Phân tích chất lượng nước

7/28/2019 Phn tch cht lng nc

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Phn tch cht lng nc

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CHNG 7PHN TCH CHT LNG NC

1 NG DNG THUYT PHN TUVVIS TRONG PHN TCH CC YU TCHT LNG NC

1.1Slc lch snghin cu v quang phQuang ph hc l mt mn hc chnh yu trong thin vn hc, n c ng dngthnh cng nghin cu v kh quyn trong hnh tinh chng ta.

Cch y 200 nm, Joseph von Fraunhofer (1787-1826) ln u tin sn xut loi myo quang ph m tnh nng khng c g snh kp lc by gi. ng y khm ph rart nhiu cc ng ti trong quang ph ca nh sng mt tri.

ng y c th xc nh chnh xc di bc sng ca nhiu Fraunhofer lines(vch) v thut ng ny ngy nay vn c dng. Tuy nhin, trong thi gian ny ngy khng hiu c nhng csvt l v ngha v nhng vn m ng y khm

ph ra.

Hnh 7-1. Thit b Spektralapparat thit k bi Gustav R. Kirchhoff v Robert W.Bunsen (1823)

Thnh tu quan trng k tip v Fraunhofer lines l qu trnh tm ra nguyn l vtl ca s hp thu v pht x vo nm 1859 vi s cng tc ca nhiu nh vt l niting nh Gustav R. Kirchhoff (1824-1887), Robert W. Bunsen (1811-1899) tiHeidelberg. Thit b m h s dng l Spektralapparat, h ghi nhn c qu trnh

pht x rt c bit ca nhiu nguyn t khc nhau. Vi phng php ny h tiptc khm ph ra 2 nguyn t mi l Csium v Rubidium, h chit c mt lng rt


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Qun l cht lng nc nui trng thy sn

140

nh (7g) t 44.000 lt nc khong gn ni Bad Nauheim, Germany. S khm phny l nn tng cho s khm ph tip theo v s hp thu v pht x ca hp thu phnt.

Nm 1879 Marie Alfred Cornu thy rng, nhng tia c bc sng ngn ca bc xmt tri trn b mt tri t b hp th bi kh quyn. Mt nm sau , Walther NoelHartley m t rt t m v s hp th UV ca O3 vi di bc sng 200 v 300 nmv n trnn r rng hn khi h pht hin ra rng O3 cha y trong bu kh quyn.

In 1880, J. Chappuis khm ph ra s hp thu trong vng kh kin (400840nm). Nm1925 Dobson pht trin mt my quang ph mi rt n nh s dng lng knh bngthch anh.

1.2i cng v quang phTrong quang ph hc, nh sng nhn thy (nh sng kh kin), tia hng ngoi, tia tngoi, tia Rnghen, sng radio... u c gi chung mt thut ng l bc x.

Theo thuyt sng, cc dng bc x ny l dao ng sng ca cng in trng vcng t trng, nn bc x cn c gi l bc xin t.

Sau thuyt sng, thuyt ht cho thy bc x gm cc ht nng lng gi l photonchuyn ng vi tc nh sng (c = 3.108 m/s). Cc dng bc x khc nhau th khc

nhau v nng lng h ca cc photon. y, nng lng ca bc x c lng

t ha, ngha l nng lng ca bc x khng phi lin tc m cc lng t nnglng t l vi tn s ca dao ng in t theo h thc Planck.

h=

h = 6,625.10 34 J.s : hng s Planck.

Louis de Broglie a ra thuyt thng nht c khi nim sng v khi nim ht casng nh sng. nh sng va c tnh cht sng va c tnh cht ht. Tng qut hn l

bc x c bn cht sng ht. Ni dung nh sau:

Ht c khi lng m chuyn ng vi vn tc v c bc sng i i vi n l chobi h thc:

p

h

mv

h==

Trong : p = mv l ng lng ca ht

l bc sng (de Broglie)

h = 6,625.10 -34 J.s l hng s Planck.


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1.2.1 Cc i lngo bc xin tBc sng: L qung ng m bc xi c sau mi dao ng y .

n v: m, cm, m, nm,o

A . (1cm = 108o

A = 10 7m =104m)

Tn s : L s dao ng trong mt n v thi gian (giy)

Trong 1 giy bc xi c c cm v bc sng cm, vy:

c

=

Lu : Bc x truyn trong chn khng vi vn tc c = 2,9979.10 8 m/s (thng lytrn 3.10 8 m/s)

n v: CPS ( VNG DY), Hz, KHz, MHz. (1CPS=1Hz; 1MHz=103 KHz=106Hz)

Nng lng bc x: Cc dao ng t (phn t chng hn) ch c th pht ra hoc hp

th nng lng tng n v gin on, tng lng nh nguyn vn gi l lng tnng lng:

hchc

h ===

n v: Jun (J), Calo (Cal), electron von (eV).

1.2.2 Cc dng bc xBc xin t bao gm 1 dy cc sng in t c bc sng bin i trong khong

rt rng: t cmt sng raio n co

A (1010 m) tia Rnghen hoc nh hn na.Ton b dy sng c chia thnh cc vng ph khc nhau.

Hnh 7-2. Cc ph ca sng in t


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Mt ngi ch cm nhn c mt vng phin t rt nh gi l vng nhn thy(kh kin) bao gm cc bc x c bc sng t 396760 nm. Hai vng tip gip vi

vng nhn thy l vng hng ngoi v vng t ngoi.

1.2.3

Stng tc gia vt cht v bc xin tiu kin bnh thng, in t ca phn t nm trng thi lin kt, nn phn t cmc nng lng thp, gi l trng thi cbn

Khi chiu mt bc xin t vo mt mi trng vt cht, s xy ra hin tng ccphn t vt cht hp th hoc pht x nng lng, hay c gi l trng thi kchthch . Nng lng m phn t pht ra hay hp th vo l:

E = E2 - E1 = h

Trong , E1 v E2 l mc nng lng ca phn ttrng thi u v trng thi cui (hay cn gi l trng thi kch thch) l tn s ca bc xin t b hp th hay

pht x ra.

Nu E > 0 th xy ra s hp th bc xin t.

Nu E < 0 th xy ra s pht x nng lng.

Theo thuyt lng t, cc phn t v cc bc xin t trao i nng lng vi nhaukhng phi bt k v lin tc m c tnh cht gin on. Phn t ch hp th hoc pht

x 0, 1, 2, 3,n ln lng t h m thi. Khi phn t hp th hoc pht x s lmthay i cng ca bc x nhng khng lm thay i nng lng ca n, bi vcng bc xin t xc nh bng mt cc ht phton c trong chm tia, cn

nng lng bc xin t li ph thuc tn s ca bc x.

V th khi chiu mt chm bc xin t vi mt tn s duy nht i qua mi trngvt cht th sau khi i qua nng lng ca bc x khng h thay i m ch c cng bc x thay i.

Cc phn t khi hp th nng lng ca bc x s dn n thay i cc qu trnh

trong phn t (quay, dao ng, kch thch electron) hoc trong nguyn t (cnghng spin electron, cng hng t ht nhn)

Mi mt qu trnh nh vy i hi mt nng lng c trng cho n, ngha l i hibc xin t c tn s hay chiu di sng nht nh kch thch. Do s hp thchn lc ny m khi chiu chm bc xin t vi mt di tn s khc nhau i quami trng vt cht th sau khi i qua chm bc x ny s b mt i mt s bc x ctn s xc nh, ngha l cc tia ny b phn t hp th.


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1.2.4 Shp th bc x v mu sc ca cc chtnh sng nhn thy bao gm tt c di bc x c bc sng t 396-760 nm c mutrng (nh sng tng hp). Khi cho nh sng trng (nh sng mt tri) chiu qua mtlng knh, n s b phn tch thnh mt s tia mu (, da cam, vng, lc, lam, chm,tm). Mi tia mu ng vi mt khong bc sng hp hn (xem Bng 7-1). Cmgic cc mu sc l mt chui cc qu trnh sinh l v tm l phc tp khi bc xtrong vng kh kin chiu vo vng mc ca mt. Mt tia mu vi mt khong bcsng xc nh. Chng hn bc x vi bc sng 400430 nm gy cho ta cm gicmu tm, tia sng vi bc sng 560 nm cho ta cm gic mu lc vng.

nh sng chiu vo mt cht no n i qua hon ton th i vi mt ta cht khng mu.

Th d, thy tinh thng hp th cc bc x vi bc sng nh hn 360 nm nn ntrong sut vi cc bc x kh kin. Thy tinh thch anh hp th bc x vi bc sngnh hn 160 nm, n trong sut i vi bc x kh kin v c bc x t ngoi gn.

Mt cht hp th hon ton tt c cc tia nh sng th ta thy cht c mu en. Nus hp th ch xy ra mt khong no ca vng kh kin th cc bc xkhongcn li khi n mt ta s gy cho ta cm gic v mt mu no . Chng hn mt cht

hp th tia mu ( = 610730 m) th nh sng cn li gy cho ta cm gic mulc (ta thy cht c mu lc). Ngc li, nu cht hp th tia mu lc th i vi

mt ta n s c mu . Ngi ta gi mu v mu lc l hai mu ph nhau. Trnhai mu ph nhau li ta s c mu trng. Ni cch khc, hai tia ph nhau khi trn vonhau s to ra nh sng trng. Quan h gia mu ca tia b hp th v mu ca chthp th (cc mu ph nhau) c ghi bng sau:

Bng 7-1. Quan h gia mu ca tia b hp th v mu cht hp th

Tia b hp th (nm) Mu

Mu ca cht hp th(mu ca tia cn li)

400 430430 490490 510510 530530 560560 590590 610610 750

TmXanh

Lc xanhLc

Lc vngVng

Da cam

Vng lcVng da cam

taTm

XanhXanh lc

LcLu : Gia cc tia mu cnh nhau khng c mt ranh gii tht r rt.

Vic phn chia nh sng trng thnh 7, 8 hay 9 tia mu cn ty thuc vo lng knhv s tinh t ca mt ngi quan st.


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Mt cht c mu, th d nh mu chng hn l do n hp th chn lc trongvng kh kin theo mt trong cc kiu sau:

- Cht hp th tia ph ca tia (tc l hp th tia mu lc)-

Cht hp th cc tia tr tia mu .- Cht hp thhai vng khc nhau ca nh sng trng sao cho cc tia cn

li cho mt ta cm gic mu .

mt hp cht c mu, khng nht thit max ca n phi nm vng kh kin m

ch cn cng hp thvng kh kin ln. Ni mt cch khc tuy gi tr cci ca vn hp th nm ngoi vng kh kin nhng do vn hp th tri rng sangvng kh kin nn hp cht vn c mu. Tt nhin c c s hp th thy c

vng kh kin th max ca cht cng phi gn vi ranh gii ca vng kh kin.

Tng ng vi mt bc chuyn in t, ta thu c ph hp thu c dng:

Hai i lng c trng ca ph hp thu l v tr v cng

- V tr cc i hp thu, gi trmax ty thuc vo E m hp cht ny hp thu cc vng ph khc nhau. Bn chiu rng ca vn phin t dao ng khrng khong 5060m.

- Cng th hin qua din tch hoc chiu cao ca nh biu (peak).Cng vn ph ph thuc vo xc xut chuyn mc nng lng ca in t.Xc sut ln cho cng vn ph ln.

Mt hp cht mu c ph hp thu tt khi nh biu (peak) cao v bn chiu rngvn ph hp.

A Peak

max

Bn chiu rngvn h

Hnh 7-3. nh v bn chiu rng vn ph

Khi bn chiu rng vn ph hp, th khi thay i nh th hp thu A thay i ln.iu ny rt c ngha trong phn tch nh lng. Gi s hp cht X c Amax500nm. Khi chng ta o bc sng 510nm... th hp thu o c s khc rt xa

i vi bc sng 500nm. T ta thy rng mi hp cht mu c mt gi trmax nht nh v n phn nh nhy ca phng php.


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Mt khc, mt hp cht i hi nh biu cao ngha l khi ta o bc sng

max th ta c hp th quang cc i, khong lm vic rng.

1.2.5 nh lut Lambert BeerKhi chiu mt chm tia sng n sc i qua mt mi trng vt cht th cng catia sng ban u ( Io ) s b gim i ch cn l I

T s TI

I=00

0

100 c gi l truyn qua.

T s AI

II=

0

00 100 c gi l hp th.

Nguyn tc ca phng php biu din theo s :

Hnh 7-4. S m t shp th nh sng ca mt dung dch

Trong :

Io: Cng ban u ca ngun sng

IA: Cng nh sng b hp thu bi dung dch

I: Cng nh sng sau khi qua dung dch.

IR: Cng nh sng phn x bi thnh cuvette v dung dch, gi tr ny

c loi b bng cch lp li 2 ln o.

Gia IA, I, dy truyn nh sng (l) v nng (C) lin h qua quy lut Lambert Beer l nh lut hp nht ca Bouguer:

Lambert (1766) lKI

Io1lg =

Beer (1852) : CKI

Io1lg =


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truyn quang (T) hay hp th (A) ph thuc vo bn cht ca vt cht, dytruyn nh sng lv nng C ca dung dch. C th vit:

nh lut Lambert Beer : lC

I

IA **)lg( 0 ==

Trong : l h s hp thu phn t, C nng dung dch (mol/L), l dy truynnh sng (cm), A l hp th quang. (Lu phng trnh trn chngi vi tia

sngn sc).

Trong phn tch nh lng bng phng php trc quang ngi ta chn mt bc

sng nht nh, chiu dy cuvet l nht nh v lp phng trnh ph thuc ca hp th quang A vo nng C.

Kho st khong tun theo nh lut Lambert Beer:

Khi biu din nh lut Lambert Beer trn th ty theo cch thc hin php o, tathng gp ng biu din s ph thuc hp thu A vo cng C ca dungdch c dng: y = ax + b

H s gc a cho bit nhy ca phng php, trong phng php trc quang ngita cho dung dch trong khong tun theo nh lut Lambert Beer tc l khong

nng m gi tr khng thay i. H s gc a cng ln v khong tun theonh lut Beer cng rng l iu kin thun li cho php xc nh.

