Tách, làm giầu, xác định lượng vết Pb và Cd trong một số đối tượng bằng kỹ thuật chiết pha rắn và phương pháp quang phổ

7/31/2019 Tch, lm giu, xc nh lng vt Pb v Cd trong mt s i tng bng k thut chit pha rn v phng php

1/83

I HC QUC GIA H NITRNG I HC KHOA HC T NHIN

M TH THANH THY

TCH, LM GIU, XC NH LNG VT PbV Cd TRONG MT S I TNG BNG K

THUT CHIT PHA RN V PHNG PHPQUANG PH

LUN VN THC S KHOA HC

H NI - 2009


2/83

I HC QUC GIA H NITRNG I HC KHOA HC T NHIN

M TH THANH THY

TCH, LM GIU, XC NH LNG VT PbV Cd TRONG MT S I TNG BNG K

THUT CHIT PHA RN V PHNG PHPQUANG PH

LUN VN THC S KHOA HCChuyn ngnh : Ho Phn tchM s : 60 44 29

NGI HNG DN KHOA HC:PGS.TS NGUYN XUN TRUNG

H NI - 2009


3/83

Li cm n

Bng tm lng trn trng v bit n su sc, em xin chn thnh cm n

thy PGS.TS. Nguyn Xun Trung giao ti, hng dn em tn tnh, chu

o y tm huyt trong sut qu trnh nghin cu v hon thin lun vn ny.

Em xin chn thnh cm n cc thy, c gio b mn Ho phn tch,

cng cc thy, c gio khoa Ho hc Trng HKHTN- HQGHN tn

tnh gip , ng vin v to iu kin thun li cho em hon thnh lun vn

ny.

Em xin cm n Ban gim hiu Trng Cao ng Cng nghip Ho cht,

cc bn ng nghip, ngi thn lun c v, ng vin gip em trong sut

qu trnh hc tp v thc hin lun vn.

H Ni, ngy 18 thng 11 nm 2009

Hc vin: m Th Thanh Thu


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MC LC

M U ....................................................................................1CH NG 1: T NG QUAN ..........................................................2

1.1. Vai tr c a n c s ch v tnh tr ng nhi m n c .......21.1.1. Cc ngu n n c trn tri t [3] ............................21.1.2. Vai tr c a n c [3] ................................................21.1.3. S phn b n c ...................................................3

1.1.3.1 S phn b n c trn Th gi i ............................31.1.3.2 Ti nguyn n c Vi t Nam ...............................3

1.1.4 S nhi m ngu n n c ...........................................41.2 Gi i thi u chung v Cadimi v Ch [15] ...........................4Trong b ng h th ng tu n hon cc nguyn t ho h c, nguyn t Cadimi (Cd) n m s 48, thu c nhm IIB, chu k V. Nguyn t Cd c cc obitan d i n 10 electron. C u hnh electron c a Cadimi (Z=48): [Kr]4d5s. ..................4Nguyn t Ch c s th t 82, thu c nhm IVA, chu k VI. C u hnh electron c a Ch (Z = 82): [Xe]4f145d106s26p2. . .4

1.2.1. Tnh ch t l, ha c a Cadimi v Ch .........................51.2.1.1. Tnh ch t v t l .................................................51.2.1.2. Tnh ch t ho h c ..............................................5

1.2.2. Cc h p ch t chnh c a Cadimi v Ch .....................61.2.2.1. Cc oxit..............................................................61.2.2.2. Cc hydroxit.......................................................71.2.2.3. Cc mu i c tr ng ...........................................81.2.2.4 c tnh c a Cd v Pb [19] ...............................8

1.3. Cc ph ng php xc nh Cadimi v Ch .................91.3.1.2. Ph ng php phn tch th tch .......................11

1.3.2. Cc ph ng php phn tch cng c ....................121.3.2.1. Cc ph ng php i n ho [16] .....................121.3.2.2. Cc ph ng php quang ph .........................13

1.4. M t s ph ng php tch v lm giu l ng v t ion kim lo i n ng .......................................................................18

1.4.1 Ph ng php c ng k t [1] .......................................181.4.2. Ph ng php chi t l ng- l ng [1,27] .....................191.4.3. Ph ng php chi t pha r n (SPE) .........................20

1.4.3.1. nh ngh a v chi t pha r n ..........................201.4.3.2. Cc c ch chi t pha r n [21] .........................201.4.3.3. Cc k thu t trong SPE ...................................22

CH NG 2: HA CH T V D NG C .....................................26

2.1. D ng c v my mc ..................................................262.2. Ha ch t s d ng. .......................................................26

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2.3. Chu n b c t chi t pha r n ...........................................27CH NG 3: K T QU TH C NGHI M V TH O LU N .............29

3.1. Kh o st cc i u ki n t i u c a php o ph F-AAS 293.1.1. Kh o st cc i u ki n o ph : .............................29

3.1.1.1. Ch n v ch o ..................................................293.1.1.2. Khe o.............................................................303.1.1.3. C ng n catot r ng (n HCL) ...............30

3.1.2. Kh o st cc i u ki n nguyn t ha m u ..........303.1.2.1. Chi u cao n nguyn t ha ........................303.1.2.2 Kh o st thnh ph n kh chy ..........................31

3.1.3 Kh o st cc y u t nh h ng khc .....................323.1.3.1 nh h ng c a n ng axit v lo i axit trong dung d ch m u ..............................................................33

3.1.3.2 nh h ng c a n n mu i ..................................343.1.3.3. nh h ng c a cc ion c trong m u ..............36

3.1.4 nh gi chung v phng php ph F-AAS............413.1.4.1 Khong tuyn tnh ca Pb, Cd v phng trnhng chun..................................................................413.1.4.2. Gi i h n pht hi n, gi i h n nh l ng c a ph ng php F-AAS xc nh Pb v Cd. .......................453.1.4.3 Sai s v l p l i c a php o .......................47

3.2 Kh o st cc i u ki n lm giu v tch chi t b ng pha

r n XAD7 .............................................................................493.2.1 Kh o st nh h ng c a pH ....................................503.2.2 Kh o st nh h ng c a th tch thu c th ............523.2.3 Kh o st t l Cd 2+/Pb2+ trong h n h p .............533.2.4 Kh o st t c n p m u ......................................543.2.5 Kh o st kh n ng r a gi i .................................553.2.6 Kh o st nh h ng c a t c r a gi i .................573.2.7 nh h ng c a th tch m u th ............................583.2.8 nh h ng c a m t s ion n kh n ng h p thu

c a Pb2+, Cd 2+ ..............................................................593.2.8.1 nh h ng c a nhm kim lo i ki m v kim lo i ki m th ........................................................................593.2.8.2 nh h ng c a m t s kim lo i n ng nhm II . .603.2.8.3 nh h ng c a m t s kim lo i n ng nhm III . 633.2.8.4 nh h ng c a m t s anion ............................653.2.8.5 nh h ng c a t ng Cation v Anion ..............66

3.3 Phn tch m u gi .........................................................673.4 Phn tch m u th c .......................................................68

K T LU N ................................................................................71TI LI U THAM KH O ..............................................................73

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M U

Nc l ngun ti nguyn thin nhin qu gi, l yu t khng th thiu

cho s sng, u c nc c s sng. Tuy nhin, cng vi s pht trinca s sng, qu trnh th ha, cng nghip ha, v thm canh nng nghip

ngy cng pht trin c nhiu nh hng xu n ngun ti nguyn ny.

Nhiu ni, cc ngun nc b mt, thm ch c ngun nc ngm b

nhim nghim trng, gy nh hng xu ti cht lng ca nc, v nh

hng n sc khe ca con ngi v ng vt, lm gim nng sut v cht

lng cy trng. Mt trong nhng cht c tc dng gy nhim l cc kimloi nng ( Pb, Cd, Hg, As). Mt s trong chng khi c nng va phi

th khng c nh hng xu ti ngi v vt nui, thm ch cn c tc dng

tt. Tuy nhin, khi nng cao chng li tr thnh nhng cht nhim c

mnh gy ra mt s tc ng xu cho ngi, vt nui v c bit Pb, Cd l

mt trong nhng tc nhn gy bnh ung th.

Do vy, xc nh lng vt cc kim loi nng l mt trong nhng vn thi s ca ha hc phn tch, nhm p ng nhu cu pht trin kinh k,

khoa hc k thut v bo v mi trng.

Hm lng Ch v Cadimi trong nc l rt nh phn tch c th

trc ht cn phi lm giu.

V vy, mc ch chnh ca ti ny l tch, lm giu, xc nh lng

vt Ch v Cadimi c trong nc ngm bng k thut chit pha rn v phngphp quang ph hp th nguyn t k thut ngn la (F-AAS).

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CHNG 1: TNG QUAN

1.1. Vai tr ca nc sch v tnh trng nhim nc

1.1.1. Cc ngun nc trn tri t [3]

Tri t c khong 361 triu Km2 din tch cc i dng (chim71%

din tch b mt Tri t). Tr lng ti nguyn nc c khong 1,5 t Km3,

trong nc ni a ch chim 91 triu Km3 (chim 6,1%), cn 93,9% l

nc bin v i dng. Ti nguyn nc ngt chim 28,25 triu Km3 (chim

1,88% Thu quyn), nhng phn ln li dng ng bng hai cc Tri t.

Lng nc thc t con ngi c th s dng c l 4,2 triu Km3 (chim

0,28% Thu quyn).

1.1.2. Vai tr ca nc [3]

Nc l dung mi tt nht trong tt c cc loi dung mi, ph bin nht

trn Tri t.

