Xác Định Đồng Thời Hàm Lượng Kẽm, Cadimi, Chì, Đồng Trong Nước Sông Và Rau Băng Phương Pháp Vôn-Ampe Hòa Tan Anot Xung Vi Phân

5/24/2018 X c nh ng Th i H m L ng K m, Cadimi, Ch , ng Trong N c S ng V Rau B ng Ph ...

Lun vn

Xc nh ng Thi Hm LngKm, Cadimi, Ch, ng Trong

Nc Sng v Rau Bng Phng

Php Vn-Ampe Ha Tan AnotXung Vi Phn


MC LC

Li cm n

M u

Phn I: Tng quan

I.Nguyn t Ch (Pb) v cc phng php xc nhI.1. Gii thiu v nguyn t Ch (Pb)

I.1.2. Cc phng php xc nh Ch (Pb)

I.1.2.1 Phng php cc ph

I.1.2.2 Phng php trc quang

I.1.2.3 Phng php AAS

I.1.2.4 Phng php chun Complexon

I.1.2.4.1 Xc nh trc tip bng ch th Ecrioccrom en T

I.1.2.4.2 Xc nh trc tip bng ch th Xylen da cam

I.2 Nguyn t Cadimi (Cd) v cc phng php xc nh

I.2.1 Gii thiu v nguyn t Cadimi(Cd)

I.2.2 Cc phng php xc nh Cadimi(Cd)

I.2.2.1 Phng php trc quangI.2.2.2 Phng php chun Complexon



I.3 Nguyn t Km (Zn) v cc phng php xc nh

I.3.1 Gii thiu v nguyn t Km(Zn)

I.3.2 Cc phng php xc nh Km(Zn)

I.3.2.1 Phng php trc quangI.3.2.2 Phng php cc ph


I.4 Nguyn t ng (Cu) v cc phng php xc nh

I.4.1 Gii thiu v nguyn t ng (Cu)


I.4.2 Cc phng php xc nh ng(Cu)

I.4.2.1 Phng php trc quang s dng thuc th DDC


I.4.2.3 Phng php Neocuprionie


I.5 Phng php cc ph

I.5.1 C s ca phng php

I.5.2 C s ca phng php cc ph

I.5.2.1 Phng php cc phsng vung

I.5.2.2 Phng php cc ph xung thng (NPP)

I.5.2.3 Phng php cc ph xung vi phn (DPP)

I.5.3 Phng php Vn-Ampe ha tan

I.5.4 Phng php Vn-Ampe ha tan hp th (AdSV)

I.5.5 Cc phng php phn tch nh lng trong phn tch in ha

I.5.5.1 Phng php mu chun

I.5.5.2 Phng php ng chun

I.5.5.3 Phng php thm chunI.5.5.4 Phng php thm

I.5.6. Cc loi in cc c s dng trong phn tch cc ph

I.5.6.1 Cc rn hnh a (RDE)

I.5.6.2 in cc mng thy tinh (TMFE)

I.5.6.3 in cc git thy ngntreo (HMDE)

Phn II: THC NGHIM V KT QU

II.1 Thit b, dng c v ha chtII.1.1 Thit b, dng c

II.1.2 Ha cht

II.2 Ly v bo qun mu

II.3 V c ha mu


II.4 Xc nh Zn, Pb, Cu, Cd

II.4.1 Thc nghim tm cc iu kin ti u cho php xc nh Zn, Pb, Cu, Cd

II.4.1.1 Pha ch dung dch cho php xc nh Zn, Pb, Cu, Cd

II.4.1.2 Kho st cc iu kin ti u cho php xc nh Zn, Pb, Cu, Cd

II.4.1.2.1 Kho st s xut hin pic

II.4.1.2.2 Kho st bin xung

II.4.1.2.3 Kho st thi gian t xung

II.4.1.2.4 Kho st tc qutth

II.4.1.2.5 Kho st thi gian sc kh

II.4.1.2.6 Kho st thi gian cn bng

II.4.1.2.7 Kho st nh hng nng ca mi cht ln nhau

II.4.1.2.7.1 nh hng nng ca Ni2+tiZn2+, Cd2+, Pb2+, Cu2+trong

nn m axetat

II.4.1.2.7.2 nh hng nng ca Fe3+tiZn2+, Cd2+, Pb2+, Cu2+trong

nn m axetat

II.4.1.2.7.3 nh hng nng ca Pb2+ti Cd2+trong nn m axetat

II.4.1.2.7.4 nh hng nng ca Zn

2+

ti Cd

2+

trong nn maxetatII.4.1.2.7.5 nh hng nng ca Cu2+ti Pb2+ trong nn m axetat

II.4.1.3 Kt qukho st cc iu kin ti u cho php xc nh ng thi

Zn2+, Cd2+, Pb2+, Cu2+

II.4.2 Xc nh Zn2+, Cd2+, Pb2+, Cu2+trong mu t to

II.4.3 Tin hnh nh lng Km (Zn), Cadimi (Cd), Ch (Pb), ng (Cu)

trong mu nc sng

II.4.4 Tin hnh nh lng Km (Zn), Cadimi (Cd), Ch (Pb), ng (Cu)trong mu rau

Phn III: KT LUN

TI LIU THAM KHO


LI CM N

hon thnh c kho lun ny em xin by t lng bit n su sc

n ging vin Thc s inh Th Trng Giang giao ti, ht lng hng

dn, ch bo, truyn t kin thc kinh nghim qu bu cho em trong sut qu

trnh hon thnh kha lun ny.

Em xin chn thnh cm n cc thy, c gio trong t b mn ha Phn

tch, cc thy gio, c gio hng dn phng th nghim thuc khoa Ha hc -

trng HV to mi iu kin gip em trong qu trnh hon thnh kha

lun tt nghip.

Cui cng em xin gi li cm n su sc n bm, anh ch em v bn

b quan tm, ng vin em hon thnh kha lun tt nghip ca mnh.

Vinh, thng 5 nm 2010

Sinh vin

Phm Th Lu


1

M U

X hi cng pht trin, vn nhim mi trng cng t ln hng

u, nhim mi trng t nhiu ngun khc nhau y l mi nguy c e da

s sng ca mun loi. Qu trnh th ha nhanh, cng nghip ha, hin i

ha cc nc pht trin l nguy c gy nhim kim loi nng cho nc, t

v khng kh. S nhim c bi cc kimloi nng nh Zn, Cd, Pb, Cugy

ra nhng bnh m v nguy hi i vi con ngi v ng vt.

Trong s cc kim loi nng th ng v Km l nhng nguyn t cn

thit cho c th nng thp, nng cao chng gy ra cc vn v tim

mch,tiu ha v thn c th dn n t vong. Ch v Cadimi l cc kim loi

c c tnh cao vi ng vt v con ngi c th gy ra bnh ung th, bnh v

xng. Khi hm lng Ch trong mu cao s lm gim hp th vi cht, gy

thiu mu,km n v suy dinh dng, t lm gim tr tu ca tr em.

V vy, vic xc nh v kim sot c hm lng cc kim loi nng l

vic lm cn thit v cp bch. C nhiu cch xc nh hm lng kim loi

trong phng php Vn-Ampe ha tan xung vi phn (DPP) trn in ccgit thy ngn treo l phng php c chnh xc, chn lc, nhy v

tin cy cao, c th xc nh c hm lng cc kim loi c nng

thp.Do vy, em chn ti Xc nh ng thi hm lng Km,

Cadimi, Ch, ng trong nc sng v rau bng phng php Vn-

Ampe ha tan anot xung viphn.

Vi ti ny chng ti ra nhim v:

- Tm cc iu kin ti u nh lng ng thi Zn, Cd, Pb, Cu.- Nghin cu nh hng hai nguyn t Ni(II), Fe(III) ti php xc nh

ng thi Zn, Cd, Pb, Cu.

- Nghin cu nh hng ln nhau ca cc nguyn t Zn, Cd, Pb, Cu.


2

- Th cc iu kin ti u chn vo vic phn tch mu t to caZn,Cd, Pb, Cu.

- Phn tch mu nc sng, mu rau cha Zn, Cd, Pb, Cu.Chng ti hi vng rng kha lun ny s gpphn b sung thm cc

phng php xc nh lng vt kim loi trong mt s i tng khc

nhau

PHN I: TNG QUAN

I. Nguyn t ch (Pb) v cc phng php xc nh

I.1. Gii thiu v nguyn tCh (Pb)

Ch (Pb) thuc phn nhm chnh nhm IV, chu k 6 trong bng h thng

tun hon.

Ch c s th t: Z= 82

Khi lng nguyn t: 207,2Cu to electron : [Xe]4f145d106s26p2

Nhit nng chy : 327,46oC

Nhit si : 1737oC

Khi lng ring : 11,34 g/cm3

m in : 2,33

Tr lng trong thin nhin ca ch l 1.10-4% tng s nguyn t ca

v tri t, tc l nguyn t tph bin. Ch l kim loi mu xm thm, rt

mm.

iu kin thng ch b oxy ho to thnh lp oxt mu xm xanh

bao bc trn mt bo v ch khng tip tc b oxy ho na. Pb tan c trong


3

cc axt. Ch ch tng tc trn b mt vi dung dch axit clohidric long v

axit sunfuric di 80% v b bao bi lp mui kh tan (PbCl2 v PbSO4)

nhng vi dung dch m c hn ca cc axit ch c th tan v mui kh

tan ca lp bo v chuyn thnh hp cht tan:

PbCl2 + 2HCl = H2PbCl2

PbSO4 + H2SO4 = Pb(HSO4)2

Pb d dng tc dng vi axit HNO3 bt k nng no, c th tan

trong axit axetic v cc axit hu c khc.

Ch c dng lm tm in cc trong cquy, dy cp in, u n

v cc ng dn trong cng nghip ho hc. Ch hp th tt tia phng x v tia

Rnghen nn c dng lm nhng tm bo v khi lm vic vi nhng tia .

Tng ca phng th nghim phng x c lt bng gch ch, mi vin gch

thng nng hn 10 kg. Ch v cc hp cht ca ch u rt c, nn khi

tip xc cn phi cn thn.

I.2.Cc phng php xc nh Ch (Pb)

xc nh Pb trong nc b mt, nc sinh hot thng dng phng

php chit trc quang vi thuc th Dithizon l phng php cho php xcnh t 0,11,0mg Pb/l.

Pb l kim loi d xc nh bng phng php cc ph, phng php ny

cho phpxc nh Pb trong nc t 0,05mg n vi mg trong 1 lit nc.

xc nh Pb trong nhng loi nc sch c hm lng nh hn 0,02 mg/l nn

dngphng php phn tch in ho ho tan.

I.2.1 Phng php cc ph

Ion Pb (II) l mt trong nhng ion c hot tnh cc ph b kh trncatot thu ngn thnh kim loi.

Trong nn NaOH 1 M phc Pb(OH)2b kh thun nghch v cho sng

cc ph vi th bn sng -0,7 V so vi cc calomen bo ho.


4

Nu trong dung dch c cha Fe (III) vi hm lng khng ln lm,

st s b kt ta hidroxit trong nn NaOH v khng gy tr ngi n s xc

nh Pb. Nu hm lng st ln kt ta Fe(OH)3s hpph Pb, trong trng

hp ny nn xc nh Pb bng phng php thm chun.

Nu trong nc c lng tng i ln Cu (II) trong mi trng kim

d n cng b tan mt phn di dng CuO22- v sng ca ng cng nh

hng n s xc nh Pb. Trong trng hp ny sau khi thm NaOH vo

dung dch phn tch lng kt ta ri dng pipet ly ra 10 ml dung dch trn

thm vo 0,5ml KCN 1M che ng. Lng xianua khng c d nhiu v

s d nhiu s lm gim bc sng ca Pb. Tu thuc vo hm lng Pb m

ta tin hnh nh sau:

Ly 25ml mu nc chovo bnh nh mc dung tch 50ml nu cn

pha long mu nc trong 25ml cha khong 0,13 mg Pb. Nu hm

lng Pb trong mu ch nm trong khong 0,55 mg Pb/l th cn ly 250ml

mu thm vo 1ml HNO3c. Lm bay hi trong bp cch thu n cn

kh, ho tan b kh trong nc ct v chuyn ton b dung dch thu c vo

bnh nh mc 50 ml. Tip theo thm vo 5 ml NaOH, 1ml gielatin nh mcbng nc ct v lc u dung dch. Nu c kt ta hydroxit th cn lng

v tin hnh ly phn dung dch trong v tin hnh ghi cc ph nhy

thch hp t -0,4-1,0 V so vi anot y thu ngn. o chiu cao sng v da

vo ng chun xc nh hm lng Pb.