Slch khi nh lut Beer:

S lch khi nh lut Beerc biu din bng s sau:

Hnh 7-5. Gii hn ca nh lut Beer v shp th quang

Khong tuyn tnh LOL (Limit of Linear Response) l khong nng tun theo nh

lut Beer )**( ClA = ngha l khi nng tng th hp th quang A tng. Ngoigii hn LOL l s lch khi nh lut Beer, ngha l khi nng tng th hp th

LOL

A

C


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quang A hu nh khng tng na. Nguyn nhn ca qu trnh ny l do nng dungdch qu ln. Ngoi ra, khong tuyn tnh LOL cn bnh hng ca mc n scca nh sng s dng, pH ca dung dch, lc ion, s pha long...

ngha ca cc i lng:- H s hp thu mol : ph thuc bn cht mi cht, bc sng , nhit , chit

sut (theo nng ). Gi tr tnh l thuyt ca mt bc chuyn c php cho

1 electron l = 105 mol-1.cm-1.

lC

A= (l.mol

-1cm

-1)

cao cho ta bit c nhy ca phn ng, l thc o nhy ca phng

php. Trong phn tch trc quang, = 103105 mol-1. cm-1 l nhy dng

cho phng php trc quang, ph thuc vo chit sut m chit sut li ph

thuc vo nng . Khi chit sut tng ln th gim v khng thay i th

phi thc hin C 10-2 mol/L.

- hp th quang A: L i lng khng c n v, c tnh cht quan trng ltnh cng hp th quang.

Gi s 2 cht A v B c nng CA v CB, hp thu ti bc sng l:

A = AA + AB = l*(ACA + BCB)

Nu mt cht tan X no c hp th quang l AX, dung mi c hp thquang l Adm, ta c:

A = Ax + Adm

o c chnh xc Ax th Adm = 0, c ngha l phi chn max ca dung mi

khc xa vi max cht tan. Nhng cht c chn lm dung mi thng c hp thu min ranh gii t ngoi chn khng.

Bng7-2. Cc dung mi thng s dng trong vng UVVISDung mi Bc sng gii hn

s dng (nm)Dung mi Bc sng gii hn

s dng (nm)

Nc ct 190 Benzen 280

HCl 190 Cloroform 245

Etanol, Metanol 210 Tetra Clorocarbon 265

n- Butanol 210 Dietyl Eter 218

n- Hexan 210 Aceton 330Cyclohexan 210 1,4 Dioxan 215


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Trong hn hp c nhiu cu t khng lm thay i tng tc, khng phn ngha hc, khng dch chuyn cn bng, th c th xc nh hn hp cc cu t

theo h thc sau:

nnii lClClClCA

+++++= .............2211

- truyn quang T:oI

IT= m )lg( 0

I

IA = do TA lg=

V T tnh theo % nn: TA lg2 =

Nu T = 100% th A = 0 (ngha l khng hp th nh sng (I = Io)

Nu T = 1% th A = 2Nu T = 0 % th =A (hp thu hon ton nh sng)

1.2.6 Nguyn l cu to ca my quang phNgun sng

Ngun sng cho my quang ph l chm bc x pht ra rn. My quang ph dng

n hydro hay n Deuterium cho ph pht x lin tc trong vng UV t 200380m

(nhng thng s dng 200-340 m) v n tungsten halogen o vng 380-1000 m.

lm vic cho c hai vng th phi c 2 loi n trn. Mt yu cu i vi ngunsng l phi n nh, tui th cao v pht bc x lin tc trong vng ph cn o.

n Deuterium: cu to sm mt si t ph xit v mt cc kim loi t trong mtbng thu tinh cha kh Deuteri hoc hydro c ca s bng thch anh bc x tngoi i ra v n khng truyn qua c thy tinh. Khi si t c t nng,electron sinh ra kch thch cc phn t kh Deuteri (hoc hidro) bin thnh nguyn tv pht ra phton theo phn ng:

D2 + Ee*2D D + D + h

Ee = *2D

E = ED + ED+ h

y l nng lng electron kch thch, bc x pht ra l mt ph c bc sng t160 nm n vng kh kin.

Bn sc

Bn sc c chc nng tch bc xa sc thnh bc xn sc, bao gm knh lc,lng knh hay cch t.

Cch t l mt bng nhm hay cc kim loi Cu, Ag. Au... c vch thnh nhngrnh hnh tam gic song song. Khi chiu nh sng qua cch t, phn cn li c tc


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dng to nn vn nhiu x c bc sng khc nhau, khi quay cch t s to ra phnhiu x ging nh trng hp nh sng qua lng knh. u im l cho phn giitt, tn sc tuyn tnh, rng ca di n nh, chn bc sng n gin, gn nh, dch to nn hin nay s dng cch t to nh sng n sc c a chung. Cch t

dng cho UVVis c 1200 vch/mm (thng dao ng t 3003600 vch/mm, svch cng nhiu th nng sut phn gii cng cao.

Hnh 7-6. S cu to ca my quang ph

Lng knh ca my quang ph dng lng knh littrow (lng knh 300) bng thch anh,c c im nh sng i qua lng knh hai ln do phn xmt sau.

Detector

Detector l b phn o tn hiu nh sng trc v sau khi i qua dung dnh (ngtrong cuvet). Cc tn hiu sau khi i ra Detector sc sc khuch i, lu giv x l trn my tnh.

Cuvet ng mu

Cuvet phi lm bng cht liu cho bc x vng cn o i qua. Cuvet thy tinhkhng thch hp cho vng UV. Cuvet thch anh cho bc xi qua t 1901000 nm.Cuvet nha ch dng trong vng Vis v ch s dng c 1 vi ln.

1.3Sdng phng php trc quang trong nh lng ha hcYu cu v cc hp cht cn xc nh l phi bn, t phn ly, n nh, khng thay ithnh phn trong khong thi gian nht nh thc hin php o (1020 pht).

H s ln c gi tr t 1035.104 L.mol-1cm-1, c th thc hin phn ng to mu vicc thuc th v cv hu c.

Detector


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Nng cc cht xc nh theo nh lut Lambert Beer. Khong xc nh nng theo phng php l 10-2 10-6 mole. Gii hn pht hin ca phng php 10-7mole.

Cc hp cht l phc cn o phi c max khc xa vi max ca thuc th trong cng

iu kin tc l >2 ln na bn chiu rng ca vn ph (khong 80 -100 m). Thd, khi phn tch Fe2+ bng phng php O-Phenanthroline. Sau khi thm thuc th ta

c phc mu vng cam (max=510 m), trong khi thuc th 1,10-

Orthophenanthroline c max = 250 m.

1.3.1 Phng php so snhSo snh cng mu ca dung dch cn xc nh vi cng mu ca dung dchchun bit nng .

iu kin: c hai dung dch trn phi c nng nm trong khong tun theo nhlut Beer.

Cx ---------------------- Ax

Ctc ---------------------- Atc

Ta cn xc nh Cx :tc

tcxx

A

CAC

*=

Khi s dng 2 dung dch chun:

)(* 112

121 AA

AA

CCCC xx

+=

Vi A1, A2, C1, C2 l hp thu v nng ca dung dch chun tng ng sao choA1 < Ax < A2 c ngha C1 < Cx < C2

1.3.2 Phng php thm chunPhm vi ng dng l xc nh cc cht c hm lng vi lng hoc siu vi lng, loi

bnh hng ca cht l. C 2 phng php l phng php s dng cng thc vphng php th.

- Phng php s dng cng thcxax

xax

AA

ACC

=

+

Trong : Ax: hp thu ca dung dch xc nh tng ng vi th tch Vx.

Ax+ a: hp thu ca dung dch c thm chun.

Ca: Nng cht chun thm vo.


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Cx: Nng cht cn xc nh trong th tch Vx

Cng thc c thit lp t: Ax = lCx

A(x+a) = l(Cx + Ca)

Cxc biu din theo n v ca Ca.

Cch thc hin:

Ly 3 ln ca dung dch cn xc nh nng cho vo 3 bnh nh mc c th tchVmL.

Bnh 1: Thm thuc th v cc cht to mi trng pH cho dung dch, dung dchgi l dung dch xc nh Cx, hp thu quang tng ng l Ax.

Bnh 2: Thm mt lng chnh xc dung dch tiu chun bit chnh xc nng Ca, tin hnh phn ng to mu ging nh bnh 1. Dung dch c hp thu tng ngl A(x+a).

Bnh 3: ch thm cc cht to pH cho dung dch, ly dung dch ny lm dung dchso snh.

p dng cng thc:xax

xax

AA

ACC

=

+

. T Cx c trong th tch Vx(mL) c th qui v

th tch ban u ca mu Vo (mL): )/( LmgV

VCC

x

oxo =

- Phng php s dng thC t nht 3 dung dch thm chun. Ly t nht 4 ln ca dung dch cn xc nh nng cho vo 4 bnh nh mc V(mL). Sau thm chnh xc mt lng V1, V2, V3 mLdung dch tiu chun c nng tng ng Ca1, Ca2, Ca3 vo 3 bnh nh mc trn.Tin hnh phn ng to mu. Bnh cn li lm dung dch so snh, cng chun b ging nh phng php cng thc.

hp thu ca cc dung dch thm so vi dung dch so snh.


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Ca1 Ca2 Ca3 CAxAx + a1

Ax + a2

Ax + a3

A

Hnh 7-7. Biu xc nh phng trnh hi quy tng quan ca phng php thmchun sdng th.

C thc kt qu trn th hoc s dng phng trnh hi qui c dng:

A = aC + b (hi quy tuyn tnh y = ax + b)

Ax = b

Cx = b/a

1.3.3 Phng php ng chunu im l chnh xc, thc hin c nhiu ln.

- Chun b t 6 dung dch chun (trong khong tun theo nh lut Beer).- Thc hin phn ng mu vi thuc th.- o hp th quang A ca dung dch max so vi cc dung dch so snh c

chun b ging nh dung dch tiu chun nhng khng cha ion cn xc nh.- Biu din s ph thuc A theo C trn th hoc tnh theo phng trnh hi qui

A=aC + b (a v b l h s cn tm ca phng trnh hi quy tng quan) (xemBng 7-3)

- Dung dch xc nh: chun b v phn ng to mu vi thuc th ging nh muchun.Bng 7-3: Dung dch chun dng xy dng ng chun

Dung dch chun C (mg/L) A1 0,00 0,0102 0,05 0,4803 0,10 0,9304 0,15 1,3705 0,20 1,8306 0,25 2,281


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153

Sau khi o c gi tr hp th quang ca cc dung dch chun, chng ta c thtin hnh xy dng ng chun v tm ra phng trnh hi quy tng quan:

y = 9.0543x + 0.0184

R2

= 0.9999

0.000

0.500

1.000

1.500

2.000

2.500

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Nng

Hs

h

pthu

Hnh 7-7. Biu xc nh phng trnh hi quy tng quan ca phng php ng

chun.

Sau khi thit lp ng chun, ta c dng phng trnh y = ax + b vi y l hpth quang, x l nng . i vi dung dch xc nh, ta tin hnh phn ng v oc h s hp thu ca mu (A mu = y), ta c th tnh c nng ca mu cn xc

nh theo phng trnh:

a

byx

=

S tng quan gia hp th quang A v nng C khi constl= l ni dung ca

nh lut Beer. Khong nng tha mn nh lut ny khi r > 0,999.

H s tng quan r bin i trong khong -1 r 1 (R2 = 0-1)

-Khi r 1 c s tng quan cht ch gia x v y theo t l thun.

- Khi r -1 c s tng quan cht ch gia x v y theo t l thun.- Khi r 0 hai i lng ny khng cn tng quan.

1.4 chnh xc trong phng php trc quang:Trong phn tch trc quang cng nh bt k phng php no khc c th chia sai sthnh 2 nhm:

- Sai s do tin hnh phn ng ha hc (ha cht, thao tc, dng c...)- Sai s ca tn hiu o hp thu ca dung dch (do h thng o).


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154

chnh xc trong phng php ny ph thuc vo hng lot nguyn nhn khc nhaurt phc tp bao gm sai s ngu nhin v sai s h thng, trong sai s quan trngnht l sai s ca tn hiu trong qu trnh o hp thu quang hc.

1.5Mt s v d p dng phng php nh lng trc quang

V d 1

hp th quang A ca dung dch anilin 2.10-4M trong nc o bc sng

=280nm l 0,252. Chiu di nh sng i qua cuvet l 1cm. Tnh truyn quang caanilin 1,03.10-3M khi o cng di bc sng nhng dng cuvet 0,5cm.

Gii:

p dng cng thc lCI

IA **)lg( 0 == vi dung dch 1 ta c:

= 0.252/(2.10-4*1) = 1,26.103l.mol-1cm-1.

p dng cng thc lCI

IA **)lg( 0 == vi dung dch 2 ta c:

A = 1,26.103 * 0,5 * 1,03.10-3 = 0.649

M: A = -lgT suy ra: lgT = -A = -0,649, do T = 0,224 = 22,4%

Vy truyn quang T = 22,4%

V d 2:

hp th quang A o c t cc mu chun v mu nc thu t ao nui c chaion PO4

3- nh sau:Nng mu chun (mg/L) 0,00 0,05 0,10 0,15 0,20 0,25 hp th quang A 0,010 0,480 0,930 1,370 1,830 2,281

hp th quang A ca mu nc ao ca 3 ln lp li l: 1,256; 1,245; 1,264. Tnhnng PO4

3- trong mu nc ao.

Gii:

T cc nng mu chun v hp th quang A. T kt qu thit lp phng trnh

hi qui ta c: 0184,00543,9 += xy (r2 = 0,9999).

T kt qu ca 3 ln phn tch lp li ta c yA = = 1,255

T ta c Lmgy

x /137,00543,9

0184,0255,1

0543,9

0184,0=

=

=

Vy nng PO43- trong mu nc ao l 0,137 mg/L.


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Phn tch cht lng nc

155

V d 3:

xc nh hng s phn ly ca Methyl da cam (k hiu HIn), ngi ta o hp thquang A ca 3 dung dch cng nng Methyl da cam cc pH khc nhau:

- Dung dch 1 trong HCl 0,1M; A1 = 0,475.- Dung dch 2 trong NaOH 0,1 M; A2 = 0,130.- Dung dch 3 c pH = 4,34; A3 = 0,175

Cho bit o bc sng = 510nm v chiu di nh sng i qua cuvet l 1cm. Tnhhng s phn ly K ca Metyl da cam?

Gii:

hp th quang ca dung dch 3:[ ] lHInlInA HInIn **3 +=

(7.1)

Vi [In-] = x; [HIn] = y ta c: x + y = CHIn = C (7.2)

lC

AIn *

2= v ton b cht ch thdng In- (7.3)

lC

AHin *

1= v ton b cht ch thdng HIn (7.4)

Thay (7.3) v (7.4) vo (7.1) ta c:

C

yA

C

xAA .. 123 += (7.5)

Qui c: == )1(; C

y

C

x0,175 = 0,130 + 0,475 (1-)

= 0,869

Hng s phn ly ca HIn:

HIn H+ + In- ; Ka

===

+

1lglg

]][[pH

HIn

InpHpK

HIn

InHK

pK= 4,34 -689,01

869,0lg

= 7.34 0,82 = 3,52 K= 3,02.10-4.