Nc khng th thiu trong cuc sng ca con ngi, trong cngnghip, nng nghip, cc ngnh dc phm, thc phm, u cn n mt

khi lng nc rt ln. Vi nhng tnh cht vn c, nc thc s l ngun

nguyn liu qu khng th thiu c.

Vi din tch chim 71% din tch b mt Tri t su trung bnh

4km bin v i dng, nc c tc dng iu ho nhit Tri t. Trong

lng i dng c n 40 nghn loi c sinh sng, tng sn lng hng nmhng chc triu tn rong bin, nhng ngnh thn mm cha Protit c gi tr v

cc nguyn t vi lng c s dng rng ri lm ngun thc phm cho con

ngi. V vy nc khng nhng quan trng i vi i sng, cng nghip

m cn khng th thiu i vi s sng ca mi ng vt v thc vt trn Tri

t. Hin nay con ngi ang tm cch s dng mt cch khoa hc cc ngun

nc mt ti nguyn v gi trn Tri t, gi cho chng khi b nhim bn,

nht l nhim cc loi ho cht c hi.

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1.1.3. S phn b nc

1.1.3.1 S phn b nc trn Th gii

Tri t l mt hnh tinh nc. Tuy nhin nhn loi vn ang ngtrc nguy c thiu nc ngt do tnh trng khai thc nc ngm ba bi v

tnh trng nhim nc xy ra nghim trng.

Lng nc trn Tri t phn b khng u, chng hn sa mc

lng ma trung bnh l di 100 mm/nm, trong khi vng nhit i lng

ma c th t ti 5.000 mm/nm. V vy nhiu ni thiu nc, b hn hn.

Ngc li c nhiu vng thng xuyn b ma gy ngp lt.Lng nc ngt con ngi s dng ban u thng c ngun gc t

nc ma. Nc ngt dng cho sinh hot chim 8%, cho cng nghip chim

23% v cho hot ng nng nghip l 63% [6].

Tiu dng nc ngt trn phm vi ton cu tng gp 6 ln trong giai

on 1990- 1995, ln gp 2 ln t l tng dn s. C khong 1/3 dn s trn

th gii ang sng trong nhng vng thiu nc, ni m nhu cu s dngnc cao hn 10% ngun nc c th ti to c.

Trnh trng suy gim ngun nc ngt trn th gii c v cht v lng

ang l mt vn ni cm v mi trng v s pht trin trong th k ti,

khong 20% dn s th gii s khng c nc sch ung, khong 50% dn

s khng iu kin v sinh.

1.1.3.2 Ti nguyn nc Vit Nam

Vit Nam l nc nhit i gi ma nn c ti nguyn nc di do so

vi cc nc trn th gii, lng ma trung bnh tng i cao, khong 2000

mm/nm gp 2,6 ln lng ma trung bnh ca cc vng lc a trn Th gii.

Hng nm, lnh th Vit Nam nhn thm lu lng nc t nam Trung

Quc v Lo vi s lng khong 550 km3. Dng chy trung bnh Vit Nam

gp 3 ln dng chy trung bnh trn Th gii .

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Ngun ti nguyn nc ca Vit Nam tng i phong ph, nhng

phn b khng u v tri rng rt phc tp theo thi gian, nht l cc mch

nc ngm. T lu, cc mch nc ngm c khai thc bng cc phng

php khc nhau. Theo nh gi ca tc gi [9] tng tr lng nc mch

thin nhin trn ton lnh th khong xp x 15% tng tr lng nc mt.

1.1.4 S nhim ngun nc

S nhim mi trng nc l s thay i thnh phn v tnh cht ca

nc gy nh hng ti hot ng sng bnh thng ca con ngi, sinh vt,

n sn xut cng nghip, nng nghip, thu sn.Ngun gc gy nhim ngun nc l do t nhin v nhn to:

- S nhim c ngun gc t nhin l do ma, tuyt tan, l lt, gi

bo, hoc do cc sn phm hot ng sng ca sinh vt, k c xc cht ca

chng.

- S nhim nhn to ch yu do ngun nc thi t cc vng dn c,

khu cng nghip, hot ng giao thng vn ti, do s dng thuc tr su, ditc v phn bn trong nng nghip.

1.2 Gii thiu chung v Cadimi v Ch [15]

Trong bng h thng tun hon cc nguyn t ho hc, nguyn t

Cadimi (Cd) nm s 48, thuc nhm IIB, chu k V. Nguyn t Cd c cc

obitan d in 10 electron. Cu hnh electron ca Cadimi (Z=48):

[Kr]4d10 5s 2 .

Nguyn t Ch c s th t 82, thuc nhm IVA, chu k VI. Cu hnh

electron ca Ch (Z = 82): [Xe]4f145d106s26p2.

Trong thin nhin, Cd tn ti dng bn vng l Cd(II). Tr lng ca

Cadimi trong v Tri t l 7,6.10-6 % tng s nguyn t (tng ng). Khong vt

chnh ca Cadimi l grenokit (CdS ), khong vt ny him khi tn ti ring m

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thng ln vi khong vt ca Km, v ca Thu ngn l xinaba hay thn sa

(HgS).

Ch trong t nhin chim khong 0,0016% khi lng v Tri t, phn

b trong 170 khong vt khc nhau nhng quan trng nht l galena (PbS),

anglesite (PbSO4) v cerussite (PbCO3), hm lng Ch trong cc khong ln

lt l 88%, 68% v 77%.

1.2.1. Tnh cht l, ha ca Cadimi v Ch

1.2.1.1. Tnh cht vt l

Cadimi l kim loi mu trng bc, mm, d ko, d rn. Ch kim loi c

mu xm xanh, mm, b mt Ch thng m c do b oxi ha.

Bng 1: Mt s hng s vt l quan trng ca Cadimi v Ch

Hng s vt l Cd Pb

Khi lng nguyn t

Nhit nng chy

Nhit si

T khi (250C)

dn in (250C)

Bn knh nguyn t

(vC)

(0C)

(0C)

(kg.m-3)

(Ohm-1.m-1)

( oA )

112,411

321

767

8,36

1,3.106

1,56

207,21

327,4

1737

11,34

4,84.106

1,74

1.2.1.2. Tnh cht ho hc

Cadimi l nguyn t tng i hot ng. Trong khng kh m, Cd bn nhit thng nh c mng oxit bo v. Nhng nhit cao, n chy

mnh lit vi ngn la mu sm:

Cd + O2 = CdO

iu kin thng, Ch b oxi ha bi oxi khng kh to thnh lp oxit

bn, mng bao ph bn ngoi kim loi.

2Pb + O2 = 2PbO

to

5
http://openimg%28%27../bitmaps/minerais/c/c0017.gif',%20'galena',%20200,%20133)http://openimg%28%27../bitmaps/minerais/m/m0008.gif',%20'anglesite',%20200,%20111)http://openimg%28%27../bitmaps/minerais/k/k0030.gif',%20'cerussite',%20164,%20170)http://openimg%28%27../bitmaps/minerais/m/m0008.gif',%20'anglesite',%20200,%20111)http://openimg%28%27../bitmaps/minerais/k/k0030.gif',%20'cerussite',%20164,%20170)http://openimg%28%27../bitmaps/minerais/c/c0017.gif',%20'galena',%20200,%20133)


12/83

Khi nhit cao, chng phn ng c vi cc phi kim nh Lu

hunh, Halogen (X2)...

Pb + X2 = PbX2

Cd + S = CdS

Cd tc dng d dng vi axit khng phi l cht oxi ho, gii phng kh

Hiro.

Cd + HCl = CdCl2 + H2

Vi dung dch: Cd + 2H3O+ + H2O = [Cd(H2O)2]2+ + H2

Ch ch tng tc trn b mt vi dung dch H 2SO4 di 80% v HCl

long do b bao ph bi lp mui kh tan (PbCl2, PbSO4). Nhng n tan c

trong dung dch c hn ca cc axit (do lp mui bao bc tan ra) v trong

axit HNO3 ti mi nng .

PbCl2 + 2HCl = H2[PbCl4]

PbSO4 + H2SO4(n) = Pb(HSO4)2

3Pb + 8HNO3 = 3Pb(NO3)2 + 2NO+ 4H2O

Ch cn c kh nng phn ng vi dung dch kim (KOH, NaOH) c,

nng gii phng Hidro.

Pb + 2KOH + 2H2O = K2[Pb(OH)4] + H2

1.2.2. Cc hp cht chnh ca Cadimi v Ch

1.2.2.1. Cc oxit

Oxit quan trng ca Cadimi l CdO, n c mu t vng n nu gn

nh en tu thuc vo qu trnh ch ho nhit, nng chy 18130C, c th

thng hoa khng phn hu khi un nng.

CdO khng tan trong nc, tan trong axit v kim nng chy:

CdO + 2KOH(nc) = K2CdO2 + H2O

(Kali cadimiat)

to

to

to

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13/83

CdO c th iu ch bng cch t chy kim loi trong khng kh hoc

nhit phn hiroxit hay cc mui cacbonat, nitrat:

2Cd + O2 = 2CdO

Cd(OH)2 = CdO + H2O

Ch c hai oxit l PbO v PbO2, tng ng vi cc s oxi ha +2, +4.

PbO tan t trong nc, khi nung nng trong khng kh b oxi ha thnh

Pb3O4.

PbO2 mu nu en, khi nung nng mt dn oxi chuyn thnh cc oxit

khc, ng thi chuyn mu dn sang vng. PbO2 l oxit lng tnh, khngtan trong nc, tan trong kim d hn trong axit.