Nu hm lng mu c cha 0,051mg Pb/l th ly 250ml mu nc

cho vo cc chu nhit thm vo 1ml HNO3c v lm bay hi dung dch n

kh. Thm vo b kh ngui 0,5ml HNO3c v c li ln na. Cho vob kh ngui 5ml dung dch NaOH 10M +1ml gielatin + 44ml nc ct

trn u (dung dch nn). Saukhi b kh ho tan ht tin hnh o ghi cc ph

t -0,4-1,0 V so vi y anot thu ngn. Da vo ng chun xc nh

hm lng Pb.


5

Nu mu cha lng ln cht hu c cn ph hu chng nh trong

phng php dithizon trn. loi oxi khng dng Na2SO3v ion Pb (II) s

kt ta di dng PbSO4, c bit vi trng hp nng Pb ln. Cn dng

khng kh tr nh N2hoc H2tinh khit cho chy qua dung dch trc khi ghi

cc ph loi oxi. Dng gielatin loi tr cc i cc ph ca Pb.

Phng php Vn-Ampe ho tan hp th (AdSV) vi thuc th 8-

hydroquinolin (pH= 7,88,5) Pb cho pic ti -0,54 V vi gii hn pht hin l

3.10-10M. Bng phng php Von-Ampe ho tan anot (ASV) trong nn m

axetat (pH= 4,6) Pb cho pic ti -0,4 V vi gii hn pht hin ti 1.10-10M .


6

I.2.2Phng php trc quang

Phng php phn tch trc quang l nhm cc phng php phn tch

quang hc. Phng php ny chuyn cc cht phn tch thnh nng lng nh

sng suy ra lng cht cn phn tch. Pb (II) l cation kim loi c kh nng

to phc vi nhiu thuc th hu c khc nhau. V vy c th p dng

phng php trc quang xc nh Pb. Vic xc nh Pb bng phng php

trc quang vi dithizon l phng php ph bin nht bi tnh u vit ca n.

Dithizon (diphenyl thiocacbazon) l thuc th hu c c kh nng to

phc cng cua vi nhiu kim loi trong c ch. Ch dithizonat kh tan

trong nc nhng d tan trong cc dung mi hu c nh CHCl3, CCl4. Trong

CCl4ch dithizonat c mu cc i hp th bc sng = 520nm. Ch

dithizonat c chit chn lc v nh lng t dung dch nc c pH = 89,

cha lng d xianua, l cht dng che nhiu kim loi khc c th b chit

cng Pb.

Nu trong mu nc cha lng ng k cc cht hu c th cn phi

v c ho chng bng cch cho vo vi ml HNO3c v HClO4c c mu

n kh. Sau tm t b kh bng axit HNO3v ho tan bng nc ct.Cc cht oxi ho cn c kh trc bng hidrazin.

I.2.3 Phng php AAS

Vi phng php F-AAS s dng ngn la l hn hp kh (khng kh-

axetilen) vi t l 5,2/1,25 L/ph (V/V) o ch bc sng = 217nm. C th

dng thuc th APDC (amoni pyrolydin dithiocacbamat) trong MIBK (metyl

isobutyl ketone) (mu c axit ho bng axit HCl n pH = 45).

Vi phng php AAS khng dng ngn la th nguyn tc caphng php l: mu c avo l, ti y n c sy kh, tip n l

tro ho v cui cng mui ca ch c phn ly di dng ch nguyn t,

trong mi trng kh tr Argon. iu kin nguyn t ho l: sy nhit

120oC 200oC, trong thi gian l 30 giy; tro ho nhit 450oC, trong


7

thi gian 20 giy; nguyn t ho nhit 1900oC, trong thi gian 3 giy.

Vng tuyn tnh l: 2 50 ng/ml.

I.2.4Phng php chun Complexon

I.2.4.1Xc nh trc tip bng ch th Ecriocrom en T

Dung dch ch c hm lng trong mu phn tch khong 20mg ch

trong 100ml th ngi ta dng 5ml dung dch tatrat (1:4) hoc tritanolamin (

TEA) to phc che cc ion kim loi gy cn tr cho php xc nhch. Sau

trung ho mt lng tng ng dung dch NaOH, trong mt s trng

hp c th cht che nh KCN, sau thm 2ml dung dch m c pH = 10 v

cht ch th, chun cho n dung dch chuyn t mu nu sang xanh.

I.2.4.2Xc nh trc tip bng ch th Xylen da cam

Trong dung dch phn tch thng khng qu 50mg Pb trong 100ml.

nu cn thit trung ho dung dch bng NaOH n pH = 23 sau thm

lng thch hp dung dch m axetat (tt hn l dng dung dch Urotropin-

hexametlyentetramin) lc pH dung dch cn phi bng khong 5, thm cht

ch th v chun cho n khi dung dch chuyn t mu tm chuyn sang

vng.II Nguyn t Cadimi (Cd) v cc phng php xc nh

II.1 Gii thiu v nguyn t Cadimi(Cd)

Cadimium (Cd) l nguyn t ho hc thuc nhm IIB, chu k 5 trong

bng h thng tun hon cc nguyn t ho hc, s th t 48, nguyn t khi

112,41. Cd c cu hnh lp v 18+2e l cu hnh tng i bn. Do nng

lng ion ho th 3 rt cao lm cho nng lng sonvat ho hay nng lng

to thnh mng li tinh th khng lm bn c cho trng thi oxyho +3. trng thi oxy ho cao nht ca Cd ch l +2.


8

c im ca nguyn t Cd

S th t

nguyn t

Cu hnh

electronNng lng ion ho

Bn knh

nguyn t, Ao

Th in cc

chun, V

I1 I2 I348

[Kr]4d10

5s2 8,99 16,90 37,471,56 -0,402

Cd l kim loi nng, mm, mu trng xanh, d nng chy, khi lng

ring 8,65 g/cm3, tnc= 32oC, ts= 767

oC, nhit thng hoa 112kJ/mol, dn

in 13. trong khng kh m chng dn dn b bao ph bi lp oxit nn mt

tnh nh kim v khng b g.Khi un nng tc dng c vi oxy vncto

thnh oxit. D tan trong axit HNO3. L mt nguyn t him,chim khong

7,6.10-6- % tng s nguyn t tng ng trong v tri t. Trong thin nhin

Cd thng tn ti trong hp kim cng vi Zn, Cu.

Cd l mt kim loi c hin i. N ch mi c pht hin nh mt

nguyn t vo nm 1817 v c s dng trong cng nghip t khong 50

nm trc. hin nay Cd l mt kim loi rt quan trng trong nhiu ng dng

khc nhau, c bit Cd c s dng ch yu trong m in, v n c c tnhkhng n mn. Ngoi ra Cd cn c s dng lm chtmu cho cng ngh

sn v cng ngh cht do v l catot cho cc ngun pin niken-cadimi; sn

phm ph ca cng ngh luyn ch v km.

II.2 Cc phng php xc nh Cadimi (Cd)

Tu theo hm lng Cadimi trong mu v yu cu ca php phn tch

m chng ta c cc phng php xc nh Cd ph hp khc nhau. Sau y l

mt s phng php xc nh Cadimi.II.2.1 Phng php trc quang

xc nh Cd bng phng php trc quang dng dithizon, ngi ta

chit bng CCl4t mi trng kim mnh cha tactrat. Dung dch dithizonat

ca dung dch Cd trong dung mi hu c c mu hp ph cc i bc


9

sng = 515 nm. Bng phng php ny c th xc nh hm lng t phn

trm mg n miligam Cd.

Hm lng Cadimi khong 0,01 0,5mg Cd/l c th dng phng

php xc nh nh sau:

Nu nh mu phn tch c cha lng ln cht hu c th cn v c

ho chng bng cch thm vo th tch nc ly phn tch 12ml H2SO4c,

35 ml HNO3c v lm bay hi dung dch trong t ht. Nu dung dch cn

c mu th li thm 5ml HNO3c v li lm bay hi ln na, ng tc ny

lp i lp li cho n khi thu c dung dch khng mu. Sau lm bay hi

dung dch n kh thm tip vo b 1ml HCl c v lm bay hi ln na.

Phn b sau khi ngui c ho tan bng nc ct 2 ln, un nng ho

tan ht mui tan, lc qua phu lc kh bng giy lc v gi ly dung dch

xc nh Cd.

Trong mi trng kim mnh cc kim loi khc nh Ag, Cu, Ni,Co

cng b chit cng vi Cd. Cc nguyn t ngn cn cn c chit trc khi

xc nh Cd bng dithizon t mi trng axit. Nu trong mu c CN -th cn

ph hu xianua bng cch thm 0,5 ml H2SO4c vo 100ml mu nc unsi 10 pht trong t ht. Sau thm 0,2 ml HCl c khuy u v yn (

kt ta AgCl lng xung) trong 2 gi. Lc dung dch ra phu bng vi ml

nc ct, trong nc lc cn c th cha mt lng nh bc

Cu, Hg v mt lng nh Ag cn trong nc lc c c chit

loi b bng dithizon t mi trng c pH= 2. Thm vo nc lc 5ml dung

dchmui xaynhet 20% iu chnh pH n 2 bng cch khuy v thm t t

dung dch NH3hoc HCl. Cho mu vo phu chit v chit mi ln bng 5mldithizon 0,1% trong CHCl3, chit cho n khi lng dithizon sau khi chit vn

gi nguyn mu xanh ban u ca n. Sau ra mu bng 10 ml CHCl3cho

n khi dung mi ra khng mu.Cui cng ra thm 2 ln mi ln 5 ml

CCl4. Nu trong mu c cha Ni th tch bng dimetylglioxim nh sau:


10

Ly 50 ml dung dch mu u hoc dung dch mu sau khi v c ho,

cho vo 10 ml dung dch kalinatritactrat 20% (nu ly mu sau khi tch

Ag, Cu, Hg th ch cn thm 5 ml dung dch tactrat l ). Thm NH3vo cho

n khi pH= 8,59, thm vo tip 5 ml dung dch dimetylglioxim 1% trong

ru etylic 96%. Cho ton b hn hp vo phu chit lc u trong 30

giy.Chit phc niken dimetylglixionat vi ln, mi ln bng 10 ml CHCl3.

Cui cng ra tng nc bng 5 ml CCl4.

Nu hm lng Zn gp 50 ln Cd th vic chit Cd khng hon ton v

phm sai s m. Cc cht oxi ho cn c phn hu bng cch thm H2O2

vo v un si k. Cc cht hu c cn c chit tch bng 5 ml CCl4 mi

ln chit.

I.2.2.2Phng php chun Complexon

Cd trong mi quan h vi EDTA v vi tt c cc cht ch th c

dng nghin cu cho ti nayk c s c mt ca km th php xc nh

complexon nguyn t ny khng gp kh khn g c lng ln v vi lng Cd

trong mu phn tch.

Trong s ln cc cht ch th c ngh xc nh Cd c thchn nhng cht sau:

Pyrocactesin tm, Naphtolic, metyltimol xanh, galleon v glyxintymol

xanh. Nhng cht ch th ny c s dng trong dung dch c pH= 10. Trong

mi trng axit yu c pH=56 c th s dng PAN hoc CuY hoc CuY-

PAN, azoxin.

Php chun Cd km la chn nhngc th nng la chn n mc

nht nh nu s dng nhng phng php c th, php tch s b cngc s dng, v d chit phc tioxyanat. Nhng phng php s dng cc

cht che hoc cc mu tng phn c ng dng xc nh hn hp nhiu

cu t. Trong trng hp ny ngi ta s dng kh nng che Cd bng KCN

v gii che n bng foocmanhit. Phng php cho php xc nh Cd khi


11

c mt Pb, cc kim loi kim th v cc kim loi khc, trc ht l s c mt

ng k ca st.

trnh phn ng vi EDTA c th che Cd bng kaliItdat ( nng

cao) l nhng cht che khng cn tr cho vic xc nh km.