Vy hng s phn ly ca methyl da cam l K = 3,02.10-4.


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2 PHNG PHP THU V BO QUN MU2.1Chun b thu mu2.1.1 Nhn nh sthay i cht lng ncCht lng nc ti mi tri lun b thay i theo thi gian (ph thuc vo lu lngv mc tc ng ca cc ngun nhim), do vy cn o cc gi tr cc i, cctiu v trung bnh ca cc thng s theo thi gian c th phn nh gn ng gi trthc. S mu thu thp cn ln v nhp thu mu cn cao lm c iu ny .Tuy nhin, vic tng cao s mu v nhp thu s gy tn km nhiu v kinh ph v nhnlc. Cho nn cn tnh sao cho va tin cy va khng qu nhiu chi ph

Theo GEMS (H thng quan trc mi trng ton cu) nhp thu mu cho nc nuithy sn nh mu sng thi gian thu mu cn tin hnh khi lu lng thp, ao h

cn xem xt chu trnh sinh hc v cn tng nhp thu mu thi im c nng sutsinh hc cao.

2.1.2 Cc iu cn lu khi thu mu La chn v ra k chai, lng mu. Dng tay cm chai, l nhng vo khong gia dng nc cch b mt nc

30-40cm. Hng ming chai, l ly mu hng v pha dng nc ti. Thtch nc ph thuc vo thng s cn kho st.

y kn ming chai, l, ghi r l lch mu thu.Bo qun mu ng qui nh nu bng 1.

2.2Cc bo qun mu2.2.1 Mu ncTy theo ch tiu cht lng nc m cch ly mu v bo mu khc nhau, cch boqun mu c trnh by Bng 7-4.

2.2.2 Mu tMu t sau khi thu, phn tch cng sm cng tt. Nu mun bo qun lu cn lmnh sau:

Tri mu cng mng cng tt trn bao nilon v phi kh trong iu kin nhit phng. Sau nghin mn, ri cho vo cc snh, em sy nhit 105oC trong 24gi. ngui mu trong bnh ht m, lc ny sn sng phn tch.


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157

Bng 7-4: Dng c thu mu v cch bo qun mu theo ch tiu phn tch

STT Ch tiu Dng cbo qun

Th tch(mL)

Bo qun

1 Alkalinity P;G 200 4oC

2 Hardness P;G 100 4o

C3 DO P;G 100 1mL MnSO4, 1mL KI-NaOH

4 CO2 P;G 100 0,5 mL CHCl35 COD P;G 100 2mL H2SO4 4M6 Chlorophyll-a P;G 500 Lc, 4oC, l nu7 SiO2 G 100 HCl 1:18 TAN P;G 500 4oC9 Nitrate P;G 100 4oC10 Nitrite P;G 100 4oC

11 NO2-

v NO3-

P;G 200 4o

C12 PO43- P;G 100 4oC

13 TN,TP P;G 500 4oCP: Plastic bottle G: Glass bottle

2.3Phng php thu muPhng php thu mu chnh xc s gp phn tng tnh chnh xc ca kt qu phntch. Ty mc ch nghin cu m vic thu mu mang tnh cht c bit hay i dincho ao c p dng ph bin hn.

thu mu hn hp i din cho ao, c th thc hin cc bc sau:2.3.1 Nguyn tc chungThu nhiu im trong ao (3-5 im hoc hn), sau trn mu li (cng nhiu cngtt), ri ly mt mu i din loi mu cn phn tch (ch tiu nc hoc bn y). mi im, cn thu ng thi 3 v tr, ri cho vo 3 x (mi mu/ x), tip tc lm nhth cho cc im khc trong ao.

Sau khi thu mu s c 3 x hn hp mu i din cho ao, tng ng 3 ln lp li.

2.3.2

Dng c thu mu v cch thu- Nn s dng ng PVC (ng knh 10 cm, di 1 - 1,2m) thu mu nc hoc

bn y ao.- i vi mu nc, chiu cao ct nc cn thu ty theo ao nng hay su, trnh

khuy ng nn y ao khi thu mu nc. Trong trng hp y ao b khuy ngtrong khi ang thu mu nc, th nn b mu thu mu khc gn ni .

- i vi mu bn y, nn thu nh nhng trnh vt cht dinh dng trong bn bthi ra Sau khi thu mu cn loi b rc, si, ... Cn trn mu hn hp cho thtu ri cho vo chai nha 200mL mang v phng phn tch.


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3 PHNG PHP PHN TCH MT S CH TIU MI TRNG NC3.1 Nhit xc nh nhit ca nc, ngi ta thng dng nhit k thy ngn c chia t 0-50oC (ti a l 100oC). Mun xc nh nhit ca nc tng mt, ta c buthy ngn ca nhit k vo trong nc su 15-20 cm, cho n khi nhit trongnhit k khng i (khong 5 pht), sau nghing nhit k v c nhit ca ncxong mi ly nhit k ln khi mt nc.

Mun xc nh nhit ca nc tng gia hay tng y ca thy vc, ta cm nhitk vo np bnh thu mu nc, th bnh xung ng v tr cn xc nh nhit , chonc vo y bnh, yn 5 pht sau ko ln v c ngay nhit nc tng .

Chng ta cng c tho nhit bng my, hin nay mt s my o pH hay DO

c ch to c tho c c ch tiu nhit .3.2 pH3.2.1 Bng hp giy so muGiy c tm dung dch ch th mu thch hp, sy kh cho vo hp s dng. Khic thm t giy s hin mu. Ty thuc pH ca nc, giy s hin mu khcnhau. Sau em so mu vi bng mu tiu chun km theo trn np hp, ta s bitc pH ca nc.

3.2.2

Phng php in th-my o pHIon H+ hot ng (pH) c xc nh trc tip bng php o in th. Sc in ngE ca t bo Galvanic c lin quan n hot ng ca ion H+ trong dung dch theo

phng trnh Nernt. in th sinh ra t t bo t l vi nng ion H+ trong munc, in th ny c o bng mt in th k v c thit b c bit d ch sangtr s pH hin trn mn nh ca my.

T bo Galvanic bao gm 1 in cc thy tinh, v 1 in cc Calomel tip xc vimu nc bng mt tia Aming cui in cc. Khi tip xc vi mu nc, in

cc Calomel s xy ra phn ng:Hg2Cl + 2e

- 2Hg + 2Cl-

in cc thy tinh gm 1 in cc Ag-AgCl ngm trong dung dch HCl 0,1M vc bao bc bi 1 mng thy tinh c nhy cm rt cao vi ion H+. in th nyca in cc s xut hin khi ion H+c mng thy tinh hp th. S hp th 1 ionH+ trn mng thy tinh s phng thch 1 ion Li+ t mng thy tinh vo dung dch incc.

Theo Peters (1975) th t bo Galvanic i vi vic xc nh pH c thc vit nhsau: Ag / AgCl, HCl (0.1M) / mng thy tinh / mu nc / Hg2Cl2, KCl / Hg.


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159

Tt cin th trong t bo Galvanic u khng thay i, trin th gia mng thytinh - mu nc v gia mu nc - dung dch KCl trong in cc Calomel.

3.3 trong (Transparency), c (Turbidity)C nhiu cch xc nh trong v c ca nc, nhng k thut ph bin nht chovic nui thy sn l s dng a secchi o trong. c c thc o chnhxc bng cch s dng my o c theo phng php Nephelometric. Ngoi ra cth xc nh lng vt cht l lng trong nc thng qua lng cht rn ho tan(TDS) v tng lng cht rn llng (TSS)

3.3.1 o trong bnga Secchia secchi dng hnh trn lm bng vt liu khng thm nc (inox, thic, tole...) chiaa lm 4 phn u nhau, sn hai mu en v trng xen k nhau. a c treo trn

mt que hay trn mt si dy c nh du khong cch mi khong chia l 5 hoc10cm.

Khi o, cm u dy th t t cho a ngp nc v ghi nhn ln 1 khong cch tmt nc n a khi khng cn phn bit c hai mu en trng trn mt a. Sau cho a secchi su hn v tr va ri v ko ln n khi va phn bit c hai muen trng, ghi nhn khong cch ln 2

trong ca nc ao o bng a secchi l trung bnh ca hai ln ghi nhn khongcch.

3.3.2 o c bng phng php NephelometricThit b o c c cc b phn d nh sng c t v tr vung gc (90o) sovi chm tia ti c gi l my o nh sng khuch tn.

Phng php ny c da trn vic so snh cng nh sng tn sc ca mu(trong iu kin xc nh) vi cng nh sng khuch tn ca mu chun ichng trong iu kin tng t. Cng nh sng khuch tn cng cao th ccng cao. Formazin polymerc s dng lm cht llng trong mu chun. c

ca nng cht llng bng formazin c xc nh n 4000 NTU. Ngoi ra, mts thit b o c c thit k xc nh c theo n v mg/L (ModelQWC-22A-TOA, Nht). Cht l lng tiu chun c s dng lm dung dch ichng l Kaolin tinh ch (theo h thng cng nghip Nht bn-JIS). C tho cd dng bng cc my o nu trn.

3.4 Tng cht rn ha tan (TDS) v tng cht rn llng (TSS)Cht rn hin din trong nc bao gm vt cht ha tan v khng ho tan. o ctng lng cht rn ho tan (TDS). Mu cn c lc loi b vt cht khng ho

tan, v nc c lc cho bc hi v phn cn li c cn tnh hm lng cht


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160

rn ha tan. Tng lng cht rn ha tan bao gm vt cht hu cv v cho tan,biu th bng mg/L.

Tng lng cht rn l lng (TSS) c tnh bng cch cn trng lng nhng cht

cn li trn giy lc c s dng khi lc nc phn tch cht rn ho tan. TSS biuth lng vt cht khng ha tan llng trong nc v c biu th l mg/L.

Vt liu v dng c dng phn tch tng cht rn ha tan v tng cht rn l lnggm: Giy lc si thy tinh, t nung 550oC, bnh lm ngui ht m, h thng lc chnkhng, cn phn tch.

3.4.1 Tng cht rn ha tan TDS (Total Dissolved Solid)Thu mu vo bnh 1 lt v y kn. Bo qun lnh 4oC

Ngm giy lc thy tinh trong 24 gi, sau sy kh

Nung cc s (a snh) nhit 550oC trong 30 pht, sau lm ngui trongbnh ht m v cn khi lng ca cc s (W1)

Lc nc bng h thng lc chn khng. Ly 100mL c lc cho vo cc s c chun b sn.

t cc s vo t sy nhit 95oC. Sau gia tng nhit ln 105oC trong1gi.

Lm ngui a v cn trng lng 2 (W2)Tng lng cht rn ha tan c tnh theo cng thc sau:

1000)(

)/( 12 xWW

LmgTDS

=

Trong : W2: Trng lng a ln 2 (mg)

W1: Trng lng a ban u (mg)

V: Th tch mu nc

3.4.2 Tng cht rn llng - TSS (Total Suspended Solid)Thu mu vo bnh 1 lt v y kn. Bo qun lnh 4oC

Lc mu bng giy lc c cu to bng cht liu si thy tinh ng knh 47 mm,

clc 0,22-0,45 m.

nh s mu trn giy lc.

Sy giy lc 105oC trong 2-3 gi.

Cn v ghi khi lng giy lc (Wo)

Lc u mu nc trc khi lc.


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Lc mu nc, ghi th tch mu nc lc (V mL)

Sy 105oC trong 2-3 gi, ht m 30 pht trong bnh ht m, cn khi lng (W1)

Nung 550oC trong 2-3 gi, ht m 30 pht trong bnh ht m, cn khi lng

(W2)Cc ch tiu v vt cht llng c tnh theo cng thc sau:

1000)(

)/( 01 xV

WWLmgTSS

=

1000)(

)/( 21 xV

WWLmgOSS

=

OSSTSSLmgISS =)/(

V: th tch mu nc lc (mL)

W: khi lng (mg)

TSS: tng vt cht llng (mg/L)

OSS: vt cht hu cllng (mg/L) (OSS = Organic Suspended Solid)

ISS: vt cht v cllng (mg/L) (ISS = Inorganic Suspended Solid)

3.5 dn in (EC) dn in l kh nng mang mt dng in ca dung dch. Kh nng ny ty thucvo s hin din ca cc ion, tng nng , tnh linh ng, ha tr ca cc ion v nhit lc o c. Cc dung dch ca hu ht cc hp cht v cl cc cht dn tt nhngngc li i vi cc phn t hu cc tnh dn in km.

n vo dn in l micromho/cm (mho/cm) hoc theo h thng n vo

lng quc t (SI) l millisiemens/m (mS/m); 1 mS/m=10 mho/cm v 1 mho/cm=1

S/cm. Trong nc ngt, dn in thng t 50 n 1.500 mho/cm (Theo Hiphi sc khe cng ng ngi M-APHA, 1989; Arce v Boyd, 1980), mi trng

nc lv mn th dn in cao hn nhiu. dn in v nng mui c linquan rt cht v nng cc ion trong mi trng, dn in tng cng vi s tngnng mui. Vic o c chnh xc dn in thng khng c i hi cao ivi nui trng thy sn, m thay vo vic o nng mui ca nc thng cs dng hn. My o n in thng c s dng c tnh nhanh mc khong ha ca nc thin nhin v mc nhim ngun nc thi cng nghip.

3.6Nng muiThut ng nng mui ch tng nng cc ion ha tan trong nc. n v tnh l

mg/L hoc phn ngn (). c tnh nng mui ca nc mt cch tt nht th


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cn tnh tng nng 7 ion quan trng trong mi trng lm cho nc thin nhin cnng mui l: Na+, K+, Ca2+, Mn2+, Cl-, SO4

2-, v HCO3- v cc ion ny thng

chim hn 95% trong tng s cc ion ha tan trong nc.

o nng mui chng ta c th s dng t trng k, nhng mc chnh xc cadng co ny khng cao. Trong lnh vc thy sn, thit bo nng mui c sdng ph bin nht l khc x k v my o nng mui.

3.7Oxy ha tan (DO)3.7.1 Phng php WinklerNguyn tc

Trong mi trng bazmnh, oxy ha tan trong nc s oxy ha ion Mn2+ thnhMn4+ c kt ta nu.

Mn2+ + 2OH- + 1/ 2 O2 = MnO2 + 2H2O

Sau MnO2c ha tan bng H2SO4m c. Trong mi trng acid, MnO2 lcht oxy ha mnh, c kh nng oxy ha I- thnh I2 bng ng vi lng I2 c trongmu nc lc ban u:

MnO2 + 2I- + 4H+ = Mn2+ + I2 + 2H2O

I2c gii phng ra s ha tan trong nc v c xc nh bng phng phpchun vi dung dch Na2S2O3. H tinh bt c s dng lm cht ch th xcnh im tng ng trong qu trnh chun ny: Khi I2 c mt trong dung dch,n s kt hp vi tinh bt hnh thnh mt phc cht c mu xanh. Khi tt c I2 trongdung dch c chun ht vi Na2S2O3, dung dch s trnn khng mu.