PbO2 + 2KOH + 2H2O = K2[Pb(OH)6]

PbO2 l mt trong nhng cht oxi ha mnh, n c th oxi ha Mn(II)

thnh Mn(VII) trong mi trng axit, oxi ha Cr(III) ln Cr(VI) trong mi

trng kim, do vy n c dng lm cquy Ch.

1.2.2.2. Cc hydroxit

Hydroxit ca Cadimi Cd(OH)2 l kt ta nhy t tan trong nc v c

mu trng, tnh lng tnh th hin khng r rng, tan trong dung dch axit,

khng tan trong dung dch kim m ch tan trong kim nng chy.

Tan trong dung dch NH3 to thnh hp cht phc

Cd(OH)2 + 4NH3 = [Cd(NH3)4](OH)2

Pb(OH)2 th hin tnh lng tnh, tan c trong c axit v kim.

C hai hydroxit trn u khng tan trong nc, chng d mt nc khi

nung nng tr thnh oxit.

Me(OH)2MeO + H2O to

to

to

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14/83

Ch(IV) hydroxit kt ta nhy, mu xm nu, khng tn ti dng

Pb(OH)4 m dng PbO2.xH2O vi thnh phn bin i. N l hydroxit lng

tnh nhng tnh axit mnh hn tnh baz.

1.2.2.3. Cc mui c trng

Cc mui Halogenua (tr Florua), nitrat, sunfat, peclorat v axetat ca

Cd(II) u d tan trong nc cn cc mui sunfua, cacbonat, hay

orthophotphat v mui baz u t tan.

Trong dung dch nc cc mui Cd 2+ b thu phn:

Cd2+ + 2H2O = Cd(OH)2 + 2H+

Cd2+ c kh nng to nhiu hp cht phc, cc phc thng gp l:

[CdX4]2+ (X = Cl-, Br-,I- v CN-); [Cd(NH3)4]2+ ; [Cd(NH3)6]2+...

Cc ihalogenua ca Cd l cht dng tinh th mu trng, c nhit

nng chy v nhit si kh cao.

Cc mui Pb(II) thng l tinh th c cu trc phc tp, khng tan

trong nc, tr Pb(NO3)2, Pb(CH3COO)2, PbSiF6.

Cc mui ca Pb(II) nh Pb(NO3)2, PbCl2 u bn v c vi con

ngi v ng vt.

1.2.2.4 c tnh ca Cd v Pb [19]

Cadimi l mt nguyn t rt c i vi mi trng sng cng nh i

vi con ngi. i vi cc ng, thc vt sng di nc, tnh c hi caCadimi ngang vi c tnh ca Ni v Cr(III)...v c phn km c hn so vi

Hg(CH3)2 v Cu. Tt nhin iu ny cn ph thuc vo tng loi, tng iu

kin ca s nh hng ca Cd. hm lng 0,02-1 mg/l Cd s km hm qu

trnh quang hp v pht trin ca thc vt. Hm lng cho php ca Cd trong

nc l 1 g/l.

i vi con ngi, Cd c th xm nhp vo c th bng nhiu cchkhc nhau, v d nh tip xc vi bi Cd, n ung cc ngun c s nhim

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15/83

Cd...Cd thng c tch lu dn trong thn, gy triu chng c mn tnh.

Nu lu c th gy mt chc nng thn v s mt cn bng cc thnh phn

khong trong xng, ph hu xng, gy thiu mu, gy ung th. Liu lng

30 mg cng dn n t vong. Cng c nhiu gi thit cho rng Cd c th

thay th Zn trong c th lm gim kh nng sn sinh t bo.

Cc hp cht ca Ch u c i vi ng vt. Mc d, Ch khng gy

hi nhiu cho thc vt nhng lng Ch tch t trong cy trng s chuyn qua

ng vt qua ng tiu ha. Do vy, Ch khng c s dng lm thuc tr

su. Ch kim loi v mui sunphua ca n c coi nh khng gy c do

chng khng b c th hp th. Tuy nhin, cc mui Ch tan trong nc nh

PbCl2, Pb(NO3)2, Pb(CH3COO)2 rt c. Khi xm nhp vo c th ng vt,

Ch gy ri lon tng hp hemoglobin, gim thi gian sng ca hng cu,

thay i hnh dng t bo, x va ng mch, lm con ngui b ngu n, mt

cm gic... Khi b ng c Ch s c triu chng au bng, tiu chy, n

khng ngon ming, bun nn v co c.

Di y l mt vi s liu c nu t tiu chun Vit Nam:

Bng 2: Gii hn cho php cc kim loi Cd v Pb

theo tiu chun Vit Nam[20]

Gii hn cho phpCd Pb

A B A B

Nc cp sinh hot 0,005(mg/l) 0,05(mg/l)

Nc b mt 0,01(mg/l) 0,02(mg/l) 0,05(mg/l) 0,1(mg/l)

Nc ngm 0,01(mg/l) 0,05(mg/l)

Nc thi cng nghip 0,01(mg/l) 0,02(mg/l) 0,1(mg/l) 0,5(mg/l)

A: Nc mt c th dng lm nc cp sinh hot

B: Nc dng cho cc mc ch khc

1.3. Cc phng php xc nh Cadimi v Ch

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16/83

Hin nay, c rt nhiu phng php khc nhau xc nh Cadimi v

Ch nh phng php phn tch khi lng, phn tch th tch, in ho, ph

phn t UV-VIS, ph pht x nguyn t (AES), ph hp th nguyn t ngn

la v khng ngn la (F-AAS, ETA-AAS)... Sau y l mt s phng php

xc nh Cadimi v Ch.

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1.3.1. Cc phng php ho hc[1]

1.3.1.1. Phng php phn tch khi lng

Phng php phn tch khi lng l phng php c in, chnh

xc c th t ti 0,1%. C s ca phng php l s kt ta nh lng ca

cht phn tch vi mt thuc th thch hp.

Cadimi thng c kt ta di cc dng CdS, CdSO4, CdNH4PO4,

sau kt ta c lc, ra, sy (hoc nung) em cn.

Ch thng c kt ta di dng PbSO4, sau c sy 700oC

a kt ta v dng cn (PbSO4) ri em cn xc nh khi lng.

Phng php ny khng i dng c t tin nhng qu trnh phn tch

lu, nhiu giai on phc tp c bit khi phn tch lng vt cc cht. V

vy, phng php ny khng c dng ph bin trong thc t xc nh

lng vt cc cht m ch dng trong phn tch hm lng ln.

1.3.1.2. Phng php phn tch th tch

Phn tch th tch l phng php phn tch nh lng da trn th tch

dung dch chun ( bit chnh xc nng ) cn dng phn ng va

vi cht cn xc nh c trong dung dch phn tch. y l phng php ha

hc dng xc nh nhanh, n gin tuy nhin khng cho php xc nh

lng vt cc nguyn t.

Vi Cadimi v Ch, ta c th dng cc php chun nh chun phc cht, chun xi ho- kh, vi cc ch th khc nhau.

Ta c th xc nh Cadimi bng EDTA mi trng pH=9-10 vi ch

th ETOO hoc mi trng pH=6 vi ch th xylendacam. Khi ch th

chuyn t mu sang vng:

H6F + Cd2+H4FCd + 2H+

H4FCd + H2Y2-CdY2- + H6F

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() (vng)

i vi Ch, ta c th chun trc tip bng EDTA hay chun

ngc bng Zn2+ hoc chun thay th vi ZnY2-, ch th ETOO.

1.3.2. Cc phng php phn tch cng c

1.3.2.1. Cc phng php in ho [16]

1.3.2.1.1. Phng php cc ph

Nguyn tc: Ngi ta thay i lin tc v tuyn tnh in p vo 2 cc

kh cc ion kim loi, do mi kim loi c th kh khc nhau. Trong

ngi ta dng in cc Hg l in cc lm vic v mt in cc c th khng

i lm in cc so snh. ng thu c l ng ph thuc cng dng

vo th p vo gi l ng Von-Ampe hay sng cc ph. Sng ny c dng

bc thang v da vo chiu cao ca sng c th nh lng c ion kim loi

cn xc nh trong dung dch. V dng gii hn Igh cc iu kin xc nh t

l thun vi nng ion trong dung dch ghi cc ph theo phng trnh:

I = k.C

Phng php ny c kh nhiu u im: N cho php xc nh c cht

v c v hu c vi nng 10-5 - 10-6 M tu thuc vo cng v lp

li ca dng d. Sai s ca phng php thng l 2-3% vi nng 10-3 -

10-4 M, l 5% vi nng 10-5 M ( iu kin nhit khng i).

Tuy nhin, phng php ny cng c nhng hn ch nh nh hng

ca dng t in, dng cc i, ca xi ha tan, b mt in cc...

loi tr cc nh hng v lm tng nhy th hin nay c cc

phng php cc ph hin i: cc ph xung vi phn (DDP), cc ph sng

vung (SQWP)... chng cho php xc nh nhiu lng vt cc nguyn t.

Cc tc gi T Vn Mc, Trn Th Su s dng phng php cc ph

xung vi phn xoay chiu xc nh lng vt cc kim loi Cd, Cu, Pb trong bia

khu vc H Ni cho nhy cao ti 1ppb[14].

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1.3.2.1.2. Phng php Von-Ampe ho tan

V bn cht, phng php Von-Ampe ho tan cng ging nh phngphp cc ph l u da trn ln ca cng dng xc nh nng

cc cht trong dung dch. Nguyn tc gm 2 bc:

- in phn lm giu cht cn phn tch ln trn b mt in cc lm

vic trong mt khong thi gian v th in cc xc nh.

- Ho tan kt ta c lm giu bng cch phn cc ngc, o v

ghi dng ho tan t in cc ch th.

