solution of NaDDC. from weight of NaDDC taken . • 5.020xlO-3

!"!olarity of stand~rd copper nitrate sJ1UtiOn, primary s,tandard • 1.0l2xlO-,4

Al1quot of the standard copper solution taken for standardization ,of the NaDDC solution

4 Spectrophotometric_

'" 5 Amp erome tric , DME, current measured at

5 Amperometric, RPE,

-0 .40~ -o.55V

Molari ty of NaDDC Solution Found1

5.12 x 10-3

5.12 x 10-3

5.08 x 10-3

• 5.00811

2 s.d~ , 3 xlO % dif •.

1.1 +1.18

+1.95 +1.18

• current m~asured at +O.35V

1.4 +0.99

.- ,

~ean of 5 ~amp1es. /

\

2 ' s .d. means standat:d deviation. 1

3Ca1culated~from the avérage ~olar~~;-found and ,the ~olar~fY from the weight of NaDDC taken. ' , -;

calcu1ated

4 ' The absorbance was measured at 435nm in the spectrophotomet;ic method, , . with ~thano1 as the b1ank, for al-cm path-length.

--;- ,

5 li T e polarograms were recorded for 25m1 of solution with 0 .1M LiCl as the supporting electrolyte, at the voltages versus the SCE.

r , , . - \ ~

'/

;.' f -,

,.

1

; "

\1 e

,

, '-t~~ ,'~ 1

: t'l

'if i;~ 1

'~~ ;

:' i. 1 , '. , (,

('

(

l'

--- -- -~-~-, 1

1

1

j 1-11

\

e) /

48

FIG.6

(a) 0, Saturated Calomel Electrode (SOR)

A, F- Meroury -1

B- Hg, Hg2C~2f ~ paste /,:

c- Saturated KC solution J'

D- salt br~dge to G.- of F1g.6b

E- Plat1num wi-re .1"1

" wire G- Copper J

(b). Ti tration assémbly Ù,sing a DME working electrode. 1 (

A- From Koch m1crobur.~tte \

B- Inlet for pi tragen 1

C- Dropping Mercury electrode .. D- Glass frit

E- Agar with"saturated Et4NCl ao:J,ution

F- satur~ted' aqueous solution of Et4NC1. 1

G- Ta SCE through a KCl sal t bridge

H- Meroury reservoir

I- Ni trogen outlet

J - Sample compartment li - <OF

.... '/ "

K- To working electrode terminal

L-: Stop-cock

• (,>

j

• Cv

~(

<1 1· 1'<-,

- ' ' . , ... -,

'.~

1

i

1

/

l' .'>

J" -~,

'j

, j

/

< j

- t 1

t l,

(

e :/

, { -

, /

FI'G. 6

G

Cb)

G

1

, 1

49

1

E

p 1

c-8

H

1

,8

1 1 1

, 1

1

"~, ' , , , :

;~

l'

\. .~

1 r'i - 1

,<; '{JIq.J

, 1 ~ l'~

/ r

, ""'''''tl_~ __ ~ ... _____ ~ ._, ._~_~

/

'.

(~

• 1 . '

50

1

(cl). Cold traJ for be~nzene 'lapor

A- From nitrogen outlet of H-cell

B- Dewar flask

'~C- Mixture of lce, water ·and salt

"

Il

c ,

D- Exhaust of gas to the atmosphere,near a fume-hood

(d). Modified burette tip for the Koch microburette

A- Dr~wn-out glass tube

B- Polyethylene tubing ,

c- Luer jO,int

l,

1 ,

III

-, ,)

.!', ,.'. l.'C ','-'..!~ __ ,---~"""--, __ """, ____ ",,,_

, "

, ~ ~;~ , '1''-'

t li! l i::~ ',l'.-• 'e.o

1:'\

~'~

,'.

,1

1

-'- ---"

-(

"

! /

(,

i

il J+."

1

'~

, FIG. S

Cc)

D~

/ J

, 1

A

- 1

- --

51

+-A

8

c

l'

\

\

1

1

" 1

, '

E " ~

, : , '

,r~ , . ,

1

t\ ~ ;.

~ 1

i' 1 il, .' ,

( l ~ l, ,

, /

~ 1

\ , 1

(

•• -q •• --------

Î

52

FIG.?

(a). RotJting platinûm electrode (RPE, bulb type)

(b) •

A- Mere-ury

1 B- Platinum wire \ . ,~. 1

~- p~num wire to the working electrode terminal

Tit~ation aasembly uaing a RPE working electrode

K- Sargent-Welch synchronous motor

B- Frbm Koch microburette

c- Rotating platinum electrode ..

D- Ve:ç-tically adjustable ni trogen inlet tube

E- Connection to working electrode terminal

F- From SOE (salt bridge)

G- Agar with saturated Et4NCl solution

H- 50-ml Pyrex beaker

1

\

\

/ o . 1

1'. l ,~

(

" \

1 1

-\ \

'1 1

/

\

! 1

____ .... _._a_o..,.., _I __ ~ ..

/

FIG. 7

Cd)

E

F_ . .,

53 .r

A

-8

A

---8

H

"'"

:1 1/ "

, .

J~

" , ~,

, ,1 ~

(

1 -

\

} Il

, ,

(

'. , .

'. ~ -

l,' ,J' ,

__ ~ ....... 4 • 4

1 1

".

54

-

FIG.8

Visible spectrum of Cu(DDC)2"J in ethanol

.,.

7

Il

Iii

, , , -1 ~

, , \ ,

li 1 li

55

( )

,FIG. 8

" q. -20 "

" '0 J " @

1 i~ >;< ~

1 16

,.J >-1-'-

;r; > ~ j ( h: 12 , ~,

0: 'II ; ,

~ r al

8 <{

0:: <! .J

, . . ~

0 4 _1',' ,:1,

2 " , ;;E'"

-<"" .\

\ ~

1

", ~~1

560 4~O 440 400 320 ",,-;:, ~ ]-

nm

lf\JdVe 1 ength

l ~

Co. " 1

-1

',,;

., 1

1 - ,

'. ... J' 1:': ... .;,..

C·-

, 1

. ' J '

~ ~ ... __ 'Or MU ' .... -.:Mt

56

Il FIG.9

Typical ti tra,t~on graph of' the 'BPectr~hotometric

ti t:y:atio-n of Cu( N03 ) 2 in ethanol, by. a~ ethanol \ }

soll;ltion of NaDDC. /

Norm~lïty of standard CU(N03)2 solution: l.012xlO-4N

Norrhali ty of NaDDC solution 51t 020~lO-3N

, . Ini tial volume of solution 50ml

Wavelength

1 , \

1 l 1

: '435nm

# 1

.. '

.j

"

, . 1"

1; "

,1 ' :..

.- JI

57 ' Il

L !

,1 (

. , 1,

FIG. 9 <:>

1. 1

, >,

~,

l-i ......

1 v'

1 Ci l.LJ of- Q ~ -~ 0 C., ~ ~ ::> ~ uS ~ CO \...Q 1 ~.

/ CC \m '\ 1 0 ! (f) . 1 Sl 0 • ,

--'-

l '

fFI --._~- ----~----

" -~--

1 -----~

"" i

, ~ 1

1

1 1 0.1 ml 1

1

1 t.

Il --, ,l-i ' -3 ~

( ML STD 5.0 x 10 1 N' Né:lDDC' .

*.' 1 . ' 1 'c 0

II , • 1

" : :1 _\,i . l' •

~t ,~ , , , , . , ri>

"

0_ • •. ....:..... _________ _

, (

"

/

58

FIG.lO L

a. Polarograms of CU(N03)a' NaDDC and Cu(DDC)2 ,alone,

and of a ti trated solution of 2xlO-.5M Cû'(NO,)2 in

.the, presence of lO-5M excess NaDDC, w1 ~h NaDDC in , ,!

. ethanol as titrant .. d

Supporting O.lM LiCl electrolyte

l

Solverît ., Eth~nol · 'r

Electrode · Do'M::S. ~ •

:,'l< > "

?'

amperometr1c t1trat1on graphs f6r the , , 1

stand rdlzatlon of NaDDC in ethanol with a standard r

solution ,di 9u(NO,)2'1n ethanol

. ,

l,

il'

" . "

, • r • I!! J

r '

.'

• 1 •

, 1

' ... , " .

.-, t 1

j, , 1 ;

/

, . l '"

r r

"

1 \

"

... .

, 1

, "

l' 1

1

'J

" '. '

'1 , '1

ri , ,

"(

"

J

1 f

H Z

" ~ :;:J u

59.

,"

,.'

FIG.IOa

/

l "?'--'-'-'-'-' a.Illa '-"- ,,;' /. . ' . . ' 1 l,

, 1 l' : 1 1 ! l'

./' / l , ~ ~\ / . .o./ .... '.. - . J' '. .. • .. • • • .. .. .. • , • • • .: o - ,','

~ o. ~ 0 • 4 • 6 0 • 8 . 1.0 l • 2 :1 !' 4, l • 1.8 .. .

./' . "..~'

-E (in 'volts v.s. SCE)

. l"

1 '" ...... Residual current. ---"Cu(NO) 2ilO-5M , 3 2 t

----Cu(DDC)2' 2x10-5M ~ NaDDe 1 lO-5M

.'

~'~'Titrated Aolution,of 9u(N03)~t wi th exce"~~aDDC , Il,, ~ .

FIG. lOb

. ~/

, , ,

x-O.30V Measured at (Fig.IOa)

1»-0.40V

,0

..

, , ~ ~ ,-'

l, " ,

\"', t~ ,

. , . , '

'1' ,

1

',\ 0,'

" , ,

f "( __ ~ l ,). ,

" ,o. ,

/

1

i

\

~

/

-. ;,~:: ~

~I

\ \

\

~~~~ 1 -_._-~ _ ................ _--

f ;", . ). ,..

(

(

Il

1

r( 'i

Il

..

Ti, •

- Il 60

o

FIG.II

a. Vol tammograms of Cu(DDC )2' and NaDDC alone. and

of a ti trated solution' of ,lO-5M Cu(NO,;) 2 rn the,

"presenc'e of IO-5M excess NaDDe, wi th NaDD'C as 1

o

tltrant

". ... ~- -~- - -- - ~

Supporting : O.lM LiCT electrolyte

Solvent

Electrode

Ethanol

R.P.E.

TypiOàl 4mp~rometric ti tratio,n graph for ~,he 1

standard~~ation of NaDDC in ethanol, with a - !

standard: solution of CU(N03)2 in -ethanol

1

1 -1

1 y

.. , .

o

'.

,1 .r,

/ t

l' ( J, _ 0;

" ,

. C· , f

, 1

" i

, . . "

!

-- - --r------- - ----.--------

.. /

" ,

FIG. lIa o • il

î I1pa

1 1

l' 1

61

",.-- ......... . ... "". ..... , .. , .... /-- ~

..... 1t0.4 / o~o

1 1>

"

1

1

•• ' 1 ./ .~.-. E (in volta v.a.'SCE)

/ / ........ Reeidual currant J ---- Cu(DDC) 10-5 /. ,2'_ M

,/ - NaDDC, 10 5M ( 1;' _._. Titrated solution of Cu(T'l'A)2'

wi th excese NaDDC 1 ~ / 1

, j

1

1 .

'- 1

L. 1 . 1 , 1 ,

1 1 Measured at +O.'5V (Fig.lla)

1

FIG.llb

1 - ---

Ipa

1 O.lml""'Ï'

1 , . ML OF 5xlO-3M NaDDC ADDED

"

1 ~) .:

, _ J , ~I

l' ! ,~ l,.

~ a ~~ , 1-." - 1 ii"4, ~\

- Q ',;':

" ,'\ .::: '. ' -

Il " ~~'ï .,

, \ -~:~ ";

q ~1

~V.A' ,;"~~ "(1 l\(i ;t?;

r~ 1 .....

,F>}

'}M fi t~

.. 1 (~

1-,J-r '~ ;~ J, 1 : t.~

,1

b",· ~ ( ,

- '1 -. "

1 1.

~ "

(

o

, ,

1 . 62

i. Cu (TTA)2

The metal chelate Cu(TTA); gaye r r~duction wave which /

sterted at -O.20V, while that of Cu(DDC)t started at labout 200mV

more negative (Figure 12a). Two aifferent titration graphe were -,

plotted. For one. the deèrease in the diffusion current of the

CU(TTA)2 wave at -O.45V was plotted againet the increments of

titrant, and 'after the end point the diffusion current at -o.45V

i, - ! due to the excess of NaDDC was-plotted. The two straight lines - 1

intersecte~ at the end point. For the other graph, t~s proce-," ,

dure w.as repeated, but at -O.20V, where CU(TTA)2 did not give e -

wave. JI •

Typical titration graphs for this system are shown in

:figure 12b. ,)

o 0

11. Pb (TTA) 12

oThe metal chelate Pb (Tr~!e titrated w~th NaDDC gave a

reduction wave which was shifted abo~re negative' / t;f 1 1 1 ~ ........

(Figure 13a). The titration was followed by measuring the

increase in the current of the anodic wave due to exéess titr,nt

added (Figure 13b).

11i. Cd (TTA)2

The meta! chelate Cd (TTA)2' gave a wave start4ng at -o.60V, ! ' . an~ Cd(DD~)2 gave a wave starting at -O.8OV (Figure 14~). The

titration was fol~ow~d both by,measuring the decrease in the / {

1/ /

" diffusion ,curre-';ue ta C/d(TTA)tYJld also by measuring the

/ 1ncreese in the, an~ic diffusion'current due to exc~ss titrant adde4,-

.. , ' 1

./ ,1

;.' jl' , ~ . , i»" .... ""' "" ':i te

Y'I ,

,', t ... '/'i. 1

~': f.~.~ :~.;~~. ~~J'~ ~; ~ ..

." .. ' F

,. .. ' ~ ,1 '" ~

(

,1

a.

(,;

b.

-·-1

, ,

. ;' "/~ ..

,,'

.f' -

--', 63 , 1

j FIG.12

li

C~(TTA)2 + 2NaDDC 1 = CU(DDC)2 + 2NaTTA

/ Polarograms of Cu(TTA)2' NaDDC, and Cu(DDC)2

, i'

alone, and of a solution 2X10-~M in Cu(TTA)Z '"'

after ti tration lii th NaDDC in '~ethanol and con- I

taining lO-~M'NaDDC in axcass

1 Supporting '. O.lM LiC1 . electrolyta

Ethanol .J 1

Soprent '" \.,~ 1 1 1 ..

Electrode p.M.E.

Typical ~perometriè titratlon grafhs for the'

che1ate-exch~gel titration of Cu(TTA)2 in etbanol,

with a standard solution of NaDDe in ethanol . ' r

\ . , t

/ 1 '1\ -

-" ~ . . -

r

,'.

. l' ,

,;

(

(

~ ..... "'iJ,~~~.-:~"

~~,

._-- ,- -_._--_._-----64

Il

FIG.12a

.' ---~.~ . . _ .. _.,,..-,./

-"/ ,'" , /" 1'/

: 1 1 1 1 i

/ .'

/

: l' 0'

t / / l, .... ~u ".1 j"-- •....•.•....... g; 0 /.. ' ....., ... ',r

:' '0 • 2 0 • 4.~ il. ~ O. 8 ]. 0 l • 2 l • 4 ./ -E (in volts

: ..... ..--.".,. 1

: ,,' '/

FIG.12b

, ...... Residual aurrent - .. _- Cu( TTA) 2' 2XIO-5M

:--- Cu(DDC) 2' 2XIO-5M' ---- ~DDC, lO-5M _._. Ti trated solution

with excesa NaDDC 1 . ,

v.s. SOE) ..

CD-O.45V Measured at (Fig .12a)

'X-O.20V

1

, l' ' ML 01' ~ lO-3M NaDDe ADDED

'.J~_, _ o l '. '~ 1 .} l ()

, ,

,~' c, - .;~: " ~ - ~ ~ -. ,

'~'-}Z:~:.t.L . ',',' / ' , "

, " -.

" -, ,

. ,

1 .

;J " , , 'i ,

, '

, >. r 10 ~ '. , .

, l' ,1

Il

c

J

~

"

, 0

. ,

.. '" l,

, ,

1 d

l '

65

FIG.13

Pb(TTA)i + 2NaDDC = Pb(DDC)~ + 2NaTTA

a. Polarograms of Pb(TTA)2' NaDDC, and Pb(DDC)~

alone, and of a solution 2xlO-5M in Pb(TTA)2

after titration with,NaDDC in ethanol and con­

taining lO-SM NaDDe in excess

, Supporting : O.lM LiCl electrolyte

Solvent : -Ethanol

Electrode : D./M.E.

b. Typical amperometric titration graphs for the

Il ,

'l, '1

Il • . chelate-e.xç.t~ange ti trat10n of Pb(TTA)2 in ethanol t

vith a standard solution of NaDDC in ethanol

" 0-

, r··

/ - 11--

\<;

" '~', , ,

~

",

~

'" 0'

..

, , , ...

'.

l ' f,

, t

1 i /

-' ,

, , ,'1'

, , ; l.l

, ,

, ! , \

~,----_._---

66

c FIG.13a

......... • ___ III __ • ___ • .".

1 O.l}Ja 1 /"'-"~/

.' 1 i 1

1

.",=

x . \ / \ )

/'" i J-o / '

1

, t;l ...• ...c'.:I. .~................. Ii' /

~Or-~~~~~~~~~~~~~--~ B 0; 2 0.4 0:6 0.8 1.0 1.2 1.4 1.6 1. a

l, .

. ,/" : / -

/

1

/ /

1

FIG.13b

. '.

(

,-."",:1 -E (in volta v.a. SC~)

o .. • .. • .. Residual r.urre!!t - _ .. _ .. Pb (oTTA ) 2' 2xl0"M

---- Pb (_DDC ) 2' 2xIO-5M ----NaDDC, lO-5M , -'-'Titrated solution of Pb(TTA)2'

with eXCeas NaDDe

--

Measured at ~O.45V (Fig.13~) 1

, '

J ~r V L l'II'<J J , ,Q. \' 1) ""'i., ..

l'

'. .~ . .1/

(

il

4'

Cl ' ,

I e /

. t f \ i

1

67 "

FIG.14",. (J , . ..

Cd(T~A)Z + 2NaDDC = Cd(DDC)2 + 2NaTTA

_c'

f

•

r a. poiarograms oi Cd(TTA)2' NaDD~. and Cd(DDC)2

L ;

,1

alone, and of a solution 2~lO-5M in Cd(TTA)'2 - !

after titration with NaDDC in ethanol and con~J'

- taining lO-5M NâDDC in excess

Supporting O.IM LiCl Etlectrolyte li \

Solvent " • Ethanol • .' f .. .-1

Electrode ' . D.M.E. Il • 1

"

b. ~ypical amperometric tit~at~on graphs ~Qr the l, l" chelate-exchange titration of Cd(TTA)2 in ethanol, . with a standard solution of NaDDC in ethanoi

'",,'" 1

" \ ' ';', 'i ' ~ - ~ ~ ,

"

'1 : , , , , .

,' ... :~ . . '". - '~\ '; ;

/ '

'.

" 1

(

1 , ,

'.

,1 r

1 1

,1 , , 1 01

,/

"-, ' ..

r ,

i 68

FIG.14a

, l O.lpo / .... _ .. ~;.,..--.-._.

1 r /

. 1

."

: 1 8 / /-z J ~. -c/ -' ...•..

~or-~p~:~~·O~~~;-·~O~/~~-~O~.~8~1-.~O~1~.~--~~--~----~ C,) _ 1",,/ i_E (in volts V.s. SCE)

E-c z o~ 0

::J C,)

}, '

.... \:,

-' ........ Residual current _ ..... Cd( TTA) 2' 2xlO-'M

---- Cd(DDC) 2'xlO-5M - 2 '

- NaDDC , ' lO-5M _._. Titrated solution

~ith excess NRDDC of Cd(TTA)2'

, --0.80V· Meaeured at (Fig.14a)

X-O.45V

Il

O.lml ..

. - ML' 0" .5JG10~3M NàDDC ,aDDED

~,' \

.' ,

" r ,-

1 '

, " , ,

.} ","t \

).t,' t !-',~" ~ ...

"

, r J

,"

1

:~

1 , ,

c

, .\:~,

" "'j , (

j • ~ , 1

"f'~ ,:,1

\":. ;1' ; .'

, ,-

i i

1 : 1

1

(

"

'-'

, 1

..J

...

-_ ...... _---.-""'~ ... _-----69

'~iv • Ni (TTA) 2 Il The sy~~em was treated in the- same way as that of Cd (TTA) 2

except that the voltages were at different valùes; the reduction

of Ni(TTA)2 occurred at a more negative potentia1 than Cd(TTA)2

(Figure 15).

v. Zn (TTA) 2

The reduction wave due to Zn(TTA)2 was quite drawn out and

merged with the reduction wave of the RTTA (Figu~e l6a). The re­

fore the fi~ration could be followed only by the increase in the

'current of the anodic wave when excess titrant was added

(Figure 161ï» • 1

/1

Results for a1l of the abov,è ~ystems are r~corded in Table 5 (p. 74).

vi. Effect of e~cess RTTA reagent on the accuracy of amperometric

titrations of metal-TTA compl~xes in ethano~-benzene 1 •

mixtures, wiV a standard soluti.on of NaDD:~, in ethanol"

The effect o~cess RTTA reagent on th~ accuracy of the Il

/

amperometric titrations of metal-TTA complexes was studied.

This work is particularly important for the praétical applica-

tion of t~e method, since in a normal extraction procedure '

there would "be an exceSB of HTTA present in the organic phase

prior to the titration.

Excess RTTA_w~~ added to the/metal-TTA solutions and

amperometric titrations were carried out as in the procedures

outlined above. The results are shawn in Table 6 (p. 75). , '

: .\ -'

-,

\ , 1

" ','

"

:~

't " ,'" ~ .~; ..

.. ~1 t~

l , ,\

'. '

" ~ . , J • ~".., _

. , -, , . 'y~ ''\'

. ' i 1 ;

1 .~

• 1

C.! , , ,

. , ,

J) ""r r ';,' "

" , d

\.

70

'-FIG.15

. . Ni(TTA)2 + 2NaDDC = Ni(DDC)2:+ 2NaTTA

" a. Polarograms of Ni~TAr2t

2XlO-5M( in Ni (TTA) 2 ,~fter

in ethanol and c9ntaining

and of a solution / . l, , 1

Supporting · · electrolyte , Solvent · · ,

Electrode · •

ti tration wi th NaDDC "

lO-~M,NaDDC in' excess 1 ','

1

, ,

O.lM LiCl

Et han Ç.il.

D.M.E. \~

• 1

-......,..

b. ,Typical amperometric titration graph~ for the

chelate-exchange titration of N1(TTA)2 in ethahol, .. 1 ~ .. _

with a standard solution of NaDDe in ethanol

li

" , \

\: 0, " "

\ \

J

~ .

, J 111 "",.

"

,lt j

, \

.. 'Ï 1 lI.'

.i . . . , . l '

J 1 ( 1 i. 1 (t';t.~ ,

, " r ~I - ... 1

, '~, ~ .J ri ~ J~ <

. ~ .- ,_.:_~ .. ~ _,.,1 '_ "'~''''._.' -'p~._t";:i.,<-.h.. .. .. -.".~. ~ •. ' . . . ,-. -.',., .".,f>, .,. J •

(-

r

r:: ',' \: ,,'

, ;

'" Il E-i z

"~ ~o u

, , .",

/

FIG.I5a

1 0 .llJ8

71

--.."./ .... "" /' '" . l ,f

Il:. '/

, // {-./ / _ . ......: ..... '.~

.'

, • • .1fIII'-. - • ...... "/' O~2

",

/ . /

1

IJO .lJ,l8 ,,-

1.0 1.2 .4 _ 1.6· 1.8

-E. (in volts V.B. SC~)

........ Residual c~Jre~t ~

---- Ni(TTA)2" 2xlO~5M Titrated solution with excess NaDDC

, x-O.40V M~a8ured st (Fig'.15a)

C) -1.15V

• C.lml

, olo • ,'II( ...

ML OF. 5x lO-}M Narine ADD~n- .

l 1. ~ ' .. .. ~,'" ~ ,

. ,

'.

f

'. ,

Jf ~' ,

" 'H~(

, ~;:, r