Thu mu

Thu mu nc vo l nt mi nu 125 mL, cho ha cht cnh bng 1 mL MnSO4v 1mL dung dch KI-NaOH, y np l li, lc u, trong l xut hin kt ta. Ch ,khi thu mu v sau khi cnh khng bt kh xut hin trong chai khi thu mu

nc.Thuc th

- Dung dch MnSO4: Ha tan 50 g MnSO4.5H2O hay 41 g MnCl2.4H2O vi ncct thnh 100 mL.

- Dung dch KI-NaOH: Ha tan 50 g NaOH v 15 g KI (hay 14 g NaI) vi nc ctthnh 100 mL.

- H2SO4 (d=1,84) hay H3PO4c (d= 1,88).- Dung dch Na2S2O3 tiu chun 0,1N: Pha mt ng Na2S2O3 tiu chun 0,1N trong

1000mL nc ct


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Phn tch cht lng nc

163

- Dung dch Na2S2O3 0,01N: S dng cng thc N1V1 = N2V2 pha dung dch cth nh sau: Ly 50 mL dung dch Na2S2O3 0,1N pha long vi nc ct thnh500 mL.

- Ch th h tinh bt 1%: Ha tan 0,49 g K2S2O3 trong 100 mL nc m (t 80-90oC)khuy u cho n khi dung dch mu trong sut, cho vo 0,5 mL formalinenguyn cht s dng c lu.

Tin hnh

- Sau khi cnh bng ha cht, yn cho kt ta lng. Tip tc lc u mt lnna kt ta hon ton, sau yn 5 pht i vi nc ngt, 10 pht i munc lmn.

- Cho tip 2 mL H2SO4 hay H3PO4m c (vn khng cho bt kh xut hintrong l)

- Lc u cho n khi kt ta ha tan. Dung dch c mu vng nu- ong 50 mL dung dch va c acid ha trn, cho vo bnh tam gic 100 mL.- Chun bng dung dch Na2S2O3 0,01N cho n khi dung dch c mu vng

nht, cho 3 git ch th h tinh bt, lc u dung dch c mu xanh, tip tc chun cho n khi dung dch chuyn t mu xanh sang khng mu th dng li.

- Ghi th tch (V1 mL) dung dch Na2S2O3 0,01N s dng chun mu.- Lm tng t 2 hoc 3 ln, ghi th tch dung dch Na2S2O3 0,01N dng chun

.

Tnh V trung bnh ca Na2S2O3 0,01N dng chun

3/)( 321 VVVVTB ++= Tnh kt qu

10008)/( xxV

NxVLmgDO

M

TB=

Trong :

VTB: l th tch trung bnh dung dch Na2S2O3 0,01N (mL) trong cc lnchun .

N : l nng ng lng gam ca dung dch Na2S2O3 s dng.

8 : L ng lng gam ca oxy.

VM : l th tch (mL) mu nc em chun .

1000: l h s chuyn i thnh lt

3.7.2 Phng php in cc oxy ha tan) - my o oxyTheo phng php ny th p sut ring phn ca oxy ha tan c o trc tip. Sau

p sut ring phn c chuyn i thnh nng (mg/L). My o oxy tnh ton


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cc gi tr ny da trn mi quan h gia nhit , ha tan ca oxy v p sutkhng kh.

u d oxy bao gm 1 in cc dng (anode) c lm t Ag/AgCl, 1 in cc m

(cathode) c lm t kim loi qu nh platinum, vng, tungsten hoc rhodium vdung dch in cc KCl bo ha ngn cch vi mi trng ngoi bi mng cm ng

polyethylene, teflon, polypropylene hoc vt liu tng t c dy thng 25mhoc mng hn (c kh nng thm oxy). Cc in cc trong h thng ny c 1 hiuin th gia chng thng khong 0,7 volts.

Khi oxy trong mu nc tip xc vi mn cm ng, mn c kh nng thm oxy v tl m oxy i qua mng cm ng c lin quan n p lc ca oxy trong mu nc. Khicung cp mt hiu in th cho u d th oxy phn t thm thu qua mng, phn ng

vi cc cathode v b kh thnh hydroxide vi t l 4 moles OH-

/mole oxy theophng trnh sau: O2 +2H2O + 4e- 4OH-

Sau 1 dng in chy qua cc anode (in cc bng bc) v OH- phn ng vi bcto thnh dng oxit bc theo phng trnh sau:

2Ag0 + 2OH- = Ag2O + H2O + 2e-.

Do , s chnh s khc bit v p lc oxy gia trong v ngoi mng cm ng lmcho oxy thm thu qua mng. V vy, nu p lc oxy bn ngoi mng cm ng thpth dng in gia 2 in cc s t hn so vi khi p lc oxy bn ngoi cao.

Ngoi ra, tnh thm ca mng cm ng bnh hng rt ln bi nhit (Mancy vJaffe, 1966) (Trch dn bi Boyd & Tucker, 1992). Th d, dng in to ra 10 mg/Loxy ha tan 10oC ch bng 1/ 4 so vi vic to ra 10 mg/l 30oC. Bn cnh , nhit

cn nh hng i vi dng in gia 2 in cc thng qua mi quan h v nhit v p lc oxy. Do , hu ht cc my o oxy ha tan trong nc thng cthit k c b phn hiu chnh nhit tng trnh sai s do snh hng canhit ln s liu o c.

Hm lng oxy ha tan trong nc cng bnh hng bi nng mui. Hm lngoxy ha tan trong nc mc bo ha gim khi gim p sut khng kh v tng nng mui. V vy, hu ht cc my o oxy thng c thit k c s hiu chnh psut v nng mui tng chnh xc trong o c.

3.8Carbon dioxide (CO2)3.8.1 Nguyn tcCO2 t do trong nc c xc nh bng phng php trung ha vi dung dch

NaOH tiu chun v phenolphthalein lm cht ch th xc nh im tng ng

CO2 + NaOH = NaHCO3 (7.6)


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Khi phn ng (7.6) t im tng ng, mt git d dung dch NaOH s lm chomi trng c tnh kim yu (pH 8-10) phenolphthalein s chuyn t khng mu sangmu hng. Mun c kt qu chnh xc ta phi dng dung dch m c pH tiu chun

bng 8,3 theo di s chuyn mu ca phenolphthalein m xc nh chnh xc im

tng ng ca phn ng

3.8.2 Phng php thu v bo qun muThu mu trong chai nt mi trng 125 mL, cnh mu bng 0,5mL Chloroform

3.8.3 Chun b ha cht- Dung dch NaOH tiu chun 0,1N: Ha tan ng chun NaOH 0,1N vi nc

ct thnh 1000mL- Dung dch NaOH 0,01N: Ha tan 100mL dung d ch NaOH 0,1N vi nc ct

thnh 1000mL.

- Dung dch m pH= 8,3: Dung dch Na2B4O7 0,05M: Ha tan 1,91gNa2B4O7.10H2O vi nc ct thnh 100mL.

- Dung dch H3BO3 0,2M: Ha tan 1,24 g H3BO3 vi nc ct thnh 100mL.- Ly 20mL dung dch Na2B4O7 0,05M cho vo 30mL dung dch H3BO3 0,2M.

Ta sc dung dch m c pH=8,3.- Dung dch ch th phenolphthalein 1%: Ha tan 1g ch th phenolphthalein

(C20H14O4) trong 100mL cn 600.

3.8.4 Tin hnhDng bnh tam gic 100mL, ln lt cho vo bnh cc ha cht nh sau (Bng 7.5):Bng 7.5. Cc bc tin hnh phn tch hm lng CO2

Bnh 1 Bnh 2

1.50mL dung dch m pH= 8,32.3 git ch th phenolphthlein,

lc u, dung dch c muhng nht.

1.50mL mu nc.2.3 git ch th phenolphthlein, lc u, dung dch

khng mu.

3.Dung dch NaOH 0,01N chun t t cho nkhi dung dch trong bnh c mu hng nhtging nh bnh 1 th dng li ( mu hng ch

bn trong 1 pht). Ghi th tch V1 (mL) dungdch NaOH 0,01N s dng.

4.Lm li cc bc 1 n 4 mt ln na ghi thtch V2 (mL) dung dch NaOH 0,01N s dng.

5.Tnh VTB = (V1 + V2)/2.


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3.8.5 Tnh kt qu100044

50)/(2 xx

NxVLmgCO TB=

- Vtb: l th tch trung bnh dung dch NaOH 0,01N ca c ln chun .- N: l nng ng lng ca dung dch NaOH s dng.- 44: ng lng g ca CO2.- 50: th tch nc em chun .

3.9Tiu hao oxy ha hc (Chemical Oxygen Demand - COD)3.9.1 Phng php oxy bng KMnO4 trong mi trng kimThu v bo qun mu

Thu mu trong chai nt mi trng 125 mL, cnh mu bng 2 mL H2SO4 4M

Nguyn tc

Vic xc nh hm lng COD c da trn nguyn tc cc hp cht hu ctrongnc c th b oxy ha thnh CO2 v H2O bi cc cht oxy ha mnh (KMnO4) trongmi trng kim.

Trong mi trng baz, ion MnO4- s tc dng vi ion OH- nh gc (OH) t do.

MnO4- + OH- = MnO4

2- + (OH)

Gc (OH) ny khng bn n s phn hy cho ra oxy nguyn t.2(OH) = [O] + H2O

Oxy nguyn ttrng thi mi sinh l cht oxy ha mnh, c kh nng oxy ha honton cc hp cht hu cthnh CO2 v H2O.

CxHyOz + (2x + y/2 - z) [O] = xCO2 + y/2H2O

Sau mi trng c acid ha bng dung dch H2SO4. Trong mi trng acid, vis hin din ca mt lng tha I-, lng MnO4

- cn li s b kh hon ton thnh

Mn2+

v mt phn I-

b oxy ha thnh I2.10KI + 2KMnO4 + 8H2SO4 = 5I2 + 2MnSO4 + 6K2SO4 +8H2O

I2c to thnh c xc nh bnh phng php chun vi dung dch Na2S2O3tiu chun ging nh phng php xc nh Oxy ha tan trong nc theo phng

php Winkler. T lng I2c to thnh trong mu tht v mu trng ta tnh clng oxy cn thit oxy ha hon ton cc hp cht hu ctrong mu nc thnhCO2 v H2O.

Thuc th


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- Dung dch KMnO4 0,1N: Ha tan 1 ng KMnO4 0,1N trong mt t nc ct,sau pha long thnh 1.000mL. iu chnh nng chnh xc bng dungdch chun C2H2O4 tiu chun 0,1N v 15mL H2SO4 1:4 lc u em un nngnh80oC. Sau dng dung dch KMnO4 va pha trn chun t t chon khi dung dch chuyn t khng mu sang mu hng nht th dng li, ghith tch dung dch KMnO4 s dng (V1). Lm li nh trn mt ln na ly gi tr trung bnh. Nng dung dch KMnO4c iu chnh chnh xc

bng cng thc: V1N1 = V2N2 . Dung dch c bo qun trong chai nu.- Dung dch KMnO4 0,05N tnh kim: Ha tan 500mL dung dch KMnO4 trong

500mL nc ct c ha tan 8g NaOH, cho vo bnh mu nu s dng.- Dung dch KI 10%: Ha tan 10g KI vi nc ct thnh 100mL.- Dung dch H2SO4 4M: Ha tan 22,2mL H2SO4 m c vi nc ct thnh

100mL.

- Dung dch Na2S2O3 0,1N: Ly 1 ng Na2S2O3 0,1N chun pha long vi ncct thnh 1.000mL.

- Dung dch Na2S2O3 0,05N: Ly 500mL dung dch Na2S2O3 0,1N dng ncct pha long thnh 1.000mL.

- 7. Ch th h tinh bt 1%: Ho tan 1 gam tinh bt trong 100mL nc m (t80oC-90oC) khuy u cho n khi dung dch tr nn trong sut, cho vo0,5mL formaline nguyn cht s dng c lu.

- Dung dch NaOH 0.4N: Ly 40mL dung dch NaOH 10N, dng nc ct phalong thnh 1.000mL

Tin hnh

Dng 2 cp bnh tam gic 100mL, ln lt cho vo tng cp bnh cc ha cht sau(Bng 7.6):


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Bng 7.6. Cc bc tin hnh phn tch COD

Bnh 1 Bnh 2

1.50mL mu nc.2.5mL dung dch NaOH 0,4N.3.5mL dung dch KMnO4 0,05N.4.em un cch thy im si ng

mt gi, ly ra ngui 10 pht.5.Tip tc vo 5mL KI 10% v 5mL dung

dch H2SO4 4M, lc u dung dch cmu vng nu.

6.Dng dch dch Na2S2O3 0,05N chun cho n khi dung dch c mu vng

nht, cho v 3 git ch th h tinh bt1%, lc u dung dch c mu xanh,tip tc chun t t cho n khi dungdch trnn khng mu th dng li ghith tch (V1) dung dch Na2S2O3 0,05N

s dng.7.Ly bnh cn li chun tng t nh

bnh trn ly gi tr trung bnh.

1.50mL nc ct.2.5mL dung dch NaOH 0,4N.3.5mL dung dch KMnO4 0,05N.4.em un cch thy im si ng

mt gi, ly ra ngui 10 pht.5.Tip tc vo 5mL KI 10% v 5mL

dung dch H2SO4 4M, lc u dungdch c mu vng nu.

6.Dng dch dch Na2S2O3 0,05Nchun cho n khi dung dch c

mu vng nht, cho v 3 git ch thh tinh bt 1%, lc u dung dch cmu xanh, tip tc chun t tcho n khi dung dch trnn khngmu th dng li ghi th tch (V2)dung dch Na2S2O3 0,05N sdng.

7.Ly bnh cn li chun tng tnh bnh trn ly ga tr trung bnh.

Tnh kt qu

10008)(

)/( 12 xxV

NxVVLmgCOD

M

=

- N: nng dung dch Na2S2O3 chun - V1: th tch dung dch Na2S2O3 chun mu nc cn phn tch.- V2: th tch dung dch Na2S2O3 chun mu nc ct.- VM: th tch mu nc em phn tch.