C th xc nh hm lng c mt cadimi v km theo mt ng

chun o mu, nu php chun c tin hnh khi c mt ca murxit

hoc xincon. Ngi ta thm cht mu d so vi km. Phc km vi cht mu

l ch th cho cadimi theo lch ca ng chun, theo hai im gy trn

ng chun c th tnh nh lng complexon tiu tn tng ng cho

php chun Cd v Zn.

I.2.2.3Phngphp AAS

Vi phng php AAS s dng l nhit in, nguyn tc ca phng

php l: Mu c a vo l, ti y n c sy kh, tip n l tro ho v

cui cng mui ca cadimi c phn ly di dng cadimi nguyn t.

S dng thuc th l APDC (amoni pyrolidin thiocacbonat) pH=9,

mu c axit ho bng axit HNO3(axit ho bng 100ml mu bng 1ml axit

HNO3). Sau tim vo l 10g mu, loi dung mi 100

o

C trong 25 giy,tro ho 450oC trong 80 giy v nguyn t ho 1950oC trong 4 giy. o

hp th ti bc sng = 228,8 nm. Da vo ng chun tnh kt qu.

Trong trng hp ny hm lng Cadimi qu nh c th nng cao nng

bng cch chit MIBK (metyl isobutyl ketone) vi thuc th APDC.

Vi phng php F-AAS s dng ngn la l hn hp khng kh-

axetylen vi t l 5,2/1,2 L/ph (V/V), cng dngthuc th APDC chit

mu,mu cng c axit ho bng axit HNO3, thm vo dung dch axetat40% pH= 34, thm 5ml thuc th APDC, yn trong 2 pht . Thm

10ml MIBK vo bnh lc mnh trong 30 giy, thm nc ct vo cho n khi

dung mi hu c ln n vch ca bnh nh mc. Sau a mu vo ngn

la ca my v phn tch mu. o hp th bc sng = 228,8 nm. V


12

da vo ng chun tnh kt qu (mu chun c chun b trong

MIBK).


Nu trong mu phn tch m hm lng Cd cao khong trn 1 mg/l th

c th dng phng php cc ph xc nh. V Cd trong nn hn hp m

ammoniac v nhiu nn khc cho cc sng cc ph thun nghch v nh

lng.

xc nh Cd bng phng php cc ph, ngi ta thng dng nn

m ammoniac-amoniclorua (NH31M + NH4Cl 1M ). Nu trong mu phn

tch hm lng Cu khng ln hn hm lng Cd c th xc nh ng thi c

2 nguyn t v nn dng phng php thm chun. Trong trng hp hm

lng Cu qu ln so vi hm lng Cd th cn che Cu bng xianua. Cc kim

loi khc nh Fe (III), Bi, Sn, Sb, s kt ta di dng hydroxit trong dung

dch m. xc nh Cd ta ly phn dung dch trong trn. Nu hm lng

kt ta qu ln cn xc nh theo phng php thm.

Zn, Co, Ni, Mn l nhng kim loi trong nn ny cho sng cc ph nhng

th m hn sng ca Cd nn khng nh hng n vic xc nh n. Nutrong nc c lng ln Pb th cn tch trc bngcch kt ta n bng axit

Sunfuric long v lc b kt ta Ch sunfat.

Tu theo hm lng ca Cd trong mu m chng ta thc hin pha

long hay c cn bt sao cho trong 25 ml mu cha t 0,051,25 mg Cd.

Thm mt git Metyl da cam v trung ho bng HCl hoc NH3n khi cht

ch th va i mu. Tip theo thm 10 ml dung dch nn, 1 ml gielatin, 1 ml

m Natri sunfit v nh mc bng nc ct, lc u dung dch, cho dungdch vo bnh in phn v ghi cc ph t -0,4 V -0,8 V so vi anot y

thu ngn. C th nh lng bng phng php thm chun hoc phng

php ng chun.


13

Nu mu cha 0,02 0,5 mg Cd/l th cn lm giu bng cch c nh

sau: Ly 250 ml mu, cho vo bt s hoc cc chu nhit, thm vo 1ml

HCl c, lm bay hi n cn kh . Thm vo phn b kh 5 ml dung dch

c iu ch nh sau: Trn 10 ml dung dch nn + 1 ml gielatin + 1 ml

Natrisunfit + 38 ml nc ct 2 ln. Cho ton b vo bnh in phn v ghi cc

ph t - 0,4 V -0,8 V. Nn xc nh bng phng php thm chun.

Ngy nay vi k thut tin tin nhiu phng php cc ph hin i c

th xc nh Cd c nng 10-9M trong cc nn khc nhau. c bit c th

xc nh c ng thi ti 5 nguyn t cho chnh xc cao ( v d: Zn, Cd,

Pb, Cu, Bi).

Bng phng php Vn-Ampe ho tan hp ph (AdSV) s dng

thuc th 5-hydroxy quinolin (8-HQ) trong nn m HEPES (pH= 7,8) Cd

cho pic ti -0,69 V vi gii hn pht hin ti 1.10-10 M bng phng php

Vn-Ampe ho tan anot (ASV), Cd trong nn m axetat pH= 4,6 V cho pic

ti -0,59 V vi gii hn pht hin ti 1.10-10M.

I.3 Nguyn t Km (Zn) v cc phng phpxc nh

I.3.1 Gii thiu v nguyn tKm(Zn)Km l tn gi ca mt nguyn t ha hc trong trong bng h thng

tun hon c k hiu Zn v s hiu nguyn t bng 30.

c im ca nguyn t Zn

Khi lng

nguyn t

Cu hnh

electron

Bn knh

nguyn t

(Ao)

Nng lng ion

ho ( eV)

Th in

cc tiu

chun (V)

Zn2+/ZnI1 I2 I3

65,37 [Ar]3d104s2 1,399,39 17,96 39,70

O,763

Km l mt kim loi mu trng xanh nht, nhit thng nhng khi

nu n 100 150oC n tr nn mm, do, d dt mng, d ko di.Trong


14

khng kh n b ph bi mt lp oxit nn mt tnh nh kim. Km c khi

lng ring l 7,13 (g/cm3), nhit nng chy 419oC, nhit si 907oC.

Km l mt kim loi hot ng trung bnh c th kt hp vi xy v cc kim

khc, c phn ng vi axt long gii phng hidr.Trng thi xi ha ph

bin ca km l +2.

Km l nguyn t ph bin th 23 trong v Tri t.Cc loi khong

cht nng nht c xu hng cha khong 10% st v 40-50% km. Cc loi

khong cht tch km ch yu l sphalerit, blen, smthonit, calamine,

franklinite.

Km trong t nhin l hn hp ca 4 ng v n nh Zn64, Zn66, Zn67,

and Zn68vi ng v 64 l ph bin nht (48,6% trong t nhin). 22 ng v

phng x c vit n vi ph bin hay n nh nht l Zn65vi chu k bn

r 244,26 ngy, v Zn72vi chu k bn r 46,5 gi. Cc ng v phng x

khc c chu k bn r nh hn 14 gi v phn ln c chu k bn r nh hn 1

giy. Nguyn t ny cng c 4 trng thi ng phn nguyn t.

Km l kim loi c s dng ph bin hng th t saust, nhm, ng tnh

theo lng sn xut hng nm.+Km c s dng m kim loi, chng hn nh thp chng n r.

+Km c s dng trong cc hp kim nhng thanh, niken trng, cc

loi que hn, bc c v.v. ng thanh c ng dng rng ri nh cng v

sc khng r cao.

+Km c s dng trong dp khun, c bit l trong cng nghip t.

Km dng cun c s dng lm vpin.

+xit km c s dng nh cht liu c mu trng trong mu nc vsn cng nh cht hot ha trongcng nghip t. S dng trong thuc m,

n c kh nng chng chy nng cho cc khu vc da trn. S dng nh lp

bt mng trong cc khu vc m t ca c th (b phn sinh dc) ca tr em

chng hm.


15

+Clorua km c s dng lm cht kh mi v bo qun g. Sunfua

km c s dng lm chtln quang, cs dng ph ln kim ng h

hay cc vt khc cn pht sng trong bng ti.

+Methyl km (Zn(CH3)2) c s dng trong mt s phn ng tng hp

cht hu c.

+Stearat km c s dng lm cht n trong sn xut cht do (plastic)

t du m.

+Cc loi nc thm sn xut t calamin, l hn hp ca(hydroxy-

cacbonat km v silicat, c s dng chngbng da.

+Trong thc n hng ngy, km c trong thnh phn ca cc loi

khong cht v vitamin. Ngi ta cho rng km c thuc tnh chng xi ha,

do vy n c s dng nh l nguyn t vi lng chng s cht yu ca

da v c trong c th (lo ha). Trong cc bit dc cha mt lng ln km,

ngi ta cho rng n c tc dng lm nhanh lnh vt thng.

+ Gluconat glycin km trong cc vin nang hnh thoi c tc dng chng

cm.

I.3.2 Cc phng php xc nh Km (Zn)I.3.2.1Phng php trc quang

Phng php trc quang l phng php n gin nhanh v nhy, c

dng ph bin xc nh cc kim loi.

Km to c nhiu phc vng cng vi cc thuc th hu c c kh

nng t phc mu vi ion Zn2+c s dng trong phng php trc quang

nh sau:

Km to phc vi 2-(5-nitro-2-piridylazo)-5-(N-propyl-N-sunfupropilamino)phenol (nitro-PADS) pH = 8 9, c bc sng hp th cc i max= 565nm.

Phng php ny c th s dng xc nh Km khi c mt ng thi ion Fe2+v

Cu2+. Do cc ion Zn2+, Fe2+v Cu2+c kh nng to phc vi Nitro-PADS cc pH

cng nh cc bc sng khc nhau. Fe(II) to phc pH = 3,4 9, max= 582nm, Cu (II)


16

to phc 1:1 pH = 2,5 4,5 v mt phc 1:2 ng thi 3 kim loi trong khong nng

0,02 0,5mg/ml mt cch ring r, c th p dng phng php xc nh cc kim

loi ni trn trong huyt thanh.

Ngoi ra c th s dng thuc th hu c 1-(2thiazolylazo)-2-naphtol

(TAN) to phc mu vi Zn2+, Fe2+v Ni2+ pH = 6,4.

Zn2+to phc vi 2-(5-bromo-2-pyridylazo)-5-ietylaminophenol (5-Br-

PADAP)

Phc Zn2+-(5 Br-PADAP) c ho tan bi ru etylic, phc c

bc sng hp th cc i max = 555nm, h s hp th phn t gam l

1,09.105l.mol-1.cm-1. Khong tun theo nh lut Bia 0,1 0,5mg

Zn2+/5ml.Phng php ny c th p dng xc nh trong nc v trong

thc n.

Mt khc c th s dng phng php trc quang xc nh Zn2+,

phc to thnh Zn2+-(5-Br-PADAP) pH= 9,5 (duy tr bi m borax) c

ho tan trong ru etylic ri c chit bi naphtalen. Bc sng hp th cc

i max= 555 nm, h s hp th phn t gam l 1,23.105l.mol.cm-1 .Khong

tun theo nh lut Bia 0 5,0 mg Zn

2+

/ml. C th s dng Natrixitrat,thioue,calgon v iaxetylioxim lm cht che.

Zn2+to phc vi 5-(2-cacbometoxyphenyl) azo-8-quinolino.

Trong mi trng mixen ion ca Natri dodexylsunfat pH = 4,0 4,8,

phc s c mu da cam, bn trong khong 4 gi. Bc sng hp th cc

i = 488 nm, h s hp th phn t gam l 4,14.104l.mol.cm-1. Khong tun

theo nh lut Bia : 0 0,42 mg Zn2+/ml v nhy Sandnll l 1,75 ng/cm2.

Zn2+ to phc vi axit 7-(4-nitrophenylazo)-8-hydroxyquinolin-5-sunfonic (P-N-AZOXS).

Km to phc nhanh vi (P-N-AZOXS) pH = 9,2 (duy tr bi m

Borax), phc bn trong khong 24 gi h s hp th phn t gam l 3,75.104

l.mol-1. Khong tun theo nh lut Bia : 0,05 1,0mg Zn2+/ml. Phng php


17

c p dng nh lng Zn trong dc phm, trong hp kim ng. lch

chun R.S.D < 2% v ng tt.

Trong phng php trc quang hiu chnh, c th s dng axit Crom

xanh K(ACBK).Zn2+to phc vng cng vi ACBK dng Zn(ACBK)2 max

= 530 nm, h s hp th phn t gam l 4,37.104l.mol-1.cm-1.