~~~' ,,: ~~ .'

(

r

, '1

/':

\ ..

"

i

·1

1 •

. .

(

"

FIG.16

Zn(TTA)2 + 2NaDDC ;::' Zn(DDC)2 + 2NaTTA, 1 1

1 a. ~POlarograms of Zn(TTA)2' NaDDCr, and Zn(DDC)2

o

. b.

alone~ and of a s~ution'2xlo-5M in.zn(TTA)2

kfter titration with NaDDC in ethanol and con­

taining~5M N~DDC in excess

" l Supporting : O.lM LiCl , electrolY1e

Solvent :' Ethanol

/ Elèctrode D.M.E. ,

Typical ampérometrio titration grap'h for the 1

oh~late-exchange t1trat1~n of Zn(TTA)2_ in ethanol, l '

- wi th a standard, so~utiC?n of NaDDC in ethanol

•

'<

' .

l,

a Il I" \~

1

l,

, ,

j

, "

.', , , :'

, ( .':

l'

. ~

l'

..

. ~

t

C_ '

(

l' -- ... -- -_._- ~.- _.-.- - _. ' ___ .1 ____

H ·z

~O u

, 73

, .

rY' -~ 1~

'1

·1 ' FIG.i.l.6a ,.. . /

,1/' l,

j.0.llJ8

,,/ ' ,/, /

/' l , •• • 1

. '1 / 1 - . .' ,/ /,' III . ' , ./. .. ~ ...... , ... 1 .

1····_ .. . , , ... " . . ~~ l'

0".2 0.4. ~.6. o.a 1.0 1.2 1.-4 . 1.6 IJa .. "i -E (in volts v.s. SCE)" IC ····· .. ··ReSid.ua'.l. currens !

: /' -;,_ .. ~n( :ITA ) 2' 2xl0· ~

/,/. ---- Zn(DDC)2, 2xlO-5M / - NaDDe: 10-5M J

l' ~ -~-.Titraled solution of Zn( TTA!}2 t il' wi t;h exceS8 NaDDe 1

1 1

\

1

1

FIG.16b 1 1

• 1

Measured at

IO.lpa

-0.50V '(Fig .16a) . \

1

1 1

J 1 O.lml

ML OF 5x lO-3M NaDDe ADDED ~ \\ .

. . "

\

- , , ~-...--.. ..

l'

; ,

JI

' .. ,

-, ,

"

1 '1

" . ,

- "

- i;\

1

. ,

'"

- - .. .r

.r'\ l"'-I

1 .. '1

Table 'S. Accuracy and Precision of Amperometric Titrations of Single Metal-TrA Complexes in Ethanol and 'Ethanol-Benzene,Mixtures, with & Standard Solution of NaDDC inêthano1. Using D .. C. Polarography

Mo1arity of standard'NaDDC solùtion -2 '" ,10 '"

Volume of solution Support1ng e1ectro1yte Electrode

l\pp1ied l!S of Metal Metal Solvent pH Voltage

Ta~ 1 2 Found .. s.d • v.s.SCE,

Volts " ,'\

- ~ Cu EtOH 7.0 -0.20 51.48 51.00 0.76 ,

-0.45' 51.48 52,.00 0.63 l:l(v/v) EtOH/~H 7.8 -0.45 51.48- 51.05 0.62

'Pb EtOH 7.0 -0.40 /166.4 167.8 1.5 l:1(v/v) , EtOH/tH 8.0 -0.40 166.4 168.0 1.7

Cd EtOH - ~ -0.45 91.00 89.95 1.0 - .....".. -0.80 91.00 92.05 0.41

. 1:1 (v/v) -0.45 91.00 89.90 0.68 ~ EtOH/!H 8tt'0 -0.80 91.00 90.08 0.44 • 7'~ -0.40 27.70 27.40, 0.36 Ni EtOH

-1.15 . 27.70 28.00 0.33 1: 1 (v/v) 7.8 -0.40 27.70 27.42 0.39 EtOH/tH -1.15 27.70 27.45 0.31

Zn EtOH 7.0 -p.50 52.48 51.98 0.77 l:l(v/v) EtOH/cjlH 7.6 -0.50 52.48 52.96 0.52

'~ean oC-4 determinations. "]

2 s.d. mean~ standard deviation. ...

z:

""

. % d'if3

'-0.94 +1.00

-0.84

,,~+0.84 ""---+0.94

-1.17 +1.14 -1.22 -1.02

-1.09 +1.07 . -1.02 -0.91

-0.96

+0.91

25ml O,lM L,1CL. DME

.. .j.

Remarks

Can be titrated at pH > 7 (limited)y the stahi1ity -of

NaDDC atf low:.-pÎl) \ ,~ \ ~ ~ ~t -::. \ "t

..... Reaction i~too slàw at pH > Il

Can be titrated at pH > 7

C~ he titrated at pH > 7'

Zn(TTA)Z did not react

quantitatively with NaDDe at pH > Il .

3 ' % difference ca1culated from the amount of metal found and the amount taken.

"' <> "

\ ,

~

,

_-__ - ... ~ 1'-;::---

" ~

\

i

) 1,

" \.

'! r

'"

;1

{

~1 ~ \', ;

"

r

(

,

(

~

( ,

Table 6.

r

Metal-TTA': Comp1ex 1)

1 1 1

Cu (TTA) 2 :

Pb (TTA)2

Cd (TTA)2

Ni(T'FA} 2 .

Zn (TTA)2

.. 75 \

, , Thè Effect of Excess UTTA Reagent, on the Aècuracy of Ampero­m~tric Titrations of Metal-TTA Complexes with a Standatd '

• 1 Solàtio~ df NaDDC ~n.Ethano1, by Usi~g,D.C.Polarography~

,Supporting e1ectrolyt-e;; O.lM LiCl "-

Solvent, . ,Hf l:l{v/v) Ethanol-bènzene Elec.trode '" D.M.E .. .

-.. ri,'

Initial Ho1ar Ratio of UTTA t'a S' " 1 ~ r Meta1-TTA Comp1ex lIg of Metal

0 5 la 0

TakE!n 51.48 51.48 51.48 ." -v

Found 51.00 51.10 50."ù9

Taken 167.8 '167.8 167.8 r

, Found 168;0 168.1 168.1

Taken 89.95 89.95 89.95 li

Found -~i' ,92 .05 .{~ 1

'" 91.95 . 92.00

Taken 27.40 ' 127 •40 27.40

Found 28.00 26.80 27.90

Taken \ 51.98 ,51.9,a- , 51.98

Found 52:-86 _.' 50.54 52.90 '.

1 In 25m1 of sQ1ution. The values repor~ed for the amount 'found ~re the means of ,4 determinations.

'. r ,

" '1. " "', 1

1 1 .

/

.-

r

; ,

......

'"i

, t',

"

,1' ,

(

..

,-

(

,. 1;

!

(

·f 76

/ .

.... ~~ .1 ---'-'-' -----:-----.. - --~ -~

\ 1 1 -

'.

) b •• Amperometric tltration of single metal complexes 1 using Â:~~'~

,-

p~larography /'

( ,

A Cambridge Univector cornponent coupled to the cQnventiona~

Cambridge D.C.Polarograph gave the equivalent of a differentiàl 1 .

polarogram. which oaa enhaneed sensitlvity. However, tt la then

nqt possible to dis tinguish:anodic from cathodie waves. The

anodic wave due to the excess.titranJ overlapped with the M-DDC

ca'thodie wave in sorne cases, thereby limiting t;\~ use of this TI'" ,

technique to sorne systems. , , ..

; II Ir , "

! l'" 'jr ~r /'';,

The A. C. polarograms of Cu(DDC) 2 and Na~DC are .... :!JhoJn in "

Figure .17 •. Cu(TTA)2 did no~ give a peak in the r~corded region. , "

However; the two peaks due to Cu(DDC)2 and NaDDC were not

resolved. Theretore the A.C.techniquè kas not useful for ~he ' /

appliCation of amperome'try to this system.

ii. Zn(TTA) 2

Zn(TTA)2 when titrated with NaDDC gave an anodic wave at a

more positive potential than the anodic peak due to the excess ,

titrant. The resolution of the peaks due to Zn(DDC)2 and NaDDC ,-

was found ta depend on the supporting eleetrolyte used. Lithium

chl~ride gave better resol,ution, 'than Et4NCl (see' Figure 18 and

Figure 19a). A typical titration graph of the system using ,

Liel as the supporting elect;olyte ls shawn in Figure 19b. , .

/1

III

,~ .....

1 ""r' .. l- , , } . r

, . ,

, ,

, '

é

". ",

"

, r

"

" " , ,/ 1.. ••

r ,l", j" ...

1: il

77

l, • -----r- -

J

.'

FIG.l7.

,

·,A. C. pol~rograms of aUI(DDC) 2 and NaDDC alone't and of .

, a ti trated solution of Cu( TTA) 2 ,~~ th ,NaDDC in ethanol

as titrant

III

, G

" Supporting O.IM Et4NCl e,lectrolyte

Solvent : Ethanol 1

Eiectrode :.D.M.E.

1. FIG.lB

. t' .-. IA,C. polaragrams of Zn(D~C)2 and NaDDG alane, and' of "

a ti trated solution' of Zn( TTA)2 wi th NaDDC in ethanol

as titrant "

Supporting : d.lM Et4NCl electrolyte ~ ,

1

SOlv~nt 1 •

': Ethanol

Electrode D. M. E.· " ,

, . ~ , -,', ,-- -,·-1,

a

Il

1 [

(

( 1

!'

l'

" L ,

!

'v

FIG.17

j.

,. : ,iii

)' -, #1'1

, ,

/ /1 1 -, 1

. ./

'. II

I1Pa ". .i,1. '. l, ·.~I

!'

.~' l' .\ ,.

1 \ \

78

------------ -

r

'­.,

, ........ R9sidual current

---.'- Cu(DDC)2' i:1.O-5M i ' ..

---L- NaDDC, IO-5M Ti trat:ed so~utiOn: of ln-'M

r

Cu(,T~A) 2'. ~nd containing , 2XIO,-5M excess NaDDC <"

___ / J \ ..

, ,

, 1

. O~----------~--------------~-----------~ 1.2 1.4 SCE)

0.2

........ Residual , , ---~ Zn(DDC) 2',

~ NaDDC, 10- M

_.-. Ti trated' ~XIO-5M

NaDDC

olution of (TTA)2', and

2XIO-5M excess

!'

/i' i

1

i' 'l, 1

1

/

1

! 1

f •

, 1

f

/ 1

/ ....!<_~-,' -;--~~"-/ 1;' il

Il

Il " l, 1

li / 1 ! 1 1 \ -Il ,\

. 1 1 I!~

-/II : l' j t'l.

• 1 r \

79 r

.~ j

FIG.19 r

, ,

.!

/. 1

1

li; . - -- )

l ' , l A. C. polarograms ;,)Of

a titrated' solut10n j.

Zn(DDC)2 and ~~DDC a1one, and of

of Z~(1TA)2 with NaDDC in ethanol 1

as titrallt , 1

1 .' .- Il

Supporting :'9.1M 1iC1 electro1yte,

'Solvent: Ethanol t

Electrode D.M.E. 1

b; 'irypica1 amperometric t.i tration graph for the chelate-, ,

exchange titration of Zn(TTA)2 in ethanol with a

standard solution of NaDDC in ~thanol by using A.C.

polarography,

•

•

' ..

'f

li

, r

, .

1. - --:".-.•. -:-;:.,-1+'. ',~."".,..'= __ ..,.",.,_.,......... _________________ """"""""_"""",,,, ______ _

" ,

\

"

, , , , ,;l, l",

1

1 1 1

t f, t

." Î' ,} , !

j

'1

1

"

r ' f

,

( - ,

, , , 1

. \

JI

(: . 1

1

r' l..

. '

FIG.19a

. . f, /, . 1 1 !

~ . 1 '\ n,Il'

l' ;. :\ "',~~ 1 \ . . 1" \ \\ ,"\'\ l , ~ • 1 \ • . \ \ il ',. 1 ~ ..... ., 'J \ • • . ........ \"

f '" \

80' r ,

"1

e

)

f

~

.

, p

, ._,_. ----".:-9 _---.:...f ~_~~_~ .... _~

, .... 1 - "',

/'

" 1 . 1 . . ,

• 0 1 ( . Residual current

Z:çl(DDC)2' 10-5M .,

NaDDC, 10-5M,

Titrated solution of

2XIO-5MfZn(~TA)2' and cont~ining 2XIO-5M exceS8 , NaDDC

-,

"'\ 0'-----' '-' -' -' --'-'-' -' .j-'-' '-'-' '-' -' '-' _. '-'--' _.-........ --------'

'\ \

E-I

~ ,...J B

0

0.2' 0.4 0.6 .8, 1.0

'\, " -E (in v ~1 ta v.s.

f "", •

"',,----\

• ~ 1

FIG.19~-\_

1.2

SCE)

Meas~red a~- -0.55V (Fig.19a)

Il .. ,

.

•

... '

'" 1 0.lm1 1

1

ML OF lO-2M NaDDC ADDED "\

. \ .

.

, ,

. "

,

~

f'

'.'

,

..

, ' , , " l'

l," l' \

(

, .

(

c ,

iii. r Pb (TTA) 2

,

._ ' .,The· A. C. polarograms of Pb (DDC) 2 and NaDDC are shown in' , "

"" Figure 20a. Pb(TTA)2 did not interfere in this poteptial range.

....:. '. Th~ amperometric. titration was followed by measuring the 'i'ncrease ~ If" .

in either peak. Typic~l titration graphs are shown in~~gure 20b. ,~

iv. C~(TTA)2

This system was similar t~{that of Pb(TTA)2' the only

difference be~ng.~hat Cd(DDC)2 a1so gave an"anodic wave at a

more positive potential. By using LiCl as the supporting . t, .

eiectrolyte, the two peaks due to 1

Cd(DDC)2 a~d NaDDC were

shown in resolved (Figure 21~). \

A typical tltration graph ls

Figure 21b.

-v. Ni (TTA) 2

, Id this system, Ni(TTA)2 and Ni(DDC)2 did ot give any

peak in the potentiai range -0.40 ,to -1.OV. The amperometric

titration wa. f:l1OW~d by the hlorease in the N.~DC P':'k wh";' l ,

excess titrant was added. A typicai graph ls th~\same as that

in Figure 21b. , \

• 1 \.

Results of these titrations, showing the accuracy and

precision of ,.the amperometric rethod :when A.C. polarography ~sJ.

',i' used, are given in Table 7 (p .. 86).

,1·

l,

C

(

i ! / ~, .

-------

82 '. 'II

'" ,

'\~I \ '. Il \

1 1

\~', "

1\" 1 \'

, :I!I"I ;J-

( 1 Î

1 \ 1

1 FIG .,20

7, 1

a. A.C.polarograrns of Pb(TT1~2" NaDDC, and Pb(DDd)2

b.

!

, ,

\

alone, and of a titratéd solution of Pb(TTA)2 with

NaDDC in ethanol 'as ti t:f'ant

Supporting\: O.IM Et4NCl electrolyte

· \ Solvent ' Ethanol

Electrode : D.M.Et

Typical amperometriè titration graphe for the chelate-

exchange titration of Pb(TTA)2 in /ie;t,banol with a

standard solution of NaDDC in et 01 by using A. C. \ 1;i ,>' polarography ,

t' , ! ~

" r

l '

-----"

Î

, c

/

(

(

" '

.. -_.,-" -, .--------------- _.