3.9.2 Phng php DichromateNguyn tc

Trong phng php ny cc hp cht hu c trong nc b oxy ha thnh CO2 vH2O bi cht oxy ha mnh (K2Cr2O7) trong mi trng acid. Mt lng bit trcK2Cr2O7c thm vo mu nc s b acid ha vi H2SO4. Mu nc ny sau

c un nng v cc cht hu c b oxy ha thnh CO2 v H2O, trong khi Dichromate b kh theo phng trnh sau:

Cht hu c+ Cr2O72- + H+ 2Cr3+ + CO2 + H2O


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Lng tha dichromate c th xc nh c bng cch chun vi ferrousammonium sulfate - Fe(NH4)2(SO4)2.6H2O.

6Fe2+ + Cr2O72- + 14H+ 6Fe3+ + 2Cr3+ + 7H2O

Lng dichromate tiu th cho vic oxy ha cc cht hu cc thc tnh ton tmN (mili ng lng) ca K2Cr2O7 thm vo mu tr mN caFe(NH4)2(SO4)2.6H2O s dng trong vic chun kh lng K2Cr2O7 tha.

3.10 Nng sut sinh hc scpC nhiu cch xc nh xc nh nng sut sinh hc scp ca thy vc nh: phng

php bnh ti- bnh sng, phng php ng v phng x C14, phng phc xc nhhm lng cc sc t quang hp trong nc, phng php xc nh sinh khi thc vtni, phng php xc nh theo hm lng oxy trong nc.

Phng php bnh ti bnh sng c s dng ph bin hn c. Hm lng oxy tdo trong nc c xc nh theo phng php Winkler

3.10.1Nguyn tcPhng php bnh ti sng da trn nguyn tc trong cth thc vt lun lun xyra hai qu trnh ngc nhau, qu trnh to thnh v qu trnh phn hy cc vt chthu c. Qu trnh to thnh cc hp cht hu cbng con ng quang hp s bdng li khi khng c nh sng, do s hp thu CO2 t mi trng v lng O2

c thi ra cng b dng li. Qu trnh h hp hp th O2 v thi ra CO2 tin hnhvi tc ngang nhau trong ti v ngoi sng. Do da trn hm lng O2 ha tantrong bnh ti v bnh sng ta c th tnh c cng quang hp ca thc vt phdu trong nc. Trong thc ti khi cng quang hp ca thc vt c coi lnng sut sinh hc scp. Theo Winberg (1960), sc sn xut ca thy vc theo nngsut sinh hc scp (P) c trnh by bng sau:

- Thy vc ngho dinh dng: P1 t 1-2 mg/L O2/ ngy, m- Thy vc dinh dng trung bnh: P1 t 2-5 mg/L O2/ ngy, m- Thy vc giu dinh dng: P1 t 5-15 mg/L O2/ ngy, m- Thy vc rt giu dinh dng: P1 t 15-20 mg/L O2/ ngy, m

3.10.2Dng c v ha chtDng c

- H thng bnh sng- bnh ti: Cc bnh ti c chun b nh sau: dng hc nbi en ton b thnh bnh v y bnh.

- a secchi: xem phn xc nh trong ca nc.Ha cht


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- Ton b ha cht xc nh ha tan theo phng php Winkler (xem mc3.7.1).

3.10.3Tin hnhDng a secchi o trong ca nc, nhn trong vi 2 xc nh tng sng.

Nu thy vc tng sng nh th ch cn thu mu v t bnh v tr gia ao v cchmt nc khong 20-30cm. Nu thy vc c tng sng ln (su), khi thu mu nccn t bnh gc ao, gia ao, tng mt v tng y.

mi v tr dng 6 bnh BOD 125mL (4 bnh sng v 2 bnh ti), thu y mu nc v tr theo nng sut sinh hc s cp. Ly 2 bnh sng phn tch O2 ban u u(DO), 4 bnh cn li dng gi t ng v tr cn thu mu nuc trn, yn trong24 gily ln phn tch hm lng O2 ha tan trong mi bnh (DOCS v DOCT).

3.10.4 Tnh kt quP (mg O2/L/ngy) = DOCS DOCT

R (mg O2/L/ngy) = DO DOCT

P (mg O2/L/ngy) = DOCS DO

P : Nng sut sinh hc (tng lng oxy c to ta t qu trnh quang hp)

R: H hp ca thy sinh vt (tng lng oxy tiu hao do qu trnh h hp)

P: Nng sut sinh hc thc (s chnh lch gia oxy sinh ra t quang hp voxy tiu hao do h hp. P l s dng (+) khi thc vt c gia tng sinhkhi, P l s m (-) khi thc vt gim sinh khi.

DOCS: Hm lng oxy cui (C) bnh sng (S), c o sau 24 gi

DOCT: Hm lng oxy cui (C) bnh ti (T), c o sau 24 gi

DO: Hm lng oxy u (), c o lc bt u

3.11 Chlorophyll-a3.11.1

Nguyn tc

Phng php chit sut bi Ethanol 90% (Nusch, 1980).

Cc sc t trong nc sau khi c lc qua mng lc ng knh 47mm, kch thc

lc 0,22-0,45m. Chng c chit sut bi ethanol. Sau c o bc sng 665nm v 750 nm cc pheophytin c o cng bc sng sau khi x l acid.

Phng php chit sut bi acetone

Phng php ny c b sung bi Lalli (1984). Trong phng php ny, chloropyll

c chit xut trong acetone v o mc hp thu quang ph4 bc sng.


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3.11.2Tin hnhHo cht

Dung dch acetone nguyn cht

Tin hnh- Ct nh giy lc mu cho vo ng nghin,- Thm 10mL acetone 100% v nghin trong mt pht- Lc qua giy lc GFF 25mm0,2m, ng thi thu mu dch chit sut vo

chai, l 10mL nu.- Bo qun lnh v ti cho n khi o mu- o mu cc bc sng 630, 647, 664 v 750 nm.

Tnh kt qu

Chl-a = [11,85(E664-E750) - 1,54(E647-E750) - 0,08(E630-E750)]/[(1/d) x (V1*1000)/V2]

(g/L)

V1: th tch acetone (10 mL)

V2: th tch nc mu c lc

d: di truyn quang (cuvet 1cm).

3.12 Hydrogen sulfide (H2S)3.12.1

Ph

ng php Iodine

Nguyn tc

H2S trong mu nc c cha H2S s b kt ta CdS khi phn ng vi CdCl2.

CdCl2 + H2S = CdS + 2HCl

Sau CdS c ha tan bng mt lng tha I2 chun, trong mi trng acid.

CdS + I2 + 2HCl = S + CdCl2 + 2HI.

Lng tha I2c xc nh bng phng php chun vi dung dch Na2S2O3 tiu

chun v h tinh bt c dng lm cht ch th xc nh im tng ng, gingnh qu trnh xc nh oxy ha tan trong nc bng phng php Winkler.

I2 + I2 tinh bt + 2Na2S2O3 = Na2S4O6 + 2NaI + tinh bt.

(mu xanh) (khng mu)

Thu v bo qun mu

Tin hnh thu mu trong chai nt mi nu, cnh mu bng 1mL CdCl2

Thuc th

- Dung dch CdCl2 2%: Ha tan 2 g CdCl2 vi nc ct thnh 100mL.


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- Dung dch HCl 4M: Cho 25mL HCl c (12M) vo v pha long thnh 100mLvi nc ct.

- Dung dch I2 0,1N: Ha tan 80 g KI trong 500mL nc ct khng, tip tc cho

vo12,7 g I2 khuy u cho tan ht, sau pha thnh 1.000mL. Dung ny sau

khi pha xong phi xc nh li nng chnh xc bng dung dch Na2S2O30,1N tiu chun. cch tin hnh nh sau: Dng bnh tam gic 100mL, cho vo20mL dung dch I2 va pha trn (dng buret xc nh th tch I2, khngdng ng ht), dng dung dch Na2S2O3 0,1N tiu chun, chun cho n khidung dch c mu vng, tip tc chun cho n khi dung dch c mu vngnht, cho 3 git h tinh bt, lc u dung dch c mu xanh, tip tc chun cho n khi dung dch chuyn t mu xanh sang khng mu th dng li, ghith tch dung dch Na2S2O3 0,1N s dng. Lm li nh trn mt ln na ly gi tr V trung bnh. Sau hiu chnh nng dung dch I2 cho chnh xc

bng biu thc: N1V1 = N2V2

- Dung dch I2 0,01N: ly 50mL I2 0,1N dng nc ct pha long thnh 500mL.- Dung dch Na2S2O3 tiu chun 0,1N: Pha mt ng Na2S2O3 tiu chun 0,1N

trong 1000mL nc ct- Dung dch Na2S2O3 0,01N: S dng cng thc N1V1 = N2V2 pha dd c th

nh sau: Ly 50mL dung dch Na2S2O3 0,1N pha long vi nc ct thnh500mL.

- Ch th h tinh bt 1%: Ho tan 0,49 g K2S2O3 trong 100mL nc m (t 80-900C) khuy u cho n khi dung dch mu trong sut, cho vo 0,5mLformaline nguyn cht s dng c lu.

Tin hnh

Thu mu nc vo 2 l nt mi 125mL, sau mnp l ra, cho ln lt vo mi l1mL dung dch CdCl2 2%, y np l li lc u mt ln na, yn 24 gi(nu cH2S s c kt ta mu vng di y bnh).

Mnp l ra dng ng cao su ht b phn nc trong trn kt ta (ch : khi ht cnng cao su gn mt nc ch khng c cm su vo y bnh v cho nc chynh ra ngoi, nu nc chy mnh kt ta b vn ln v cun tri ra ngoi, lm kt qukhng chnh xc ).

Ha tan kt ta bng 5mL HCl 4M v 5mL dung dch I2 0,01N. Chuyn dung dch tl nt mi sang bnh tam gic 100mL, trng l nt mi bng 30mL nc ct, nc ctny cng cho vo bnh tam gic.

Dng dung dch Na2S2O3 0,01N chun cho n khi dung dch mu vng nht, chovo 3 git ch th h tinh bt, lc u dung dch c mu xanh sau tip tc chun t t cho n khi dung dch chuyn t mu xanh sang khng mu th dng li, ghitng th tch V1 (mL) dch Na2S2O3 0,01N s dng.


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Lm tng t nh trn cho l cn li, ghi th tch V2(mL) dch Na2S2O3 0,1N sdng. Tnh VTB = (V1+V2)/2.

Bnh chun: Dng 2 bnh tam gic 100mL, ln lt cho vo tng bnh cc ha chtnh sau:

30mL nc ct, 5mL HCl 4M v 5mL dung dch I2 0,01N, lc u dung dch c muvng nu .

Dng dung dch Na2S2O3 0,01N chun cho n khi dung dch trnn mu vngnht, cho 3 git ch th h tinh bt vo, lc u dung dch c mu xanh, tip tc chun cho n khi dung dch chuyn t mu xanh sang khng mu th dng li ghi thtch V0 Na2S2O3 0,01N s dng. Lm tng t nh trn cho bnh cn li ly thtch V0 trung bnh.

Tnh kt qu

100017125

)()/( 02 xx

NxVVLmgSH TB

=

- VTB: Th tch trung bnh dung dch Na2S2O3 s dng trong 2 ln phn tchmu nc

- V0: th tch trung bnh ca dung dch Na2S2O3 trong 2 ln phn tch mu trng- N: Nng ng lng ca dung dch Na2S2O3 s dng.- 17: ng lng g ca H2S.

3.12.2Phng php Methylene blueNguyn tc

Nguyn tc ca phng php ny da trn phn ng ca sulfide (S2-), ferric chloridev dimethyl-p-phenylenediamine to nn methylene blue. Ammonium phosphatec thm vo sau khi hin mu kh mu ca ferric chloride. Sau nng S2-c xc nh bi my so mu quang phbc sng 664 nm.

Thu mu v bo qun

Tin hnh thu mu trong chai nt mi nu, bo qun lnh 4oC

Thuc th

Dung dch PRE 1: 500mL HCl 37% pha thnh 1000mL vi nc ct.

Dung dch A: Ha tan 4g C8H14Cl2N2 trong PRE 1 thnh 1000mL.

Dung dch B: Ha tan 16g FeCl3.6H2O trong PRE 1 thnh 1000mL.

Dung dch chun


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- Dung dch Na2S.9H2O 100mg/L: ha tan 0,750g Na2S.9H2O trong 1000mLnc ct khng oxy (nc ct khng oxy: un nc ct ln si khong 10 phtem khi bp bt kn ngay ).

- Dung dch Na2S.9H2O 5mg/L: ha tan 5mL dd Na2S.9H2O 100mg/l vi ncct thnh 100mL

Thit lp mu chun

Bng 7.7. Cc bc thit lp mu chun phn tch H2S theo phng phpMethylene blue

STT Nng muchun (mg/L)

Th tch dung dch chunNa2S.9H2O 5mg/L (mL)

Th tch nc ct(mL)

1 0,00 0,0 100,02 0,02 0,4 99,63 0,04 0,8 99,2

4 0,06 1,2 98,85 0,08 1,6 98,46 0,10 2,0 98,0

Tin hnh

- ong 20mL mu nc.- Ln lt cho thuc th vo 1mL thuc th A, 1mL thuc th B- Ch5 pht khi mu xanh xut hin chng ta em o hp th quang bc

sng 665nm.

Tnh kt qutng ng vi nng C ca mu chun ta c hp th quang A. Da vo stng quan ny chng ta c th lp phng trnh tng quan dng A = aC + b

Trong :

A: hp th quang

C : nng cht chun (mg/L)

Sau khi thit lp phng trnh, chng ta o hp th quang ca mu cn phn tch

v th vo phng trnh chng ta s tnh c nng ca S2- c trong mu nc.

a

bAC

=

tnh hm lng H2S khi thu mu nc chng ta phi o pH v nhit . Da vobng tra (xem Chng 3, Mc 5, Bng 3.5) xc nh t l phn trm ca H2S chatrong tng sulfide, t tnh ra hm lng H2S.


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3.13 cng tng cngVic xc nh cng tng cng ca nc c thc hin theo phng php chun

Complexon.

3.13.1Nguyn tc

Trong mi trng pH=10 ion Ca2+ v Mg2+ s kt hp vi thuc th EDTA (EthyleneDiamineTetra-acetic Acid) (EDTA - K hiu Na2H2Y ) hnh thnh phc cht bnvng, khng mu Calcium hay Magnesium ethylene diamine tetraacetate.