Dng thuc th Phenylflorua (PF) khi c mt triton X-100 v

xetylpiridin clorua (CP). Bc sng hp th cc i max= 573 nm, h s hp

th phn t gam l 1,09.105 l.mol-1.cm-1. Khong tun theo nh lut Bia:

0,04 0,4 mg/ml. C th s dng phng php ny xc nh Zn2+ trong

insulin.

Km to phc c vi 2,3,7-trihydroxyl-9-ibromo hydroxyl phenyl

florua (DBH-PF) khi c mt CPB v trixon X-100. Phc ny c mu ta

pH = 11,4, s dng dung dch m Na2HPO4-/NaOH. Bc sng hp th cc

i 610 nm, h s hp th phn t gam l 1,78.105l.mol-1.cm-1. Khong tun

theo nh lut Bia: 0 326 mg Zn2+/l. tng nhy v chn lc ca

phng php c th thm Natri metaphotphat. Phng php ny c ng

dng xc nh Zn

2+

trong qung pirit. chnh xc t 0,02 0,4%.S dng thuc th N- hydroxyl- N, N-iphenylbenzamidin (HDPBA)

v iphenylcacbazon (DPCZO) xc nh Zn2+trong khng kh. Chit phc

Zn2+vi HDPBA trong CHCl3 pH = 8,2 10,3 vi s c mt ca DPCZO

v NH4SO4. C s chuyn mu t hng sang vng, bc sng hp th cc i

max = 525 nm, h s hp th phn t gam l 1,27.105l.mol-1.cm-1. Khong

tun theo nh lut Bia: 00,8 mg/ml trong pha hu c.

nh lng Zn ngi ta cn s dng phng php chun trcquang. y l phng php tng i ph bin trong vic nh lng km.

S dng chun trc quang xc nh Zn2+thng dng EDTA vi ch th

XO. Phc gia Zn2+-XO c duy tr pH = 5,4 5,9 bi dung dch m

axetat, khong tuyn tnh l 50 160 g/l, lch chun tng i


18

0,31%.Phng php c p dng xc nh Zn (II) trong dung dch km

tinh ch vi thu hi 99,0 101,4%, sai s 0,76%.

xc nh Zn (II) trong ng thau, ngi ta ho tan mu trong axit

HNO3, sau oxi ho bi KClO3, chun bng EDTA vi ch th XO v

xanhbromocrezol pH = 5,5. S dng KF, thioure, BaCl2lm cht che, th t

cho cc cht che: KF ri sau l thioure v dung dch oxi ho c un si

t nht trong 2 pht kt ta hon ton MnO2. Sai s tng i l 0,12

1,0%.

Ngoi ra c th s dng 2,2-bipyridin nh mt thuc th che chn lc

gin tip xc nh Zn. Zn (II) trong dung dch mu ban u c to phc

vi lng d EDTA, lng EDTA d c chun bi Pb(NO 3)2 pH =

5,0 6,0 dng XO lm ch th. Lng d 2,2-bipyridin oc thm vo, lc k

hn hp, EDTA trong phc b y ra c chun vi dung dch Pb(NO3)2.

I.3.2.2Phng php cc ph

xc nh km bng phng php cc ph, ngi ta dng nn NH31M

+ NH4Cl 1M . Trong nn ny th na sng ca km ng vi s trao i 2

electron l -1,35 V so vi cc Calomen bo ho. Phng php ccph chokh nng xc nh c km vi hm lng nh nht l 0,01 mg/l. Sai s ln

nht khong 5 %.

Nu trong mu nc cn cha ng thi ng, Cadimi v Niken vi hm

lng xp x hm lng Km th dng nn ny ta c th xc nh c cc

nguyn t , v sng ca chng trong trng hp ny hon ton tch khi

nhau. Nu ghi cc ph t -0,2 V th cc sng thu c trn cc ph ln

lt l Cu, Cd, Ni, Zn.Oxi ho tan trong dung dch c kh bng Natrisunfit. Nu cc nguyn

t ng, Cadimi, Niken v Coban c trong nc vi hm lng ln hn hm

lng ca Km nhiu th chng s cn tr vic xc nh Km v sng cc ph

ca chng th dng hn sng Km. Nu trong my cc ph c b phn


19

chnh dng khuch tn ta s dng n b chnh dng cc ph ca cc kim

loi cn tr . Khi hm lng ca chng khng qu cao th c th b chnh

c v thu c sng ca Km khi ghi cc ph t -0,8 V. Nu vic b chnh

khng thc hin c, th cn tch Km ra khi mu bng phng php chit,

gii chit Km li tng nc v xc nh n bng phng php cc ph.

Trong trng hp khng cn phi tch Km th nn xc nh n bng phng

php thm. Sau khi ghi cc ph dung dch cn phn tch, thm lng nh

dung dch chun c nng thch hp vo dung dch phn tch v ghi cc ph

ln na. lng Km c thm vo nh th no sng th hai c chiu cao

gp ri hoc gp i ca chiu cao sng th nht.

Cch tin hnh nh sau:

Trong bnh nh mc dung tch 50 ml, thm vo 25ml mu nc hm

lng ca km trong l 1 25 mg. Nu trong mu c hm lng Km nh

hn 0,15mg/l, th ly 250ml nc thm vo 1 ml HCl c v lm bay hi n

cn kh hai ln nh nhau v ho tan b kh trong 25ml nc ct. Sau thm

tip vo 5ml dung dch nn, 1ml gielatin, 1ml Na2SO3v nh mc bng nc

ct,lc u dung dch trong bnh, chuyn 25ml dung dch vo bnh in phnv ghi cc ph t -0,8 V n -1,5 V, nhy ca my sao cho sng thu

c c chiu cao t nht 20 mm. Thm vo bnh in phn 0,2ml dung dch

chun (loi no tu thuc vo nng Km trong dung dch mu) v ghi cc

ph dung dch ny nhy c. Chn nng dung dch chun thm vo sao

cho sng th hai c chiu cao gp ri hoc gp hai ln sng th nht.

Nu trong nc c ng, Cadimi, Niken vi hm lng hm lng cho

php xc nh cng vi Km, th cng tin hnh nh trn v ghi cc ph t -0,2V n -1,5V. vic xc nh cng c tin hnh theo phng php thm

chun.

Nu hm lng ca cc nguyn t ngn cn qu ln th cn tch Km

trc nh sau: ly mt th tch nc sao cho hm lng km trong t 0,01-


20

0,5mg trong 50ml. Ly 50ml thm vo 2 git metyl v trung ho cn

thn bng HCl long hoc bng NH3 long cho n khi cht ch th va i

mu. Thm tip vo 20ml dung dch che. Chit km mt vi ln, mi ln bng

20ml dithizon, chit n khi ln chit cui mu xanh ca dithizon khng thay

i. Gp tt c cc phn chit khc, thm vo 25ml HCl 1:5 v lc phu

gii chit km tr li tng nc. Gi tng nc v lp li s gii chit hai

ln na, mi ln 25ml HCl. Gp ton b dung dch nc thu c, lm bay

hi trn bp cch thu n cn kh v ho tan b kh trong nc ct. Tin

hnh xc nh km nh trn.


Phng php AAS da trn nguyn tc tt c cc nguyn t khi trng

thi nguyn t u c hp th bi mt bc sng nht nh, cng hp

th th hin nng ca cc nguyn t c trong mu.

Nu ta chiu mt chm tia sng c bc sng xc nh vo m hi

nguyn t th cc nguyn t t do s hp th cc bc x c bc song ng

ng vi nhng tia bc x m n c th pht ra c trong qu trnh pht x.

Ph sinh ra trong qu trnh ny gi l ph hp th nguyn t.Phng php quang ph hp th nguyn t ha hi c p dng vi mt

s nguyn t c kh nng nguyn t ha nh: Hg, As, Se, Zn

Phung php AAS l phng php hin i c chnh xc cao, c th

xc nh lng vt cc kim loi trong cc hp cht v c v hu c vi cc

i tng nghin cu khc nhau.

Vi php o AAS c nhy v chn lc cao. Gn 60 nguyn t ha

hc c th xc nh bng phng php ny vi nhy 10 -4 10-5%.I.4 Nguyn t ng (Cu) v cc phng php xc nh

I.4.1 Gii thiu v nguyn t ng(Cu)

ng l nguyn t ha hc trongbng h thng tun hon c k hiu Cu v

s nguyn t bng 29, thuc nhm IB.


21

Cc hng s vt l ca ng

S th t 29

Khi lng nguyn t 63,56

Cu hnh electron [Ar] 3d104s1

Bn knh nguyn t (Ao) 1,28

m in 1,9

Khi lng ring (g/cm3) 8,94

I1 II2 III3Nng lng ion ho (eV)

7,72 20,29 36,20

ng l mt kim loi c mu vng nh , c dn in v dn nhit

cao (trong s cc kim loi nguyn cht nhit phng ch cbc c dn

in cao hn),l kim loi mm, d dt mng, d ko si. ng c l l kim

loi c con ngi s dng sm nht do cc ng c nin i khong

nm 8700 trc cng nguyn (TCN) c tm thy. Ngoi vic tm thy

ng trong cc loi qung khc nhau, ngi ta cn tm thy ng dng kim

loi (ng t nhin) mt ni.ng c ghi chp trong cc t liu camt s nn vn minh c i, v n c lch s s dng t nht l 10.000 nm.

Trong thi ca nn vn minh Hy Lp, kim loi ny c bit vi tn gi

chalkos. Trong thi k La M, n c bit vi tn aes Cyprium(aesl thut

ng Latinh chung ch cc hp kim ca ng nh ng v cc kim loi

khc, v bi v n c khai thc nhiu Sp). T nhng yu t lch s ny,

tn gi ca n c n gin ha thnh Cupruml tn gi Latinh ca ng.

Trong Thn thoi Hy lp- La m cng nh trong thut gi kim, ng c

lin quan n n thn Aphrodite (V N) v v p rc r ca n, vic s

dng thi c i ca n trong sn xut gng, v s lin h ca n vi Sp, l


22

qu hng ca n thn. Trong thut gi kim, k hiu ca ng cng l k hiu

cho sao kim

Trong t nhin ng c th tm thy nh l ng t nhin hoc trong

dng khong cht. Cc khong cht chng hn nh cacbonat azurite

(2CuCO3Cu(OH)2) v malachite (CuCO3Cu(OH)2) l cc ngun sn xut

ng, cng nh l ct sunfua nh chalcopyrite (CuFeS2), bornit (Cu5FeS4),

covellit (CuS), chalcocit (Cu2S) v cc xt nh cuprit (Cu2O).

Phn ln ng trch xut c trong cc ml thin trong cc khong

sn c t hn 1% ng.

C hai ng v n nh l Cu63v Cu65, cng vi mt s ng v phng

x. Phn ch yu ca cc ng v phng x c chu k bn r mc pht

hay nh hn, ng v phng x bn nht, Cu64, c chu k bn r 12,7 gi, c

hai cch phn r, to ra hai sn phm khc nhau.

ng l vt liu d dt mng, d un, c kh nng dn in v dn nhit

tt, v vy n c s dng mt cch rng ri trong sn xut cc sn phm:

Dy in.

Que hn ng. Tay nm v cc vt khc trong xy dng nh ca. c tng: B dn sng cho cc bc x vi ba. Vic s dng ng trong cc mch IC tr nn ph bin hn thay

th cho nhm v dn in cao ca n.

L mt thnh phn trong tin kim loi. Trong nh bp, chng hn nh cho rn. Phn ln cc dng bng niken trng dng bn n (dao, na, tha) c

cha mt lng ng nht nh.

L thnh phn ca gm kim loi v thy tinh mu. .


23

Cc hp cht ca ng u c.

I.4.2Cc phng php xc nh ng (Cu)

I.4.2.1 Phng php trc quang s dng thuc th DDC

Ion Cu (II) to c phc vng cng vi DDC (ietyl dithiocacbamat),

phc c mu nu, kh tan trong nc nhng tan nhiu trong mt s dung

mi hu c nh clorofom. Trong dung mi ny phc c mu nu nh

vng. Do nh lng ng bng thuc th ny ngi ta thng tin

hnh chit trc quang. tng tnh chn lc ca phng php thng chit

phc bng clorofom t mi trng cha ammoniac, amoni xitrat v

complexon III l nhng cht dng che cc ion cn tr vic xc nh ng.