Cc tc gi L Lan Anh, V c Lidng phng php Von-Ampe

ho tan trn in cc mng Hg, git Hg treo xc dnh hm lng Pb trong

tc, trong nc tiu ca ngi nhm chun on lm sng[2].

1.3.2.2. Cc phng php quang ph

1.3.2.2.1. Phng php ph hp th phn t (UV-VIS) [7]

iu kin bnh thng cc phn t, nhm phn t ca cc cht bn

vng v ngho nng lng gi l trng thi c bn. Khi c mt chm sng vi

nng lng ph hp chiu vo th cc in t ho tr trong cc lin kt ( , ,

n) s hp th nng lng chm sng, chuyn nn trng thi kch thch vi

nng lng cao hn. S hp th ny l ngun gc sinh ra ph hp th.

Nguyn tc: phng php xc dnh da trn vic o hp th nhsng ca dung dch phc c mu to bi ion cn xc nh vi mt thuc th

v c hay hu c trong mi trng thch hp khi chiu bi chm sng. Trong

khong nng cht phn tch nht nh th hp th quang t l thun vi

nng cht phn tch, y l c s nh lng cht phn tch:

A = k.C

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Phng php ny xc nh nng cht khong 10-7 M n 10-5 M v

l phng php s dng kh ph bin.

V d: Xc nh Cd v Pb bng cch chuyn n v dng Cadimi-

dithizonat v Ch-dithizonat trong mi trng pH 5-6:

Cd2+ + 2H2Dz (xanh) = Cd(HDz)2 () + 2H+

Pb2+ + 2H2Dz (xanh) = Pb(HDz)2 () + 2H+

Sau , chit phc ny vo dung mi hu c CCl4 hoc CHCl3 ri em

o hp th quang ca n ti = 515 nm i phc ca Cd v 510 nm i phc

ca Pb. Gii hn ca phng php ny i vi Pb l 0,05 ppm, vi Cd l0,01ppm.

Phng php trc quang n gin, tin li, nhy tng i cao nn

c s dng ph bin xc nh cc kim loi c hm lng nh. Tuy

nhin, nhc im ca phng php ny l khng chn lc, mt thuc th c

th to phc vi nhiu ion.

Bng phng php trc quang, cc tc gi Trn Thc Bnh, Trn THiu, Phm Lun xc nh Cu, Ni, Mn, Zn... trong cng mt hn hp theo

Phng php Vierod ci tin bng Pyridin-azo-naphtol(PAN) vi sai s < 4%

nhng bc sng khc nhau.[4]

1.3.2.2.2. Phng php ph pht x nguyn t (AES) [10]

Khi iu kin thng, nguyn t khng thu v pht nng lng

nhng nu b kch thch cc in t ho tr s nhn nng lng chuyn nn

trng thi c nng lng cao hn. Trng thi ny khng bn, chng c xu

hng gii phng nng lng tr v trng thi ban u bn vng di dng

cc bc x. Chnh bc x ny gi l ph pht x nguyn t.

Tc gi Phm Lun ng dng phng php ny a ra quy trnh

xc nh mt s kim loi trong cc mu nc ngt vi mt s kt qu nh

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sau: Gii hn pht hin ca Na l 0,05ppm, K v Li l 0,5ppm v Pb l

0,1ppm.[11]

Hin nay, ngi ta dng mt s ngun nng lng kch thch ph

AES: ngn la n kh, h quang in, tia la in...c bit ngun kch thch

plasma cao tn cm ng (ICP), tia laze c nhy cao c ng/ml.

Ln u tin, cc tc gi V Hong Minh, Nguyn Tin Lng, Phm

Lun, Trn T Hiu p dng thnh cng phng php ph ICP-AES

xc nh chnh xc cc nguyn t t him trong mu a cht Vit Nam.[13]

Nhn chung phng php AES c nhy kh cao, li tn t mu, cth phn tch ng thi nhiu nguyn t trong cng mt mu. V vy y l

phng php dng kim tra nh gi ho cht, nguyn liu tinh khit, phn

tch lng vt ion kim loi c hi trong lng thc, thc phm. Tuy nhin

phng php ny ch cho bit hm lng tng kim loi, cn khng cho bit

trng thi lin kt ca n trong mu, mt khc chnh xc ph thuc rt

nhiu vo chnh xc dy chun nn sai s l khng nh.

1.3.2.2.3. Phng php ph hp th nguyn t (AAS) [10]

* S xut hin ca ph AAS:

iu kin thng, nguyn t khng thu hay pht nng lng v gi l

trng thi c bn (ngho nng lng, bn vng). Nhng khi trng thi hi t

do, nu ta kch thch chng bng mt nng lng di dng chm tia sng c

bc sng xc nh th cc nguyn t s hp th bc x c bc sng ng

ng vi tia bc x m chng c th pht ra trong qu trnh pht x. Khi

nguyn t chuyn ln trng thi c nng lng cao (trng thi kch thch). Qu

trnh m cc nguyn t t do trng thi hi hp th nhng bc x c trng to

ra ph nguyn t nguyn t , ph ny c gi l ph hp th nguyn t AAS.

*Nguyn tc:

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Php o da trn s hp th nng lng ca nguyn t t do trng

thi hi khi chiu chm tia bc x qua m hi ca nguyn t trong mi

trng hp th. tin hnh o th phi qua cc qu trnh sau:

- Qu trnh ho hi v nguyn t ho mu: chn cc iu kin v loi

trang b ph hp chuyn mu phn tch t trng thi ban u (rn, dung

dch) thnh trng thi hi ca nguyn t t do.

- Chiu chm sng bc x c trng ca nguyn t cn phn tch qua

m hi va iu ch trn. Khi , cc nguyn t trong m hi s hp th

tia bc x v to ra ph AAS.

- Thu phn ly chm sng v chn mt vch ph hp th ca nguyn t

phn tch o cng thng qua mt h thng my quang ph.

Phng trnh nh lng ca phng php l:

D = K * Cb

D: Cng vch ph

K: H s nguyn t ho mu

C: Nng nguyn t cn phn tch

b: Hng s bn cht, ph thuc vo bn cht ca cht phn tch

Cng vch ph c th c nh gi thng qua chiu cao pic, din

tch pic hay hp th..Trong khong nng nh, b=1. Khi , s ph

thuc ca cng vch ph vo nng nguyn t phn tch c dng tuyn

tnh, v thng qua ta c th nh lng cht phn tch mt cch d dng.

Trong php o ph AAS c hai k thut chnh l: k thut nguyn t

ho bng ngn la (F-AAS) v k thut khng ngn la (ETA-AAS). K

thut ETA-AAS cho nhy rt cao, ng thi gii hn pht hin ca cc

nguyn t khi s dng phng php ny rt nh. Tuy nhin thc hin th

i hi trang thit b t tin, gi thnh cao nn trong nghin cu ny chng

ti la chn k thut F-AAS.

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Vi k thut F-AAS tc gi [38] xy dng mt quy trnh hon chnh

xc nh cc kim loi nng: Cu, Fe, Pb, Cd, Co, Nitrong cc mu sa v

soda vi hiu sut 95%. Cn tc gi [37] li xc nh lng vt cc kim loi

nng trong nc sau khi sau khi lm giu vi lch chun tng i nm

trong khong 0,8 2,9%, gii hn pht hin t 0,006 0,277 ppm.

Cng nh phng php AES, phng php AAS cho nhy v

chn lc cao ( gn 60 nguyn t ho hc c th xc nh vi nhy 10 -4-10-5

%, nu s dng k thut ETA-AAS th c th t n.10 -7%). Hn na, php o

tn t nguyn liu, t thi gian, li khng cn s dng ho cht tinh khit cao,

c th xc nh ng thi hay lin tip nhiu nguyn t trong mt mu. Kt

qu phn tch n nh, sai s nh nn c s dng ph bin xc nh cc

nguyn t trong mu qung, t, , nc khong, mu y hc, sinh hc. Ngoi

ra nhiu nc trn th gii, phng php AAS tr thnh phng php tiu

chun nh lng nhiu kim loi. Tuy nhin phng php phn tch ny

cng ch cho ta bit thnh phn nguyn t ca cht trong mu phn tch m

khng ch ra trng thi lin kt ca nguyn t trong mu.

Vi nhng u im ni bt v ng dng rng ri ca php o AAS (c

th l F-AAS), chng ti quyt nh s dng php o ph F-AAS xc nh

lng vt mt s ion kim loi nng Pb2+, Cd2+ trong nghin cu ny.

1.3.2.2.4 Phng php khi ph plasma cao tn cm ng ICP- MS

Khi dn mu phn tch vo ngn la plasma (ICP), trong iu kinnhit cao ca plasma, cc cht c trong mu khi s b ho hi, nguyn

t ho v ion ho to thnh ion dng c in tch +1 v cc electron t do.

Thu v dn dng ion vo thit b phn gii ph phn chia chng theo s

khi (m/z) s to ra ph khi ca nguyn t cht cn phn tch. Sau , nh

gi nh tnh v nh lng ph thu c.

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K thut phn tch ICP-MS l mt trong nhng k thut phn tch hin

i. K thut ny c nghin cu v pht trin rt mnh trong nhng nm

gn y. Vi nhiu u im vt tri ca n, k thut ny c ng dng rt

rng ri trong phn tch rt nhiu i tng khc nhau c bit l trong cc

lnh vc phn tch vt v siu vt phc v nghin cu sn xut vt liu bn

dn, vt liu ht nhn, nghin cu a cht v mi trng...