Eriochrome black T (C20H13O7N3SNa) c s dng lm cht ch th xc nhim tng ng. Eriochrome black T kt hp vi ion Ca2+ v Mg2+ hnh thnh phccht khng bn vng c mu hng ca ru vang. Khi dng EDTA chun , cc ionCa2+ v Mg2+ s kt hp vi EDTA hnh thnh phc cht bn vng, khng mu, v

khi c Eriochrome black T t do, dung dch c mu xanh l .M2+ + M-Eriochrome black T + Na2H2Y = Na2MY + 2H

+ + Eriochrome black T

(Mu hng ru vang) (mu xanh l)

Trong qu trnh chun ion Ca2+ v Mg2+ bng Na2H2Y lun gii phng ra 2 ion H+,

phn no lm acid ha mi trng, do trong qu trnh chun phi cho dung dchm vo mi trng pH ca mi trng khng i trong sut qu trnh chun ,dung dch m thng l NH4OH, NH4Cl.

Nu trong mu nc c cha mt lng ng k ion Fe3+, Cu2+, Ni2+,... th s chuynmu ca cht ch th s khng r rng, nn cn phi che nhng ion ny trc khichun bng cch dng cc ion CN- hoc S2- che cc cation .

3.13.2Thu v bo qun muThu mu trong chai nha v bo qun lnh 4oC

3.13.3Thuc th- Dung dch Na2H2Y (EDTA) tiu chun 0,1N:

Cch 1:Ha tan 18,612 g EDTA (C10H14O8N2Na2.2H2O) (sau sy 80

o

C, ngui trong bnh ht m) trong 400mL nc ct sau pha long thnh1000mL.

Nu khng c mui C10H14O8N2Na2.2H2O ta c th pha t acid t doC10H14O8N2, cch pha nh sau: Ha tan 14,6 g C10H14O8N2 v 4,5 g NaOHtrong khong 400 mL nc ct khuy u cho cc ha cht ha tan hon ton, ngui ti nhit phng, sau dng nc ct pha long thnh 1000mL,dung dch ny sau khi pha long xong phi chun li bng dung dch

NaCO3 tiu chun 0,1ppm bit nng chnh xc ca dung dch. Cch tinhnh nh sau: Dng buret 10mL dung dch CaCO3 tiu chun 0,1ppm, cho vo


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bnh tam gc 250mL tip tc cho vo 90 mL nc ct (2 ln ct) v 2mL dungdch m pH=10 lc u, dung dch c mu hng ru vang, dng dung dch

Na2H2Y mi pha trn chun trn t cho n khi dung dch chuyn t muhng ru vang sang mu xanh lth dng li, ghi th tch dung dch Na2H2Y

s dng. iu chnh nng dung dch Na2H2Y cho chnh xc bng biuthc: V1N1 = V2N2.

Cch 2: Pha long 1 ng Na2H2Y (EDTA) 0,1N vi nc ct thnh 1000mL.

- Dung dch Na2H2Y 0,01N: ly 50mL dung dch Na2H2Y 0,1N dng nc ctpha long thng 500mL.

- Dung dch pH=10: Ha tan 6,7g NH4Cl trong 57mL NH4OH m c (d=0,91)sau dng nc ct pha long thnh 100mL tip tc cho tip 1mL dung dchMgSO4 0,05N v 0,5mL dung dch Na2H2Y 0,1N lc u.

- Dung dch CaCO3 tiu chun 0,1N: Ha tan 5 gam CaCO3 trong vi git dungdch HCl 1:1, pha long vi nc ct thnh 200mL, un si 5-10 pht, dngdung dch NH4OH iu chnh pH ca mi trng v bng 7 sau pha longvi nc ct thnh 1000mL.

- Dung dch MgSO4 0,05N: Ha tan 1,232g MgSO4.7H2O trong mt t nc ct,sau pha long thnh 100mL.

- Ch th Eriochrome black T: Ly 100g NaCl tinh khit phn tch em rang hocsy kh 110oC, ngui nghin mn bng ci chi thy tinh sch. Cn 0,5gch th Eriochrome black T cho vo 100g NaCl trn trn u v nghin mn,

cho vo l nu y np kn.3.13.4Tin hnhTrc khi tin hnh cn iu chnh pH ca mu nc v bng 7-8, sau tin hnh

phn tch theo cc bc sau:

- Dng ng ong 100mL, ong 100mL mu nc iu chnh v 7-8 cho vobnh tam gic 250mL, tip tc cho vo 2mL dung dch m pH=10, v mtlng nh ch th Eriochrome black T (mt nhm bng ht u), lc u nu cion Ca2+, Mg2+ trong mu nc s c mu hng ru vang.

- Dng dung dch Na2H2Y 0,01N chun t t cho n khi dung dch chuynt mu hng ru vang sang mu xang l th dng li, ghi th tch dung dch

Na2H2Y 0,01N s dng V. Lm li nh trn ln na ly gi tr V trungbnh.

Nu s chuyn mu khng r, tc l trong dung dch c cc ion cn nh: Fe3+, Cu2+th cn tin hnh chun li vi mu nc khc v cch tin hnh nh sau: Sau khicho 2mL dung dch m pH=10 vo mu nc ta cn thm vo 1mL dung dch KCN5% che cc ion cn, sau mi thm cht ch th vo v tin hnh chun nhtrn.


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3.13.5Tnh kt qu cng tng cng (mg CaCO3/L) 100050xx

V

NxV

M

-V l th tch dung dch Na2H2Y (mL) dng chun .

- N l ng lng ca dung dch Na2H2Y s dng.- VM: th tch mu nc em chun

3.14 kim tng cngTrong nc thin nhin kim c gy ra do s hin din ca cc mui acid yu,tn ti di cc dng bicarbonate nh: KHCO3, NaHCO3, Ca(HCO3)2, Mg(HCO3)2...cc cht ny c to thnh trong t do tc dng ca CO2 vi nhng cht khong ctrong t nh

CO2 + CaCO3 + H2O Ca(HCO3)2

Mt s trng hp, kim trong nc c gy ra do ion carbonate, bicarbonate,silicates, phosphates, ammonium v hp cht hu cbin i trong nc. Tuy nhin,cc ion ng quan tm l HCO3-, CO3

2-, OH-. Khi pH nc ln hn 4,5 th trongnc tn ti ion bicarbonate, khi pH ln hn 8,34 thi trong nc c ion CO3

2-. Phngphp xc nh kim l phng php chun acid.

3.14.1 kim carbonate hay kim phenolphthaleinCho phenolphthalein vo mu nc, mu hng xut hin nu mu nc c cha ionCO3

2-. Chun bng H2SO4 0,01N cho n khi mt mu (pH =8,34), khi ionCO3

2- c trung ha. V vy kim phenoltalein cn c gi l kimcarbonate.

CO32- + H+ = HCO3

-

3.14.2 kim tng cngCho ch th methyl orange vo mu nc dung dch c mu vng cam. Chun bngdung dch H2SO4 0.01N cho n khi dung dch tr thnh mu cam (mi trng

acid, pH khong 4,5). Khi tt c cc ion OH-, CO32-, HCO3-, NH4+, PO43-... ctrung ha hon ton. V vy, phn tch vi ch th methyl orange chng ta c kim tng cng

HCO3- + H+ H2O + CO2

Thu v bo qun mu

Thu mu trong chai nha v bo qun lnh

Thuc th

Dung dch PRE 1: ha tan 27mL H2SO4 98% vi nc ct thnh 1000mL


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Phenolphtalein 1%: ha tan 1g Phenolphtalein trong 100mL C2H5OH

Dung dch H2SO4 0,1N: ha tan 100mL PRE 1 vi nc ct thnh 1000mLhay pha long 1 ng H2SO4 0,1N chun vi nc ct thnh 1000mL.

Dung dch methyl orange 0,1%: ha tan 0,1g methyl orange vi nc ctthnh 100mL

Dung dch chun

- Dung dch KHCO3 1N: ha tan 10,011g KHCO3 vi nc ct thnh 100mL- Dung dch KHCO3 0,1N: ha tan 10mL dung dch KHCO3 1N vi nc ct

thnh 100mL.

Tin hnh

ong 100mL mu nc cn phn tch vo bnh tam gic 250mL

Thm vo 3 git dung dch Phenophthalein, dung dch c mu hng nht. Chun bng dung dch H2SO4 0,01N n khng mu, ghi th tch (V1 mL) H2SO4 001N sdng chun .

Sau thm tip 3 git dung dch methyl orange, dung dch c mu vng cam. Tiptc chun bng dung dch H2SO4 0,01N n pH bng 4,5 dung dch t mu vngcam chuyn sang mu cam, ghi th tch (V2 mL) H2SO4 0.01N.

Lm tng t nh mu nc i vi mu chun KHCO3i chng.

Tnh kt qu

kim tng cng (mg/ CaCO3/L) 100050xxM

NxV

M

- V = (V1 + V2) : tng th tch dung dch H2SO4 0,01N cho c 2 ln chun - N: nng ng lng dung dch H2SO4- VM: th tch mu ong em chun

3.15 acid (Acidity) acid biu th kh nng phng thch ion H+ trong nc, do s c mt ca cc loiacid nh: acid carbonic, acid tanic, acid humic bt ngun t s phn hy cht hu c,mt khc do s thy phn cc mui t cc acid mnh nh Sulfat nhm, st to thnh.Khi b cc acid v cthm nhp vo, nc s c pH rt thp

Trong nc thin nhin lun duy tr mt th cn bng ngia cc ion HCO3-, CO3

2-, kh

CO2 ha tan, do nc thng ng thi mang hai tnh cht i nhau: tnh acid vtnh kim.


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Trong thc nghim, hai khong pH chun c s dng biu th s khc bit trntng ng vi hai lai cht ch th l methyl orange (pH = 4,24,5) v

phenolphthalein (pH = 8,28,4)

3.15.1Nguyn tcDng dung dch kim mnh nh phn acid ca c acid v cmnh cng nhacid hu choc acid carbonic yu.

Lng acid v cmnh khi nh phn thng vi ch th methyl orange, chun tmu chuyn thnh mu da cam v c gi l acid methyl

Sau tip tc nh phn xc nh acid tng cng vi ch th phenolphthalein,dung dch t khng mu chuyn sang mu hng (tm)nht, c gi l acid tngcng

3.15.2Dng c v thit b- Bnh tam gic 250mL- ng ong 100mL- Burett

3.15.3Chun b ha cht- Dung dch NaOH tiu chun 0,1N: ha tan 1 ng chun NaOH 0,1N vi nc

ct thnh 1000mL- Dung dch NaOH 0,02N: Ly 200mL dung dch NaOH 0,1N ha tan cng vi

nc ct thnh 1000mL- Ch th Phenolphthalein 0,5%: cn 0,5g phenolphthalein ha tan trong 50mL

Ethanol 98%, cho nc ct vo thnh 100mL- Ch th Methyl orange 0,05%: cn 0,05g methyl orange ha tan trong nc ct

thnh 100mL

3.15.4Tin hnh phn tchNu mu nc l nc ung, nc cp sinh hot, trc khi chun nn thm 1 gitNa2S2O3 0,1N loi b lng Cl

- cn d.

Nu pH nc < 4,5- ong 100mL nc mu cho vo bnh tam gic, sau cho vo 3 git methyl

orange. Dung dch c mu .- Dng NaOH 0,02N chun cho n khi xut hin mu da cam. Ghi nhn th

tch dung dch NaOH (V1 mL) dng tnh acid methyl hay cn gi lacid khong.

- Tip tc thc hin bc xc nh acid tng cng.Nu pH nc >4,5

- ong 100mL nc mu cho vo bnh tam gic, cho vo 3 git ch thphenolphthalein. Dung dch khng mu


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- Dng NaOH 0,02N chun cho n khi dung dch chuyn t khng mu sangmu hng (tm) nht. Mu phi bn t nht 5 pht. Ghi th tch V2 mL dungdch NaOH 0,02N dng tnh acid tng cng

3.15.5Tnh kt qu acid khong (mg CaCO3/L)

MV

xV 10001

acid tng cng (mg CaCO3/L)MV

xVV 1000)( 21

(Khi pH mu nc ln hn 4,5 th V1 = 0 )

3.16 St tng s (Fe2+ v Fe3+ )3.16.1Phng php so mu ThiocianateNguyn tc

Cc mui ha tan ca st trong nc thng c xc nh bng phng php so muThiocianate. Phng php ny da trn nguyn tc trong mi trng acid, Fe2+ b oxyha thnh Fe3+ bng mt tc nhn oxy ha thch hp. Fe3+ mi to thnh v Fe3+ csn trong mu nc s kt hp vi SCN- hnh thnh mt phc cht c mu mu,cng m hay nht ph thuc vo hm lng ion Fe3+ c trong mu nc banu.

10Fe2+ + 10H+ + K2S2O7 = 10Fe3+ + K2S2O8 + 5H2O

K2S2O7 + 3SCN- = Fe(SCN)3 (Mu mu)

Thuc th

- Dung dch Thiocianate ammonium hay potassium: Ha tan 50g NH4SCN hayKSCN trong mt t nc ct sau pha long thnh 100mL.

- Dung dch Potassium persulfate: Ha tan 1,7g K2S2O8 trong mt t nc ctsau pha long thnh 100mL.

- HCl c d= 1,18- Dung dch Fe3+ tiu chun 0,2mg/mL: Cho 20mL H2SO4m c vo 50mLnc ct, ha tan 1,4g Fe(NH4)2(SO4)2.6H2O vo dung dch ny. Cho tng git

KMnO4 0,1N vo cho n khi dung dch trnn mu hng nht th dng li.Sau pha long thnh 1.000mL.

- Dung dch Fe3+ tiu chun 0,1mg/mL: Ly 50mL dung dch Fe3+ tiu chun0,2mg/mL pha long thnh 100mL.

Tin hnh

- Xc nh st tng sLy 2 bnh tam gic 100mL, cng kch thc ln lt mi bnh cc ha cht

sau:


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Bng 7. 8. Tin trnh phn tch hm lng Fe tng s trong nc

Bnh 1 Bnh 21. 50mL mu nc2. 1,5 mL HCl c lc u3. 2,5mL K2S2O8, lc u4. 1,5 mL KSCN, lc u dung

dch c mu mu.

1. 50mL nc ct.2. 1,5 mL HCl c lc u.3. 2,5mL K2S2O8, lc u.4. 1,5 mL KSCN, lc u dung dch khng

mu. Dng dung dch Fe3+ tiu chun0,1mg/mL chun t t cho n khidung dch c mu mu ging bnh 1th dng li ghi th tch V1 dung dchFe3+ tiu chun s dng. Lm li nhtrn mt ln na ly gi tr V1 trung

bnh.

- Xc nh Fe2+Ly 2 bnh tam gic 100mL, cng kch thc, ln lt cho vo mi bnh ccha cht nh sau:

Bng 7.9. Tin trnh phn tch hm lng Fe2+ trong nc

Bnh 1 Bnh 21. 50mL mu nc.2. 1,5 mL HCl c lc u3. 1,5 mL KSCN, lc u dung

dch c mu mu.