Nu ng tn ti trong nc di dng phc bn xianua th trc khi

phn tch cn phi ph hu phc bng cch lm bay hi mu nc sau khi

thm vo 0,5 ml H2SO4c v 5ml HNO3c. Sau khi lm bay hi mu

n kh, thm vo b 1 ml HCl c v lm bay hi ln na.Tip theo thm

nc ct hai ln vo, lc v gily phn nc lc phn tch.

Trong mi trng c cha ammoniac, xitrat, v complexon III a s cc

kim loi khc khng gy cn tr cho php xc nh Cu bng phng phpny, ch c Bimut (Bi), bc (Ag), Hg vn phn ng vi DDC v c th b

chit cng vi phc ca Cu. Tuy vy ch c phc ca Bi c mu vng l c

nh hng cn phc ca Hg v Ag khng mu hp th nh sng trong min t

ngoi, nn thc t khng nh hng n vic xc nh ng.

xc nh Cu di dng phc CuDDC c th dng NaDDC lm thuc

th hoc c th dng phc PbDDC v c th tin hnh chit trao i xc

nh Cu. Phc ng bn hn phc ch nn y ch ra khi phc ca n v Cuc chit hon ton t tng nc sang tng hu c.

I.4.2.2Phng php cc ph


24

Cu (II) c hot tnh cc ph, trong nhiu nn khc nhau cho sng cc ph

nh lng. Trong a s cc nn cc ph, sng ca ng nm trong khong

th kh dng so vi kim loi khc, t 0 0,6 V. V vy xc nh Cu bng

phng php ny rt thun li v kh chn lc. Nn hn hp m ammoniac

l mt trong nhng nn tt xc nh Cu.

Trong nn ny cc ion kim loi b kh th m hn nh Cd(II), Co(II),

Ni(II), Zn(II), Mn(II)khng gy nh hng n vic xc nh Cu. Oxi ho

tan trong nc c kh bng cch thm vo lng d Natri sunfit Na2SO3.

Cromat, Co(III), Tl(III) cng cho sng cc ph trong khong th c sng

ng nn gy cn tr nu hm lng ca chng ng k. Nu trong nc c

hm lng ln Fe(III), Al(III), Bi, Mn l nhng kim loi kt ta hidroxit trong

mi trng ammoniac, th kt ta c th hp ph mt phn ng, trong

trng hp ny trnh sai s nn tin hnh nh lng ng bng phng

php thm chun, khng nn dng phng php ng chun.

Nu trong nc c cha lng ng k l cht hu c th cn phi v c

ho mu nh sau: thm vo th tch nc ly phn tch 1 2 ml axit H2SO4

c, 3 5 ml HNO3c v lm bay hi dung dch trong t ht cho n khixut hin khi trng SO3. Nu dung dch thu c cn c mu th thm 5ml

HNO3c v lm bay hi ln na, ng tc ny c lp licho n khi thu

c dung dch khng mu. Sau lm bay hi dung dch n cn kh. Phn

b sau khi ngui c ho tan trong nc ct hai ln, un nng ho tan

ht cc mui tan, lc qua phu kh bng thu tinh xp v gi ly xc nh

ng. loi tr cc i cc ph dng dung dch gielatin.

Nu mu cha t 2 50 mg Cu/l, th ly 25 ml dung dch mu cho vobnh nh mc dung tch 50 ml. nu mu nc ch cha khong 0,2 3 ml

Cu/l th ly 250 ml cho vo cc chu nhit sch, thm vo 1 ml HCl c v

lm bay hi trn ni cch thu. Sau khi ngui tm t bng 1 ml HCl c,

ho tan mui bng nc ct v chuyn ton b dung dch vo bnh nh mc


26

+ methanol cho dung dch mu vng, cho quang ph hp th phn t ti bc

sng = 457nm. Phn ng ny rt c trng cho Cu. Mu vng ca phn ng

tun theo nh lut Bia cho ti nng ca Cu l 0,2 mg/ 25ml dung mi.

Mu n nh trong dung dch nc c pH = 2 9, mu n nh trong CHCl3-

CH3OH trong nhiu ngy.

Mu c cho phn ng vi Hydroxylamin-Hydrocloric kh ion Cu2+

thnh ion Cu+. Dng xitrat natri to phc vi ion nhm trnh kt ta khi

tng pH. iu chnh pH =4 6 bng NH4OH, thm dung dch Neocuproine

trong methanol to phc vi ng v sau c chit bng clorofom. Sau

khi pha long CHCl3bng CH3OH ti mt th tch chnh xc. Mt quang

ca dung dch c o ti bc sng = 457 nm.

Mt lng ln Cr v Sn c th nh hng n php o. trnh nh

hng ca Cr th thm axit sunfur kh Cr(IV) thnh Cr(III). Thm 20 ml

Hydroxylamin-Hydrocloric khi c nhiu thic hoc mt lng ln cc cht

oxy ho c trong dung dch. Xianua, sunfit v cc cht hu c c th loi tr

trong qu trnh phn hu mu.

I.4.2.4Phng php AASVi phng php F-AAS th s dng ngn la l hn hp khng kh-

axetilen vi t l 5,2/1,2 L/ph (V/V), o Cu bc sng = 324,76 nm.

Vi phng php AAS khng dng ngn la, th mu c sy 120oC

200OC trong thi gian l 30 giy, tro ho nhit 450oC 600oC trong

thi gian l 20 giy, nguyn t ho nhit 2400oC trong thi gian l 3

giy.

Xc nh ng trong cc hp cht trn nn ca Fe ngi ta dng vicchit dng xalixialdocximat ng pH = 3, y ngi ta che Fe bng xitrat.

S phun bi dch chit trong ngn la axetylen-oxi, xc nh bc sng =

324,7 nm v cho php xc nh n 0,5 g/ml Cu, cng pht x ca ng

trong dung dch chit so vi s pht x trong dung dch nc tng ln 10 ln.


27

lmdung mi ngi ta dng clorofom, hay amiaxetat. Xalixialdocximat

ng ho tan tt trong clorofom nhng amiaxetat mc cao hn clorofom

cho kh nng tng pht x quang ph. ng cng c chit di dng 8-

oxiquinolat ng vi dung mi l MIBK pH cadung dch chit l 3 5,

= 324,8 nm c nhy tng 6 8 ln so vi trc quang trong dung dch

nc, dng ngn la Hidro-Oxi.

I.5Phng php cc ph

I.5.1 C s ca phng php

Phng php cc ph l nhm cc phng php phn tch da vo vic

nghin cu ng cong Vn-Ampe hay cn gi l ng cong phn cc, l

ng cong biu din s ph thuc cng dng in vo in th khi tin

hnh in phn dung dch phn tch vi in cc git thu ngn.ng biu

din cng dng ti thi im s kh ion cn phn tch b gy t ngt

pha trn, to nn ng gi l sng cc ph.Da vo v tr sng c th xc

nh thnh phn nh tnh ca cht in ly, da vo chiu cao ca sng c th

xc nh hm lng ca ion b kh.Phng php ny thch hp cho vic phn

tch nhiu ion kim loi nh Cd, Co, Cu, Mn, Ni, Sn, Zn, Fe, Bi, U,V v nhiukim loi khc trong cc i tng : t, , qung,kim loai, hp kim y l

phng php c chnh xc, chn lc, nhy v tin cy cao.Khi cc

hp cht c in th na sng khc nhau ln ( thng th khi E1/2 100

mV) ta c th xc nh ng thi nhiu hp cht trong cng mt dung dch

m khng cn tch chng ra khi nhau.

Phng php ny c Heyrovsky pht minh vo nm 1920 v cho n

nay cng vispht trincakhoa hckthut, phng php ny ngy cngccitin. Cscaphng php ny l datrn phnnginho ca

cc chtin ho trong dung dch in li trn in cc git thu ngn treo

theo phnng:

Ox + ne Kh


28

Trong :

Ox : Dngoxi ho

Kh : Dngkh

n : Se trao i.

Phng trnh nhlngl phng trnh Incovic :

Id= 605 . n . D1/2 . m2/3. t1/6. C

Id: Cngdng ccigiihn( A )

n : Selectron tham gia vo phn ng incc

D : Hskhuchtn ( Cm2/s )

m : TcchygitHg (mg/s)

t : Chu kgitcainccgit(s )

C : Nngchtphn tch. ( mM )

Tuy nhin do nhhngcadng tinnn nhycaphnngch

t c 10-4 10-5M. Nhng cng vi spht trin ca khoa hcv k

thut c nhiucitincp dngvimcchtng nhycaphn

ng. y chng ti giithiuhai hngchnh :

+ Hngthnht: Tndngcc thnh tucakhoa hckthutintloitrdng tinnng cao tsn hiuo/tn hiunhiu( nh: Phng

php ccph sng vung, ccphxoay chiu chn pha, cc phbin i

u, ccphxung vi phn,)

+ Hngth2 : lm giu chtphn tch ln bmtinccbngphn

ngkhhay oxi ho kttacht, sau ho tan snphmkttav ghi tn

hiuho tan ( phng php Vn ampe ho tan ).

I.5.2 C s ca phng php cc ph :Phng php ccphngdngdng khuchtn, mtstrnghps

dngthm ilu, cn qu trnh inchuynth phibngmicch trittiu

n. Trong mitrnghphuhtngita phitrittiu cdng indi v

ilu sao cho chti tiinccchtheo hintngkhuchtn v dng


29

sinh ra l dng khuchtn. lm ciuny ngita phicho vo dung

dchinphn mtdung dchnnc nnggpc10 100 lnhoc1000

lnso vichtphn tch.

- Qu trnh xyra trn inccgitcatot thungn :inccso snh csdngc dintch ln, inccchth thu

ngn c dintch b. Qa trnh xy ra in cc ch th ch yu trn thu ngn.

Nu trong dung dch khng c qu trnh no ph th th v dng c mi quan h :

I = E / R

Phnngtrn inccxyra :

Mn+ + ne + Hg M(Hg)

Thincccatot cxc nh:

RT CMn+ . aHg. fMn+

EK= Eo+ ln

nF CM(Hg) . fM(Hg)

Trong dng khuchtn phthucvo :

Nngkim loitrong dung dch, nngion kim loinhn electron

ticatot.

I = KM( CoM - CM )

CoM : Nngion kim loisu trong lng dung dch.

CM : Nngion kim loist bmtinccv nhnelectron tiin

cc.

nlc CM= 0 ( ion gninccht vcatot < vp.incc) th sinh ra

dng giihn:Id = KM . C

oMn+

Dng inny cgil dng khuchtn :

I = Id - KM.CMn+

V :


30

CMn+= ( Id I )/ KM ( KMl hstl)

Tng t, nngkim loi trong hnhng cng t lvi cng

dng :

CM(Hg) = I . K = I . 1/K

Lc thincc:

RT ( Id- I ) . aHg. fMn+.KaE = E

o+ ln

nF KM.I . fM(Hg)

Trong : fMn+, Ka, KM, fM(Hg), aHgl hngs.

Lc E phthucI, Id.

SphthucE I l phng trnh sng ccph.

- Cc phng php ccphxung :Nhm ny gm3 phng php sau :

+ Phng php ccphsng vung ( SWP )

+ Phng php ccphxung thng( NPP )+ Phng php ccphxung vi phn ( DPP )

Nguyn l chung canhm phng php ny l :

in cc lm vic c phn cc bng dng mt chiu c in p

khng ihocbin iuccng thm vo nhng thiimxc nh

nhng xung in p gin on c bin v rngxc nhvung gc,

bngcch ny sutthigian txung dng faraday IFtng theo t-1/2, dng t

instng theo e-kt.Ktqul trong php o vpha ktthc thigian txung hunhcho

cdng faraday, tithigian ny dng tin( ic) hunhtrit tiu hon

ton :


31

ic =R

Ea . e-t/R.CD

Trong :

-

Ea : Bin xung- R : intr- ic: Dng tin- t : Thigian sau khi p xung- CD : Thtch lpkp caincclm vic.Phng php cc ph xung thng c p dng vi cc loi in cc

gitthungn v inccrn.