1.4. Mt s phng php tch v lm giu lng vt ion kim loi nng

Trong thc t phn tch, hm lng cc cht trong mu, c bit l hm

lng cc ion kim loi nng thng rt nh, nm di gii hn pht hin cacc cng c phn tch. V vy, trc khi xc nh chng cn phi tch v lm

giu.

tch v lm giu cc kim loi nng trong nc thng dng mt s

phng php di y:

1.4.1 Phng php cng kt [1]

Cng kt l phng php kt ta cht cn phn tch bng cch a

thm nhng cht kt ta ng hnh, thng gi l cht gp, vo i tng

phn tch cng kt cc nguyn t khi hm lng ca chng rt nh. Nh

vy m cht phn tch s c thu gp li. Khi hm lng ca n tng

ln rt nhiu. Ngi ta c th chn mt s hyroxyt kh tan nh: Fe(OH)3;

Al(OH)3hoc mt s sunfua hay mt s cht hu c lm cht gp.

Khi s dng cht hu c cng kt, c th kt ta c nhng lng

vt ti 10-3- 10-5%. Vic dng cht hu c kt ta c u im hn so vi cht

v c v kt ta d lc ra. Bng cch thay i pH ca dung dch c th tin

hnh kt ta ln lt v tch c nhiu cation kim loi khc nhau vi cng

mt cht kt ta hu c. Hn na, phn t hu c d dng b phn hu khi

nung kt ta, t thu c nguyn t cn xc nh trng thi lm giu,

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tinh khit. Mt khc, cht gp hu c cn c kh nng cng kt c lng

vt nguyn t khi c mt lng ln nguyn t khc.

Tomoharu Minami v cng s [40] tin hnh xc nh lng vt ion

kim loi Co2+; Ni2+ trong nc sng bng php o ph hp th nguyn t sau

khi lm giu chng nh cng kt ln Scandi hydroxyt ( Sc(OH)3 ) pH= 8-

10

Cc tc gi [29] tin hnh cng kt vi lng cc ion kim loi: Cu 2+;

Pb2+; Cd2+; Co2+; Ni2+; Mn2+ trong nc ln Bimut(III)ietylithiocacbarmat

pH= 9, sau xc nh bng phng php ph F-AAS.

Phng php cng kt c u im: n gin, hiu qu cao, nn mu

phn tch c chuyn t phc tp sang n gin hn. Tuy nhin nhc im

chnh ca phng php l mt nhiu thi gian, nn phng php ny t c

s dng.

1.4.2. Phng php chit lng- lng [1,27]

* Nguyn tc:

Phng php da trn s phn b cht tan khi c to thnh dng

phc lin hp hay ion phc vng cng khng mang in tch gia hai pha

khng trn ln, thng l cc dung mi hu c v nc.

Tch v lm giu cht bng phng php chit lng- lng c nhiu u

im hn so vi mt s phng php lm giu khc v s kt hp gia

phng php chit vi cc phng php xc nh tip theo (trc quang, cc

ph..) c ngha rt ln trong phn tch.

* Mt s h chit thng dng trong tch, lm giu Pb, Cd:

- H chit Pb, Cd- dithizonat trong CCl4 hoc CHCl3, sau xc nh

chng bng phng php ph hp th phn t (UV-VIS).

- C th chit phc halogenua hoc thioxianat Cadimi bng cc dung

mi hu c: xiclohexano, metyl isobutyl xeton (MIBK), dietyl ete

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- To phc chelat vi NaDDC (natridietyldithiocacbamat) t dung dch

m amoni xitrat pH= 9,5 dung mi chit l MIBK.

1.4.3. Phng php chit pha rn (SPE)1.4.3.1. nh ngha v chit pha rn

Chit pha rn (SPE) (Solid- Phase Extraction) l qu trnh phn b cht

tan gia hai pha lng- rn. Pha rn c th l cc ht silicagen xp, cc polime

hu c hoc cc loi nha trao i trao i ion hay than hot tnh. Qu trnh

chit c th thc hin iu kin tnh hay ng. Cc cht b gi li trn pha

rn c th c tch ra bng cch ra gii vi dung mi thch hp. Thngthng th tch cn thit ra gii hon ton cht phn tch lun nh hn rt

nhiu so vi th tch ca dung dch mu ban u, v th c h s lm giu cao.

1.4.3.2. Cc c ch chit pha rn [21]

V c bn, c ch chit SPE ging vi c ch tch trong phng php

sc k lng hiu nng cao (HPLC) bao gm 3 c ch chnh, l: c ch hp

ph pha thng, c ch hp ph pha o v c ch trao i ion. Tuy nhin

SPE khc vi HPLC l: trong HPLC s tch cht phn tch ra khi nhau trong

h dng chy lin tc ca pha ng, cn SPE gi cht phn tch li trn pha

rn sau ra gii cht phn tch ra khi pha rn vi dung mi ph hp. Cc

cht phn tch s c tch khi dung dch ban u vi nng m c hn

v tinh khit hn.

* C ch hp th pha thng ( normal phase) [21]

L s hp thu cc cht phn tch t dung mi khng phn cc ln b

mt phn cc ca pha rn. C ch ca qu trnh tch da trn lc tng tc

phn cc nh: cc lin kt hydro, cc tng tc phn cc - , tng tc

lng cc hay tng tc lng cc- lng cc cm ng. C ch ny lin quan

n s hp thu cc nhm chc ca cht tan ln cc v tr phn cc ca pha

tnh chng li tan ca cc cht tan trong pha ng.

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Trong SPE pha thng, thng s dng cc loi pha tnh khng lin kt

nh: silica, alumina v mage silica, nhng ph bin nht vn l silica. Ngoi

ra cn c mt s vt liu pha lin kt cng c s dng trong SPE pha

thng nh nhm aminopropyl, cyanopropyl, propydiol.

ra gii cht phn tch ra khi cht hp thu, thng s dng dung

mi phn cc c kh nng ph v cc lin kt gia cht phn tch vi b mt

cht hp thu.

* C ch hp th pha o ( reversed- phase)

Ngc vi c ch hp th pha thng, pha tnh y l cc cht khngphn cc (nh C-18) cn pha ng l pha khng phn cc. C ch l tng

tc khng phn cc cn gi l tng tc Van Der Vaals, hiu ng phn tn

hay s phn tch.

Cc cht hp thu trong SPE pha o thng l hidrocacbon C- 8, C- 18

v mt s loi khc nh: C- 2, C- 4, cyclohexyl, nhm phenylCc cht

phn tch c tnh k nc s c khuynh hng hp thu mnh.

* C ch trao i ion:

Da vo s trao i ion ca cht tan (mang in tch) trong cc dung

mi phn cc hay khng phn cc vi cht hp thu trao i ion. C ch tng

tc ion ny c nng lng cao. V vy, cc cht tan phn cc c th hp thu

hiu qu t dung mi phn cc cng nh t dung mi khng phn cc. Trong

qu trnh hp thu s xut hin s cnh tranh trao i ion. Qu trnh ny phthuc vo chn lc ca ion hay s lng ion cnh tranh cc v tr.

Pha tnh thng l silica lin kt vi nhm chc anion hay cation. Nu

l cc cht trao i cation mnh th dng silica lin tip vi nhm sunfonic

axit, cn l cht trao i yu thng lin kt vi nhm COOH.

Vic ra gii cc cht phn tch hp thu trn pha tnh c th tin hnh

theo nhiu cch: nu l trao i cation c th dng H+

ca axit mnh hoc

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dng cc cation mnh hn (v d ra gii Na+ dng dung dch K+), nu l trao

i anion th dng OH- hoc cc anion khc.

1.4.3.3. Cc k thut trong SPE* K thut iu kin tnh: Gm 3 bc chnh

- Phn b cht tan gia hai pha rn- lng, cho mt lng pha rn vo

mt th tch xc nh dung dch mu cn phn tch, iu chnh mi trng

ph hp. Sau lc hay khuy trong mt thi gian xc nh.

- Tch hai pha rn - lng: Bng cch lc hay ly tm

- Gii hp cht phn tch ra khi pha rn

* K thut SPE iu kin ng

Vt liu pha rn (pha tnh) c np vo cc ct (c c nh hai u)

hoc vt liu c c nh trong cc mng li ri p thnh cc a mng

mng v c c nh trong cc ng nh, ct nh. Dung dch phn tch chy

qua ct lin tc v trong qu trnh cht phn tch b hp thu ln pha tnh.

* Cc bc chnh trong k thut SPE bao gm:

- Hot ha ct cht hp thu (pha rn) bng cch thng cho dung mi

thch hp chy qua ct chit thm t cc ht pha rn, hot ha cc nhm

chc, ui bt kh, ra sch pha tnh, lp y dung mi vo cc khong trng.

Sau khi hot ha, pha rn cn c ngm trong dung mi.

- Hp thu: mu phn tch chy qua ct vi tc ph hp, cht phn

tch c gi li cn cc cht khc i ra khi ct. C ch lu gi c th l lc

Van Der Waals, lin kt hydro, lng cc- lng cc, trao i ion, to phc

vng cng Mt s cht l khc cng b hp thu cng vi cht phn tch.

- Ra ct: tin hnh ra ct bng dung mi nhm loi b cc cht l b

hp thu cng vi cht phn tch.

- Ra gii: dng dung mi vi th tch ph hp ra gii cht phn

tch ra khi ct (h s lm giu cng cao th lng dung mi ra cng t).

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Dung dch ra gii phi c i lc vi cht phn tch mnh hn so vi pha tnh.

Sau , xc nh bng cc phng php la chn.