83

FIG.20a

Residual current

'( n Pb( TTA)2' lO-5M

~ 1\ . --...:- Pb( DDC) lO-5M

,!\ f i <,'>~ NaDDC 1 î~-5M " '\ '. ~ '\ <1 _._. Ti trateçl, solution of

'\ \ ! .'\ fi '\ 2XIO -5M Pb(TTA)2: and .\ \. 1 1 d

":\\ ' i ~ \ con taingng 2X:IO".-SM

• \' \ f \ exCess NaDDC '. ,\ 1

l "'\\ !. \ j ''1\ 111 a ' .• \ .. / \ ~/\\ l',

. ~ . 1 . " \.:j \\

.. " .. ">... __ ....•.•• ,. O~~---------~--~~.----~---~--~---~-----~

0.4 0.6 0.8 1.0 1.2 1.4

-E (in volts v.à. SCE)

x -O. 55V Measured a;t

1 ;' !' + \ Ci) -0 • 85V 11..1 a l,

f~~j >

/ +

/m ! l' _~xj 1 O.lml 1

(Fig.20a)

O~~4~ _________________________________ ~

'1

(

1",'

, , .,

,', "

t. .1

l'

(

(' ~ .'

,

1

"

(

Il

.' ..

o

r .~

84

FIG.21

J!" :/

_. __ J;-' __ .......... ______ • ___ • ___ .

a. A:C. polar;ograms of Cd(DDC)2and NaDDC alone, and of

b.

a titrated solution of Cd(TTA)2 vith ~aDDC in ~than9l

itrant \

Supporting e1ectrolyte

J, O.lM~iClh

:1 1

Solvent Ethanol' 1

Electrode, D.M.E. ;/

J f

li Il

Typical amperometric' ti tration fr,aph for the chelate­

"exchUnge titration of Cd(TTA)2 i~ ethanol with a

standard solution of NaDDC in ethariol by.uBin~ A.C.

polarography

, (

\ \ II.

\ \

a /

..

'fi .

1

, l " f "'----. ----t ~

l' f.B (._-~ ~ "l-J '., , \ '; ,

i,

'. , f

" , a,

i f

f •

•

1

;

1 ,

l '

'L~, 85

f-t Z

~u U

'1

,. ,

, "

1

1

" ,

":., .... Residua\l current , • é

.. - ---- Cd(DDÇ)2' lO-SM

~ NaDDC, IIO_~Q~ _._. Ti trated solution of

2XIO-5M Cd(~TA)2" and containing 2XIO-5M excess NaDDC

. . . . . , ' .. O~--------------------~----------~~--~~

O. ?' 0.4 0.6 0 • 8 l' L •. O 1. 2 ' 1. 4 L

-E (in volts v.s. SCE)

. FIG.2lb ~

.'

"

, , '

" Measured at

e.. j d' / ,,-~~

+ '

l' /

l ,/

,~

.1

-O.55V (Fig:21~)'

-

. .

-)O-'H ..... o<.- /.... O.lml 1

O~?--------------------------------------~

~',

"

1: . '1

.' ,

1 ' {

, f )

• 1

,- /

l '

/ 1 "

-'

, J j J

, ~

l,

, ,

, , l~~

~ @

~ ~ ~ _-11..-_...J..1 ________ J

L -~ ----.-. .... :- "~j~.

i)

?

. -, ~

- '-

,t

;>

e ~ ~ ,,-

-~---....._-

Table 7. Accuracy and Prec~sion of Amperometric Titrations of Single Metal-TTA Complexes in Ethanol and Etnanol~Benzene Mixtures with a Standard-Solution of NaDDC in

cf!'

Metal ., ".(' -

Pb

Cd

Ni

Zn

Ethanol Using A.C.Polar~raphy

M~larity of stand~rd NaDDC Volume of Solutiotr Supporting electrolyte Elec~rode \.: ' ~,

Solvent pH LI App1fed' Voltage'" v.5:"SCE, Volts

EtOn- 7.2 -0.55 -0.82.

1:i(v/vJ _ }.8 -0.55 EtOH/fh :...().82

;EtOR 7.8 -0.55 - -0 .92

4

solutio~ = 0.01 25m1

1,0.lM LiC1 = DME·

1

\.lg of Metal

Taken

\83.2 '83.2

83.2 83.2

45.50 45.50

1 ,Found ,~

82.5 84.0

84.2 83.8

44.96 45.00

1:1{v/v) 8.0 -0.55 45.50 46.04-EtOR/$H -0.92 45.50 1 46.12

EtOH 8.2 -0.55 13.85 13.69

1 :l(v!v) 8.2 -0.55 13.85 ,,,, 1,3.71 EtOH/$R

EtOH 1

. 7.6 " ';'0. 5 s---- 26.24 26.00 1.: l(v!v) .,:.,., 8.0 '-"'-0.55' 26.24 26.02 EtOR/!éH J

~ean of 5 det~rmination~. \1

.f~ '-~

,

" ....

s.d •

"-"-" 1.0 1.2 . 1.3

_ 0.68

0.56 0.56

'. 0.88

"- LI

0.15

0.21

0.33

0.31

2 . % d1fference between the,~amount of metal fou~d and the amaunt taken.

~~ :" -..

:~,~

~~"'" .~

"

% d'if2

-0.78 +0.94

+1.19 +O.'ZO -1.18 -:-1.11

" +1.17 +1.34

"'-. -1.16 0

-1.02

. -0.92

-0.85

" ~

"'~-

-.

A

" ..... ( .'

"'" 00 cr.

).

" /

"l., -... . "\

~

---------------------------------------~~~:.,.'îît-lt"i~:" .'.."'i'- :', '" - .:-' • -':;-'-~--.!I!.i ••••••••••••• I!l!III!!!!I •••••••••••••••• !!!:::::===;;;;;;;;;;';;;;;''';''-_ ... -

. , (

•

.Ir

(

\ .,

. t • 1

87

c. ~i~ary metal systems

The amperometric titration tech~ique used'~uccessfully for

1 i 1 the titration of' single metali..'tTA complexes by a standard solution'

~f~aIrtlC was next tested for its appliéability to binary systems.

1 The bihary metal-TTA mixtures Cu-Pb, Cu-Ni, Pb-Zn, Cd-Zn, Pb-Cd

and Cu-Zn ~ere chosen for analysis, and the me..tal ratio~_l:l,

.r 10:1 and 1:10 were used.

, ~ f . In aIl of these binary systems, the total metal concentration

t i t. .'

was determined by an amperometric titration'. f In order to deter-1

mine one of the metals in the binary mixture, one of two methods

(see Appendix 4) was used depending on the system:

1

1)' . In çases where only _~me of 'the metal-DDC compléxes ~n the

2)

1.

1 mixt~re has an absorption maximum in the visiple reglon, this 1

metal was determined from the .. absorbance of the analyte at

the end of the titration.

f

In cases where the reduction wave of one of the metal-DDC o

. 1 J ' f complexes "in the mix_tu1e was completely r'1801ved frP.lll the

other one, the: diffusion current of the first wave was used

~·to çetermi'ne .t e ~oncentration of that meta!. / 1

Il Cu and Pb, the titrat10n with a

,standard solutio in.ethanol was monitored by measuring (

the decreas e in /

and

the cathodic currents 'due to.!b(TTA)Z 1

each inc.rement of titrant (se~ Figures 22a and \!-~

, ,,1'! .,

/

1 1

( .

• 1 1

, ' '.

" ,

(

t f ~

• 'II, ...... , .............

(

.'

( 1

1

.. j

" o

1

a. D.C. polarograms of a mixture of Cu(TTA)2 and

b.

Pb(TTA)2 before atid after titration with NaDDC

in etpanol as ti~ran~

Typical .

mixture

Supporting : 10.lM Li01 electro1yte

Solv.ent ; ~thano1 , "

Electrode D.M.E.

-':Ji \. , ( . ...:. ".

ammerometriC' ~itration g~:~~ o~ the

of Cu(TTAJ2 Pb(~TA)2 in ethanol,

with a standard solut o'f NaDDC in ethanol "

)1

, 1

-1

-

'-- ",,',. --............,~~àl:;;:;1~~~ _________ .;..,.j~ ______________ ,_,

, , ,

,

-,

"r,

" , ,

, t"" " , ,

,;./1

" '

1 ! , ,

(

J.

\'

, ; 1

1

-.-J,

FIG.22a

/ 1

/_', 89 o

< _.

IlIfW - '--:r---'- -- .. _. 1

1'" /.1

1]

~ /1. _1 i O~-O~.;~~~··~:~·~~~-'·-·g~·~~~~~~·;-~~~-··~·~~~~~-··~~-:~;-·~1-.~4-' ~1~.~6--~·--~ ./ -E (~n volts ~.s. 8CE)

"../

/ ... ' .... Residual current1/ i ,. ----Cu(TTA)2 and Pb('TTA)2 t_~~ether.

:// / each Ici-SM, before tit~ation. -·-·Titrated solution contlaining 'l(i':PM

excess NaDDC.

"------------'--~----------','

FIG .22b , , :1

l ,.

't. l~easured at -0.60V .(Fig.22a) .'+. '

't-lo.ll1 a '+, ~ , +'~ ~ O~----------~~~-~~~--------------~---~ S -}'.-~- . / -"

·1

li

O.lml 1

~L OF 5XlO-3M Na~DC ADDED 1

1

r

.'

, '

1

i:

(

l'

90 / li \ 1

22b) •

, The equivalence poin~ obtained from such a titrati~n gave

the. total metal concentration (Figure 22b). However, Cu(Dq~) 2

(

is colored (it has an absorption maximum at, 435nm, Figure 8)

and Pb(DDC)2 is not. Therefore, by measu~ing the absorbance of

the final titrated solution and referring this value to the !

;i / ~!"lti prepared calibtation curve, l'the amount of Cu(DDC) 2 was found

(see also Ap~endix 4). The concentration of Pb was then calcu-l

" ....

lated by ~ifference. '.

J Varying the pH up ta 9.0 did/not affect the titration. ....

~eyond a -pH of Il, the tit~ation became veryqslow, and the r

r

reac on was not/quantitativè. This slow rate was probabl~ due

to the sI formation of Pb(DDC)2 at high p~ values~ \

etaI ratios of 10:1 and 1:10, the procedure used , For Cu-Pb

was e~sént1ally the e as tnat for the 1:1 raFio. The prac-I ~~

/ - (-

tica1 ~wer limit for the Cu:Pb,ratio ia deter~ined by the

minimum. yalue at whieh the absor~nce of Cu(DDC) 2 can' be l' .

measured for normal path lengths, and_. this !s approkim_ately "

5 x 1O-6N; Pb(DDC)-; doe's not inter-fere in the absorbance

measur~ent • , 1

were ethanol as the solvent. Wi th

1:1 e hanol-benzene as solvent, a round maxi~m appeared on th , , l' ,~~-$'

polarog aphic wave of the CuJTTA) 2' j which wa~ not suppressed by : /'-'-----

\ // '\ 'adding T iton-X-IOO. Hewever, as 1 1

the NaDDC titrant wa8 added

( ~"I/

'(/ during the titration, -the maximum

\ gradually disappeared, ~d it

Il , !

. >/. ..

1 ~ ... ~,

, , , 1 . '

. , ,1

'~ ,

';[' , ~ T \ 1

r> '~

1

---

c

(

o

_ _ .... tocz;

91

)

did not affect the results of the titration' (i~~his c~~, the • ; 1- •

first point on the titration graph was rejeeted).

iL Cu (TTA) 2-N:t(TT;\> 2 mixture ~ ·,:1 ~j

The complexes CU(T'rA)2 and Ni(TTA)2 s'lso reacfed simultaneously ~

with NaDDC. Therefore the total metal was determ~ned as before,

::; by plotting the anodic current due to the exeess titrant added

(Figure 23). Varying the pH did not

h~r.tion.· \.

have any etfect on the

1 • 1 ; Both Cu (DDC) 2 and Ni(DDC) 2 liav~ absorption peaks in the

visible regiort of the spectrum. - r

r

Cu (DDC) 2 has an absorp,tfon ),

maximum at 435nm and has a higher ~bsorptivity tpan N-tCDDC) 2 t

which has a ma~iMUm at 386nm.

It was "possible as for the· Cu-Pb mixtures to de termine the

Cu concentration from its absorbance in the final titrated

solution; and the differ~nce between the total metal ~ontent and r

Cu alone gave the value for Ni.

. . - (dit became too severe when the.Iatio

Il '.

c~ ,

However, interferenc~ from Nt

o!.Ni-Cu was ,higher than 1:1,

even after applying a côrrection due to the absorbance of

Ni (DDCr 2 a; -;35nm." 1 -,,,,,_J. ~

Therefore, the solution was analysed after the titration'of "

r

Doth metals,'.l?Y measuring the diffusion current due to the, - 1

Cu(DDC)2' and hence obtaining its concentration~rom the polar-

ographie c,!-libratiol} eurve. Then from '~~e differen~e between

the total metal and Cu, the amount of Ni.wa~ determined. The

resu~ts found this way ,proved do be satisfact~ry and are shown t-

,J'-

in 'rab1e 8 on page 104. , ,

.. ,.

/,

(, . ' -»; .. ",' ,,'f

'1

1

r

{

;.

•• r'

c f

01 /

p Il l,

1

/4 ; , ' <

... ' >~

a. ,. D. C. polarogra,ms 'af 1 • 1

Ni(TTA)2 bafo

in ethanal

" ... ,b. Typical

;:

c. 1 -~. ,..~

of CU(TTA)2 and

titration with NaDDC

.1M LiCI

J

ti tratian graph of the 1

Cu(TTA)2 an~Ni(TTA)2 ïn-athanal t

1

with a st

1 /

j. 1.

, 1

r ,

dard

1

, i. , f

of NaDDC in eth~nol

" ·,-1-~

.

( '1

..

• 1

•

r

J'

(

r";to ~r'

~ -' f

.

,"

/

~I'

-.

/

~f f

, ;

i, ( Il " . ,

Q

1 J' t

/ 1

f, 1

93

F~b. 23a , -;

1 y"

l ~ , O.lIJS ,.. __ -----.1 1

/ .1 , ./ ?-.-._._ ...... ,- - - --r ,

f-I " /. _

! O~~~'r-'~'~~~~~/~·~··~·~·_:_·~·~·~··_·~·_··~·_·_·~·_··r-~~------~ ~.- ,,~ ............• :..,:: '-" - ' --~

U

Il

1 -E (in volts v.s. SCE) ./ " "

/' -'-..... Residual current ,/ < --- CU(T'TA)2 and Ni(TTA)2 together,

: / 5 :/. each 10-- M, beiore' ti tration.

-·-·Titrated solution containing:10-5M excess NaDDC. .

r

'f

FIG.2~b .--;

, 10.1 • 8

,"

O.lml _ ~

Maasured at'-O.40V '(Fig.23a)

...

o , ri

,

f' .

r "

(

1

(

1 1

!'

94

! ratio or 1:10~r Cu-Ni also gave ~atisfactory results,

alth~Ugh,dUe to the hi~her rat~o of Ni to.Cu, interfererce of Ni in

the absorptiometric determination of t~e Cu(DDC)2 was tao large. L!

Therefoie ,Cu~DDC)2 was d~termined by measuring its diffusion /"

current.

When the ratio of Cu:Ni was 10:1, the Interference from 1 .

- . Ni(DDC)2 in the absorption measurement of the titreted solution

was ~it~ smaU (less,i than 1%). Therefore botfr-'l:1ie absorb!?ce

as weIl as diffusion current of the Cu(DDC)2 could be, used. The f'

result shown in Table 8 was obtained by the diffusion':::'current ! 'method.

l, . -, As in the çase with the Cu-P~ mixture, a round polarographic

. ,

~aximUm was .observid initially when benzene was_~resent in ~he

,aystem. This maximum also disappearéd 0\1 the ad4ition of NaDDe ~ 1

duti~g the' titrat!on'of the mixture. This suppression of the

maximum' .by NaDDC has also been observed by -;;ther workers (59T. f

.'

The total metal wes determined as before, by plotting the ï'

anodic current due to the excess titrant added~ However, as !

seen from Figure 24a, the ~nô~ic waves due to the NaDDC were .1

n6t we1l resolved in D.C~polarograms. However, in the A.C.) -\

polarograms, resolutionwas better and was suffic,ient to uia,l<e ',' , )Pol'

possible the meàsurement of the increase in the diffusion

cu~rent due to the'exc~s~ NeDDe added after the end point: Thus

, .

1

1· 1

1

" , '

c

(~

1\

pu.

!' '

-" "/1

this diffusion current was plotted against the volume of titrant !' -1 .

added, to give the titration graph (Figure'24b, p. 97). ,

Pb was then· d~termineq in the titrated solution by measuring 1 _~, •

(

the cathodic diffusion cutrent of Pb(DDC)2 i~ the D,C.po1arogram,

'and its concentration was read from a calibration curve. From , '

the' differen e of total metal 'determined by the ~DDC titration,

and,

was

that o

etermined by its diffusion curr~nt, the Zn content

difference.

a pH vàlue of Il, both metais were tftrated. Beyond

eaction of Pb (TTA):! 'tlith NaDD~ became V!ry slow, and

(TTA)2 was nct quantita~ive~

a Pb:'Zn ratio of 10:1, the system could be analysed as 1

described above for a 1:1 molar ratio. But with a Pb:Zn of 1:10 t' •

interference from the anodic wave due to Zn(DDC)2(~O.42V versus

SCE) -became tOf greàt to determine the total me~a1 co~tent.

Therefore, the conc~ntration.of Pb alon~ was determined in this

case, by the cathodic diffusion current of Pb(DDC)2' .,from the

\ D.C.polarogram. Thus the Zn content could not be determined.

IWith the addition of benzene to the' sYBte~', a hump waB

observed in the base-line of the A.C.polarogr~ (Figure 25, p. 99). 1· . (

The origin of this wave was not understood. It might be assa-

ciated wit,h the adsorp tion phenomena of organic compoundà on the

, \ DME. This wave was rep~oducib1e, and aIl other waves cou Id be

corrected for this baseline change in the 88.1le ragion. ........ /1

Therefore,

quantitative determination~ in ethanol-benzene solvents were still l '

possible. . ,

1 (

( r

, or'

a. ,; i

t "

•

(, 1 1

b.

/

( ./

, , <

ii

...... ".140 Il

r

96

FIG.24 !

D .. and A.C. polarograms 'of à mixture of Z,b(T1A)2

and Pb(TTA)2 after tit~ation wit~ NaDDC, and

D.C.polarogram of the mixture before tit~n J

Supporting . C.lM LiCl . elect:z;-olyte ./

Soltént . Ethanol, .. , .

Electrode D.M.E. ., ri ---,,,.

Typic-al 1 ~.r- '1"

ampe~ometric titration graph of the ~

mixture of Zn(TTA)2 and Pb(TTA)2 with_ a, standard

solution oi NaDDC by using A. C. pOlarJgraphy

/,

\

, ,

' ..

'"

/ '

[.,

(

1

(

r '

FIG.24a

Il\Ja(A.c.)

97

/ .

/ "'. /,..~/

/ 1 / .

/ . ./

,JJ!. -' o .1lJa l (D.C. )

... ;.t. '. H .......... --;,. v •• ••

ffio~~~···~~~~~~~~~~~~----------~ p:: Q~'2 0.4 01. .• 6 0.8 1.0 1.2 ;1..4 [5' u /1 -~ (in volts V.6. SCÈ)

. ,// ...... Residual current(D.C.) . V"/" --,- Zn('rTA)2 and Pb(TTA)2 together, f ,/'., each 10-5M, befare titratian.(D.1. :1' - ;-._. Ti trated solution containing .10-5~

excess NaDDC.(D.C.)' , 5

--~ TitrFte~,solution~containing 10- M exc&ss NâTIDC. (A.c·)1 -1 / _.~

FIG.24b

i, O.lml i

o~----~~-----------~----------------~ ML OF 5XIO-3M NaDDC ADDED

• 1

- l { .