I.5.2.1 Phng php cc ph sng vung :

Hnh 1.1 : Cc thnh phn in p trong SWP

: inp mtchiu

: inp xoay chiu

t

E


32

Hnh 1.2 :Dngtn hiuo caphng php SWP

Phng php ccph sng vung c a ra bi Barker v Jenkin

(1582 ). Phng php ny inccgitthungn cphn ccbngmt

inp mtchiubinthin theo thigian, ccngthm vo mtinpxoay chiudngvung gc c tns125 200Hz v c bin c ththay

i t1- 5mV. Mcd incccphn cc thngxuyn bnginp

xoay chiucngvo inp mtchiunhng nhmtthitbngbngi

ta chghi cngdng vo khongthigian hpvo cuimigit, c th

l 2 giy sau khi tothnh gittrong mtkhong100 200 giy ngvicui

nachu ktrong iukin.

Trong thctngita thngo cngdng inhai thiim,sau khi npxung khong17ms v sau khi ngtxung 17ms.

Hiucahai gi trdng inny l tn hiuura. Sphthucca

hiudng inny theo thinccc dngnhpc nhtrn.

i

E

ip= i1 i2


33

tinhpc l Epctng ng nhE1/2trong ccphcin. Bng

phng php ccphsng vung c thtnhyti10-7M v chn lc

l 10000.

Nhcimcaphng php ny l nhygimkhi tng tnh thun

nghchcaqu trnh incc. Gi trnhipcctnh theo phng trnh :

ip = K . n2. D1/2. EA . CA

Trong :

K = Hngs

n : Selectron trao itrong phnng

D : Hskhuchtn

EA : Bin xung

CA : Nngchtphn tch trong dung dch

Hinnay phng php ccphsng vung cmrngthnh phng

php Von ampe sng vung. Ton b qu trnh o caphng php ny

trn gitthungn vibcqut thnhanh vixung sng vung 5 10 giy,bin xung 50mV cthm vo, thigian txung vitns250 Hz c

tcqut 1000mV/s v thiukino ny chxyra trn gitthungn l

tt


34

I.5.2.2 Phng php cc ph xung thng ( NPP ) :

Hnh 1.3 :Dng inp phn cctrong NPP

Hnh 1.4 :Dngthcaphng php NPP

t

EA

t1 2t1

E

E

I

ID

E1/2


35

IF = n . F . C . S . tD ./ .p1

1 ( * )

D : Dintch bmtincctithiimo

C : Nngchtinhot

D : Hskhuchtn

t : Khongthigian tnh tkhi npxung nkhi o dng

p = ln [(RT

Fn. ) . ( E - E21/2) ]

E : Thxung

E1/2 : Thbn sng

Trong phng php ny in cc git thu ngn c phn cc bng mt

in p mt chiu chn trc v c gi khng i trong sut qu trnh o gi

l in p khi im tng ng vi chn sng cc ph trong cc ph c in.

Trong mi chu kgit incccphn ccbsung bngmtxung

vung gc c khong thi gian tn ti rt ngn 40 100ms tu theo tiu

chuntngncv tngmy. Sau thigian xung bngtv thincc

trvinp khiim. Bin xung tng dntheo thigian vimttc

uging nhtcqut thtuyntnh trong ccphcin.

Cngdngcghi theo 1 trong 2 cch :

- Ghi cngdng timtthiimsau khi txung thngl 17mstrckhi ngtxung.

- Cngdng ccphcghi 2 ln: ln1 trckhi ngtxung vln2 sau khi ngtxung. Thngl 17ms trcv sau khi tv ngt

xung. Cch ny cho hiuqutthn v thu cngE I l dng

pc nhtrong ccphsng vung.

Dng Faraday cthhinbngphng trnh ( * ).

Phng php ny c thtnhy10-7M cho chai qu trnh thun

nghchv khng thunnghch. V nhiudkinthunlicho php phn tch


36

chthuc. Trong mts trnghpngay cphng php cin khng

cho sng ccphr rng th n vncho sng ccphr rng

I.5.2.3 Phngphp cc ph xung vi phn (DPP)

Hnh 1.5 : Dnginp phn cctrong phng php DPP

Fei : Bin xung

Estep : Bcthmtxung in

tstep : Thigian npxung in

Hnh 1.6 : Dngtn hiuura caphng php DPP

ip= i1 i2

E

i

Fei

Estep

Chu k gittstep

E

t


37

Trong phng php ccph xung vi phn in cc git thu ngn

c phn cc bng mt in p mt chiu bin thi n tuyn tnh vi tc

chm ( 1 2 mV/s ) nhng vo cui mi chu k git (git ri cng

bc nh b g ), trn khung in p bin i mt chiu ngi ta t thm

mt xung vung gc vi bin thay i trong khong 10 100 mV v

di xung c 400 100 ms. Cng dng l hiu ca gi tr dng ghi

17ms trc khi np xung v 17ms sau khi ngt xung.

u imcaphng php ny l c nhycao ( 10-7M ) ivicc

hp cht v c cng nh hu c, phn ng thun nghch cng nh khng

thunnghch. Hn nadngngccph l dngpc c ccinn sau

mi lnghi ngnn li trvvtr ban unn chn lccaphng

php ny tng ln nhiu ln : c thxc nhng thinhiunguyn tm

khng cntch hay lm giu.

Tuy nhin cnlu rngdo giihnpht hincctiutrong ccph

xung vi phn l thphn nhiuso viphng php cinnn nhhng

caintrho cncxem xt k. Thngnngnninli philn

hn chtphn tch 20 50 lnloitrnhhngcasinchuynv loitrnhhngcadninthpdo nngnnnhphisdngh

o 3 incc.

I.5.3Phng php Von ampe ho tan :

Nguyn tc:

Thitbdng mtmy ccphtghi c 3 incc: cclm vicl ccgit

thungn tnh, chyul inccHMDE.

inccso snh thngl calomen hocccAgCl c thkhng i.inccph trl incc platin.

Npbnh c mtlnhdnkh trl kh nithocargon vo dung

dchuikh oxi ho tan. Khi inphn lm giu chnthinphn thch


38

hpv gikhng itrong sutqu trnh inphn. Thny phikhost s

b.

iviqu trnh kh trn catot thin phn thng m hn 300

500mV so vithnhv iviqu trnh anot thinphn thngdng

hn th nh mt lng tng t. Khng phi th nh cng m hay cng

dng th cng ttv lc skm tnh chnlcv gimhiusutinphn.

Trong qu trnh in phn s khuy dung dch t 2000 4000

vng/pht khuch tn dung dch di dng chy tng chkhng phi l

chuynngxoy. Sau qu trnh inphn th ngngkhuyv c mt thi

gian nght3 60s cho ton bhthngdung dchcyn tnhv kim

loicphn b utrn hnhng.

Bcho tan kttaclm giu trn incc:

inccsbphn ccngcviqu trnh inphn v ghi o dng Vn

Ampe. Nuqu trnh inphn l qu trnh catot th qu trnh ho tan s l

qu trnh anot v ngvn ampe ho tan ocgil ngvn ampe

ho tan anot. Khi qut thtrong qu trnh vn ampe anot th thsqut t

m sang dng.+ Cchcaphng php Vn Ampe ho tan Anot ( ASV ) :

Bc1 :

Lm giu chtphn tch trn catot :

Mn+ + ne + Hg M(Hg)

Bc2 : Ho tan kttatrn anot : qu trnh anot, qut thtm sang dng

dn.M(Hg) - ne Mn+ + Hg

Phng trnh pc :

ip = K . n3/2. D1/2M(Hg) . CoM. V1/2. r2. tacc


39

Trong :

ip : Dng pc

D1/2M(Hg) : Hskhuchtn cakim loiM trong hnhng

K : Hngs

n : Selectron trao i

r : Bn knh git

tacc : Thigian lm giu

V : Vntcqut

Lngkim loiclm giu catot trong hnhng:

iacc . taccCoM =

VHg. n . F

( F : l hngsFaraday )

Trong : VHg = AF . v

AF: Dintch bmtmng

v : dy camng

+ Cchcaphng php vn ampe ho tan catot ( CSV ):Bc1 :

2Hg Hg22+ + 2e

Hg22+ + 2A- Hg2A2

Bc2 :Hg2A2 + 2e 2Hg + 2A

-

Trong phng php CSV qu trnh lm giu l qu trnh anot, qu trnh ho

tan l qu trnh catot, thqut trong qu trnh ho tan tdng sang m.


40

I.5.4 Phng phpVn ampe ho tan hp ph ( AdSV ) :

( Absorbtion Stripping Voltammetry )

Trong phng php Vn ampe ho tan anot v catot phng php

lm giu bnginphn csdng tuy nhin c nhiuqu trnh lm

giu m in phn khng th thc hin c nh i vi niken v coban

khng tan trong thungn. Khi ngi ta chuyn cht cn phn tch vo

dngmtphcchtc thhpphtttrn incc.

Ngy nay y l hnglm giu chyu, cbitivihpchthu

c. C 3 trnghphpphxyra :

+ Trnghp1 :

Thm vo dung dchmt thucthc khnng hpphttln bmt

inccti mtthxc nh. Sau khi bhpphn stophcvichtcn

xc nhtptrung n ln bmtincc.

B1 :

Rdd Rh.ph

Rh . ph + M

n+

(MRnn+

)h . ph

Trong trng hp ny qu trnh hp ph xy ra trc phn ng ho

hc. Khi xc nhtinhnh qu trnh ho tan inho cht clm giu

bnghpph.

B2 :

( MRnn+)h . ph + ne M + nRh . ph

Trnghp2 :

Chtcnxc nh tham gia phnngho hc tophcvi thuc th

thch hp c trong dung dch ri phc b hp ph ln b mt in cc

(thngxyra viniken v coban ).


41

Cchcaqu trnh :

B1 :

Mddn+ + nRdd MRndd

MRndd (MRn)h . ph

B2 :

(MRn)h . ph + ne Mdd + Rdd

+ Trnghp3 :

Stophcsau khi c sthay isoxi ho cachtphn tch :

B1 :

Mm+ ne M( m n ) +

M( m n ) + + ( m n )Rdd ( h . ph) MR( m n ) h . ph

B2 : Qu trnh xyra trnghpny tng tnhtrnghp1.ngVn ampe ho tan hpphc dngmtnhpc. Epc v Ipc

phthucvo nhiuyut: nninli, chttophc, bnchtincclm

vic, kthutghi o ngvn ampe ho tan,

Dng capc trong phng php vn ampe ho tan hpph:

ip = K . A . = K . CA[R

D . Tacc + 2 taccD )./( ]

Trong :A : Dintch bmtcc

: Lngchthpph

D : Hshpph

K = Hngs


42

R : Bn knh git

ip max = K . A . max CA . tacc2

Mtkiuhpphmixuthingny l inphn lm giu thE1,

sau thigian inphn tngtchuynvthE2ho tan cht, ngay lp

tcqut thngc tr li. Ion kim loivabho tan cha khuch tn khi

bmthpphbhpphln bmtdidngphcv bkhvkim loi.

Nusdngphng php ny c thnng nhyln 10 100 lnso vi

phng php vn ampe ho tan anot thng thng.

Ngoi lm giu bnghpphngita cn kthpvixc tc. Vng

lpclpi lpli( c thnng nhyln ti10

-12

M ).I.5.5Cc phng php phn tch nh lng trong phn tch in ho :

I.5.5.1 Phng php muchun:

Ngita sdnghai dung dchcacng mtcht:

Dung dch1 : c nngCxcachtphn tch cnxc nh

Dung dch2 : l dung dchchun bitchnh xc nngCc.

Tinhnh ghi ccphcadung dch 1 v 2 trong cng mtiukinc

: hxv hctng ng.Do stuyntnh giah v C nn ta c :

Cc

Cx

hc

hx

hc

hxCcCx

I.5.5.2 Phng php ng chun :

lp phng trnh ng chun ta chun bmtdy dung dch c

nng bitcachtcnxc nh : C1 , C2, , Cn( thngn = 1 3 )

(theo cpscng).


43

Ghi ccph cady trn ta c: h1, h2, , hn( chiucao cc pc

tng ng). Tcc gi trvthv lpphng trnh ngchuns

phthuccanngv chiucao pc.

Phng trnh ngchunc dng:

y = ax + b

Vi dung dch nghin cu c nng Cxcha bit ta ghi c cc ph l hx.