Bng 3: Gii thiu mt s vt liu pha tnh trong SPEVt liu Cu trc C ch

C- 18 -(CH2)17CH3 Pha oC- 8 -(CH2)7CH3 -C- 2 -CH2-CH3 -Xiclohexyl -(CH2)2- cyclohexyl -Phenyl -(CH2)3- phenyl -Cacbon -

Polime ng trng hp Polystyren -Polime ng trng hp Acrylic ester -Cyano -(CH2)3- CN Pha thngAmino -(CH2)3- NH2 Phathung+tr.i ionDiol -(CH2)3OCH2-CH(OH)-

CH2(OH) -Silicagel -SiOH -Florisil MgSiO3 -Cacboxylic axit -CH2- COOH Trao i ion

Aromatic sunfonic -(CH2)3- Phenyl- SO3H -

1.4.3.4. u im ca phng php chit pha rn so vi chit lng- lng

So vi chit lng- lng th SPE c u im hn:

- y l phng php tin hnh nhanh hn, thao tc n gin

- Tn t dung mi hn. c bit trong chit lng- lng cn s dng

lng ln dung mi t tin, li c hi gy nhim mi trng.- Yu cu tch n gin hn

- H s lm giu cao hn

Chit pha rn l mt k thut chit mi ra i, k thut ny c ng

dng nhiu trong phn tch lng vt, siu vt v dng tn ti cc ion kim loi

trong cc i tng khc nhau.

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Cc tc gi [37] np nha Amberlit XAD-16 vo cc ct SPE thu tinh

di 100 mm, cao 25 mm tch, lm giu cc ion kim loi trong nc h ( Cu,

Pb, Cd, Cr, Ni). Sau gii hp bng HCl 1M trong axeton. XAD-16 l sn

phm Amberlite dng Polystyren, c kh nng chu mi mn tt, c bn,

xp cao, phn cc thp v quan trng hn l n c din tch b mt ring ln

(800 m2/g) ph hp hp thu kim loi nng.

Cc tc gi [38] rt thnh cng khi s dng nha Chromosorb 102

( sn phm ng trng hp styrendivinylbenzen ) vi din tch b mt 300-

400 m2/g, kch thc ht 80- 100 mesh nhi ct thc hin tch cc kim loi

Cu, Pb, Cd, Co, Ni trong cc sn phm sa, soa ng gi.

Azeredo [23] to ct SPE vi cht mang l silica ph 8-

hydroxylquinolin tch, lm giu Cu2+, Zn2+ v sau xc nh chng bng

phng php ph nguyn t khng ngn la.

xc nh Cu trong nc cc tc gi [39] tin hnh lm giu Cu

trn ct tch np cacbon hot tnh sau khi to phc vi 1- Nitrosol-2- Naphtol

hoc Hexametylen dithiocacbamat. Ra gii Cu ra khi pha tnh bng HCl

2M trong axeton. Cn Bortolli, Gerotto, Marchiori, Mariconti, Palonta,

Tronco [25] th thc hin tch, lm giu Cd, Cu, Co.... theo phng php SPE

bng cch cho cc ion kim loi to phc vi ietylithiocacbamat ri hp thu

ln pha tnh C-18. Ra gii chng bi metanol ri xc nh theo phng php

ICP- MS v ETA-AAS.

Phng php chit pha rn c s dng khng ch tch, lm giu

cc nguyn t dng tng m cn c s dng xc nh cc trng thi

lin kt ho tr khc nhau ca cng mt nguyn t [24]. Tc gi H. Tel, Y.

Altas v M. S Taner [28] s dng ct nhi c cha TiO2 tch ring

Cr(III) v Cr(VI) ra khi nhau ri xc nh tng dng bng php o ph

nguyn t. Trong khong pH=2, Cr (VI) hp ph tt ln TiO2 (hn 99%)

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trong khi Cr (III) hu nh khng hp ph (nh hn 1%) v nh vy Cr (VI) b

gi li trn ct chit cn Cr (III) i ra khi ct.

Trong nhng nm gn y, chit pha rn l mt k thut c ng

dng ph bin nhiu phng th nghim. Mt khc nh nh cng ngh hin

i, vic bin tnh cc vt liu hp thu c in tng hp ra nhiu pha rn c

cc tnh nng u vit, lm cho phng php chit pha rn ngy cng hiu qu

hn.

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CHNG 2: HA CHT V DNG C

2.1. Dng c v my mc

Dng c v my mc s dng bao gm:

- My o pH 211 HANNA

- My quang ph hp th nguyn t AA-400

- Cn phn tch, cn k thut

- My nc ct 2 ln

- Bp in, t ht, t sy- Cc ct nha SPE

- Pipet cc loi: 0,1; 0,2; 0,5; 1; 2; 5; 10 ml

- Cc thy tinh chu nhit loi: 100; 250; 500; 1000 ml

- Bnh nh mc cc loi: 10; 25; 50; 100; 500; 1000 ml

2.2. Ha cht s dng.

Tt c ha cht s dng u dng ha cht Merck:

- Dung dch chun Cd2+ 1000 ppm trong HNO3 2%

- Dung dch chun Pb2+ 1000 ppm trong HNO3 2%

- Thuc th: Cn 0,10 gam Ammoniumpryrrolydinedithiocacbamate

(APDC), pha ha tan bng nc ct hai ln thnh 100 ml c dung dch

0,1%.- Cc dung dch axit HNO3; HCl; CH3COOH 10%, u c tnh ton

pha t cc dung dch c ban u HNO3 65%; HCl 36%; CH3COOH 99%.

- Dung dch NH4Cl; CH3COONH4; CH3COONa nng 10%: Cn mi

mui vi khi lng tng ng l 10,0 gam, sau ha tan chng bng 90 ml

nc ct hai ln.

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- Dung dch NaOH 1M: Cn 4 gam NaOH dng vin trn cn k thut,

ha tan bng nc ct hai ln, chuyn vo bnh nh mc 100 ml, sau nh

mc n vch.

- Dung dch CH3COOH 1M: Dng pipet ly 5,7 ml dung dch

CH3COOH 99 %, pha nh mc trong bnh 100 ml.

- Dung dch KH2PO4 0,1 M: Cn 1,3608 gam KH2PO4 tinh th trn cn

phn tch, ho tan trong bnh nh mc 100 ml sau nh mc n vch.

- Dung mi hu c Axeton

- Cc dung dch Na+

; K+

; Mg2+

; Ca2+

; Zn2+

; Ni2+

; Fe3+

; Cr3+

. u cchun b t cc loi ho cht tinh khit.

- Nha Amberlite XAD-7 ca hng Merck.

2.3. Chun b ct chit pha rn

* Nha Amberlite XAD-7 thuc loi cht hp ph polyme c cu trc

v cch ch to tng t nh cc loi nha trao i ion, nhng khng cha

cc nhm chc trao i ion. Polyme ny thng c dng cu khng tan trong

nc, tu thuc vo bn cht vt liu polyme, vo iu kin tng hp m cht

hp ph polyme c phn cc, xp, din tch b mt khc nhau. S

tng tc hp ph trn cht hp ph polyme gm: Tng tc Vande- Waals

v cc tng tc c th k nc nh cu lin kt hyro, tng tc lng cc-

lng cc.

* Nha Amberlite XAD-7 l Polymetaacrylat, c b mt phn cc

trung bnh, c xp 55%, c khi lng ring trng thi t l 1,05 g/ml,

c din tch b mt l 450 m2/g. c ng dng tch v lm giu cc kim

loi nng trong mu nc v cc mu mi trng.

* Cn 0,5- 1 gam nha XAD-7 c ngm trong nc ct 2 ln trong

nhiu gi, sau cho ln ct v c ra bng:

- 100 ml dung dch HNO3 1M

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- 100 ml dung dch NaOH 1M

- Nc ct 2 ln n pH= 6-7 (Theo giy ch th)

- 30 ml Axeton c- Nc ct 2 ln, kh ngoi khng kh.

* Nha XAD-7 dng sch c np ln cc ct nha mini (V=1ml)

c lm sch v kh c s dng lm ct chit pha rn. Ct c nhi vi

70 mg nha XAD-7. Mt lng bng thu tinh c t y trnh lm

mt cc ht nha. Sau mi ln s dng nha trong ct c lm sch bng

nc v dung dch m ph hp. Sau c ngm trong nc ct cho nkhi s dng ln sau.

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CHNG 3: KT QU THC NGHIM V THO LUN

3.1. Kho st cc iu kin ti u ca php o ph F-AAS

3.1.1. Kho st cc iu kin o ph:

m bo cho php o ph t hiu qu th phi chn c nhng

thng s ti u nht. Di y chng ti tin hnh kho st v chn cc iu

kin m bt k php o no cng thc hin.

3.1.1.1. Chn vch o

Qu trnh sinh ph AAS l do nhng nguyn t trng thi hi b kchthch bi ngun sng pht tia pht x. Cc nguyn t c kh nng hp th

bc x c bc sng nht nh, ng ng vi tia m n pht ra. Tuy nhin qu

trnh hp th ny khng xy ra vi tt c cc vch ph m ch vi vch ph

nhy, c trng .

Theo mt s ti liu th vch ph c trng ca Pb; Cd nh sau:

Bng 4: nhy tng ng vi bc sng ca Pb; Cd

Pb Cd

(nm) nhy(ppm) (nm) nhy(ppm)

217,0 0,08 228,8 0,03

283,3 0,2 226,5 < LOD

216,4 3,2 326,1 < LOD

368,3 8V i tng phn tch mc vi lng nn cn o nhng vch c nhy

cao. Nn chn bc sng o ph theo bng sau:

Bng 5: La chn bc sng o ph F-AAS ca Pb; Cd

Nguyn t (nm)

Pb 217,0

Cd 228,8

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3.1.1.2. Khe o

Khe o nh hng trc tip n tn hiu hp th ca nguyn t phn

tch. Vi cc nguyn t Pb, Cd chn khe o l 0,5 nm. Vi khe o ny tnhiu pic nhy, n nh cao, 100% din tch pic ca vch ph s nm

trong khe o.