1. 50mL nc ct.2. 1,5 mL HCl c lc u3. 1,5 mL KSCN, lc u dung dch

khng mu. Dng dung dch Fe3+ tiuchun 0,1mg/mL chun t t chon khi dung dch c mu muging bnh 1 th dng li, ghi th tchV2 dung dch Fe

3+ tiu chun sdng. Lm li nh trn mt ln na ly gi tr V2 trung bnh.

Tnh kt qu

Fe tng s (mg/L) = 100050

1,0x

Vx

Fe3+ (mg/L) = 100050

1,0 2 xVx

Fe tng s (mg/L) = 100050

)(1,0 21 xVVx


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3.16.2Phng php o-phenantrolineNguyn tc

St b kh thnh dng Fe2+bng cch un si vi acid v hydroxylamine v c x

l vi 1, 10 phenanthroline pH 3,2 - 3,3. 3 phn t phenanthroline to hp cht cngcua vi mi mt nguyn t Fe2+ thnh dng phc cht c mu -cam. Sau cxc nh bi my so mu quang phbc sng 510nm.

Thuc th

- Dung dch A - HCl m c- Dung dch B - Dung dch Hydroxylamine 10%: ha tan 10g NH2OH.HCl vi

nc ct thnh 100mL.- Dung dch C - Dung dch m pH = 5: ha tan 250g CH3COONH4 trong

150mL nc ct sau thm 700mL CH3COOH m c.- Dung dch D - Thuc th o-phenanthroline: ha tan 0,1g o-phenanthroline

trong 100mL nc ct lm nng 800C.

Dung dch chun

- Dung dch Fe2+ 200mg/l: ho tan 1,4g Fe(NH4)2(SO4)2.6H2O vi 20mL H2SO4m c vi 50mL nc ct. Dau thm vi git KMnO4 0,1N dung dch sc mu hng nht, pha long thnh 1000mL.

- Dung dch Fe2+ 100mg/l: ong 50mL dung dch Fe2+ 200mg/l pha long thnh100mL

Thit lp mu chun

Chn 6 bnh tam gic c dung tch 100mL, cng kch thc, khng mu ln lt chovo cc ha cht sau:

Bng 7.10. Cc bc thit lp mu chun phn tch Fe tng s bng phng phpo-phenantroline.

STT Nng mu chun(mg/l)

Th tch dung dchFe2+ 100mg/l (mL)

Th tch nc ct hay ncbin lc c S%o = S%o vi

nc mu (mL)

1 0,0 0,0 100,02 0,4 0,4 99,63 0,8 0,8 99,24 1,2 1,2 98,85 1,6 1,6 98,46 2,0 2,0 98,0

Tin hnh

- Ln lt ong 25mL ca 06 mu chun vo 06 bnh tam gic- ong 25mL mu nc cn phn tch vo bnh tam gic,- Thm vo: (cng cch lm cho mu chun v mu nc )


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1mL dung dch A

1mL dung dch B

- Sau , em un trn bp cho cn cn khong 10-15mL, em ngui.-

nh mc li vi nc ct thnh 25mL,- Tip tc thm vo 5mL dung dch C v 0,5mL dung dch D,- Lc u,- em so mu bc sng 510nm

Ch , nu mu dung dch qu m ta nn lm li bng cch pha long, sau khi ghikt qu t my ta x l l vi h s pha long s cho kt qu nng ca mu m tacn o.

3.17 Silicate (SiO2)3.17.1Nguyn tcSiO2 v cc dn xut ca n trong nc thng xc nh bng phng php so muMolybdosilicate. Phng php ny da trn nguyn tc trong mi trng pH t 3-4SiO2 v cc dn xut ca n s tn ti di dng H2SiO3 (acid Silicic), acid Silicic skt hp vi Molybdate ammonium hnh thnh phc cht Molybdosilicic acid c muvng, cng m hay nht ph thuc vo hm lng H2SiO3 c trong mi trng.

H2SiO3 + 12(NH4)2MoO4 + 24HCl = H8Si(Mo2O7)6 + 24NH4Cl + 9H2O

3.17.2Thu mu v bo qun

Thu mu trong chai nt mi trng 125mL, cnh mu bng 1 mL HCl 50%

3.17.3 Chun b thuc th- 1. Dung dch Molybdate ammonium 10%: Ha tan 10g (NH4)2MoO4 hay

(NH4)6Mo7O24.4H2O trong mt t nc ct nng pha long thnh 100mL,cho vo bnh polyethylene s dng.

- 2. Dung dch HCl 50%: Ha tan 50mL dung dch HCl trong 50mL nc ct.- 3. Dung dch H2C2O4.2H2O 10%: Ha tan 10g H2C2O4.2H2O trong mt t nc

ct, sau pha long thng 100mL.

- 4. Dung dch Na2B4O7.H2O 1%: Ha tan 10g Na2B4O7.H2O trong mt t ncct, sau pha long thnh 1000mL.

- 5. Dung dch K2CrO4 0,63%: Ha tan 0,63g K2CrO4 trong mt t nc ct,sau pha long thnh 100mL.

3.17.4Tin hnhLy 2 bnh tam gic 100mL, cng kch thc ln lt cho vo mi bnh cc ha chtnh sau:


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Bng 7.11. Cc bc tin hnh phn tch SiO2

Bnh 1 Bnh 2

1.50mL mu nc2.1mL HCl 50% v 2mL

(NH4)6Mo7O24.4H2O lc u. yn 10 pht, sau tip tc chovo 1,5mL H2C2O4.2H2O 10%,

lc u, dung dch c mu vng.

1.25mL dung dch Na2B4O7.H2O 1%, v29,5mL nc ct, lc u dung dch khngmu.

2.Dng dung dch K2CrO4 0,63% chun tt cho n khi dung dch c mu vngging nh bnh 1 th dng li, ghi th tchdung dch K2CrO4 0,63% s dng.

3.17.5 Tnh kt qu1000

50)/(2 x

VLmgSiO =

Vi V l th tch dung dch K2CrO4 0,63% s dng.

3.18 Ammonia (NH3) v Ammonium (NH4+)3.18.1Phng php Nessler (American Public Health Association, 1989)Nguyn tc

Trong mi trng bazmnh NH4+ s bin thnh NH3. NH3 mi hnh thnh v NH3

sn c trong mu nc s tc dng vi phc cht Indo mercurate kalium (K2HgI4),hnh thnh phc cht c mu vng nu, cng mu m hay nht ty thuc vohm lng NH3 c trong mu nc.

2 K2HgI4 + NH3 + 3KOH = Hg(HgIONH2) + 7KI + 2 H2O

(mu vng)

K2HgI4 + NH3 + KOH = Hg(HgI3NH2)+ 5KI + H2O

(mu nu)

Nhng trong nc thin nhin thng cha cc ion Ca2+, Mg2+ (nc cng), trongmi trng bazmnh cc ion ny s to thnh cc hydroxide dng keo, lm cho

dung dch b vn c cn trqu trnh so mu. khc phc hin tng trn, phidng mui Seignett (KNaC4H4O6), hay EDTA (EDTA) cho vo mu nc phn tch, cc mui ny kt hp vi cc ion Ca2+ v Mg2+ hnh thnh cc hp cht ha tan,khng mu trong dung dch.

M2+ + KNa C4H4O6 = K+ + Na+ + M C4H4O6

M2+ + Na2H2I = Na2MI + 2H+


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Thuc th:

- Dung dch NH4Cl tiu chun N-NH4+ 1mg/mL: Ha tan 0,3822g NH4Cl trongmt t nc ct khng m (un nng 100oC trong 2 gi), sau pha longthnh 100mL.

- Dung dch N-NH4+ tiu chun 0,01mg/mL: Ly 1mL dung dch N-NH4+1mg/mL, dng nc ct khng m pha long thnh 100mL.

- Nc ct khng m: Cho 20mL H2SO4c vo 1 lt nc ct, lc u ri emct li mt ln na.

- Dung dch Seignett: Ha tan 50 g KNaC4H4O6.4H2O trong mt t nc ctkhng m, sau pha long thnh 100mL.

- Dung dch EDTA: Ha tan 50g EDTA trong 60mL nc ct khng m, sau cho vo 10g NaOH khuy u cho ha tan v pha long thnh 100mL.

- Dung dch Nessler: Ha tan 15g HgI2 v 10g KI trong 500mL nc ct khngm, sau cho vo 40g NaOH, Khuy u cho NaOH ha tan hon ton, lng vi ngy v gn ly phn nc trong cho vo bnh nu s dng. Nukhng c sn HgI2 th pha nh sau: Ha tan 9g HgCl2 v 15,5 g KI trong 5mLnc ct khng m, sau cho vo 40g NaOH, khuy u cho NaOH ha tanhon ton lng vi ngy, gn ly nc trong cho vo bnh nu s dng.

Tin hnh:

Chn 11 ng nghim c dung tch 25mL, cng kch thc, khng mu ln lt chovo cc ha cht sau:

Bng 7.12. Cc bc thit lp mu chun phn tch TAN bng phng phpNessler

ng nghim 1 2 3 4 5 6 7 8 9 10 11

Dung dch N-NH4+

0,01N mg/mL0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 0

Nc ct khng m(mL)

9,9 9,8 9,7 9,6 9,5 9,4 9,3 9,2 9,1 9,0 0

Mu nc 0 0 0 0 0 0 0 0 0 0 10

Dung dch Seignetthay trion B (mL) 0,2 0,2 0,2 0,2 0,2 0,2 0,2 0,2 0,2 0,2 0,2

Dung dch Nessler(mL)

1,0 1,0 1,0 1,0 1,0 1,0 1,0 1,0 1,0 1,0 1,0

Nng N-NH3 tngs

0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 ?

Ly ng nghim th 11 (mu nc) em so mu vi 10 ng cn li. Mu trong ngnghim th 11 trng vi mu ng nghim no th nng TAN (tng m amn)

bng vi nng TAN trong ng . Khi so mu cn cc ng nghim trn nnmu trng, v nhn kt qu t trn xung di phn bit mu r rng. Phng php


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ny so mu bng mt thng nn rt n gin v d thc hin nhng chnh xckhng cao, t c chnh xc cao chng ta c th p dng so mu quang ph.

Ch , kt qu thu c t phng php ny l hm lng tng m amn (TAN),

TAN = N-NH3 + N-NH4+

. tnh c hm lng N-NH3 v N-NH4+

khi thu munc chng ta phi o pH v nhit , da vo tra (xem phn l thuyt Chng 3,Mc 7.1) xc nh t l NH3 cha trong TAN, t tnh ra kt qu:

Tnh kt qu

Hm lng N-NH3 (mg/L) =100

IxTAN

Hm lng N-NH4+ (mg/L) = TAN - N-NH3

-I l t l phn trm ca N-NH3 cha trong TAN

3.18.2Phng php Indophenol BlueNguyn tc

Phn ng Berthelot da trn s th hin mu xanh ca dung dch khi ammonia phnng vi phenol v alkaline hypochlorite v c gi l phng php Indophenol hoc

phng php Phenate. Phng php ny c p dng cho phn tch mu nc thivi cng tng cng nh hn 400mg/L v nng nitrite nh hn 5mg/L (Scheiner,1976)

Trong phng php Indophenol, phenol v Hypochlorite phn ng trong mi trngkim hnh thnh phenylquinone-monoimine, ri tr li phn ng vi ammonia tothnh Indophenol c mu xanh, c minh ha qua phng trnh sau:

Cng mu ty thuc vo nng hin din ca ammonia, v sodiumnitroprusside c thm vo lm tng cng hin mu trong dung dch. Nng

ca tng m amn - TAN (NH3 v NH4+) sc xc nh bi my so mu quangphbc sng 630 nm (i vi nc ngt) v 640 nm (nc l- mn)

Tin trnh phn tch nc mn, l

Thu mu vo chai nha 125mL, bo qun lnh cho n khi phn tch mu xong

Thuc th- Dung dch A: ha tan 4g phenol vi dung dch ethanol 95% thnh 500mL.- Dung dch B: ha tan 0,375 g sodium nitroprusside (sodium nitroferricyanide)

v

i n

c ct thnh 500mL.

2 - O- + NH3 + 3 ClO- O - - N = = O + 2H2O + OH

- + 3Cl-

Phenol Indophenol (mu xanh)


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- Dung dch C: ha tan 7,5 g trisodium citrate v 0,8g NaOH vi nc ct thnh500mL.

- Dung dch D: dung dch oxy ho: Ly 2 mL sodium hypochlorite (NaOCl, 5%)pha vi dung dch C thnh 100mL (chun b ngay trc khi s dng).

Dung dch chun- Dung dch (NH4)2SO4 500mg/l: ho tan 0,2358g (NH4)2SO4 ) vi nc ct

khng m thnh 100mL.- Dung dch (NH4)2SO4 5mg/l: pha 1mL dd (NH4)2SO4 500mg/l) vi nc ct

khng m thnh 100mL.Thit lp mu chun


Bng 7.13. Cc bc thit lp mu chun phn tch TAN bng phng phpindophenol blue cho mu nc l, mn.

STT Nng muchun (mg/l)

Th tch dung dch(NH4)2SO4 5mg/L

(mL)

Th tch nc bin lc cS = S ca mu nc

(mL)1 0 0 1002 0,2 4 963 0,4 8 924 0,6 12 885 0,8 16 84

6 1,0 20 80Tin hnh phn tch

Dng pipete ht 3 mL mu nc v mu chun cho vo cc ng nghim khc nhau.

- Thm 1 mL dd A, trn u.- Thm 1 mL dd B (nitroprusside), trn u.- Thm 2 mL dd D (dd oxy ho), trn u.- trong ti nhit phng khong 1-2 gicho phn ng xy ra hon ton

(mu th hin r).

Phn tch bc sng 640 m i vi cuvet 1 cm di truyn quang. Mu Zero lnc bin lc c S = S ca mu nc

Tin trnh phn tch nc ngt

Thu mu vo bnh 1lt, bo qun lnh cho n khi phn tch mu xong

Thuc th- Dung dch PRE 1: nc ct khng m- Dung dch PRE 2: phenole stock solution: ho tan 312,5g phenol trong

methanol thnh 500mL.- Dung dch PRE 3: sodium hypochlorite 5%


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- Dung dch PRE 4: dung dch NaOH 67.5%: ha tan 67,5g NaOH thng 100mLnc ct khng m.

- Dung dch A- Ha tan 150g Na3PO4.12H2O v 150g C6H5O7.2H2O trong1000mL nc ct khng m.

- Dung dch B- Ha tan 75mL PRE 2 vi 0.1g Na2[Fe(CN)5NO].2H2O trong100mL nc ct khng m.- Dung dch C- Ha tan 75mL PRE 3 vi PRE 4 thnh 100mL.