Thay hx= y vo phng trnh ngchunta tnh cCx

I.5.5.3 Phng php thm chun :

Nguyn tccaphng php ny l dng ngay muphn tch lm nn

chunbmuubngcch lymtlngmuphn tch nhtnh( c

nngCx) rithm vo nhnglngchnh xc nguyn tcnxc nh

theo tngbcnng, chnghn C1, C2, C3, ( theo cpscng), ta thu

cdy muu:

Cx+ C1, Cx+ C2, Cx+ C3,

Chncc iukinphn tch thch hpta tinhnh ghi o ccph

cacc mutrong dy muu chunbtrn ta thu cchiucao cc

pc tng ng: h1, h2, h3, Tta xy dngcthcah theo C.

Hnh 1.5 :ngchun

h

h2

h1

C1 C2 C0

M

A


44

Da vo th ny ngi ta xc nh c nng cht phn tch

trong dung dch, bng cch : ko di ng chun t A ct trc honh ti

imM . KhongOM l nngCxcntm.

Phng php thm chun c u im l : qu trnh chun b mud

dng, khng phisdngnhngho chtc tinh khitcao, loitrc

hon ton nhhngvthnh phncngnhcutrc vtl cacc chtto

thnh mu.

I.5.5.4 Phng php thm :

Trong phng php ny ngita tinhnh nhsau :

Sdngdung dchphn tch cha bitnngCx, tinhnh ghi ccph

cpc tng nghx.

Thm vo dung dch trn mt lng bitchnh xc nngcht

cnphn tch Cch, tinhnh ghi ccphcpc l htng.

Ta c :

htng = hch + hx hch = htng - hx

Do stuyntnh caC v h ta c :

hx/ hch = Cx/ Cch Cx = Cch. hx/ hchI.5.6 Cc loi in cc c s dng trong phng php phn tch cc

ph :

I.5.6.1 Ccrnhnh a( RDE )( Rotating disc electrode )

l mtmtphnghnh trn ngknh 3 5 mm lm bngcc vt

liutrnhplatin, vng v cc loicacbon c tinh khitcao, trv c b

mtdnhbng dintch bmtkhng i.

Platin qu himnhng kh gia cng bmt cho dintch bmtcdintch khng i, v qu thhiro trn platin nhnn khongthsdng

hp cbitl viqu trnh catot.


45

Vt liu ttnhtsnxutinccrnhnh al cacbon thutinh

c bnho hccao, khng thay i kckhi ngm nhiugitrong nc

cngthu, dnhbng bmt.

Thc nghim chng minh rng ly cc loi giy nhm mn nh

bng bmtin ccaquay bng than thu tinh th b mt thc ca n

bngbmthnh hccan:

S = . R2

Ngoi cacbon thu tinh c th dng cacbon ngm tm hoc cacbon

nho chtoincca.

Khongthhotng cainccny rtrng:

- Trong mi trngaxt : + 1 -1 V- Trong mi trngkimhoctrung tnh : + 1 -1,8 V.

I.5.6.2 in cc mng thu tinh ( TMFE ):

( Thin Mecury film electrode )

Loiccny rtthunlicho vicxc nh lngvtcc kim loid

tohnhngvithungn.

Chcnthm vo dung dchphn tch mtlngHg

2+

vinng10-5 10-4M, khi inphn lm giu kim loiphn tch th ion Hg2+cngb

khng thihockh trc to thnh mtmng mngv u thungn

trn bmtccrn. Kim loicnxc nhcho tan u trong mng ,

dng inccTMFE hnchcshnh thnh hpchtgian kim loihoc

dung dch rnkhi xc nh lngvt camt s ion kim loi c mt trong

dung dch.

Thng thngngi ta dng in ccmng thu ngn trn nn thanthutinh . C 3 loithan thngdng :

+ Grafit ngm tm: loiny t sdngv c lxphpthkh

+ Grafit cacbon ( than thutinh ) : cdng nhiunht


46

+ Grafit nho : i khi cngcdng tuy nhin hnh dngcan c

thbbinitrong mtstrunghp.

- Mng mngthungn ctora bnghai cch :

+ Tomng mngtrc

+ Tomng ngthi

Micch c mtu vit ring cp dngcho tngi tngkhc nhau

tuv tr ca ion kim loi tomng. Nng thungn thngcdng

gp100 1000 lnso vinngcaion phn tch.

I.5.6.3 in cc git thu ngn treo (HMDE)

inccgitthungn bao gm3 loi: inccgitthungn treo

(HMDE ), inccgitthungn ri cngbc( SMDE ), v inccgit

ri DME

inccgitthungn l mtgitthungn c kch thcnhv bt

ngngknh khong1mm c treo trn mtmao qunbng thu tinh

hi lm gia c mtmu nhngnplatin dnin. m bo tnh

chnh xc v lplicaphp xc nhyu cucagit thungn tnhl

c kch thckhng iv lplicao. V sau milno phitomtgitkhc gingnhgitban u.

u imcainccgitthungn :

+ Khongthcho php cathungn rtrng, nn xc nhcmt

slnkim loi. Trong mi trngaxt khongthaxt ttl -0,15 -1,2V v

trong mi trngbazkhongthttl -0,15 2V.

+ Dng inccthungn thunlicho vicchn nnphn tch, chn

th in phn, c lp li cao. C th xc nh c nng thp tuphng php.

Nutrong qu trnh ghi ccphcachtphn tch gitthungn b

ri cngbc theo mtchu k nhtnh th cgi l inccgit thu

ngn ri cngbc( SMDE ).


47

u imcainccSMDE cngnhDME l inccgitri nn

incclun c lm mi, nhng SMDE lic u imnhHMDE kch

cnhv tnhlngtrong qu trnh xc nh.

Chai loiinccHMDE v TMFE c u imgingnhau vgii

hn pht hinv nhy.

Viin cc mng thu ngn ( TMFE ) nng kim loi trong hn

hngin cccao hn, tckhuch tn kim loi ra khiin ccTMFE

nhanh hn v c cimqu trnh inho lp mng. Mtkhc nudng

TMFE quay, iukinilu l schuynkhitthn do TMFE c

nhyv phn giitrong mt strnghpcao hn.

Tuy th i vi phng php s dng TMFE cc hp cht gian kim

loidhnh thnh khi phn tch theo phng php Vn ampe ho tan, gy

ra sbindng tn hiudnnsai s.


48

PHN II : THC NGHIM V KT QU

II.1. Thit b, dng c v ho cht :

II.1.1 Thitb, dngc:

II.1.1.1 Thitb:

Ttccc php o ucthchintrn my ccphxung vi phn

797 VA Computrace ( Metrohm ThyS) vih3 incc: incclm

vicl inccgitthungn ( HMDE, SMDE ) v inccso snh l in

ccAg/AgCl, inccph trplatin.

II.1.1.2 Dng c :- Pipet cc loi- Ccthutinh : 250, 500 ( ml )- Bnh nhmc- My o pH Milwaukee ( snxutItalia )- Cn phn tch c chnh xc 0,01mg

II.1.2 Ho cht :

Tt c cc loi ho cht s dng trong nghin cu u c cht lngSuprapure ca MERCK, cc dung dch chun kim loi c pha t dung dch

gc nng 1000mg/l ca MERCK, nc ct s dng l nc ct hai ln.

Ho cht:

- Dung dchchungcZn2+ 1000ppm- Dung dchchungcPb2+ 1000ppm- Dung dch chun gc Cd2+ 1000ppm- Dung dchchungcCu2+1000ppm- Dung dch m axetat pH =4,6- Tinh th NaOH- Axit HNO3c


49

II.2 Ly v bo qun mu :

Cc bphncadngc, thitbulm bngTeflon khng kim loi

trnh gy nhimbnkim loicho mu, bnh ngmulm bngnhaPE

Trckhi dng bnh ngmu ctrng ra3 lnbngchnh mu.

Mu c bo qunbng cch: 1,5 lit mu + 5ml axit HNO3c tinh khit

trnh cc kim loi Zn, Cd, Pb, Cu b hp th ln thnh bnh cha mu.

mu trong t lnh 4oC ch phn tch.

II.3 Quy trnh v c ho mu

Vi tng loi nc ca mi sng, ly 500ml mu cn phn tch c

axit ho trn thm vo 5ml axit HNO3c, un trn bp in cho n khi

dung dch gn cn, nu c mu th li thm 5ml HNO3c v lm bay hi ln

na, ng tc ny lp i lp li cho n khi dung dch khng mu. Ri lm

bay hi dung dch n cn kh. Phn b sau khi ngui ho tan trong nc

ct, un nng ho tan ht mui tan. Lc qua phu lc kh, gi ly ng th

tch bng 500ml xc nh Zn, Pb, Cu, Cd.

Vi tng loi rau th ta x l mu nh sau:

1.

Ra rau, ra li theo nc ct kh t nhin.2. Xay mt lng rau ti bng my xay sinh t.3. Cn 1g cho vo bnh Kendan c th thay th bng cc chu nhit.4. Thm 12ml hn hp (HNO3:HClO4) t l (5:1).

Dng a thu tinh trn u yn qua m hoc vi gi

Ci nhit ca bp 200oC trong 40 pht. Khi un y phu trn ming

bnh. Ch khng cn mu

mu ngui, nu thy dung dch trong gn nh mt mu th dngthm t t 10ml HCl 3N

un si 25 pht 150oC ngui thy dung dch trong trng l c

nh mc sang bnh 50ml occ ph


50

Song song tin hnh mt mu trng khng c raumi ch ha nh mu

tht

II.4 Xc nh ng thi Zn, Cd, Cu, Pb.

II.4.1 Thc nghim tm cc iu kin ti u cho php xc nh Zn, Cd, Cu,

Pb.

II.4.1.1 Pha ch dung dch cho php xc nh Zn, Cd, Cu, Pb .

- Dung dch chun Zn2+10ppm

- Dung dch chun Cd2+1ppm

- Dung dch chun Cu2+2ppm

- Dung dch chun Pb2+3ppm

- Dung dch chun cha ng thi Zn2+ 10ppm, Cd2+ 0,1ppm, Cu2+

2ppm, Pb2+3ppm

- Dung dch m axetat(pH=4,6)

- Dung dch HNO3 1M

Cch tin hnh:

- Dung dch chun Zn2+10ppm: Ly 1ml dung dch Zn2+1000ppm nh

mc n 100ml bng nc ct 2 ln ta c dung dch Zn

2+

10ppm- Dung dch chunCd2+1ppm: Ly 0,1ml dung dch Cd2+1000ppm nh

mc n 100ml bng nc ct 2 ln ta c dung dchCd2+1ppm

- Dung dch chun Cu2+2ppm: Ly 0,2ml dung dch Cu2+1000ppm nh

mc n 100ml bng nc ct 2 ln ta c dung dch Cu2+2ppm

- Dung dch chun Pb2+ 3ppm: Ly 0,3ml dung dch Pb2+ 1000ppm

nh mc n 100ml bng nc ct 2 ln ta c dung dch Pb2+3ppm

- Dung dch chun cha ng thi Zn2+ 10ppm, Cd2+ 0,1ppm, Cu2+

2ppm, Pb2+3ppm: Ly 1ml dung dch Zn2+1000ppm; 0,01ml dung dch Cd2+

1000ppm; 0,2ml dung dch Cu2+1000ppm; 0,3ml dung dch Pb2+1000ppm ri

nh mc n 100ml bng nc ct 2 ln ta c dung dch cha ng thi

Zn2+10ppm, Cd2+0,1ppm, Cu2+2ppm, Pb2+3ppm


51

- Dung dch m axetat pH=4,6: Ly 47,46ml andehit axetic 99,2% pha

thnh 500ml trong bnh nh mc bng nc ct 2 ln ta c 500ml dung

dch CH3COOH 2M. Ly 68,04g CH3COONa.3H2O pha trong 250ml bng

nc ct 2 ln ta c 250ml dung dch CH3COONa 2M. Ly 23,5ml dung

dch CH3COONa 2M v 26,5 ml dung dch CH3COOH 2M pha long bng

nc ct 2 ln thnh 500ml dung dch m axetat pH=4,6

- Dung dch HNO3 1M:

T dungdch gc HNO3 c C% = 65%; D = 1,39kg/l. Ly 69,73 ml

HNO3 c pha long bng nc ct 2 ln nh mc ti 1 lit ta c dung dch

HNO31M

II.4.1.2 Kho st cc iu kin ti u cho php xc nh Zn,Cd,Pb,Cu.