3.1.1.3. Cng n catot rng (n HCL)

n catot rng c nhim v ch pht ra nhng tia pht x nhy ca

nguyn t phn tch. Cng dng in lm vic ca n HCL c lin quan

cht ch n vic sinh ra chm pht x v phi c t sao cho n c nhy v n nh cao. Thng thng cng n HCL s dng nm trong

khong 60- 80% cng cc i ghi trn thn n (Imax). Khng nn t n

gi tr cng Imax v gi tr n lm vic khng n nh, nhy

cng nh lp li km v rt d hng.

V nhng l do trn, chng ti chn cng dng n lm vic tng

ng vi cc nguyn t nh sau:

Vi Pb chn cng n l 8 mA.

Vi Cd chn cng n l 2,5 mA.

3.1.2. Kho st cc iu kin nguyn t ha mu

3.1.2.1. Chiu cao n nguyn t ha

Chiu cao n nguyn t ha cng l mt trong nhng yu t quytnh n nhy, chnh xc ca php o. V vy trong php o ph hp

th nguyn t ngi ta phi chn chiu cao ca n nguyn t ha mu sao

cho ngun n sc phi chiu vo phn trung tm ngn la nguyn t ha

mu.

kho st chiu cao n nguyn t ha, chng ti tin hnh nh sau:

Pha vo cc bnh nh mc 50 ml dung dch ca cc nguyn t Pb; Cd vi

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nng tng ng l 4ppm; 1ppm (Trong nn HNO3 + CH3COONH4). Thay

i chiu cao n nguyn t ha, ghi s ph thuc ca hp th (Ab s) vo

chiu cao n. Kt qu thu c nh sau:

Bng 6: nh hng ca chiu cao n NTH n php o ph F-AAS

Nguyn tChiu cao n NTH (mm)

5 6 7 8 9

Abs-Pb

Ln 1 0,0774 0,0794 0,0791 0,0766 0,0763

Ln 2 0,0770 0,0796 0,0790 0,0763 0,0761

Ln 3 0,0775 0,0798 0,0796 0,0762 0,0765TB 0,0773 0,0796 0,0792 0,0764 0,0763

Abs-Cd

Ln 1 0,1487 0,1502 0,1510 0,1527 0,1518

Ln 2 0,1480 0,1501 0,1513 0,1538 0,1523

Ln 3 0,1483 0,1502 0,1517 0,1515 0,1532

TB 0,1483 0,1502 0,1513 0,1527 0,1524

Kt qu trn cho thy ti chiu cao n tng ng 6 mm vi Pb v Cd

th tn hiu hp th cao, n nh v lp li tt nn chng ti chn cc gi tr

.

3.1.2.2 Kho st thnh phn kh chy

Thnh phn v tc ca hn hp kh t to ra ngn la l yu t

quyt nh n giai on nguyn t ha mu, nh hng trc tip n kt qu

php o. Mun kt qu chnh xc th phi kho st thnh phn kh nhm chn

c nhit ph hp.

Trong php o F-AAS chng ti s dng hn hp: Khng kh +

Axetilen trong thnh phn ca khng kh c gi c nh 469 l/h. V vy

kho st thnh phn kh chy chng ti ch thay i tc ca dng kh

Axetilen.

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Chun b dung dch ca Pb2+; Cd2+ ging phn trn. Thay i tc

dng kh Axetilen ng thi ghi li hp th quang. Kt qu thu c nh

sau:

Bng 7: nh hng ca tc kh chy n php o ph F-AAS

Nguyn tTc kh chy l/h

55 60 65 70 75 80

Abs-Pb

Ln 1 0,0761 0,0780 0,0784 0,0785 0,0780 0,0794

Ln 2 0,0769 0,0789 0,0788 0,0788 0,0789 0,0781

Ln 3 0,0762 0,0783 0,0786 0,0780 0,0781 0,0780

TB 0,0764 0,0784 0,0786 0,0784 0,0783 0,0785

Abs-Cd

Ln 1 0,1424 0,1505 0,1513 0,1515 0,1502 0,1521

Ln 2 0,1522 0,1501 0,1517 0,1526 0,1540 0,1504

Ln 3 0,1563 0,1507 0,1515 0,1542 0,1536 0,1542

TB 0,1503 0,1504 0,1515 0,1528 0,1526 0,1522

T bng trn cho thy vi tc dng kh Axetilen l 65 l/h vi Pb vCd thu c hp th quang cao v n nh nht nn chn tc ny cho

cc php o sau.

3.1.3 Kho st cc yu t nh hng khc

Trong php o ph AAS c rt nhiu yu t nh hng, nhng gy nh

hng nhiu nht l cc yu t ha hc, nh hng ca chng rt a dng v

phc tp. Cc nh hng ca yu t ha hc c th dn n nhng hng sau:

Gim tn hiu ph ca nguyn t phn tch do to thnh hp cht bn

nhit kh ha hi v kh nguyn t ha mu.

Tng cng tn hiu ph do to thnh hp cht d ha hi v d

nguyn t ha, hay hn ch c nh hng ca s ion ha v s kch thch

ph pht x ca nguyn t phn tch.

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Tng cng tn hiu ph khi nguyn t phn tch tn ti trong nn

ca mu l nhng hp cht d ha hi. Lc , cc cht nn ny c tc dng

nh l mt cht mang cho s ha hi ca nguyn t phn tch v lm cho n

c ha hi vi hiu sut cao hn.

Gim cng tn hiu ph khi nguyn t phn tch nm trong nn

mu l nhng hp cht bn nhit, kh ha hi. Lc ny cc nguyn t nn

km hm s ha hi ca nguyn t phn tch v lm cho n c ha hi vi

hiu sut cao hn.

Chnh v nhng l do trn m vic kho st nghin cu nh hng ca

cc yu t ha hc n php o l rt cn thit.

3.1.3.1 nh hng ca nng axit v loi axit trong dung dch mu

Nng cng nh loi axit trong dung dch mu lun nh hng n

cng vch ph ca nguyn t phn tch. Axit cng kh bay hi th cng

lm gim cng vch ph v c th to thnh nhng hp cht bn nhit vi

nguyn t c mt trong mu, cn cc axit d bay hi nh hng khng ngk v i khi cn lm tng tn hiu ph. V th, trong qu trnh x l mu

ngi ta thng dng axit d bay hi nh HCl; HNO3.Do vy, chng ti

ch kho st nh hng ca mt s loi axit d bay hi n php o ph.

Bng 8: nh hng ca mt s loi axit n tn hiu ph F-AAS

Nguyn t

Nng HCl (%)

0 1 2 3 4 5

Abs-Pb

Ln1 0,0751 0,0770 0,0784 0,0773 0,0762 0,0760

Ln 2 0,0757 0,0771 0,0783 0,0776 0,0767 0,0764

Ln 3 0,0754 0,0773 0,0782 0,0771 0,0764 0,0761

TB 0,0754 0,0771 0,0783 0,0773 0,0764 0,0762

Abs- Cd Ln 1 0,1383 0,1496 0,1503 0,1500 0,1492 0,1481

Ln 2 0,1385 0,1493 0,1506 0,1202 0,1494 0,1490Ln 3 0,1382 0,1495 0,1503 0,1509 0,1500 0,1484

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TB 0,1383 0,1495 0,1504 0,1503 0,1495 0,1485

Nguyn t

Nng HNO3 (%)

0 1 2 3 4 5

Abs- Pb

Ln 1 0,0750 0,0774 0,0791 0,0784 0,0789 0,0788

Ln 2 0,0757 0,0773 0,0793 0,0782 0,0782 0,0786

Ln 3 0,0754 0,0770 0,0793 0,0780 0,0779 0,0792

TB 0,0754 0,0772 0,0792 0,0782 0,0783 0,0788

Abs- Cd

Ln 1 0,1380 0,1501 0,1512 0,1511 0,1507 0,1508

Ln 2 0,1382 0,1509 0,1514 0,1509 0,1505 0,1503Ln 3 0,1389 0,1510 0,1516 0,1526 0,1501 0,1502

TB 0,1384 0,1507 0,1514 0,1515 0,1504 0,1504

Nguyn tNng CH3COOH (%)

0 1 2 3 4 5

Abs- Pb

Ln 1 0,0756 0,0779 0,0781 0,0780 0,0775 0,0773

Ln 2 0,0750 0,0782 0,0786 0,0779 0,0771 0,0772

Ln 3 0,0759 0,0786 0,0783 0,0785 0,0774 0,0770

TB 0,0755 0,0782 0,0783 0,0781 0,0773 0,0771

Abs- Cd

Ln 1 0,1389 0,1485 0,1509 0,1490 0,1480 0,1486

Ln 2 0,1380 0,1491 0,1510 0,1497 0,1471 0,1480

Ln 3 0,1381 0,1477 0,1508 0,1485 0,1463 0,1420

TB 0,1383 0,1484 0,1509 0,1490 0,1471 0,1462

Da vo bng s liu, chng ti thy: Khi c mt ca cc axit trn thtn hiu o ( hp th quang) u cao hn khi khng c, v gi tr Abs t

cao nht, n nh nht vi nn axit HNO3 2% cho c hai nguyn t phn tch.

V vy, trong thnh phn nn ca mu o ph chng ti chn axit HNO3 2%.