1 'j,

.."

, . . '

i ()

(. i-

Il ~1'

1

\ \ \ '

1 f'

t' ~:

1 1"'

il ': • 1

g

r ~;

~ f{\

~J ?t 1 .; ) C' .

, ,

#.

1 1 l

/

.,.f ~~' t: 98

-' \ - ~ '"; \~>

.& -~ ,

'f

'1

;' , (

FIG.25

.. Residual current fo~ an t.C. polarogram of a solution

'\of O.lM ~~Cl in ethanol and ~n l:l!'(v~v) ~than~l-\ ~enz ne mixture, using a drop~ing mercury electrode,

-1-(t'

.. . " ,0

,/

\

.,' 1 1 "

Q,

, , 1

o

- ,

\ ,

. ' -f

, "','

. ','

(

.

,/

.. 1

'\

of

1/

fi

1

1\,'

.,'

~

.. /

: -(

..-,

~ .

t"~

,,(1~

; t 1

h i

l f :- j f.'

,I o ,

f , ,

(' { .

! ' " :~'

,-

} ,

/1J4 t

~

,

A

"

E-I

ffi ~ ::J U

,

0

\1/\. ... r

/

') / \

. .., 0

FIG.25

f.

' ..

0.2 0.'4

, :

!I,

J ,1

f" \ _ 1011;)( , ;'''.4PW4'QA = ".al . ~

(,

99 1 "Ii f ,

41 (JI)

~~~ J ) ,1

f

- ethanol , ... ',1.. '1 : 1 (v Iv) ethanol-benzene

~ '" J.

0

r ...

lJ.la

/

"f'}-

. ". ~ ... .. .... .;.i" ~

0.6 0.8 , log 1.2 1.4 1.6 1.8

-E (in volts v.s. SCE)

r'

,.

,/

, .

; r ,< " 1

Il '" ~~ ). ' .. ' ,i ,v ,

"

, î .. 'f

Ji-

I.!

(

1 " .

, ' . ,

/ 1

100

l '

iv. Cd(TTA)2-Zn(~TA)~mi~tures 1

As in the case 6f Pb(TTA)2-Zn(TTA)2' a D.C.polarogram did

not give good resolution of the Zn(DDC) 2 wave, from that due to:

-NaDDC. Therefore the total metal content could not be determined

/ amperometrically by D.C.polarography. However, A. C. polarogra~/) ,

l

could be used because then these t~o anodie waves 'were resolved

(Figure 26)._' The total metal content ~as then determined as in

the case of thé 'above b;l.nary mixtures.

In order ta determine the content of one of the/two metals

in the titrated binary mixture, \)

aD. C.'Polarogram of the soludon

at the end of the titration was obtained. 1 0 • ( ) The campI ex Cd DDC 2 /

has a reduction wave starting at -0.70V (see D.C.po1arogram in

Figure 26a). Zn(DDC)2 did not interfere since its reduetion

wave showed up at a more negative potentia1.' Therefor~, Cd was ô 1

1

determined from the diffusion ~urre~t of the Cd(DDC)2 ~ave. The 1

difference bet eeni the total meta! Iconcentration and that of Cd •

gave. the conee of Zn in the mixture. l

With a Cd Zn }atio of 10:1, the above procedure still gave! i ( 1 _ 1

good/results. But'with a Cd:Zn ratio of 1:,10, the wave at - 1

: -O~. 42V. which du, to Zn(DDC) 2 started to interfere with the

to:exeess NaDDC added and made ite difficult to 1'" rI

pofnt of the titrat~on. .~P this ,case, only a 1

D. C. p01arogr

/

(

1

and the Cd

of the mixture ~o'~ini~" exce •• tit; •• t was ru

centration was dete_rhed fro"!, the diffusion eurr nt'

, 1

! •

,/1

il

o

l 1

l 1

.1 ,

, -::

('

~[ '\ il ,,'!

1 ) ,

I~\.

..... :-

i l._.~~..,--....,..--.-....,..

.' ~

101

J

FIG. 26

/

a. D.C. and A.C. polarogram, ot a mixture of Zn(TTA)2

and Cd(TTA)2 ,after titration, wi~~ NaDDC, and

D.C. polarogram of the mixture before titration

Su~porting : O.lM LiCI electrolyte

Solvent Ethanol

~lectrode D.M.E.

b. Typical amperometric ti tration graph of the ; ..

mixture of Zn(TTA)2 and Cd(TTA)2 with a standard 1

Bo'flution of NaDDC by· using A.C.polarography

.. ~ .

~

1

·1 1

r '

J

o

-.~~~.~'-Q __ « ___ -.,~,,~_ .. ___ gM~J ______________________________________________ 1 ___ _

o

, ~a

(

~ ..

(

j

.'

"

FIG. 2 6a

11\.1 a (A.C.)

H

102 ' , y,"

",/ /,,,,,/

, 1 / .

. -.- ~.-

' ..

•

.... S1 0 ~ ~~O~J*2~O-.~4~P~··~.~O~.=8~1~.~~~--~--------~

. ' ........ ' ..

u /~ -E (in volts v.s. 8CE)1 i .. ·· .. Residual current (D. C. )

/~ ---Zn(TTA)2 and Cd(TTA)~ t~gether, ,-

/1 each lO-5M, beflore titration. (D.C.)

/ : /

-'-'Titrated solution containing 10-5M excess NaDDC. (D .,C.) , 5

l " \ - Ti trated sOlutlo,in con1laining 10- ~_. _

excess NaDDC.(A.C.)

1

FIG.26b

Measured by A.C.polarography at -:;:0. 55V. Frg.26a)

1

/ I~\.Ia /1 /

~/ ,1 .1/

/ -<,f-

T -x-x-x-x":'x-x4 ,0 .lml

o~--------~----------------~--~----~ ,

ML OF 5XIO-3M NaDDC ADPED

".'

i ~-;,,!~ 1 _____ " .•• ~ _________ ~ ____ ~"~ ___________________________________________ ~ ____ ~ __ _

'.

(

'1 _. __ }"""cl!!_ ... ,.;_ ...... _ .. _ ...... _a.;:.' .... I1_"' __ " ____ ~'*"'~ ___ _

103

... ~1

due to, th~ Cd(DDC)2 wave. Thus, th~ zi~c;~ontent couJd not be ,

determined.

At pH values great;r than Il, the complex Zn(TTA)2 d~d'not

reaet ~th NaDDC whereas Cd (TTA)21 did. Therefo~e, on~y Cd was

determined at this pH. o \

v. Pb (TTA)2-Cd (TTA) 2 mixtures ,

r In this m~tal pair, the total metal concentration could be ~,,;

determined amperometrically, by mefsuring the anodic current of

the excess titrant. Ho~ever, both Pb (DDC) 2 ,and Cd(DDC)2 have i

cathodic waves at a~out the· same potentiaL Moreover, bath have'

no absorption in the visibl~ region. Furtherm~~~, both Pb(TTA)2

and Cd (TTA) 2 reacted with NaDDC at pH'.o'greater than 7 f (see. 'Pb-:Zn , r r

an4 Cd-Zn, above). Therefore, lit was impossible to determine

the individual metaIs in the mixture by using the teèhniques ( .

prescribed in thr.wark'r'·,

vi. 'CU(TTA)2-Zn(TT~)2 mixtures 1·

The totall.metal content of a, Cu (TTA) 2-Zn(TTA),2 mixture could

not be determined amperometrically by DME for two reasdns. First,

the anodic wave due to Zn (DDC) 2 an? NaDDC~ere not res91ved in -a D-C polarogram. Second, the anodic wave due tp NaDDe (as eXceS8

t:

:"TI< titrant) and the cathodic wave due to Cu(DDC)2were not resolved "r

in an A.C.po~~rogram •.

Results for the amperometric titrations of bi~ary met;1F

A systems are shawn in Table 8.

. . .

--

""

------ ~

ACèura~y and Precision of Amperometric Titrations of Binary Meta1-TTA Com~lexes in Ethanol and Ethano1-Benzene Mixtùres with 'a Standard Solution of NaDDC in Ethanol

Mo1arity of standard NaDDC solution = 0.005 Vo1ame of solution =' 25ml SUP20rting Electrolyte =1 O.lM LiC1 E1e~trodé =' D~

~

« '\

\

" "

, \'

---"

'~

~ Mo1ar Ratio

Solvent (Ml) : (M2) Applied ~-~ -~~~" 1. i '.., '

H 1 ~ g Ml 2 ' ~,g M2 1 1 2 \ p VO tage d % dif d % dif J. SCE 1 ~. '., 1 s. . 1 • , ,

~. i~ -' Takenl Found J Taken Found l" i /' .of" 0' ! 1 ... ~_ Cf

, 1 1 1 6.8 -0.60(D.C~ 32.1Y 32.70 0.40 ~.70 104.0 103.1 1.0 -0.87,absorptiometry

9.0 -D.6D(D.CO 32.15 32.~O 0.36 +1.07 104.0 102.9 1.1 -1.07 EtOH 10 1 7.5 -0.60(D. q 58.45 59.20 0.61 +1.27' 18.9 '18.7 0.19 -1.06 l 10 7.8 -o.60(D.C~ 5.85 5.80 0.05 -0.86 189.0 187.2 2.0 -0.96

~l(v/v) EtOHlcpH 1 : 1 7.5 -0.60CD.G __ 32.J_5 3~"-60 0 __ 44 +1.:J8_104._4 10J.0 1.1 -0.97

Cu Ni---1 f- 7-:3 ':O-:-46(D.C~ 25.72 26.05 0.31 +1.15 23.56 24.10 0.26 +2.20 8.2 -0.40(n.C1 25.72 25.84 0.26 +0.50 23~56 23.95 0.25 +1.62 po1arography 9.2 -0.40(D.C~ 25.72 26.38 0.34 +2.50 23.56 24.16 0.31 +2.48 " .... 7.1 -0.40(D.C~ 58.45 60.02 0.70 +2.60 5.33 5.40 0.06 +1.30

EtOH 10 1

1 10 7.4 -0.t.0(6.cJ 5.85 -S.73 0.07 -2.ao 53.3652.54 0.60 -1.56 1!1(v/v} 1 II

EtOH/cj>H 1 1 7 .8' -o.40(D.C~ 25.72 26.08 '0.32 +1.38 - 23.56 24.00 0.29 +1.83 Pb Zn 1 1 7.0 -0.55(A_~~104.0 103.5 11.1 -0.50 154.0,153.0 1.6 -0.65

EtOH 8.0 -o.55(A.CJ104.0 103.3 1.2 -0.67, 154.0 152.9 1.5 -0.72 p01arogrâphy 10 1 7.2 -0.55(A.C,)189.0 18A •• 2 2.2' -1.00 28.00 27.45 0.32 -2.0

1 10 7.5 -0,.55(A.Ç,) 18.91 18':75 0.20 -,0.85 280.0 ---(4) 1: 1 (v/v) ) ~~

EtOH/tli _ .1-=-.1_ . 7.5 -0.55(A.G.)104.0jlOj.4 1.2 -0.58 154.0153.1 1.7 -0.78 Cd Zn 1 1 S.O -0.55(A,C) 56.2a ... 35:-S00.62--0. 70 1!)4.0 154.3 1.6 +0.19

EtOH Il.5 -0.55(A.CJ 56.20 55.60 0.64 ~1.0& 154.0 po larography 10 1 7.0 -0.55(A.C~102.2 101.3 1.0 -0.96 28.0 27.8 0.31 -0.7

1 10 8.0 -0.90(D.C.) 10.23 '10.35 0.11 +1.17 ~80.0 1:1[VTv) EtOH/~H 1 : '1 '" , 7.8 -0.55(A.C) 56.20 55.70 0.59 -0.90 154.0 153.0 '1.6 -0.65

~ean'of 4 determinations. 4Cannot be determined. 2 -. %difference beeween the amount of meta1 taken and the amount found.

3 ' !he ~unt of Ml Was found b~ direct mea~u~ement ($ee Laat cplumut and the total of Ml and fo~nG b1 d!tec~ tltratiDn. l'nQ .~~nt OT ~2 was fnen ~~~nd ~~ dl(feren~e. ~.

, :\

1-' <::)

~

, ,

1 -l

1

q.

l , ( [ ", \'

(

(

c

, r

" .

1 \'

I~

105-

/

Procedure for the amper?metric titration of metal-TTA systems ~Y

using ,a RPE ! il

a. Single metai systems

Standard soluti~n~ of metal-TTA were preparea as deseribed

" in Section IV.C.le.

Each of the complexes Cu(TT~2' Pb(TTA)2. Cd(TTA)2' Ni(TTA)2'

• ~! and Zn(TTA)2 in a l:l(v/v) ethanol-benzene solvent was titrated

J _

separately w~th a standard NaDDC solution in ethanol. The

analyte wAs O.lM in LiCI, with LiOR added ta provide tpe require

pH, and these also served as the supporting electrolyte. The

cûrrent-volt~ge curve was' recorded from +O.10V to(-O.40V versus

SCE.

At pH values above 7:0, none of the metal-TTA complexes . i

produced a wave ~,the range O.OV to +1.OV versus SèE.

1. Cut'ITA} 2 '.

The current-voltage c~rve obtained )during ~he titration of ~ ~II ~F. "

Cu(TTA) 2 with NaDDe was found to depend on the pR of the solution:

With O.lM LiCI, and at a 'pH less than 8.5, an ox'idation wave

appeared which started at +O.50V and reached it~ diffusion value

at +O.7QV versus ,SCE, when the Cb:D~~ r~tio was less than 1:1.

As more DDC was added, the value of the.diffusion current at , ,

+O.70V did not change. However,'a shift of ,the wave to less

positive val~es wasl~b8~rved. Thus, ~hen the ratio ~Cu:DDC had

reached 1:2~ the wave started at +O.jsv and reached its .

r , "

c

('

"

1. 1

r

• i

';

-----------/ ---- --_._-

106

diffusion value Beyond of 1:2 for

started at

O.05V àn~ reached its maxim~m value at +O.20V (Figure 27a).

For solut~on havin~ a pH les~ than 8.5, the wave which f

, started at +O.50V was at;tributed to the oxidation of the

Cu(TTA)(DDC) mixed complex, rand tna one starting at +O.30V was

attributed to ~e oxidation of CH!j>DC) 2' .,

,,,. When thé pH of the solution for titf8tion exceeded 8.5, the

, . oxidation wave observed 'at pH less than B.5 due to the complex ~

did not appear. Instead there was a wave which started rat '1

,

" r

/ -- -+,---- .. ~

+O.30V, and the 'diffusion c.urrent incre~sed in proporUon ta the ,'. /

N;;illDC added, up to 'the end point.,

,A typical titration gr~ph i8 shown in Figure 27b. '"

"

There was sorne slight evi~ence'of a wave due to t4e oxida­

tion of thelb-DDC complex (Figure 28a). However, this wave f

occurred atsuch a high positive potentiaI th~t with the present

system, its diffusion'current W8S not regiatered before the

oxidatio)'{ of the solvent occurred/.

" Plots of the voltammetric eurrent at.two dif~erent voltages

vere made against the volume of titrant added, t'o give the

titration graph~ (Figure ~8b).

,.

J rli§b; •• '''9' 'iŒWS55G

, J

,.

r •

---- --- -~--

(

, 1

1

.... ~ 1

~,( [~,-", 1 ~ 1

<,

"'­J '.f

Supporting O.IM LiCI electrolyte

Solvent l:l(v./v) ethanoi-benzene -;-~-- .. --- -------------------------~~-

Electrode : tt.P.E.

b. Typical amperometric t1tration gr.aph of Cu(TTA)2 l, ,

with a standa~d solution of NaDDC in ethanol

, r

\

Iii ' , .

"

- 1

\

l ' , 1

. ,

(

"

"

" <'

c

( 1

!(}8

"

FIG.27a

, ....... Residual current ---- Molar ,ratio of ICU( TTA)2/NaDDC = III

Il _ .. _ .. ~olar .ratio of CuC TTA)2/NaDDC = 1/2

-·-·Titrated solution of 2xlO-5M Cu(TT~)2' conta~ning lO-5M excess NaDDC, .

f-i Z '~

gj 0 .' B.:' .+{,.:S

... " .. , • .,.. ...... ...-" .... _. f" !:? ............ ..... .

-0.4 :!

1 u

E (in volts v.s. SCE)

FIG'.27b " X+0.34V

Measured a~ Cl) +0.65V

(Fig.27a)

- ° l '

.' / /~

o 0/

. IJ/ / --:1° .... 6 ... '-7. :t-,r 1 /

'/ . loT , . :f

/ j-/ O.lml 1 P X-X-i<->'-*:->t..f-. Il,

(

O~--------------------------~----------~ ML O'~ 5xlO-3* NaDDC

, '

[ . , ---. '-\ . , . "

1 ~. ,1

r if,'

/

.. '

1 1 1 1 1

!..

Il #

)

1

1

/

, ~ 1 l (

f '

i

J r r' i r ,l '. }

, ~ J

109

FIG.28

a. Voltammogram of a titrated soIut10n af Pb(TTA)2

w1tb NaDDC as titrant and containing exceSB NaDDC

Supporting e~ectrolyte

O.ull LiCI

Solvent- ~-: Lü(v/y) ethanol-benzen,e _ .' ----- l /"ctrode :/ R.P.R.

1

,b. Typical amperometric titration grap~s of Pb(TTA)2

with a standard.sol~tion of NanDC~h"a~~l

l •

/'

\

",'

i! /

...

l ,

l 'l

\

1

1 ~ ! "

1

(

'i (

, 1

/

\

0

110

FIG.28a

/< ' , ,

........ Residual curren t

-'-' Titrated solution of lO-~M Pb"( T~A):~ . 1

and containing 2XIO-5M excess NaDDC.

•••••••••• , ••• " ••••• )._ ••• ,. "'0'

~./O +0.4 . -0.4 1

i E (in vol t sv. s.

,,; .... ,­, .

FIG.28b

_ ..... ,/

~.?-

SCE) " ,

" \ ,

X +0.40V Measured at', (fJ,Jf~28a)

• (1) +Q • 60V '~.

Il)l8 laJ .. '~I " / /0/TI

C) if-

ri! - I~<.( . / '/ ----.

, 0/-.0>/+ O.lml ti)""'o- ;f

~~~*-X-~ , ~

l~L OF 5x~0-3M Na~)DC A~DED j 1

..

, ,

.'

. "'

, '

1,.,.1

, , "

,,'

t ~' : ,;

" "

.; . i

-...

/

c'

, ' 1

(

, ______ 1 ___ ,

111 (.

iil. èd(TTA~2' Ni(TTA)2' and Zn(TTA)2 o

JNo oxidation vave due to the oxidation of these metal-D~C

complexes vas observed (Figure 29a). <:...l'he titrati.on graph was

\ ,

'obtained by plotting, the' diffusion current due to excess titrant' ,

againJt the volume added (F~gure 29b). {;

For a11 of the above ~éta1-TTA complèxes, the RPE gave a

higher v,oltammetric sensitivity than the DME. The reason ls that

the solution was stirred,by the rotating electrode, 50 that more

e1e:troact"~pecies wer~ brought~to the electrode surface than /'

by diffu~'ion alone, so t'he c~r];:ent, would be expected to b~ en-

/hartced. r

Results sbowing the accuracy a~d precision~f th~ titrations

, for the single,matal-TTA systems, using a RPE:, are shown in

Table 9.

b. Binary metai system \11

The ~tal pairs, Cu-Ni, Cu-Pb, Cu-Zn, and Cd-Zn vere taken

for analysis. In each case the meta! was present as the TTA '

complex. IThe proceduresus~d ,are those described in Section IV.C.l.e.