Dung dch chun:- Dung dch (NH4)2SO4 500mg/L: ha tan 0,2358g (NH4)2SO4 trong 100mL

nc ct khng m.- Dung dch (NH4)2SO4 5mg/L: pha 1mL dung dch (NH4)2SO4 500mg/L thnh

100mL vi nc ct khng m.Thit lp mu chun:


Bng 7.14. Cc bc thit lp mu chun phn tch TAN bng phng phpindophenol blue cho mu nc ngt.


Th tch dung dch(NH4)2SO4 5mg/l (mL)

Th tch nc ct khngm (mL)

1 0 0 1002 0,2 4 96

3 0,4 8 924 0,6 12 885 0,8 16 846 1,0 20 80

Tin hnh

Ln lt ong 25mL mu nc v 25 mL tng nng mu chun cho vo bnh tamgic 50mL. Sau , cho vo tng bnh cc dung dch sau:

- 1mL thuc th A- 1mL thuc th B- 1mL thuc th C

Ch20-25 pht, xut hin mu xanh (mu sn nh sau 25 pht n 24 gi) em o

hp th quang bc sng 630 m. Ch , nu mu xanh qu m ta nn lm libng cch pha long, sau khi ghi kt qu t my ta x l l vi h s pha long s chokt qu nng ca mu m ta cn o.

Tnh kt qu

Cc mu chun thit lp c em o hp th quang, tng ng vi nng Cca mu chun ta c hp th quang A. Da vo s tng quan ny chng ta cth lp phng trnh tng quan dng A = aC + b


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Trong :

A: hp th quang

C : nng ca mu (mg/L)

Sau khi thit l phng trnh, chng ta o hp th quang ca mu cn phn tch vth vo phng trnh chng ta s tnh c nng ca TAN c trong mu nc.

a

bAC

=

3.19 Nitrite (NO2-)3.19.1Nguyn tc

Nitrite (NO2-) trong mi trng acid mnh s hnh thnh HNO2, HNO2 mi hnh

thnh s kt hp vi acid sulfanilique cho ra mui Diazonium sulfanilique.NaNO2 + 2HCl + HSO3-C6H4-NH2 = HSO3-C6H4-N=N-Cl+ NaCl + H2O

Sau mui diazonium sulfanilique s kt hp vi thuc th. napthylammine cho

ra . Napthylammine diazonium sulfanilique.

HSO3-C6H4-N=N-Cl + C10H9NH2 = HSO3-C6H4-N=N-C10H8NH2 + HCl

. napthylammine diazonium sulfanilique l mt hp cht c mu hng, cng m hay nht ty thuc vo hm lng NO2

- c trong mu nc lc ban u. Nng

c xc nh bi my so mu quang phbc sng 543 m. Phng php nyc gi l phng php Griess llosvay, Diazonium.

3.19.2Cc bc phn tchThu mu v bo qun

Thu mu vo chai nha 125mL, bo qun mu lnh cho n khi phn tch mu xong.

Thuc th

- PRE 1: Cn 5g sulfanilic acid v 250g natri acetate ha tan vi nc ct thnh500mL.

- PRE 2: ha tan 0,5g 1-naphthylamine v 25mL acetic acid vi nc ct thnh500mL.

- Dung dch A: Ha tan 100mL PRE 1 vi 100mL PRE 2.- Dung dch B: Dung dch acetic acid nguyn cht.

Dung dch chun

- Dung dch NaNO2 500mg/l: ha tan 0,2463g NaNO2 trong 100mL nc ct.- Dung dch NaNO2 5mg/l: ha tan 1mL dd NaNO2 500mg/l vi nc ct thnh

100mL.Thit lp mu chun


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Bng 7.15. Cc bc thit lp mu chun phn tch nitrite bng phng phpGriess llosvay, Diazonium.

Mu nc ngtSTT Nng mu

chun (mg/L)Th tch dung dch

NaNO2 5mg/L (mL)Th tch nc ct (mL)

1 0 0 1002 0,1 2 983 0,2 4 964 0,3 6 945 0,4 8 926 0,5 10 90

Mu nc l, mnSTT Nng muchun (mg/L)

Th tch dung dchNaNO2 5mg/L (mL)

Th tch nc bin lc c S%o= S%o ca mu (mL)

1 0 0 1002 0,1 2 983 0,2 4 964 0,3 6 945 0,4 8 926 0,5 10 90

Tin hnh

- Lm ng chun: ong ln lt 20mL tng nng chun cho vo 6 bnhtam gic c k hiu nng chun b.

- ong 20mL mu nc cn o vo bnh tam gic khc.- Ln lt cho thuc th vo: 1mL thuc th A v 5mL thuc th B- Ch40 pht dd s c mu hng nu c nitrite (mu sn nh sau 40 pht n

4 gi), ta em so mu bc sng 530 m.- Mu Zero l nc bin lc c nng mui tng ng vi nng mui ca

mu nu phn tch mu nc l.

Ch , nu mu hng qu m ta nn lm li bng cch pha long, sau khi ghi kt qut my ta x l l vi h s pha long s cho kt qu nng ca mu m ta cn o.

Qu trnh tnh ton kt qu tng t nhphng php Indophenol blue o TANhay phng php Methylen blue o H2S.

3.20 Nitrate (NO3-)3.20.1Phng php khCadmium

Nitrate (NO3-) trong nc s b kh ton b thnh nitrite (NO2

-) bi ct Cadmium

c x l bi CuSO4. NO2-

mi hnh thnh v NO2-

sn c trong nc sc xcnh bi phng php diazonium.


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3.20.2Phng php phenoldisulfonic acidNguyn tc

Nitrate (NO3-) c trong nc tc dng vi phenol disulfonic acid to thnh phc cht

khng mu nitrophenol disulfonic. mi trng baze mnh, phc cht ny c muvng. Cng mu vng cng m th nng NO3- cng cao

Thuc th

- Dung dch acid Phenoldisulfonic: Ha tan 3g phenol trong 20mL H2SO4ctrong mt cc thy tinh chu nhit, ngui cho vo l nu s dng.- Dung dch NH4OH nguyn cht (khong 25%). Nu khng c, c th thay

bng 68 g KOH ha tan thnh 100mL vi nc ct.- Dung dch Nitrate tiu chun N-NO2- 0,01 mg/mL: Ha tan 0,722g KNO3 (sau

khi sy kh 105oC v ngui trong bnh ht m) trong mt t nc ct, sau pha long thnh 100mL. Ly 1mL dung dch va pha long trn pha longthnh 100mL, ta sc dung dch N-NO3

- tiu chun 0,01mg/mL.

Tin hnh

Chn 12 ng nghim cng kch thc, c dung tch 25mL, ln lt cho vo mi ngnghim cc ha cht sau:

+ 3KOH (2)+ 3H2O

phc cht mu vng

OHHSO3

SO3H

NO2 OHSO3

SO3H

N- OK

OHHSO3

SO3H

+ NO3-

OHHSO3

SO3H

NO2(1)+ H2O

Phenol dissulfonic acid Nitrophenol dissulfonic(phc cht khng mu)


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Bng 7.16. Cc bc thit lp mu chun phn tch nitrate bng phng phpphenoldisulfonic acid.

ng nghim 1 2 3 4 5 6 7 8 9 10 11

Dung dch N-NO3-

0,01 mg/mL (mL) 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2Nc ct (mL) 9,8 9,6 9,4 9,2 9,0 8,8 8,6 8,4 8,2 8,0 7,8Mu nc (mL) 0 0 0 0 0 0 0 0 0 0 10Dung dch acid

Phenoldisulfonic

(mL)

1 1 1 1 1 1 1 1 1 1 1

NH4OH c (mL) 1 1 1 1 1 1 1 1 1 1 1Nng N-NO3

-

(ppm)0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2

Ly 10mL mu nc, cho vo chn sem un cch thy cho n kh. Nu c NO3-

th trong chn s c kt ta. Ha tan kt ta bng 1 mL dung dch acidphenoldisulfonic, khuy u cho kt ta ha tan, cho dung dch trong chn s vo mtng nghim th 12, sau ra sch chn bng 10mL nc ct, nc ra ny cng chovo ng nghim, tip tc cho vo ng nghim 1mL NH4OH c lc u, em so muvi cc ng nghim trong gam mu ging nh phng php xc nh TAN bng

phng php Nessler. c kt qu chnh xc chng ta c th p dng phng phpso mu quang ph.

3.20.3Phng php salycilateThu mu v bo qun

Thu mu vo bnh 1 lt, bo qun mu lnh cho n khi phn tch mu xong.

Thuc th

- Dung dch A - Ha tan 5g natri salicylate thnh 1000mL vi nc ct.- Dung dch B - Dung dch H2SO4 98%- Dung dc C - Ha tan 100g C4H4KNaO6.4H2O thnh 1000mL vi nc ct.- Dung dch D - Dung dch NaOH 10N: ha tan 400g NaOH thnh 1000mL vi

nc ct.

Dung dch chun

- Dung dch KNO3 500mg/l: ha tan 0,3609g KNO3 trong 100mL nc ct.- Dung dch KNO3 50mg/l : ha tan 10mL dd KNO3 500mg/l thnh 100mL vi

nc ct.

Thit lp mu chun


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Bng 7.17. Cc bc thit lp mu chun phn tch nitrate bng phng phpSalicilate.

Mu nc ngt

STT Nng mu chun(mg/L)

Th tch dung dchKNO3 50mg/l (mL)

Th tch nc ct (mL)

1 0,0 0 1002 2,0 4 96

3 4,0 8 92

4 6,0 12 88

5 8,0 16 84

6 10,0 20 80Mu nc lmn


Th tch dung dchKNO3 50mg/L (mL)

Th tch nc bin lc cS%o = S%o ca mu (mL)

1 0,0 0 100

2 0,1 2 98

3 0,2 4 96

4 0,3 6 94

5 0,4 8 926 0,5 10 90

Tin hnh

- Ly 10 mL mu nc, cho vo 1mL thuc th A- em sy 1050C cho n cn- ngui.- Cho vo 1mL thuc th B- Ch10 pht- Cho tip 20mL thuc th C- V 5mL thuc th D, dd s c mu vng anh nu c nitrate.- Ch15 pht xut hin mu vng anh (mu n nh sau 15 pht n 6 gi), sau

o hp th quang bc sng 410m.

Ch , nu mu vng anh qu m ta nn lm li bng cch pha long, sau khi ghi ktqu t my ta x l l vi h s pha long s cho kt qu nng ca mu m ta cno. Ghi kt qu hp th quang A v da vo phng trnh hi qui tnh ra nng ca mu


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3.21 Orthophosphate (PO43-)3.21.1Phng php xanh molybdenNguyn tc

Ln ha tan trong nc c lc qua mng lc 0,45 m. Cc mui orthophosphatetrong mi trng acid, ion PO4

3- s cho mt phc cht mu vng chanh vi thuc thMolybdate ammonium.

PO43- + 12(NH4)2MoO2 + 24H

+ = (NH4)2PO4.12MoO3 + 21NH4+ + 12H2O

(-phospho molybdate NH4+)

Dng -phospho molybdate NH4+, trong s hin din ca cc cht kh nh SnCl2,

v.v..d b kh thnh dng - phospho molybdate NH4+c mu xanh. Cng mu

m hay nht ph thuc vo hm lng ion PO43-

c trong mu nc lc ban u.(NH4)3PO4.12MoO + Sn

2+ + 16H+ = (NH4)3PO4.(4MoO2.2MoO3)2 + Sn4+ + 8H2O

V c xc nh bi my so mu quang phbc sng 690 m.

Ha cht

- Dung dch Amonium molybdateCn 25 g (NH4)6Mo7O24.4H2O ha tan trong 175 mL nc ct

ong 280mL H2SO4m c pha vi 400mL nc ct, ngui

Trn ln hai dung dch li ri pha long vi nc ct thnh 1000mL

- Dung dch SnCl2Cn 2,5g SnCl2.H2O ha tan trong 100mL Glycerin (Cung cp nhit). Boqun dung dch t lnh

- Dung dch chun P-PO43-Dung dch KH2PO4 500mg/l: ha tan 0,2197g KH2PO4 trong 100mL nc ct

Dung dch KH2PO4 5mg/l: ha tan 1mL dd KH2PO4 500mg/l thnh 100mL vinc ct

Thit lp mu chun



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Bng 7.18. Cc bc thit lp mu chun phn tch orthophosphate bng phngphp xanh molypden .

STTNng mu chun(mg/l)

Th tch dung dchKH2PO4 5mg/l (mL)

Th tch nc ct(mL)

1 0 0 1002 0,2 4 963 0,4 8 924 0,6 12 885 0,8 16 846 1,0 20 80

Tin trnh phn tch

- Ly ln lt 50mL nc mu c lc loi b vt cht l lng c trongnc vo bnh tam gic, cng vi 50mL tng nng chun cho vo 6 bnh

tam gic c k hiu sn nng .- Cho vo 2mL dd amonium molybdate, lc u- Cho vo 5 git SnCl2, lc u- o hp th quang bc sng 690m

Tnh kt qu

Tnh nng P-PO43- hin din trong mu da trn vic phng trnh hi qui tng

quan gia hp th quang v nng cht tan cn phn tch tng t nh cc ccphng php Methylen blue (phn tch H2S), Indophenol blue (phn tch TAN),

Salicilate (Phn tch NO3-)...

3.21.2Phng php Acid ascorbic (4500-P E: Standard methods, 1998)Nguyn tc

Ammonium molybdate v potassium antimonyl tartrate trong acid trung tnh phnng vi orthophosphate to thnh 1 dng acid d a (heteropolyacid) acid-

phosphomolybdate b kh thnh dng c mu xanh tp trung molybde bi acidascorbic.

Nng ca P-PO43- sc xc nh bi my so mu quang phbc sng 880m.

Thuc th

- H2SO4 5N: Pha 70 mL H2SO4m c vi nc ct thnh 500 mL.- Dung dch Potassium antimonyl tartrate: Ha tan 0,12 g

K(SbO)C4H4O6.1/2H2O trong 400 mL nc ct. sau pha long thnh 500mL.

- Dung dch ammonium molybdate: ha tan 20 g (NH4)6Mo7O24.4H2O trong 500mL nc ct.


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- Acid Ascorbic 0,1M: ha tan 1,76 g trong 100 mL nc ct. Dung dch n nhkhong 1 tun 4oC.

- Thuc th kt hp (combined reagent): Trn cc thuc th trn li vi nhautheo t l sau c 100 mL thuc th kt:

50 mL H2SO4 5N

5 mL potassium antimonyl tartrate

15 mL ammonium moly

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