II.4.1.2.1. Kho st s xuthin ca pic:

kho st s xut hin ca pic Zn(II),Cd(II),Cu(II),Pb(II) chng ti

tin hnh lm nh sau:

Ly 20ml nc ct 2 ln + 0,05ml dung dch chun cha ng thi Zn2+

10ppm ,Cd2+0,5ppm, Pb2+1ppm, Cu2+1ppm + 0,5ml dung dch m axetat

pH=4,6 cho vo bnh in phn, tin hnh in phn Up=-1,2V, qut th t-1,2V +0,2V v tin hnh ghi o ng xung vi phn chng ti thu c kt

qu nh sau:

Upic(Zn) l -1,20,05V

Upic(Cd) l -0,5880,05V.

Upic(Pb) l -0,380,05V.

Upic(Cu) l 0,03080,05V.

II.4.1.2.2 Kho st bin xung. kho st bin xung, chng ti s dng in phn th in phn

Udp=-1,2V qut th t -1,2V +0,2V, thi gian sc kh N2l 300s, thi gian

in phn l 30s


52

Ly 20ml nc ct 2 ln + 0,05ml dung dch chun cha ng thi Zn2+

10ppm, Cd2+0,5ppm, Pb2+1ppm, Cu2+1ppm + 0,5ml dung dch m axetat

pH=4,6 cho vo bnh in phn

Tin hnh ghi o ng vi phn ca dung dch cc bin xung khc

nhau, kt qu thu c bng 2.1

Bng 2.1: S thay i chiu cao pic Zn, Cd, Pb, Cu theo bin xung.

Chiu cao pic

h (A)

Bin

xung (V)

Zn Cd Pb Cu

0,02 4,80.10-8 2,07.10-8 1,27.10-8 6,14.10-8

0,03 6,87.10-8 2,90.10-8 1,81.10-8 8,74.10-8

0,04 8,78.10-8 3,70.10-8 2,30.10-8 1,15.10-7

0,05 1,01.10-7 4,28.10-8 2,64.10-8 1,32.10-7

0,06 1,09.10-7 4,66.10-8 2,90.10-8 1,43.10-7

0,07 1,18.10-7 4,98.10-8 3,09.10-8 1,54.10-7

0,08 1,20.10-7 5,10.10-8 3,16.10-8 1,58.10-7

Qua bng 2.1 chng ti rt ra c kt lun:

Khi bin xung cao th chiu cao pic tng, khi bin xung gim th

chiu cao pic gim. Tuy nhin nu bin xung cao qu th ng nn cao,

ng khng p cho nn ta chn bin xung 0,05V

II.4.1.2.3 Kho st thi gian t xung

kho st thi gian t xung chng ti t cc iu kin o nh th

nghim II.4.1.2.2, nhng thay i thi gian t xung v kt qu thu c

bng 2.2

Bng 2.2 S thay i chiu cao pic theo thi gian t xung


53

Chiu cao pic(A)

Thigian t

xung(s)

Zn Cd Pb Cu

0,01 1,48.10-7 6,43.10-8 3,69.10-8 1,75.10-7

0,02 1,01.10-7 4,28.10-8 2,64.10-8 1,32.10-7

0,03 1,64.10-7 6,54.10-8 3,66.10-8 1,37.10-7

Qua bng 2.2 chng ti thy khi thi gian t xung = 0,01s hay 0,03s

th chiu cao pic tng nhng nn cao.Qua kt qu thc nghim thu c gi

tr chiu cao pic n nh v nn thp thi gian t xung l 0,02s

II.4.1.2.4 Kho st tc qutth.

Cc iu kin o nh 2 th nghim trn thay i tc qut, kt qu thu

c bng 2.3

Bng 2.3 S thay i chiu cao pic Zn, Cd, Pb, Cu theo tc qut th

Chiu cao pic

h (A)Tc

qut th (V/s)

Zn Cd Pb Cu

0,085 9,22.10-8 3,94.10-8 2,53.10-8 1,18.10-7

0,1 9,72.10-8 4,18.10-8 2,67.10-8 1,26.10-8

0,12 1,01.10-7 4,34.10-8 2,73.10-8 1,31.10-7

0,15 1,01.10-7 4,28.10-8 2,64.10-8 1,32.10-7

Qua kt qu thc nghim thu c bng 2.3 chng ti nhn thy khi

gim tc qut th t 0,15V/s xung 0,085V/s th chiu cao pic li gim,

nn cao. Chng ti chn tc qut th l 0,15V/s v lc chiu cao pic ln

v n nh, th p, nn thp.


54

II.4.1.2.5 Kho st thi gian sc kh

kho st s nh hng ca thi gian sc kh (loi oxi ho tan) n

chiu cao pic v nn pic chng ti tin hnh nh sau. S dng cc iu kin

o: th in phn, thi gian in phn, bin xung, thi gian t xung, tc

, qut th nh trn v sc vi p sut PN2=1atm, thay i thi gian sc kh

chng ti thu c kt qu th hin bng 2.4

Bng 2.4 S thay i chiu cao pic Zn, Cd, Pb, Cu theo thi gian sc kh.

Chiu cao pic

h (A)

Thi gian

sc kh (s)

Zn Cd Pb Cu

5 9,22.10-8 3,64.10-8 2,00.10-8 1,52.10-7

30 1,09.10-7 3,89.10-8 2,34.10-8 1,23.10-7

200 1,14.10-7 3,79.10-8 2,43.10-8 1,18.10-7

300 1,19.10-7 3,89.10-8 2,48.10-8 1,23.10-7

600 1,16.10-7

3,72.10-8

2,47.10-8

1,15.10-7

Qua bng 2.4 chng ti nhn thy khi thi gian sc kh l 300s th chiu

cao pic t gi tr ln nht, th p, nn thp. V vy chng ti chn thi

gian sc kh l 300s

II.4.1.2.6 Kho st thi gian cn bng

Sau khi in phn thng ngng khuy dung dch, nu dng cc git

thu ngn tnh hoc cc mng thu ngn iu ch ti ch trn b mt cc a

th cn c thi gian ngh tc l yn h thng trong mt khong thi gian

ngn (5s60s) lng kim loi phn b u trn b mt cc. kho st

thi gian cn bng ti php o chng ti tin hnh vi cc iu kin o nh

cc th nghim trn v thay i thi gian ngh trong mi ln in phn v

chng ti thu c bng sau:


55

Bng 2.5S thay i chiu cao pic Zn, Cd, Pb, Cu theo thi gian cn bng

Chiu cao

pic h (A)

Thi gian

cn bng (s)

Zn Cd Pb Cu

1 1,38.10-7 4,35.10-8 2,91.10-8 1,35.10-7

2 1,24.10-7 3,93.10-8 2,68.10-8 1,19.10-7

3 1,32.10-7 4,17.10-8 2,82.10-8 1,28.10-7

5 1,36.10-7 4,27.10-8 2,90.10-8 1,29.10-7

10 1,31.10-7 4,08.10-8 2,78.10-8 1,23.10-7

30 1,40.10-7 4,36.10-8 2,97.10-8 1,29.10-7

Qua kt qu thc nghim thu c bng 2.5chng ti thy thi gian

cn bng l 1s hay 30s th chiu cao pic ln nhng th xu, nn cao. Khi

thi gian cn bng tng t 2s n 5s th chiu cao pic tng nhng thi gian

cn bng l 10s th chiu cao pic li gim. V vy chng ti chn thi gian cn

bng l 5sII.4.1.2.7 Kho st nh hng ca nng mi cht ln nhau.

II.4.1.2.7.1 nh hng nng ca Ni2+ ti Zn2+, Cd2+, Pb2+, Cu2+ trong

nn m axetat

kho st nh hng nng ca Ni2+tiZn2+, Cd2+, Pb2+, Cu2+ trong

nn m axetat chng ti tin hnh th nghim nh sau:

Ly 10ml nc ct 2 ln cho vo bnh in phn, thm vo 0,05ml

dung dch Zn2+10ppm+Cd2+0,1ppm+Pb2+3ppm+ Cd2+2ppm + 0,5ml dung

dch m axetat pH=4,6. Tin hnh ghi o ng Vn-Ampe ha tan anot ca

Zn2+, Cd2+, Pb2+,Cu2+ cc iu kin o : bin xung, thi gian cn bng,

thi gian sc kh ti u kho st trn, th in phn Udp= -1,2V, qut


56

th t -1,2V:+0,2V. Sau thm ln lt tng th tch khc nhau ca dung

dch Ni2+1ppm. Tin hnh ghi o ng xung vi phn cc iu kin o nh

trn, chng ti thu c bng sau:

Bng 2.5 : nh hng nng ca Ni2+tiZn2+, Cd2+, Pb2+, Cu2+ trong

nn m axetat

V Ni2+

1ppm

(ml)

Chiu cao

pic Zn2+

(A)

Chiu cao

pic Cd2+

(A)

Chiu

cao pic

Pb2+(A)

Chiu

cao pic

Cu2+(A)

T l nng

Ni:Zn:Cd:Pb:Cu

(CM)

0,000 -1,8.10-7 8,59.10-10 1,30.10-8 2,44.10-8 0:100:1:30:20

0,025 -1,78.10-7 8,55.10-10 1,29.10-8 2,38.10-8 5:100:1:30:20

0,125 1,81.10-7 8,56.10-10 1,29.10-8 2,44.10-8 25:100:1:30:20

0,325 1,67.10-7 8,56.10-10 1,20.10-8 2,37.10-8 65:100:1:30:20


57

Hnh 2.1nh hngnng Ni ti Zn, Cd, Pb, Cu trong nn axetat

Qua bng 2.5 v hnh 2.1 chng ti nhn thy chiu cao pic Zn2+, Cd2+,

Pb2+, Cu2+thay i khng ng k khi thm th tch Ni2+ t 0,025ml n

0,125ml. Khi thm th tch Ni2+ t 0,325ml tr ln chiu cao pic Zn2+ ,Pb2+,

Cu2+ thay i t bin.Nn ta ni 0,325ml Ni2+1ppm tr ln thm vo mu

phn tch th gy nh hng ti php o Zn2+, Cd2+, Pb2+, Cu2+. Vy kt qu t

l nng gii hnNi bt u nh hng tiphpxc nh ng thi Zn, Cd,

Pb, Cu trong vng nng kho st l 65:100:1:30:20

II.4.1.2.7.2 nh hng nng ca Fe3+tiZn2+, Cd2+, Pb2+, Cu2+ trong

nn m axetat

kho stnh hng nng ca Fe3+ tiZn2+, Cd2+, Pb2+, Cu2+trong

nn m axetat chng ti tin hnh th nghim nh sau:

Ly 10 ml nc ct 2 ln cho vo bnh in phn, thm vo 0,05ml

dung dch Zn2+10ppm+Cd2+0,1ppm+Pb 2+3ppm+ Cu2+2ppm + 0,5ml dung

dch m axetat pH=4,6. Tin hnh ghi o ng Vn-Ampe ha tan anot caZn2+, Cd2+, Pb2+,Cu2+ cc iu kin nh trn . Sau thm cc th tch khc

nhau ca dung dch Fe3+1ppm. Mt ln na ghi o ng Vn-Ampe ha tan

anot cc iu kin o nh trn, kt qu thu c bng 2.6

Bng 2.6nh hng nng ca Fe3+ tiZn2+, Cd2+, Pb2+, Cu2+ trong

nn m axetat

V Fe3+ 1

ppm (ml)

Chiu cao

pic Zn2+

(A)

Chiu cao

pic Cd2+(A)

Chiu cao

pic Pb2+(A)

Chiu cao

pic Cu2+(A)

T l nng

Fe:Zn:Cd:Pb:Cu(CM)

0 3,30.10-7 1,41.10-9 2,28.10-8 5,18.10-8 0:100:1:30:20

0,025 3,24.10-7 1,40.10-9 2,24.10-8 5,09.10-8 5:100:1:30:20


58

0,075 3,21.10-7 1,36.10-9 2,25.10-8 5,09.10-8 15:100:1:30:20

1,075 2,88.10-7 1,16.10-9 1,98.10-8 4,60.10-8 215:100:1:30:20

1,575 3,10.10-7 1,20.10-9 2,00.10-8 4,80.10-8 315:100:1:30:20

Hnh 2.2nh hng nng Fe (III) ti php o ng thi Zn, Cd, Pb, Cu

trong nn axetat

Qua bng 2.6 v hnh 2.2 chng ti rt ra c kt lun :

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