The RPR was used throughout.

/

This pair vas chosen in or der to compare its' behavior"with c',

the,RPR with that prevlJu'sly reeorded for a DME., In using a

~E, ,the Cu-DPC complex ga~ an oxldation wave but that of Nf did . l '

in h Il ,If not t e vf tage region of ipterest. However, lt was not

j ,1 1 1

--i-..

/

, ,

"

. \ ,

~­

" .,

.1

. i 1

, t

-r

i,

J

1 1 , , ,

i

~I ,-. .,.

~ l

'\

(

a.

\

( bO!

\.

- j

1

~ -

112' .. /',

1 1 1 •

FIG.29 ..

Voltam~o~ram of-a tlitrat~d'solut'ion of Cd(rrTA)2

wi th, Na~DC ,a~ ti t'rant and containing exc~ss ~aDDC

'II

/ ,

Supporting : O.iM LiCl electrolyte

Solvent l:l(v/v)

Electr:ode R.P.,E._

" , 1

ethanol-benzene - ~ - - ----0 -,

Typical amperome~ric,tit:r:at.ion graph qf Cd(TTA)2 /

with a standard-solution of NaDDC in ethanol 1 • . ,. , !

- 1'~ ~

/

~ : i . :'

,1 " 1

/ g,

, ,

, . . ' \; ~~'

, , ..

. /

/

(

. '

~i

(- "

/ ,

• 1

r -~ \

, ,

, .. , /

1

.' ! " j

"

. '

l' . ,,'

" , ' .

" ~

'/ .r

of -.1.

> -

/'

...

, ,

,l

! ' "

'1'

>~

"

, , , , ..

l' l

~ t. 1

" ~

. , i , 1

t , (

! J' ~. ,. 1 \ ! 1 t <' ~ , . ( 1

. t , i

J ".

, 1 ,.

a

O(

l '

" \

c ," ,

, \, ~l

\ '

-' :

"

fp

1 \

1

. , .' (

;;

l'

E-t

_ , 1

" . , ----. __ ._--.. -------_. -- .. ------..--

1 113

-,'

FIG.29a

..•... Residual current

_._, Titrated solution of 10-5M Cd(TTA)~ and containi~g 2XIO-5M excess NaDD6.

~ O~--~~'~"-'-"-'-"-'-"-'-'-'-"-'-'~'-'~~--'---'-'-'-'-''-'-'-'~~~----~ B ,' ... +0':8 +0.4 ;' 0 "'-0.4

f-4 Z

~ u

0

,,' ",'

.,--"... ...... .,.....--.

~i E (in volts y. s. SCE)

FIG.29b o 1

( Î 1 !,

t

' .

!

Il •

Measured at +O.40V (Fig~29a)

O.lml ['

ML OF 5XIO-3M NaDDC ADDED

" "

L: .. ___ 1 ,H

(j

\

o

ï,

/

" \~ ~~

~ ,~

"

al

! î

,I 1 1

~ 1

î

. 1

"

C ','

- --, -_._--".,;;..- 'i ,.. .

é> Table 9. Accuracy and Precision of Amperometric Titrations of Si:nglé

Metal-TTA Complexes with a Standard Solution of NaDDC in Ethanol

Molarity of standard NaDDC solution

Volume of solution

?upporting electroly~e

Solvent

Electrodé

:::

=

"" = =

~ . 0.001

20ml

O.lM LiCI

1:I(v/v) EtOH/~H

·R.P .E.

.[)

Applied Voltage lJg of metal dif2 -Metal pH ù V.s. SCE, volt Taken J'ound1 s.d. %

Cu 7.5 +0.34 25.74 25.96 0.26 +O'~84

+0.65 25.74 25.96- 0.26 +0.84 r

Pb- 8.0 +0.40 83.21 82.66 0.76 -'. -0.67

Cd -7.8 +0.40 45.50 45.86 0.44 +0.78

Ni ,.'-'l

7";'8 +0.40 13.85 13.74 0.15 -0.80

Zn 7.8 +0.40 26.24 26.50 0.22 +0.98

1 determinatiôiu~ Mean of 5

2% foùnd ./ /

difference between the amount of metal taken and the amount rri .

.} .;.f)

,

, "

. 1

r

)

i . ___ <"----...,.y ••. -'---.,.,~~_~~_w".~~ ____________________ ....... ___ • ______ _

, "

, , J , , ',l!

è ,

, ~ 1

/1

o (, , 1

j 1

~

1

• f ( 1 t

/,

possible to take ad1/antage of this fact to detemine the copper

alone in the mixture. by a titration. because the oxidation wave

due to Cu-DDC :bmplex was found to increasb ste:dily until the

end point for both metais was reached. ,This could be due to

b~th metal-TTA being titrated simultaneously, Le. the e9ui1i-

brium constants Kp and KZ for the foIlowing ,reactions: r , l ,1 ' ~ K

Cu (TTA)2 + 2 NaDDC ~

Ni (TTA) 2 + 2 NaDDC

were about the same.

Cu(DDC)2 +

1

2 NaTTA

Ni(DDC)2 + 2 NaTTA ,.

The total metal content of each solution was determined by

mea~ur1ng. ... 'ihê diffusion current of the wave of the tl~rant NaDDC,

for several increment~_ of it after the end point. A titration

graph ls shown in Figure 30.

The Cu(DDC)2 content"of the titrated solution was th en

determlned by measurlng its absorbance, and the Ni content was l ,

found from the difference of the total metai and that of Cu alone.

Mo1'lr ratios of' 1:1 and 10:1 for Cu:Ni were taken for

analysis. Th.~ interf,~rence of Ni(DDC)2 witb the absorbance of

the sought-for Cu(DDC) 2 prevented the use of DlUch high~r propor-,

tions of N~. Thus,! for a 1:10 Cu:Ni mo1ar ratio, interference 1

fx;om Ni(DDC) 2 became tao serious for quantitative work. Results

are shaWn in Table 10 (p. 122).

- 1

o

'\ \.

, r<­~, ,

a

/

\

. ? (

! t r. } !

, 1

(

(

(

r

a.

b.

..

;

!

\ 116

J • 1-

FIG'. 30 ,

Vol of a titrated solution of a mixture

(TTA)2 and Ni(TTA)2 with NaDDC in ethanol

as contalntng e cess NaDDe

Supporting el ectrolyte

Solvent

Electrode

•

:'l:l(V!V) ethanol-benzene

: R.P.E

~ 1 Il Typical amperometric titrat on graph of the

mixture of ~U(TTA)2 and Ni( TA)2 with a stand9-rd

solution of NaDDC in ethanQ

'.

1 1 (

1 ')

• 1

, r

L 1

/

1 1-

'. ;' , '

J. , ' .. '

î ' 1

, ,

,

!'

.J

(

(

(

"

, 1

1

., , 1

l'

H

1"1 1

_ thC!Mt

117 "

.' FIG.30a

.......... Re s idual cUfren t ,. -' "-',Ti trated 50 ution of a mixture of

1 Cu(TTA)2 and Ni(TTA)2' each lO-J<=M,

and contaïning 2 X l~;;?M excess NaDDC. , ~~'r]

. . . .. ffi ~ O~--~~--------~~-----------------4 p tO':8

• • • ',;.'''-- •• t .............. +0.4 1 0 -0.4

u ..

/

./ 1

FIG.30b

..-' ..... -'" /'

1 1 "" E ( in volts v. s. SCE)

. ' llla l

. ;:,-' ri

" Measured at +O.40V (Fj,g.30a)

-x-x-x-;--x---x- x

- -- ... --------- _1 _

/ /

• -.lé· :of -.-k.'!'" ./ -,.' , ;t'

/ t:.(

X, O.lml

1 1

O~------~--------------------------~--~ ML OF 5XIO-3M NaDDC ADDED

~--

J" 1

'.

",

1 r 1 !

F

1 Î'

!

1 1

--1

(

(

. ... ·-if

·1 1

_.1-_"_. _--.... .• ~ ________ _

118

\

i1.

In this titration. CU W(iS, (ound ta be titrated before Pb.

-By measuring the current at +0.60V for each incrbment of NaDDC, II

a titration graph as shown in Figure 31 was obtained. There are

four straight-line portions, and the intersection of eacfi pair

th en gave three equivalence points. The tirst break in the 1

grap? corresponded to a 1:1 molar ratio of Cu:titra~t; and the

seco~d ta a 1:2 molar ratio. By comparing this part of the

graph with that obtained on ti~rating Cu(TTA~ alone (Figure 27b, p. 107),

one can conclude that Cu (TTA) (DDC) was first formed, and it -

was then converted ta the Cu (DDC) 2 ~omplex on the add:[tion of

more titrant. Beyond th~ 1:2 molar ratio of Cu:DDC, Pb(TTA)2

started to be titrat~d.' Therefore"the third break in the . 1 -

titratfon graph. corresponded to the total metal content. \ 1 1

Th.ese results demonstrate"that ,for this system one titration ~

was'suff±c1ent to determine each individusl metal concentration • •• ';" r

That is, no sepkrate meas~rement>of the-diffusion ~urrent ~f \ ..

Pb{DDC) 2 the Cu(DDC)2 was required.

for Cu:Pb were used. Due ,

1 { ~. f'- of

to the curvature near/~h equivalence points, th~8e,ratios were 1"'; ~ ,

.. , - r' foqnd to be about 'the lim±ts for this ,binary system. ~

li~. Çu(TTA)i-Zn(TTA)2 ... ('~ ~ ,

A~> in the Cu (TTA) 2-Pb ('fTA) 2 $ys tell!. ~hree breaks were 1 J

. observed in the titration graph. / The first two c:orrespon4~d to

< ,

.> 1·:

-'/ .

(, P,

.'

'8

~!,

(

1 J

------------- -

119 . ; -

<'

,

FIG.31 .'

, Il

Typical amperometric titra t,ion graphs of a mixture

of Cu(TTA) 2 -and Pb( TTA) 2' each 10-5M, wi th a standard

solution of NaDDC in ethanol

Supporting : O.lM LiOl electrolyte

" Solvent l:l{v/v) ,ethanol~benzene

Electrode R.P.E. 1

FIG.32 ,',

Typical amperometric titra tion graphs of a mixture

'of CU(TTA)2 and Zn(~TA)2' eaéh lO-5M,',with a'standard

solution of NaDDC in ethanol

Supporting : O.lM LiC1 electrolyte

,

Solvent' (

Electrode

l:l(v/v) ethanol-ben~ene

. '

, J

"

.' 1 ./

• t 1 .

"

) ..

Î ,

,0

, ,

l , ' < 1

~ z '{

~ ~

!, =:J U

f-l' c

~ " ,~.

,,",

1 "

(

1 u

o '

;

.~' ( ,

1

, 120 \

Measured at x +0. 40V

[1) +0. 60V

ML OF-5xlO- M NaDDC ADDED

FIG.32

1 x+0.40~·1 Measured at

rD +0.60V

, ,

O.lml 1

o"-------~----------------------------------~ . "

ML OF 5XIo-3M1 NanDa ADDED

J ~ ,.1

1 1

1 , i

;.: , > . r

~, 1 j

1

'1 1 i'

t , \ , ;~

1: i: 1 ~ ~

"

-,.

/ .

1 •

(

c·

il 1 , i

t , , , , HF

t C-, r ,

1 t , t f f

~ J i

----------

121

Cu(TTA)(DDC) and Cu(D~)2 complexes. The Slope of the third 1

str~ight line was smaller than that of in the case of. Cu-Pb. - 1

The s1ight1y higher slope in this latter system canob~ accounted

for ~y the tailing in this region of the Pb(DDC)2: wave which

was not present in the Zn(DDC)2 system. A typical titration

graph is shawn in FiguI'é'32 (p. 119).

Thë* tit·ration w~s able ta be carried out when the molar

ratio Cu:Zn,was between 1:,1 and 1:5 without any problem. When

the ratio of,Cu:Zn reached-5:1, it was difficult to recognize

the th.ird straight-line portion on thè:titration graph due to

the relatiyely large curvature during the titration of' the Zn.. / '

This uncertainty is reflected in the relatively large error j/ recorded ij Table, 10 ~- -j ,

/ "

/ 1

By the titration of this pair, it was posslb,le only to A " ;, 1

ob tain, the total metal concentration with a RPE. A typical

titrsyion graph was simila!,to that for thf Cu-Ni system , - ;;

(Figure 30b). At a pH above Il, Cd(TTA)2 alone i8 titrated b~

NaDDC. However, it was nat poEfsible to monitor the excess NaDDC' .­(

in the solution sfter the cadmium end point, beèause the oxida-

tion wave of NaDDC became drawn out and ~erged with the solvent

deco.mposition wave (this latter wave was shifted to., a less _

" positi~e value at high pH).

Results for these binary metal-TTA systems are give~ in

Table, 10.

.",

, \ ,

'1

~

Table la.

!

,,' (

~ l'" 1

~ ,

... " Accuracy and Prècision of Amperomet~c Titrations Standard Solution of NaDDC in Ethanol

~ .. ~ \.~~'". ~ ~ _~~!rJ. ,j' ... ~ ..... ~-.. ....... ~' ~'"

With A -#

Mo1arity of standard NaDDC Volume of solution Supporting-e1èctrolyte

solution

of Binary Meta17TTA plexes

::: 0.005

. l .Boivent . Electrode

't~

::

= ==

20ml O.lM LiCl l:l(v/v) ethanol-benzene R,P.E.

Metals Mo1ar Ratio ~plied­pli \1"61 tage lJg Ml % dif ].J g M2 s . d •

Ml MZ (Ml) (M2) v.s. Taken- Found SCE, Volt

s.d. %dif Method >,

Taken Found

1 1 ,8~5 +0.40 12.87 l2~90 0.05 +0.23 13.86 13.85 Q.lO -0.10 absorptiometry Cu Ni

,~ ~-'l

. for Ml 10 : l 8.5 +0.40· 23.40 23.25 0.10 D.64 2.52 - 2.48 0.03 -1.60 ,

1 : -1 8.0 +0.60 12'.,87 12.61 0.07 -2.0 41.6D 42.38 -0.50 +1.86 amperometry • i for both

Cu Pb " " 5 : 1 8.3 +0.60 42.90 4l.9~ 0.44 -2.2 13.87 14.70 0.20 +5.60 meta1s

,1 5 8.6 +0.60 4.29 4.36' 0.03 +1.8 13.87 13.66 1.50 -1.50

1 1 ~

8.4 +0.60 12.87 12.83- Ô.08 ·-D.31 13.12 13.34 0.18 +1.60 'amperometry

------------------------~--------------------------------------------- for poth Cu Zn 5 1 8.3 +0.60 42.90 42.75,0.22 -0.36 ,4.37 ,4.:n, 0.08 -0.92 metals

-~_.- ---- ---------

1 5 8.3 +0.60 4.29 "4.37 0.04 +~.8/ 43.70 43.80 0.49 +0.30

j "\

, 1

~r

.;; '" ~ _1-_ .,.

"

\.

",

.... N N

, !

\ -1

"

,1

(

>'

~

J'

,\ /'

·1 r 1· ( 1 " 1 f \ ' 1 , i

.1 1 i

, " 1 ....

t .

. "l ".

. (

. "

4 ma

c. Ternary metal system

Only one three-metal-TTA system was attempted, namely tha~ ,,-

of CU(TTA)2-Pb(~A)2-zn(TT{~2.)1A mol;; ratio 1:1:1 for Cu:Pb:Zn - .

was subjected to analysis using the proceùure described in

Section IV.C.l.c. The solvent was a 1:1 (v/v) ethano1-benzene r

mixture. A' RPE was used. and the titrat.ion with a standard'

solution of NàDDC in ethanol was followed amperometrica1ly •

By measuring the increase in the current at a voltage ~f

'+O.60V, the titration graph shown in Figure 33 w~s obtained. , "

The three metal-TTÂ complexes ~ere found to be titrated

successively; Cu (TTA) 2 was th~ first to be' titrated, and it gave

two breaks correspo?dingto the Cu (TTA) (DDC) and CU(DDC)2 complex

respectively. The second break was taken as the equivalence 1

point for Cu. The third break indica~ed the end point for ,

..-' " Cu+Pb, and the fourth for CU+Pb+Zn. Therefore, one tit;:ration .r'

'could give the three individual m~tal concent~at1ons • Vari~~s metal ratios were tried, and the results are ~own

----;, J,

in Table Il! The limits possible'for these ratio were the s~e l '

as those in the binary metai systems discussed in the preceding

section.

\</

1/

.1

'i' c

1 ( Î

l

l

, 1

,. . - --.._-...... __ ... _~ .. .~--------- ...

124

... FIG.33 il

Typical amperomètrÏ:c titration graphs of a'\ mixture

of CU(TTA)2' Pb(TTA)2 and Zn(TTA)2' each lO-5M, with

a st'andard solution of 1 ~~DDC in ethanol,

J

Supporting O.lM LiCl el,ectrolyte

Solvent

]neotro~de

: l:l(v/v) ethanol-ben~ene

R.P.E.

[ ,

/ , '

!

J ~

, . ff ,~ .. ~,

" .

• ..

. "

-\

1 •

f

,./

r , "

.;

L

" _·1 •

) , , ~~: , , ,

, " ""

\ ---- .

Ci

,4 ;. ,

{ 1 l

i " 1

1 -. t . f

! • r

~ C' t· t ~

.. Î 1 , 1 ! ! . ,1 ,

. ..

, l,

"

\ \

, \ -<'1

----" .,._-

125

, \

FIG.33

x+O.40V Measured at

- <:) +0:60V

Il .o~'

O.lml"

o~--------------------------------~-------

/

\ ,[

, ,0

..

ff

l, .,

, ,.

" 1

, il

'1-, . "

(----

, 00

- 1

/

/

l1'ablé 't . ,.

1 ,

--)---

126

1 -

Accuracy and Precision o&Amperqmetric Titrations of Ternary ~etal-TTA Complexes with a Standard Soluti~n of NaDDC in Ethanol ,

t'

- 1 '

-.......

<S

Molarity of standa'rd NaDDC solution :: 0.005

= 20m1 Volume ,of ,solubion

Suppor~ing electrolyte ~

Solvent

Electrode

= = =

O.lM Lie1

l:l{v/v) E~OH/~H

R.P.E.

Metà1 Cu Pb Zn > f

.-molar ratio . 1 1 1

(}.tg taken 12.87 41.60 13.12 l

p.95 }.tg found 42.25 . ' 12.90

s.d. 0.12 0.)"6 p.11 % dif2 +0.60 +1.50 -1.50

" r

mo1ar ratio 5' ;t , " .... 1 , ,

Ilg taken 32.17 1 32.11 Ilg found

1120 ~ 80 6.56 .;"f r

19.9i '" 6.64'

s.d. 0.29 0-.22 0.05 '% dif2 -0.20 -4.40 +1.20

molar ratio \'1 1 (

1 5 '.

lJg taken <1 6.44 20.80 32.80

jJg found 1 6.39 21.00 32.'40,

s .""d-. 0.04 o .1§' .r~' O.~O. '.

% dif2 -0.78 'l'Y

+0.95 -1.20

~ean of 4deterIllinat:l.ous'. The titration graphs gave breaks corresponding to each meta1. / o',..·~ *'" ' "

2 % difference between the ~mount of metal taken ajld the amount-found'. ", +t

l' r , \

1 -J ,

_~.1

0'

f

, i

," ,1

,1

f

--.

..

r'

, , ,

, ' , , .

o '.

, , : ,-

-: L

!

l~ .!

{ .

, 'J Î

".

"' ... ~ 'i

-;., ~,',,' ~\I"" ..

( 1

'C': \ . " .. ~ • J

,.

~ -- ~ -_-..-- '-

v. DISCUSSrOtf

"

(A) < ,Il

Problems in Nonaqueous Voltammetry

Voltammetry ~n nonaqü'eous ,m:edia is different in severa!

respects from that in water. On~ of the difficult1es enco~ntere,d is the ,) ~~ ~

relatively high resistance of most non~queous solut~ons conFàining the

supporSing elec,trolyte.', ;1pieal resista;ce values of the systems used ~ , ,

in 'the present work are snown in Table 12. The res1stance 18 of the , )

Qrder of 10-50 times as high as 1n aqu,ous systems., r"

The voltage apylied aer08S the two electrod~s was assumed te

be' the effecti~e voltage at~e working electrod~or cases ~here the \ r ., ~

resistance of the ~olut~on was smai1. In general r

,'.

'" E + e1ectrode E .

applied 1

fi solut1on E ref.

.­.... " ,

• .,.6 since the current is normally of the order of magnitude 10' amp., there-

" • ' l " ~

fore if Rsolution is 100-200 ohms (commonly the resistanee in aqueous ~ -

Il '1) voltammetr;), 1t 1s reasonable ta wr1te: "

E .. E -' E applied electrode ;l" ref.

~

,When,R 1 1 ls large, the aR term will become aigni-so ut on solution

ficant. ,Therefore, in order to 'get the effeëUve voltage on the electrode, ,

:I:R. éorrection~, have to b,e ,ade (26). '": ' " 1 iii ,A three-electrode or tl p()te~tiostatiè ~8teJa. can he used ''to ., .., , .

, 'f

mintmize t~1s iR correction, by the introductfon of a coun~e~ electrod~.

cutre~t ~assing thr~gh the reference ,~lect~ode (which may lead to J~ift

(- '1

, 1 , "

','

, ! ",

,,J ....

, .... ' , , ~:

i'

(

t , f

l'

l'

1 ~

i $

!, ~

1 ~( 1 ( 1

;~.

1 ' .

l'

128

Table 12. Resistance*;&i the Polarographic Cell for Several Solyents and Supporting Electrolytes, Measured Aeross the TerminaIs of 'th~ Working Eleqtrode'(DME or RPE) and the Reference Electrode (SCE)

Solvent ~

Ethanol !

l:l(v!v)

Supporting Electrolyte

O.lM Et4NCl11

Resistance, 1 ohms

1500

~

~ Ethanol-benzene O.lM Et4NCl 2200

{

"

1

o Ethanol

l:l(v/v) Eth a,nol-b enzene

O.lM LiCl 2900

O.lM LiC! 5080

*The resistance of the solution Was measuréd by a condu~tivity bridge (Indust~ial Instrument lnc. Madel RC l6B1).

l'

~--~ ,

, ," ..

1 /

.. . !

.'

1"' ... l "

,r

• 1

:st ciaa:az:œ::uzé:_ 4

1

1

1

1

~~. < .... ,...~ ..... -

(

, ~ \ i' g<

~ f",

t r

, ; (, ~

"

o

1 Il 1-

129,

of the reference potentfal) fs also avoided 1n this case.

In using an aqueous SeE or Ag/AgCI as the reference eleceÇode,

a large liquid junction potential will be introduced f?r t! nonaqueous

syJtem. In some cases, the use of a mercury-pool electrode can solve the

problem" while in others a specially designed reference electrode in organic

solvents has-to be used (27).

Thesè consideration~ are particularly importanf ~n Ith~ the~;_e:.-_\ ~ " -

tical study of the E1/ 2 v~tues of a system. ... -~

However, in this work, the main interest was in the determination

of the diffusion curr,ent of the electroactive specie~. Therefore the

above two problems can be tolerated. , Difficulties in choosing a suitable buffèr system posed a~othe~_

problem. Buffering the solution is very important in org~nic voltammetrY 1

sinee in Most cases the electrode,process involves hydrogen ions.

solvents.

Few inorganic salts are sufficiently soluble- in~most organic - 1 ~ 1

This fact limits both the solvent used, and the Bupporting

electrolyte.

lyte).s ~iClJ.

The 'most widely used salt for use as a supporting electro-1 1 1

~oreover, in the present work, a-tiCl/LiOH pair in

;t4ano1 and in eth.ano~-benzene mixturfs gave some buffering action-.

Another class of compounds commonly used aS,a supporting elect-

rolyt1e is that of. the' tetralkylammon~um salts, part~cula~.1~ tbe chlorides,

bromides, iod~es, nitrates _and perchlorates of the t~tramethyl,

tetraethyl, an~tetrabutyl ~onium ion~. They are ~e~'soluble in -"" ~ ,

ethanol, and when co~pled witn·tetraethylakmpnium hydroxide, theyl-

exnibited a buffer~ng effect. 'Moreovér, they enable )JOlarograms to be 1 /'.

" ,

-4

..

" '

;. j' , ,f

(

lille

1 . ( 1

,. i

'1

,J

1 (

! 1 1 1

~ . ,

/f"

./

.(

Il ' 130

record~d to more negative pote~ials th~n did LiCl. For exemple,

tetraethylammonium chloride when usedl as supporting e~ectrolyte gave a

cathodic range down to -2.4V. This reagent was used in some df the

present work, particular~y dur1n~the prelimina~ survey of the polaro-

graphy of the va~j;o s chelati~g agents. ' '

1 rometr1c titrations carr1ed-out in the present work

1

involved mostly' h~ reduct10n of the metal ion or the metai complexe

Therefore wheth r the solution was efficiently buffered or not did no~>; ~'i-

ffect t~e accuracy of the results. Hydrogen-ionà' :d~ust-

ary only because of the instability oL the sodium

diethyldithiocarbamate (which was the. titrant used throughoutY at pH

below 7. 'At a pH about 8, smaU fluctuation! ixÎ.....the concentration of the 1

~hydrogen ion h'ad no effect -on the accuracy of 'the titrations, as· in .. evide~t from the data However, in some case~

/

pH values much higher 8 slowed down or even stopped the t~t~at~on

reaction, as in the and Zn(TI'A) 2 •

; <.

. ,

1

f

f~" ,1

1 ~ l ,',

,1

, 1

1· '

~ " ~ .' , ~ }>

~: 1

f' l. ;, >,

! ! \

A

, i ,

J

(

C

r

___________________ ~_.~I __ _

131 J/

(B) Theoretical Consideration of the Current-Voltage Curves

Detai1ed theoretica1 studies of the current-voltage curves

obtained in this work ~eue not carried out. However, attempt will be

made to describe hhe o;igi~ of some waves • •

A~1 the chelates used in the preliminary survey contained

1 \

po1arographica11y reducible gro~ps. Most of the electrode processes for

the chelating agents were pH dependent, since the~ inv61ved hydrogen ions.

/

1 Il / With the buif'er used in' this work (LiC1/LiOH or Et4~Cl/Et4NOH), the initial

and final pH of the solution 'was found to be the same'. The voltages .

reported fbr aIl the polarograms in the presept w,ork were without,,iR drop

corrections, an9 we~e with reference to a SCE.

8-Quino lino 1

rl0 V'N J

OH 1 A detailed study of the' polarographic behavior of 8-quinolino1

. 1 in water was conducted by Kolthof~ (12). He f6und that in the pH ,range

2.5-6.0, it gave threê waves. " Il ,.

At'higher.pH values ,he observed only two

/

wav~s. He attrib,uted the tirs t'one to the reduction of B-quino1inol to ,

'"'" , ! the dih!dro compound, and the second more dra~n-out wave, to that of the ,

~

reduction to the dihydro compound~ the 8-quin01inate anion produced in f 1

However, there have,bee~ other interpretations~ the

For examp1e, Stock (19) propos:~d the .formation ~he' di~ydro~~:or Jthe first wave) apd tetrahydro-(for the second wave) 8-

the basic medium.

reduction 'waves.

quinolino1.

ri !

"

-

j 1 l~

, t 1

(

(

f ( ! j

1

.J

-> ~.: ,"

,;l .

2~N1troso-l-naphthol

. A stllall before the wave wh1ch startéd at

-O.60V. This prewave was prob bly due to the adsdrption of the ~mpound

o~to the mercury drop, where it would be reduced beforJ the reduction

potentiel of the -NO group was

~

pro cess for the -NO group has

1

-NO

Since hydrogen iops are of'

p~ of the )solution caus~d a shift

Diphenylth1oca~bazone (dithizone)

0, H H

" .1 N-N \ C=-s

0 / \. ,;) N=N .

The polarography

at -O.60V. The- latter electrode

postulated (13) as follows

2e -NHOH

reduction, a change in

, een s tud1ed by Tomcsanyi

o

(51.52,53) • He reporte~ bath a redu'ctiOl1 .an oxidation waveJ an~ •

rtt:r1bu~ed the cathodic wave ta the aao group to gi~e

the hydrazo compound

/,

!,

, ~,

.1 "

'I\" l'

" . ,. ,(

, l

(

(

,.-l

1 il ' ,

C H -N=N 6 5 "

C H -NH.:.N 6 5

C -., C H :"NH-NH 6 5 ,

~ ~ C H -NH-N

6 5

C -

~,:..r -----~ a DME, he att!ibute~ the'anodic wave to the fo~ation of the mercury

chelate:

2HDz- + Hg = Hg(HDZ)2 + 2e

1-2-pyridylazo-2-naphthol

HO

O."N=N-f

1 N f , 1 •

The re~uctionof this compound Jas 8uggested as being due to

the following electrode process (54)

-N-N-

( 1

. 2e • -NHNH-

Dimethylgoyoxime, a-Benzo±noxime and Salicylaldoxime

1 . 0" :!IH O·~ -c - C 6H r'JOH"

Ir . a-b enzoinoxime

. . 1 CH3-C-C-CH

Il 1 U . 3 HON NOH

d~ethylg1yoxime

r ,

'. 'l'

, , ,

, "

/

/

(

1

1. 1

1 ( t -

! 1

J

-----------, ___ e

134

1

0> 0, CH=NOH

(_ ~ OH' C

Salicyla1doxime ..

The shapes of the polarograms of these three compounds were

Each exhibited irre:versib1e W'av~ which were due ta the reduct-" .. ;­

ion of the oxime group (i3). The fa ct that the starting potentials were

different is probab1y due to the difference in the substituent groups in

each compound.

2-tpenoy1trif1uoroacetone (HTTA)

CJlI IIH2

s C-C-C-CF Il Il 3 o 0

E1ving et al (22, 55) studied the polarographic be~avior of

this compound in,water and in some anhydrous solvents. lt exhibited two

or more waves depending on the pH and- s6lvçnts; beyond\ a pH value of 7. J 1

two waves appeared. Duk to ",he dit ferenèes in the proportion of enol to #Jt-:fJ

1 " keto forme th~t exist at various pH values and solvents, the ~eduction

waves are close1y rel,sted to the pH of the system. r .'

The electrode process in ethanql and in vater consists of' the

reduction of the -C"O grouJI to the C-oH group. At pH~aluesabove 7, the.

first of the two reduction waves occurred at a poténtial starting at ~v'

-1.4V,· and was shifted to a more negative potential at a pigher pH ~a1ue.

This fact was one of the mbst ~mportant reasons for choo,dng the' metal-1 1

·,1

1

, : :'j ,1

1 , J , ' .. ~

" J ". !

" .

' ..

, ' l ' . ,

',l,

(

c

-(

1 -.-.-

135

chelates of RTTA as the species to titrate in the present work, sinee

this choiee gave a clear ra?se df potentials for the polaràgrams 'or the

metal and the metal complex, without interference from free RTTA present

in the solution being analysed.

Sodium dieth~ldithiocarbamate (NaDDC) . 1

At a bME, tbe electrode proeess proposed was as follows (21)

with a rapid dèepmposition of the,R2NCSSHg formed: Il

Th~ NaDDC was also found to be

(R2NCSS)2Hg +, HgO

oxldized at ~ (.58 ~ 59).1'- In water,

there were two oxidation waves observed. The first was attributed to

'the oxidation of the sulphur in the sulphydryl group (at a voltage of

+O.40V versus SCE),.and the second to the oxidation of the sulphur linked

to the carbon by ~ doubl'e bjlnd (+0. 8OV) • However, in this work, o~ ustng l

athano1 or l:l(v/v) ethanol-benzene as the solvent,

w'ave was observed (starting at O.OV). Jf

l ' ;'V' J d" The polarograms of sorne me~l nitrates or

1

cOmp~exes, and m~tal-DDC compl~es in ethanol or an

, '

only fne oxidation

\ ' 1 ;'- ~

ChIO~ metal-TTA

ethânol-benzene

\

"

/ "

1 1:

." '~,

"

• r

. , j l ,'-

, 1

."

(

i'

1

"

1

! 1 C _. 1

! 1 1

[. 1 1

..J

-""'---~----_.--_. _. -----""-----

136

mixture were shownrin Figures ~, 3, and 5 respective1y. 1

A comparison of

the E1/ 2 values of the metal nitrates or c~lorides in v~ter and,in

ethanol (from ref. 56), with those obtained in the present work for these

salts in ethanol are shown in Table 13.

The differences in the EI/2 values obtained from the literature 1> ~~ ..

and those in this work are probably due to diffërenc~s in the experimental

conditions. Specifieall~ differences in the liquid junetion potential

of the systems~ in the value of the iR drop aeross the cell~ and in the

chloride-ion activities (the sUPllorting elèctro,lyte was O.2M LiCl in the

literature, and D.IM LiCI in this work).

However, it is particularly to be emphasized that for the non-, 1

aqueous syst~s~used in the present wQrk, the electrode reactions wfre

irreversible. Therefore, it would be ~uite incorrect ta consider the . Il . (

El~2'values re:orted in Table'13las aïrthin? ~ore .than em~irica1 quantities,

th~t have some praetieal utility but no theoretical significance.\ , \

The oEl/2 values ~f Cd and Ni reported in Table 13 were found to

become less negative as the die~~fttriF constant was d~creased (from . /' \

,waté'r = 78.5 to ethanol = 2 .3). D~Vries explained this shift by

suggesting that the c plexes formed in- low [d~e1ectriè media we-re less t" /" ,

stable and reqUire~ ,Jess .~nergy \o~ the r~dU~tiOn than those iormed in

the media of ~high dielectiic con'tant. In this connection, it must' _be f

noted that some of thése electrode reactions were reversible, and some

.~ not, so that caution'is neeessary in any interpretations.

!\ "

.C>

f,j

~I 1

(

i ~

t c 1

i

J

Il

1 Table 13.

. 2 Metal

Cu

Pb

Cd

Ni

Zn

\

, ,

,l37

H;lf-wav_e Potentials of the éu, Pb, Cd, Ni and Zn Obtained in Wate'r and in Ethano~ with a Drolwtng Mercury Electrode and O.lM, 0.2M LiCl as Supporting Electrolyte

3 Water

-0.169

-0'.638

-0.926

-1.032

Ag/AgC~

1 El / 2 in Volts, Versus

\

; .. 3 Ethanol'

1 -0.280

-0.797

-1.209

\

lIt i5 to be noted that Ref. 58 doés not specify whether or-not the eIectrôde l reaction w~s revlrsible; hut in tpe present work it was irreversible for! aIl five etaI systems reported here.

2 The metals were present as chlorides for columns 2 and 3, and as' 'nitrates for column 4 (except for Ni,which was present.as chloride); HTTA was absent. The pH was 7.0 for the solutions in,column 4.

-:3 _.-r- J ,.< , Ref., 58 (Ei/2 corrected for IR drop).

4 This work (E1/ 2 not corrected for IR drop which was approximately 0.003 volt) •

. , !

, "

, < , ,

li

,'J ,1

{

c •

(,1 , 1

Il

138

\J

Il

Some metal-DDC complexe' were also studied polarograp~ically

by Cordova et al (48). ,Some of his E1/ 2 valu~s are shown in Table 14.

Again, it i8 important to note that he did not report whether or not the

electrode reaetions were reversible.

In general, a shift'in the po\arographic waves to a more

·-r:e'gative value ~as 'observed when the metal was complexed with TTA. and

an even large~ ne~ative shift when the !TA was rep~aced by DDC. The

shift in the reduction wav~ ,\f a meta.l ia related to the stability oI

the complèxed metal by the'following equation (57),,'provided that the , '

electrode reaetion 1s reversible: 1

-0.059 n log Kf 0.059p log

n (X) + 0.~59 '.1~~ ~n+

r MX

where ,

El / 2(e) ,.. half-wave potential for the wave of the complexed metal.

El / 2(u) = half-wave pote~tial for the wave of the free met~1 ion.

n = number of electrons involved' in the ele,etr,ode proe~ess.

p

a formation constant of the complex

(MX ) ,.. __ ...IP ___ _

(Mn+) (X)p

= number of ligands combined with thé meta~ 'ion.

(X) = activity of the ligand.

- diffusion coefficient ofl the free metai ion.

• diffusion coefficient of the complexed metal. . , /

p

Il

,"

, " 1 •

r .. ,

-(

i t • 1

1

c

f\ 1

\ \

. Table 14. Half-wave Potentials for lhe DiethylditlUocarbamates of Cu,' Pb, Cd, Ni and Zn in Two Solvent Mixtures, Obtained with a Dropp1ng Mercury Electrode

Metal-DDC Complex

CU(DD~'f;' III

~~(DDC)2

Cd(DD~)~'

lÜ(~DC)2

Zn (DDC)2

(~\

.. '

1 E1/ 2 in Volts, Versus SCE

2 J Methanol-benzene . Ethanol-benzene

1

-0.82 -0.60

-0.81 -0.80

-0.94 -1.00

elongated wave elonga ted wave /

elongatèd wave elong,ated vave

lIt is'to be noted that Ref.o 50 does not specify whether or not the electrode- reaction was reversible; but in the present work it was ___ Irreversible for all five metal complexes reported here.

2 \ . Ref. 50: 0 SM LiCl was the supporting electrolyte. ( '.

-" 3This work: O.lM LiCl was the supporting electrolyte, at pH'" 7.0. El/'2 not corrected f,or the lR ,drop 1n the cell.

./

'0

r

M

i ,

1. 1 \

, ;

1 ! 1

1

Ip , '. C f 1 ; j

, 1

j

j

l ,

- ~

Il

(

/

(

,1

'140 --,

Whi1e this relationship cannot strictly be app1ied tà the , ,

\

present nonaqueous systems containing the TTA versus the DDC complexes of a .'

metai ion" neverthe1ess 1t is a fact that in many cases' in' tn~ present

work the' conversion of a M(T'l'A) 2 comp~ex to.a 1.t(DDC) 2 co~plelC during the \ 0

titration was quantitative. Thus, the greatet:':stability

- -com;lex does agree with th~ Ilhift in the -','El

/2" ~~lue on

of the M(DDC)2

\ g~ing from

" - -The Meta1-DDC complexes of Pbi Cd, and Zn gàve D.C.anodic

1 ~

waves at less negative potenti.als than that due to NapDC (pre'sent as

excess titrant) at

waves did not vary

a DME. However, on using A.C.polarograpllY, tliê'~ë

directly as Jhe éoncentrati;n ~f the eTecfroactive . , species in the solution. Instead t the anod~c wave due to M (DOC) 2 in- -1,_

~ - r

creased initially as >NaDDC was add"èd to thê metal-TTA solution düt'-ing the ..

titration. When NaDDC was added beyond- the equivalence point, _the wave

started to decrease. ~ finding is consistent with that of Miller (60).

He found that in A.C.pol~~ography, a~od{c processes interfered,with each !, ...

- ~ other 1 and the wave heights were' reduced by the discharge of comj>Qunds a;_

!. • more negative potentials.

.. 1 /

1 '

<1' " -- ,

---,,~ f "

F

1

,/ 1

I~

i

~l

. '

0'

C.' D, :!

j,l "

!. ! (

-'

1

" ~. , )

r 'r ~ ,

~-

t; t, \'

1 .', ,

--~-- , '

------ -----,-------~-

141

"

~

\ ('C) Titrations '\ /

. The analytical technique developed in this work consisted

, . i essentia~ly in the amperometric titrati0!l of metal-TTA complexes, ~lone

, ' . ~ . land in pairs, in an ethanol or

. soluti/'n of NaDDC in ethanol. \ \'

a~curate. ,U :!

ethanql-b.enzene mixture,l by a standard 1

The method was {ound to'be-precise and

\ In aIl cases, the firta1 equivalence point corresponded to a

, . molar, ratio of_l:2 for metal:DDC.

\

th~ chelàte excbang.e titr~tion in \ -\

Therefore, the'overall reaction of Oi

M(TTA)2 t 2NaDOC • M(DDC)2 + 2NaTTA

Since\ quantita'tive results were obtained, the stability of the metal-DDC ,- ~I )

.... ' ..; 0

complVces were much "greater than the metal"'TTA complexes. This conclusion

was also supported by'the data ~n Table' J. Here, an exceas f~ee HTTA/ was :' 1 Il • 1

added td\ the M(TTA) 2 solution be,fore t.~ titration. !fle results of these \ ' ~,~

titrations were 'comparable to those obtained.when excess HTTA was absent. , ,

.The titratlon graphs themselves did not reveal the formation - r \

of any add~cts or mixed complexes except in the case of copper. Using a • \ D

RPE, OXidati\~ wavel3 of the Cu(TTAHDDC) c~mPlex and that -OfI.U(DDC) 2,

~'Omp!~x weX:e"'~bse~ed. Therefore the proposed éxchange. rea~ons involved \ ,;) ,

-'. Cll (TTA) 2 T NaDDC • Cu (TTA) (DDC) + NaTTA

\ f~

,il

Cu ("rrA),(DDC) +. NaDDC ... Cu (DDC) 2 '\

\' +' NaTTA q'.oi..

One of the Dasic differences be'twefi!n

" "(Ir i 8pec~roPhotome~\1c'> a~d

-' 1

.amperometric titrati~ns in chelate-excnange titratioDS i8 the presence .~.

-- --} -

are ,

"

in th~ latter method, of ahother ligand which may form a complex w1tb ~he m~tal

/1-

, ,<

,-, '

;p 1 .'

" J'

, , l ,~

" . ,

f ------_._---

1 /'0

.) 142

in the 80luÙon. 1 This ligand cpmes from the supporting electrolyte, or

" from the buffer used. The 9upporting electrolytes are normally present

id a much higher concentration (O.lM/' than the metal (lO-4M- IO-SM).

'{herefore .. they may act ~ a competittve ligand, and ~y even displace~

in par~" th~ or~ginal me ta1 chel~ tes.

In the titration of two metal-TTA complexes present together, .

the concentration of the support:1.ng e1ectro1yte affec~ed the titration.

For a.lM LiCl vith a mixture of 1:1 Cu(TTA)2 and Pb(TTA)2' Pb(TTA)2 was ,

ltitrated on1y after the Cu(TT~) 2 was quantitative!); converted to Cu(DDC)2' , - ( r

However.;' as the concentration'-~f LiCl was increased to a.5M, the titra\:ion

'of CU(~TA)2 and Pb (TTA) 2 was simu1tane?us, and no distinct equivalence

point Iwas observed due to the individual metal. Inst~ad_, only the totaÎ

metal content could be determined. This effect was probably due to the

complexation of copper with the chloride 1.on at t'lie high chloride concen-

tration. The Cu (TTA) 2 and Zn(TTA) 2 pair also exhibited the same behavior. )

Spectrophotometric titrations carried out for the mixture of

Cu(TTA)2:-Pb(TTA)2 and CU(rI'A)2-Zn(TTA)2 in O.lM and a.SM LiCl showed

the same ph;nOll).enon a~ the amperometric titration, namely that in O.lM ,

"> •

.. LiCl, the QtitTation graph (plot ,of

versus the volume of titrant) gave

absorbance at 435nm ~ue}o Cu (DDC) 2 .... -=- lp .

a break corresponding to the Cu end .{

point alone, whUe in O.5M LiC~ a break corresponding only to the total

metal concentration (i.e. Cu+Pb, or CU+Zn) was observed. ,

J.

The;: procedure developed in this work permitted the amperometric

titration of ~etal-TTA complexes, present alone or in mixtures (pai1.'S and ' .

threes). Good precision and accuracy vere achieved.

il·

.1

/

Hl!iIl&i&ilt&U

, 1

\ .

Il

_,l, , ., ç; "

>,

i l' t ~

1 l'

r.

1 J

1

,

! 1 i

r " ! ",1

(

(

,.

t:~ . ,

l ,

/

143

1 APPENDIX l

1 .

• 1/

Standardisation of Metal Solutioris t Using a Stan~ard Solution of NaDDC .

in Ethanol

1 l' J,

jf

1. Cu- B~ker -Analysed Cu metai (Cat. no. lp~, 99.9%) W8.S taken to be

a prilnary standard.

-3 2. Pb- A 1.0x!0 M solution of Pb was prepared br diss~lvin~ an

1

accurately weighed amount of Pb meta! (Fisher L-24) in 10 ml of

hot 1: l nitrie acid. The solution was then e"aporat~d to mois t

dryness, and the residue was dissolved in ethanol and diluted

to 1 litre.

Standardisation of this solution by NaDDC was carried out·

as follows: an aliquot of tHe stock solution of Pb was trans-

feged to the sample atm of a polarographic H-cell, ~nd the • " ~ , 1

solution made up to 20 m1 by adding 0;% Et4NCl and ~ontaining

~nough Et4

NOH to buffer the solution to a pH of 7+1. Nitrogen .- 1/ -pre-saturated witli ethano~ was passe.d through the, sample for 15

minut~s, to -femove oxygen. A D-C polarogram of the solution . - . 1 .'.

was then recorded, using a DME and a voltage range from a,o,v to

-o. 6V versus SCE. The Pb wave s tarted a t -0,3 2V, and reached . /

its lim:l.ting current at -0.55V (see Figure 34a). The voltage

was then adjusted to -O. 70V, and an amJ)t!rômetric titration was ' ......... ~-

carried out with the NaDDC-Bolution as titrant. This NaDDe' " ,

solution had been standardised by using Cu mea, as t~e prima!}'

" Il

:

1 "

~J '.

" \

(

144

=

l ' standard (see p. 40) • 'l1le attalnment of equilibrium was indicated

by a constanF current value, an~ seemed to be almost instantaneous - ,

1

in this case. A longer per+od (1-2 min) was allowed near the

end po:int. Several in~rements of titrant,were also added beyond

the end point. A plot of the current at -0.7V versus ml of

titraht added gave the titration graph, and the intersection of

the ~o straight~line portions of the graph gave the equivalence.

lt was found adequate to determine this point by manually drawing

the two straight lines, and reading their point of intersection.

Results are shown in Table 15 (p. 154).

3. Cd- A 1.0xIO-~ stock solution of Cd in ethanol was prepared from

C~ metal (BDH), by the procedure described above for Pb. The

standardisation procedurei'was the same as for Pb except that

the voltage at which the current measured was set at '-0.80V

..,: (see ~igur~ 35). Results are shawn in Table 15.

4. N~- A l.dXIO"'~ stock solution of Ni. in ethanol was prepared from

, ., NiCl. 6H20 (Anal~lr) dissolved in etha~o1. The ~tanda!dization

procedure W8S the ssme as for Pb, except that ~h€- cur/rent was 1

measured at -O.40V (see Figure 36). Results are s o~ in

Table 15.

5). Zn- A lxlO-~ stock solution of Zn was prepared fr Zn metal by the .

procedure described above for Pb. The standardization. procedure

was the same as for the above metals, except that the anodie •

/

" , ~ 1

'1

i '1

" .'

, , ,

(

" ~ \

t

~ ~ c ~ -, }i r

f f

.:

/ /

l '

1-

J

JI

.... , ~

• •

J 1 J

, r 145

- current due ta excess NaDDC was measured, 1ru;-tea~1 of that of the

metal ion. The voltage w~ set at -O.48V (see Figure 37). /

Resulta are shawn in Table 15.

ft.. -1-. ~,

J,

1 . o

1

J

•

, , '" C-'

...

!

, ,

, l·

':1 1

" . ,

" " ~;. ·f

',; '1 (

[~

'i'; .;

-- "" .... ~

f ~

r:, ,i

, '~

',1 -J

J gj ,t'j', ,,',

"'!

'k} ~ c

s ., . c. ;' '. "

~,

;. >

f. \" t-:A't , 1

tC> f'

r ~ " t • , ,

f l ! (

.)

b.

Il

, \

" 1>

146

FIG.34

, 1

D.O.polarograms of Pb~N03)2' brfOre titration,

and after titration with NaDD9 in ethanol as

ti t~anta' and having lO-5M NaD -O. i·n . exce~s o

Supporting • O.IM Liel • electrolyte "

Solvent ' Ethanol ~"""'Ti • -,.;--

-Electrode, • D.MIE. •

, .

Typical amperometric ti tratioJ ",~raph of the

Pli(N03

)2 with a standard sOlutkon of NaDDe in

ethanol

b

, 1

i

1 ,

'.

, ,

;.

l,

, (

•

ri

t, ( , ri ~,

! J f ~ , ,\

i

,/ ,

147

FIG.34a

-...,.--'--.-,.-._._._ .. _. _.-.-,,- . / --

f f

, ! 1 f

/' ••••. J-'-'~ • • • • • • • ••••••••.•. , . . .y. , ï'O~--O.-:2~··-·/._·~-·~-~--~~.~-·--O-.-8--'1--.O---1-.-2---1-.4----1-.~6------~ u i.

E-4 Z

~ 0 U'

i- -E (in volts v.s.SOE)

· .-./' · , · ,,' "v'

FIG.34b

/

, I,a.lml

.-! :....~T/

........ Residual current

---- Pb(N03)2' 2xlO-5M

-'-' Ti trated solution of with excess NaDDO

Measured at -O~70V (Fig.)4a) Il

" J

ML OF lO-2M NaDDD ADDED ... ~ .... ,

, ,

-~

, .

r 1 1 .. ,J ~':"'-'::'.2:::....~_..::.-~_...:.li.:..-.i...~~aM. .......

", - '1

" " ,

"

"

1

:1

,1

(

(

( ': ~

, J

148

- FIG.35

a. D. C. polarograms of Cd(N03

)2/ before titration,

and aftel' ti tration wi th NaDDC 'in ethanol as

ti trant, and having lO-5M NaDDC in" excess

Supporting electrolyte

Solvent

Electrode

, (

1

O.lM LiCl

Ethanol

D.M.E.

b. Typical amperometric t~tration graph of the

Cd(N03

)2 ,with a standard -solution of NaDDC-in /1

ethanol 1

,J,

. !~ , i

t,.

'li! "

t' ,).

(

\ , ,1 ~'

1 1 1

(,

(

, 1

149

FIG.35a

----- .......... _.-. -- _. /" /

1 ;

/ 1 " 1 1

1

H \ ~II ".....,,/ •...•• ;.. • •.•..•••• Z ." '" . '/' .• '.

~O~~--~--------~~~ u 0',2 0.4 fb.6 0.8 1.0 -1.2 1.4 1.6

/' . / : ./. :1

i /

,....,....

O.1'bl1

i 1

-E (in volts v.s.SCE)

........ Residua1 curreht

---- Cd(N03 )2' 2xlO-5M d

Titrated solution of Cd(N03 )2 / wi th excess NaDDC

/ /

Measured at -0.70V (Figi35a) , 1

-' ~ .. '

t-----41 '

\ . , \ \

•• ,- f

'., ~.'l;\ ... ~. '/ ••

1 1 f 'î.'

>1 , -, ' ,

~,

i( ~, -r f, "1

\'

"

, \ , t

i

1

1

,

r ,'/

-----~--~---

150

FIG.36 ..

a. D.C.polarograms ~f NiC12 ·6M20 before titratio~, and

after titration with NaDDC in eth~ol as titrant,

and baving 10-5M NaDDC in excèss

; ~

b.

Supporting · O.lM LiC1 · e1ectro1yte -,

Cl Solvent · Ethano:). · Electrode ;f: D.M.E.

Typical amperome~~c' titra~ion graph of the NiC1 2

wi. th a standax:<! IOlU tian of NaDDC in ethanol

( !

1

( ,~

( )

'-1) 1

, ;,

,.

, ,

1 " 1 , '!

1

, ~

1 ~ 1

(

------- ~-' _._----------- ~ ~

E-t Z

~ 0 u r

E-t

151

FIG.36a

./ -- - -- - -,...... ... /.... /

1 . 1 .1

1 ,1 1 1

1 . 1 .1 • ~ .-. .(_ ........ /. ............... . .......... ,..... ~ ....... .... ./'

o.~ 2 O. 4 O~ 6 i

./ . 1

0.8 1.0 1.2 1.4 1.6

, .... ". . ......

/ -E (~.p. volta v. s.SPE)

/

" /. :/ :'/

FIG.36b

, , ........ Residual current

---~ NiC1 2 • 6H20 2xlO-5M -.-. Ti trated solution of NiC12 ,

with excess NaDDC "

Measured at -O.40V (Fige36a)

~ ~ "Il<-X~-X-x_x-x-x~. ~ 01----c..> - ~ , .,

~~ T. . ~. ~~,

1

10.1118

O,lml 1 _

ML OF IO~2~ NaDDC ADDED

," !'

1 .

, '". i

. ; 1

,-~ ,

t i ~, ., ,?

.:.:."

" .;

~I'

1 , [

1 !

q l - !

(

, C': , ,

~-.' j-

j'l e~

': --,

r

152

FIG.3?

.-l .. _______ -.:... __ ..

, "

a. D.C.polaragrama of Zn(N03 )2' before titrat1on, and " after t1tration with NaDDC in ethanol as titrant,

and- having lO-5M NaDDC in excess

J

Supporting : O.lM LiCl electrolyte

Solvent

Electrode D.M.E.

,(

'-1.

b.' Typlcal amperol1letric titration graph of the~Zn(N03.)2 . w~th a standard àolution of NaDDe in ethanol

1

-f . ~-

,.'

\.

1 • , , "

-' . '

1 )-

i J'

"1 1

"

~

~ ''/ Îc

F' (" l

"

, , t

"

f-t :z;

-1

~~ 0 B

l

l

1 \ 1

Le 1 ,

J

·1 ---,- -----....!..- ---- -------..:..:..--- .,--.---

1 FIG.)7 a

IO.l}la

153

{ ,~

, , , , , " ,

J

, -.". .. -.. -, , , >/

.1 ,/

/ /~

-'

,,' " ••••• •• ",.... , • • ••• ~...-: • • 1 ., ' ....

-",-' - .. "

- fIG.}7~

, ' {.

1.0 1.2 1.4 1.6

-E> (in vol ta v. s. SCE) /

... ..... Residual curren t () -5 ---7, Zn, NO} 2" 2xlO 1 M

_._, Ti tra:ted solution with excess NaDDe

, . .,J,Measured at ... 0. 45V, (Fig.37a) .

~_ .. "1C :r '. .. ~

"')(-X-)(.~_ ....

Io,lpa

O.lml

.. u. "

\ 1

. ,

'" ".!->~,-';'~?;~~~:4~ !lt."~$!~i",;T· ~ "'J\<!\.;:t-A~"·; ... ,1 1 ,'_:-'.: .... ( ..... ,

, -. .c-"': ~'" t~ ,~I~~ "',~ 1->

\

(

~able 15.

Il

( Metal

Po -j, Il' Cd

---" j,,'

154 \

Results for the Standardization of Metal Soluti9ns in Ebhanol with a Standard So:l.ution of ~aDDC in Ethanol by IUsing an Amperometric Procedure

1 "- '

Molar1ty of standard solution of Nàtmc'

Aliquot of metal solution taken

SupportiIlg electrolyte

Volume of solution

Eiectrode

{ Il Applied Voltage v.s.SCE, Volt

-0.70

-0.80

-:0.40

-0.48

\)

J.lg of Metal found l

208.02

112.50

58.86

"

88.~6

s.d'.

2.51

1.'40

0.51

0.90

- ,1

.

, ,

== 0.01

- ,l.OOml

- O.lM Lie!

• 25ml

2 Molp.ri ty of

Metal Solution

1.004xlO -3

1.OOlxlO-3

l.OOlxlO -3

1.035xlO -3

•

the weight 0/ ~eta1 found / , Two uncertaiJ

)/ / figures are

IJ ,

/ :; 1 Il

~ ... 1

(.-- ....

/

, ,

, . , :' ;: " " , -" fI r"~'- ~""\--.;i:.........",--"""";_ ... ,-_-:,,,, ... :,,_, .. -iW·~ ,.' .. , "." "'oii' .. ' '."'iII'lIIIiIlIi' Iii-.' ____ ... _ ...... ..

1

1 l

'l, >t , "1

"

",

\

1. 1

! t

! ,~

(.

. .

II·

/

•• 0

• 0

,,'

, 155

.....

APPENDIX/2 / Il

Care and Ipretreatment of the Rotating P1atinwn E1ec~rode

1 The prob1em invo1ved i~ using a sol~d el~ctrode is associated

with the condition of the e1ectrode surface and its possible effect on

the e1ectrod7 procesB., This iB especia11y fmPorta~~ when studyiog t~e

theoretiea1 aspect of an ,e1ectrode proeeBs. In quantitative work, it is

a1so desirable that the condition of A the eleetrode surface be reproducib1e, .-

rin arder ta get comparable resu1ts. (This prob1em doe~ not exist in a

.dropping mercury e1eetrode, sinee .eaeh mercury drop has a new surface.) , . , JI 1

Adsorptioq~f gases, or the formatipn of a coating ~y the end-

product of the e1ectrode oxidation or redu'ction which then produc~s a

D;lore or' 1ess complete1y insulating film 00 the e1ectrode surface, imposeS'

difficu1ties in the use of a solid e1ectrode.

P1atinum e1ectrodes that have1been ~sed'at Li~hiy eathodic / / 1 Il

potentia1s have-been fpund to be cove.red with a sorbed layer of hydrogen. \, ... '1

Lf these e1,ectrodes are then used agailn without prior treatment t a current-

voltage curve wou1d be optained for, the dissolution of the hydrogen-gas

film. This wouid give erranous réliluIt:s when qu~ntitative measurements • D"

are requ1red in this anodie region. Ko1thoff and Tanaka (61) investigat~., li. 1 -~

thia particular effeét, and proposed methods of electrode pretreatment. • .,.~ ~I

-l'The other prob1em ia the pos8ibility of a chemieal reaetion of

the electrode mate~,ial-;. Although platinum i8 an "~nert" meta1, it can t • l"l'

.readily be oxidiz~d when it is used in voltammetry--name1y by e1ectr~lytic

" .

.", . \

• 1 , "

"

!

.. \

, . •• ~ t

1 1~..".J.

~/t '~i l '~

j~.I.~ .,l''~

."

~l " 1· •

\ ;J.

"f ' r, , 1

\.f'~(

" ..

, . '.

" [

<'

i,

" \ <

,,~

1 ','. ~

'{

~, li.'

~~ ~,

. "

.,.;

(

1 1

1

1

If

"

156 / <.

oxidation, or by a chemical oxiqant (62-67). This oxidation w 1d also

produce ~n anomolous resid~al current and thereby Interfere with the

analysis. .The effê~f an·adsorbed hy.drogen film and the oxidation of

solid e1ect~odes are 1iscussed in detail 1n a mqpograph bylAd~s (68). " , . The method of e1ectrode pretreatment for the platinum e1ectrode

1 <

used in this work 1s as follows (68): The electrode when not in use was stored j ,

in concentrated nitric acid. Before use, the electrode was washed w~ll

with distilled'water and then short-circuited against a reference SCE in /

an ~+r"7fr~e O.lM solution (}f perébloric 'acid until the cur!ent decreased 1 .,!,.' , .,

to tlearly zero. Th:ljs w,as referred to as a "clean electrode" by Kolthoff ~ ,

(61). This "c1ean e1ectrode" was then rinsed with distilled wât~r then , o

ethanol, and then placed in the titration cell containing the air-free , .J-~~'" Y

sampie. The applied potential was adjusted to -O.20V vfrsus SCE untii

~he cathodic c~rrent decayed t~ zero. This ensured the Femoval of any "

"

surface oxide present. The 'potential was th en ma~e slightly anodic-

(about +O.05V versus SCE)'unti1 the current decayed ta zero. This proce-

dure reoxidized any sorbed .hydrogen on the surface'. The electrode was

then ready for the analysis. Reproducible results were ohtained if the

procedure was fbllowed closely for e~ch ~nalysi8.

\,

'. "

'.

, ' ..

.'-

. i i'

1 l'

r ~;

----------"-

(

III

157

APPENDIX. 3

Preparation of the Calibration Curve for the Polarographic Determination

of Pb(DDC)2' Çu(DD?)2' and Cd(DDC)2 in Ethanol and Ethanol-Benzene 1 III

Mixtures. /

1. Pb (DDC) 2

----~_., .... ~ ..

, The Pb(DDC)2 complex gives a well-defined wave starting at

--0.70V, whicn"reaches its diffusion ~alue at -O.90V versus SCE.

Polarogràms with different concentrations of Pb(N03'2 ranging from

-6 5 1 l.OxlO to 1.0xlO- M with excess NaDDC present in ethan~l as solvent

were run in an ethanol or ethanol-benzene solution a.lM in LiCl and

C,orîtaining LiOH to buffer the solution to a pH of 8.0. The diffusion

current for each concentration of Pb(DDC)2 when plotted against the

number, of l1g of Pb added resulted in a linear calibration curve.

2. CU(DDC)2 and Cd(DDC)2

The calibratio~lcurves for Cu(DDC~2 and Cd(DDC)2 we~e obta~ned

in the, same way as for Pb.

, " o

, ~, \ \ ,',

T,~ "

-, ,

..

o

il

l '

') /~ ;v,

, t~i -" '-: ~ l

, 1 " .

, J',. ) r .. r r 'r~~

, "ri

. , ,,'

~ , f, fi ~ ~ -,

~ ~ ~ '! ~ !

t f 1

~

!

1 1

! 1 i

,1

" l "

(

(:

...

/ .~

4":- ",'_

Il

"

158

APPENDIX '4

Preparation of the Calibration Curve for the Spec~rophotometriC Deter-

m1nation of Cu(DDC)2 Complex

1 The Cu(TTA)2 ,~Qmplex reaets with NaDDe to give a eolored cam-

plex Cu(DDC)2 in ethanol or ethanol-henzene mtttur~which has an absorp­

tion maximum at 435nm. In certain systems uch as Cu-Ni and Cu-Pb

mixtures, Dy subject1ng the final titrated olut1on ta an ab sorbance' 1

measurement, it was possible ta de termine t e Cu concentratipn irr these

binary m,tal systems.

An aliquot of a atandard eopper nitrate solution in ethanol was

transferred,to a 50-ml volrmetric flask. excess of Na~DC in ethano~ was added. Then O.lM LiCl in ethanol or ~:l 1thanol-benzene W~~ used tb dilute the resulting solution ta the mark. 'The absorbanee of the

.... resulting solution was measured against a conslsting of O.lM LiCl

1 ~ in ~thanol or 1:1 ethanol-benzeneifmixture, using a Beekman double beam

spectrophotometer. The speetrum was seann d from 560nm to 340nm. On

plotttng the absorbanee at 435nm for l ' es ~f' aliquots against the

concentration of Cu added, a linear graph was obtained. ~ ~ ~

. +4 Since at 435nm, Cu(DDC)2,has a very large olar absorptivity (10 ),- it

is possible to, 'work in a low ~oncentration rangJ. For absorbance\ measure­

ment in the Cu-Ni,m~xture, the absorbance at 435nm was cçrrected tor the

absorbance of Ni(DDC)2 at this ~avelength from a known spectrum of _ J

Ni(DDC) 2 alone.

i •

f -

" '

'. , "

.'

"

'0' r'

;

f j(

~ t,

(,

f' (, _l • \,

, 1

o

f

1/, ! • 1

1

." Il ,

, f

C" ,: ,)'

~ ,

.-l-___ ~ _______ ~ __ ._ .. _

" ;

APPENDIX 5 Il

, '.

Test fot Reversibility of the Electrode Reactions at the DME, of the

Chelating Agents and Metal Chela~es used '1~ the Present Work.

For a reversible electrpde reaction at 25°C, a polarographic 1

wave can be described algebraically by the follow1ng equat1on:

E • E + ~ log id - i 1/2 n i

where E • applied voltage (versus the SeE)'.

El/2 ~ half~ave potential

id • diffusion çurrent

i • current at any given value of E ,1

n • number of électrons involved in the electrode process

straigbt

:---.... """,- id - i . It follows that a' plot o~ E "V~Og i should' give a '

0.059 1 Une with a slope o.f ----n-. If such a p ~for a given system

doeâ giv.e a 'straight line with the theoretical siope the electrode re-l

actiOn was considered to be l<eversible (Binee this ejluation was 'derived , , 1

from the Nernst equation, which is only'for a revers1blê·reac~ion). !

~ In c~ses where the electrode reactlon 18 not reversible. elther ,

the plot will not give a straight'line or eise the slope will not giva

,the correct value of n.

ln the present work, certnn reagents (e.g. -benzoinoxime. DMG 'll

a~d salicyaldoxime)4II'e waves which were.so drawn-out along the voltage

o

, , 1.

,:~

.' ,

, ~ .

1

(

-160

axis that it was obvious the electrode reaction was Irreversible. For i - i

other reagents, plots of E versus 'log di"'" were made for :the polarographic

waves studied, and straight lines were obtained. id i

An,example of a plot of E versus ,log i ls shown in 1

Figure 38. The electrode reaction involved sodium diethyldithiocarbamate

in ethanol, using LiCl as supporting electrolyte. A~ straight line wa~ . ,

ob tained • HOW'e~e~, the n value calcula ted f rom the slope was b. ~6 where- " 1

as the theoretical value of n should be 1 if the electrode reaction was

reversible and proceeded as follows:

R2NCSS- + HgO • R NCSSHg + e 2 _1 ( i'

The n value obtained in 1:1 ethanol-benzene ~ixture was 0.-80. A Hst of ~ l "/ - •

reagents tested by th1s met~od and ~heir n.ValreS are shown in ~able 16. ~

In general, thé wàves became more dra~out al~g the voltage axis, the

gre~ter the proportion of ,benzene in the syster. However, some ,of the n '_ 1

valués are close to an 7~tegral number whlch mry indicate a reversiblé

/ . 1 electrode reactiôn.' / i

il 1/ 1. JI

'.

-/

r

) J

, .' 1 1

1/ . 1

-l' .. , ,

(l~ ~, ,'J,. p' ", , ,

'. , ' -"

" , .

l '" ,"

','

','I

J' ,

,. ,

, , 1 •

" ., , ,f

. IL

161

. FIG.38

1 A plot of l~g versu~ E to test for re-

,. . versibility of the anodic wave of NaDDC in ethanol

o !

o

'. o ;" ',: '"t;" ~'j;:( ,;:J:',/

~I jd"r~_ ' 1 r-, ~';..- 1

~~ '-,

'11,'

,.'

" , .,

c

~1' ~

~ , ~\ ~ . r'

l, e; 1 !' .. 1 .-", .; ~ t ~ "

ï 1 ~ " ,

0'

·F J G. 38

l '

0.8

1 0.6

.0

1 . 0.4

. .:J' ' 0.2

01 0

0 '-

-0.2

'-0.4

"'" x

0.52,

,.1

j 1 ~N

0.51

, .

E

_ .. ,.... -, _" <f' ::, ~ ~" '.... .. !' '," "

"

162

';!

l'

"

0.50 0.49. 0.48 0.47 l- I

vo1~, v. $, SCE o ,

~ ,'. f ï

"

'" . r '~, \ ~

,w ~ l'

- , . . ' , , ~ t,- ..l ~, 1

j ~ ~)'

i ~'.'

., .;; ~";~~~:t\ . :_..A-

') \ ~,,:.%î" w'i;;i!t~ if _~ -;: ,2L.=.''' .. ''''''''-''''''''

163 • 'i~

1/ , -(

Table 16. A List of n Values for the Polarographic Waves of Some Chelating Agents and Metal Complexes in Ethanol and 1:1 (v/v) Ethano1-Benzene Mixture With O.lM LiCl as the

, Supporting Electrolyte

'n n ~:1 v/v .:

Reagent Nature of the Wave pH Ethanol Et~lpH , j ,

a-QuinaUne1 * . first cathod;l..c W'ave 7.2 (1) -- (2) , second cathodic wave ;-~, 7.2 (2) -- (2) 1" " t dipheqylthiocarbazonel cathodic 6.8 0.71' -- (2) ~" b.

--(2) l anodic 6.8 0.93

;~ -HPAN / cathodic 7 ~O 1.20 -- (2)

1"

'. 2-nitroso-1-naphtho1 cathodic 7.0 0.45 _-!.. (2) ,ç

()

DMG*\ cathodic .7.0 -----<2) -- (2) / , .,

(2) :-- (2), . Cupron* cathodic 7.0 -- . -- ... "

salicy1aldoxime* cathodic 7.0 -- (2) -- (2) ~ .

\ (!. NaDDC. anQdic 8.0 0.86 0.80 -' '" ..

f· HTTA first ~thodic 7.8 1.10 -- (1) \ -"

~ 'tJ li ~ 'i. Il

. ,'OJ 1

, second cathodic 7.8 -- (2) -- (2) r f

, -, i .;< Y.

!~

Cu (N03)2 cathodic--- 8.0 0.92 -- (1) ( t.. 1

, '

Cu (TTA)2 cathodic 8.0 0.82 -- (1) , , -L'j

Cu (DDC) 2 cathodic 8.0 0.63 -- (2) ·1

!},r

, !'1~

Pb (N03)2 cathodic 8.0 .1.40 -- (2) "

Pb (TTA) 2 cathodic 8.0 1.10 -- (1)

1 " t Pb (D~C)2 8".0 1.18 ,

cathodic 1.20 ,-1 f\~ ,

Cd (N03)2 cathodic 8.0 1.40 1.35 'j

1 li ,~

1 Cd (TTA)2 'çathodic 8.0 1.23 1.20 l'; 1.

'1'

Cd~~DC)2 cathodic - 8.0 1-.35 1.30 ..

~iC12 . .,.. cathodic 8.0 (2) -- (2) (, '

Ni(n:~)2 cathodic 8.0 (2) -- (2) ,

Ni(DDC)i . çathodic ,

8.0 (2) -- (2) ",

Z~(N03)2 cathodic 8.0 (2) .-- (2") ~

Zn (TTA)2 ~/ cathodic 8.0 (2) ·"'.(2) , -e-~ Zn(6DC)2 cathodic 8.0 0.85 -- (2) - , '''':-; ~ 1

~ ,~

. *O.lM ,Et4NC1'was used' as s~pporting electrolyte. ..

~

/l~t

~~t~ .. id "" i .

~flj ~::r10t of,log i agàinst E ~id no~)ive a "tr,aight line. e~"

h " [ , • • 'l' IL . ::: " .

?t ( ejDrawn out waves, • , .. rA

oDviously irreversi1;,le. 1

:~~/::' }: IJ ~;-• .f

:~_f '..Jo ~ 1

:T(" ,i

1.- .. ,~._~/!\: .of ~t.

(

, ,/

c-"

. "

164

CLAIMS TO ~I~NAL RESEARCH ---. ,.

1. The polarogr~phy o~8-quinolinol, 1-2-pyridylazo-2-naphtho1 (HPAN),

2-thenoyltrifluoroacetone, sodium diethyldithioc~amate, and the r ... .,,/ .

chelates withl Cu, Pb, Cd, Ni, and Zn was studied in athano1 and i 1

1:1 (v/v) ethanol-benzeJe solvents, using a dropping mercury elec

2. Chelate-eichange titrations of the 8-qufnolinate, PAN and thenoy1 .., -.... trifluoroacetonates of Cu, Pb, Cd, Ni and Zn in ethanol and in 1;

(v/v) ethanol-benzene solvents with a standard solution of sodium

'1 , d~ethyldith1ocarbamate~ in ethanol were mon~_tored by amp,erometry,

using ~ dr~pping mercury èlectrode. On1y the ti~ration of'the 1

1 - "Yf thenoyltrifluoroacetonates proved to be pract}cal; slqw reaction ates

3.

, ----..

and/or ovetlapping polarograms made titration of the other chelat s

imprac tica!.

A deta11ed study of the chelate-exchange amperometric titrat10ns f , 1 - . ,the thenoyltrifluoroacetonates of Cu, Pb, Cd, ~i and Zn alone and as

Dinary mixtures in the ethanol and in ethanol-ben~ene solvents wi h

sodium diethyldithiocarbamate as titrant was carried put in the p e-

sence and absence of excese HTTA. Both A.C. and D.C. polarogra hy

were explored. In addition, these titrations we~e monitored by . ,

voltammetry, using a rotating platinum electrode. The precision rnd

the accuracy of aIl the titrations wêre ,determined.' The te~ary (, , ~ 1

-' -: mixture Cu-Ph-Zn wu also titrated successftÏlly 'by us1ng. a rotatipg 1

platinum electrode.

J '

-, -, . ;~. '~,.) ~ r, _

, "

/1

---

1 -

"

'. "

f' , • ~ .' ", ~,

~ ~ :" ~ r !' ,

( ; .

.. t, , , ! ~\) ~ ,

\<, ,

~.

"

" ,"

165

SUGGESTION) FOR FUR THER WORK

The use of amperometry was shoWn in the presen~ work to be a .

feàs~b1e method ~or mortitoring che1~te-exchànge titrations in ethan01

and e~hano1-benzene BoIvent mixtures. Extensions of the work COU~d be:

,1. To app1y the procedure to the ana1ysb of actual a1:10ys, aince this .r " : ,

is an u1timate aim of ,the present line of investigation.

~2. To determine the effect of'other s01vents on the che1ate-exchange ~

3.

/1

, l ' titrations, since solvents other than benzene are also used in

so1vent~extraction separations.

To study the effect of other support~g

comPlex~Jg ~t high concentration (such

on the chelate-exchange,titrations.

"

!'~"" "

1 /-

" 1

. '

, ~II

" , ,

" ' ,~ .'-

eIectrolytes known to be non-

as nitrates or perchlorates) '1

/ I!

~ - .. " , '

.' , . \ \ " , '

, , .. , l'·, " .- L "'':L';'-:: '!. 1

J __ ~~rol._.'"

" , , '8',

.' ...... '1.

, , l ' ~ ... )5~ ,,4

, J, ~ -,

, i

"'t' .... o1'>-.. ~,_-..""t" ..... ____ _

'. ~,

~ 166

( , 1

REFERENCES

1. y .. iMarcus. Chem.'Rev. 63,139 (1963). ~

2. Y. Marcus and A.S. Kertes. Ion Exchange and Solvent Extraction of

Metal Complexes. Wiley Interscience, New York. 1969.

3. Ani! K.De, Shripad M. 'Khopkar~ Robert A. Chalmers. Solvent t ~f •

Ex\ràction of Metals. Van Nostra~d Reinhold Company, London. ,

1970. ,

4. Yu" A. Zolotov. Extraction of --chelate Gompoulld,s. ~nn Arbor,

1970. . " \

5. Chelates' in Analytical Chemistry. Edited by H.A. Flaschka,

A.J. Barnard Jr. Vols. 1-5. Marcel Dekker, lnc., N.Y. 19"67-1976.'

6. K. Burger. Organic Reagent~ in Metal Analysis. Pergamon Press.

1973.

7. P. Grey. Ph.D.-Thesis. McGii1 University, Montreal, Quebec. 1968.

8. M. d'Amboise. Ph.D. Thesis. McGill University, ~ontreal, Quebec.

o 1973.

9. C. Bàrroso. M.Sc. Thesis. McGil~ University, Montreal, Quebec.

1972. "

1

• 10. M. I<.opanica and v. Starll. Ta1ants 21, 1073 (1974)'.

11. Taitiro Fujinaga, H.A. Brodowoky, Toyoshi Nagai and Kazuo Yamaéhit~.

"Use of a Ternary Mixtu~e as a Solvent in Po1arogt;aphic Analysis" .'

from Modern Aspects of Po1arographY. Edited by Tomihito Kambara.

•

Plenum Press, New York. 1966.

~ I.M. Ko1tnoff, J.J. Lingane. po1arogr~hYI Vols. 1 & 2'. Interscienee

Pub1ishers-, Ine. 1952. '. ,1

..

i 'r ".

~ , " , ,

, 1

1 , . ! \

" ,

t l, f

1 ; ,

J .j ~;ti, r~·t ,

''l''~''--,,,,,_'T''' ___ -'''''''' _________ 'T _______ ~~_

(

,(li ~

167

13. P. Zuman. Topics i~ Organic Polarography. Plenum Press, New York~

1970.

14. P. Zuman, 'C.J. Perrin. IOrganic P01arography. ... Wi1ey-Interscience,

1969. '­'/

, .

1 15. P. Z':l~n. ,Coll. of Czeéh. Chem. Comum. -15,1107 (1950).

P.J ./-iVing • "polarogr.phY in Org.nie Analysis" fram progres. in,

polfrogr~hY. Edited by P. Zuman, l.M. Kolthoff. Vol. 2.

----16.

lnterscience Publishers. 1962.

, 17 to Henning Lund. Ta1anta 12, lQ65 (1965).

18. jDonal.d J. Pietrzyt. Anal. Chem. 46, 52R (191

74).

19.1 J'. T. Stock •• J .. Chem. Soc. 586 (1949)!~ 1 1 . - t ,

20. ,j Michael ~pritzer and Louis Meites. Anal. Chim. ·Acta 26 58, (19q2).

21. D.J. ~,~l1s, A. TownsMmd and P. Zuman. Anal. Chim~ Acta !b 51

(1968) .

22. Philip J. E1ving and Philomena G. Grodzka. Anal. Chem. _33, 2 (1961).

23. Paul Arthur and Harold Lyons. Anal-. Chem. 24~ 1442 (1952).

24. F. Wi!leboordse. Po1arography in Some Nonaqueous Solvents. Ph.D. 1

Thesis. University of Amsterdam. 1959.

25. I.M. Ko1thoff. Polarography 1964. Edited by G.J. Hills. MacMillan.

1966. p. ~1.

-26.~ard B, Schaap and Peter S. Mckinney •. Polarography 1964. Edited

by G.J. H1l1s. MacM-Ul!.~. 1966. p. 197.

27. c'.P. Kulnar and D.A. Pantony. Potarography 1964. Edited by . . G.J. Hills. MaCMillan. 1966. p. 1061.

28. Red! Takahashi. Talmta 12, 1211 (1965). 1 .- 1 - 1 . -'.

29. B.K. Afghan, R.M. Dagnà11 and'K.C. Tho1Jlpson. Ta1anta 14, 715 (1~~7).

J'

, J

'1

,. , ,

. , ~

'C

, .

l' C '!'~', •

. "

t J f· .

1 , ~

i ';1.

t j f f

1

/'

/

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168

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