3.1.3.2 nh hng ca nn mui

Nn ca mu trong php o F-AAS thng lm gim cng vch

ph ca nguyn t phn tch do tn ti hp cht bn nhit trong mi trng

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hp th. V th hiu sut ha hi, nguyn t ha khng cao. gim bt yu

t ny, ngi ta thng a vo mu nhng cht ph gia ph hp nhm ngn

cn s hnh thnh cc hp cht bn nhit.

Trn c s , chng ti tin hnh kho st vi mt s nn mui nh:

NH4Cl; CH3COONH4; CH3COONa v chng d ha hi v c kh nng loi

c hp cht bn nhit. Nng Pb2+; Cd2+ trong cc th nghim kho st

tng ng l 4; 1 ppm, cn nng cc nn ph gia c tng dn. Kt qu

thu c nh sau:

*Nn NH4Cl

Bng 9: nh hng ca nn NH4Cl n tn hiu o ph F-AAS

Nguyn tNng nn NH4Cl (%)

0 1 2 3 4 5

Abs- Pb

Ln 1 0,0759 0,0781 0,0784 0,0790 0,0784 0,0786

Ln 2 0,0764 0,0779 0,0786 0,0789 0,0781 0,0790

Ln 3 0,0766 0,0782 0,0788 0,0788 0,0777 0,0781

TB 0,0763 0,0781 0,0786 0,0789 0,0781 0,0785

Abs- Cd

Ln 1 0,1481 0,1501 0,1506 0,1493 0,1508 0,1427

Ln 2 0,1468 0,1509 0,1509 0,1480 0,1511 0,1483

Ln 3 0,1442 0,1512 0,1503 0,1439 0,1584 0,1436

TB 0,1464 0,1507 0,1506 0,1471 0,1534 0,1448

*Nn CH3COONa

Bng 10: nh hng ca nn CH3COONa n tn hiu o ph F-AAS

Nguyn t Nng nn CH3COONa (%)0 1 2 3 4 5

Abs- Pb

Ln 1 0,0760 0,0770 0,0782 0,0762 0,0770 0,0771

Ln 2 0,0766 0,0762 0,0786 0,0775 0,0776 0,0775

Ln 3 0,0764 0,0769 0,0785 0,0768 0,0778 0,0780

TB 0,0763 0,0767 0,0784 0,0768 0,0774 0,0775

Abs- Cd Ln 1 0,1492 0,1520 0,1505 0,1496 0,1502 0,1496

Ln 2 0,1447 0,1503 0,1508 0,1480 0,1518 0,1501Ln 3 0,1480 0,1526 0,1512 0,1495 0,1526 0,1514

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TB 0,1473 0,1516 0,1508 0,1490 0,1515 0,1504

* Nn CH3COONH4

Bng 11: nh hng ca nn CH3COONH4 n tn hiu ph F-AAS

Nguyn tNng nn CH3COONH4 (%)

0 1 2 3 4 5

Abs- Pb

Ln 1 0,0760 0,0792 0,0789 0,0789 0,0785 0,0777

Ln 2 0,0768 0,0790 0,0780 0,0790 0,0782 0,0775

Ln 3 0,0765 0,0799 0,0782 0,0789 0,0780 0,0772

TB 0,0771 0,0794 0,0784 0,0789 0,0782 0,0774

Abs- CdLn 1 0,1403 0,1510 0,1511 0,1492 0,1492 0,1495Ln 2 0,1419 0,1516 0,1500 0,1502 0,1409 0,1482

Ln 3 0,1429 0,1514 0,1501 0,1500 0,1476 0,1490

TB 0,1417 0,1513 0,1504 0,1498 0,1459 0,1489

T s liu ba bng trn chng ti nhn thy: Khi c mt cc cht nn

th tn hiu ph thu c cao hn khi khng c cht nn. Tuy nhin vi nn

CH3COONH4 th cho tn hiu ph nhy hn, n nh hn nht l ti gi tr

nng 1%. V th chng ti la chn nng nn mui trong mu lCH3COONH4 1%.

3.1.3.3. nh hng ca cc ion c trong mu

Trong mu phn tch, ngoi cc ion cn quan tm (Pb2+; Cd2+) th cn

c rt nhiu ion khc. Cc ion ny c th nh hng n php o ph, hoc

khng gy nh hng n php o ph. Tuy nhin bit mt cch chnh xc

th chng ti tin hnh kho st chng.

3.1.3.3.1. nh hng ca cation

kho nh hng ca cation, chng ti tin hnh kho st theo tng

nhm nguyn t nh sau:

- Nhm kim loi kim

- Nhm kim loi kim th

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- Nhm kim loi nng nhm II, III

- Mt s anion

- Tng cc cation v anionTrong nng ca Pb2+; Cd2+ c gi khng i (ging nh cc th

nghim trn). Cc ion kho st c cho vo mu vi nng tng dn. Kt

qu c trnh by trong cc bng sau (Ch : Gi tr hp th quang Abs l

gi tr trung bnh ca ba ln o lp li).

* nh hng ca nhm kim loi kim

Bng 12: nh hng ca nhm kim loi kim n tn hiu ph F-AAS

Nng (ppm)

Na+ 0 50 100 200 500 1000

K+ 0 50 100 200 500 1000

Abs- Pb 0,0761 0,0766 0,0768 0,0773 0,0788 0,0782

Abs- Cd 0,1515 0,1517 0,1508 0,1510 0,1527 0,1503

* nh hng ca nhm kim loi kim th

Bng 13: nh hng ca nhm kim loi kim th n tn hiu ph F-AAS

Nng (ppm)

Mg2+ 0 50 100 200 500 1000

Ca2+ 0 50 100 200 500 1000

Ba2+ 0 50 100 200 500 1000

Abs- Pb 0,0791 0,0792 0,0796 0,0795 0,0798 0,0796

Abs- Cd 0,1515 0,1513 0,1525 0,1523 0,1508 0,1503

* nh hng ca mt s kim loi nng nhm II

Bng 14: nh hng ca mt s kim loi nng nhm II n tn hiu ph-FAAS

Nng (ppm)

Mn2+ 0 10 20 50 80 100

Ni2+ 0 10 20 50 80 100

Zn2+ 0 10 20 50 80 100

Abs- Pb 0,0762 0,0770 0,0762 0,0776 0,0787 0,0788Abs- Cd 0,1513 0,1530 0,1512 0,15108 0,1518 0,1500

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*nh hng kim loi nng nhm III

Bng 15: nh hng ca kim loi nng nhm III n tn hiu ph F-AAS

Nng (ppm)

Al3+ 0 10 20 50 80 100

Fe3+

0 10 20 50 80 100Cr3+ 0 10 20 50 80 100

Abs- Pb 0,0762 0,0774 0,0785 0,0783 0,0794 0,0786

Abs- Cd 0,1513 0,1510 0,1528 0,1504 0,1506 0,1502

T s liu cc bng trn, chng ti thy cc nhm cation kim loi

(vi nng kho st) u khng nh hng n php xc nh Pb v Cd.

* nh hng ca tng cation

Bng 16: nh hng ca tng cation n tn hiu ph F-AAS

Nng (ppm)

Na+ 0 50 100 200 500 1000

K+ 0 50 100 200 500 1000

Mg2+ 0 50 100 200 500 1000

Ca2+ 0 50 100 200 500 1000

Ba2+ 0 50 100 200 500 1000Mn2+ 0 10 20 50 80 100

Ni2+ 0 10 20 50 80 100

Zn2+ 0 10 20 50 80 100

Al3+ 0 10 20 50 80 100

Fe3+ 0 10 20 50 80 100

Cr3+ 0 10 20 50 80 100

Abs- Pb 0,0761 0,0772 0,0785 0,0790 0,0780 0,0792Abs- Cd 0,1514 0,1512 0,1521 0,1515 0,1526 0,1523

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Nhn xt: Khi c mt tng cc cation th cng khng nh hng n

php o.

3.1.3.3.2. nh hng ca anionTrong mu phn tch, ngoi cc cation ra th cn c cc anion. Ty tng

hm lng v tng i tng mu m chng c hay khng gy nh hng.

Phn thc nghim ny chng ti khng kho st nh hng ca Cl - v

NO3-, v kho st nh hng ca axit HCl, HNO3 trn. Chng ti ch

kho st anion SO42-; H2PO4-. Mu th nghim pha vi nng Pb2+ l 4 ppm;

Cd2+

l1 ppm trong nn HNO3 2% + CH3COONH41%. Ghi s ph thuc caAbs vo nng ca cc anion ta c kt qu:

Bng 17: nh hng ca ion SO42- n tn hiu ph F-AAS

Nng (ppm)

SO42- 0 50 100 150 200 500

Abs- Pb 0,0763 0,0778 0,0761 0,0778 0,0782 0,0781

Abs- Cd 0,1514 0,1522 0,1511 0,1519 0,1507 0,1506Bng 18: nh hng ca ion H2PO4- n tn hiu ph F-AAS

Nng (ppm)

H2PO 4 0 50 100 150 200 500

Abs- Pb 0,0763 0,0779 0,0760 0,0777 0,0771 0,0782

Abs- Cd 0,1514 0,1506 0,1512 0,1509 0,1528 0,1507

Bng 19: nh hng ca tng anion n tn hiu ph F-AAS

Nng (ppm)

SO 24 0 50 100 150 200 500

H2PO 4 0 50 100 150 200 500

Abs- Pb 0,0763 0,0767 0,0766 0,0779 0,0776 0,0787

Abs- Cd 0,1514 0,1553 0,1509 0,1522 0,1514 0,1505

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Nhn xt: Vi kt qu trn th cc anion kho st tng

ng vi nng chn khng nh hng n hp th

quang ca Pb v Cd.

3.1.3.3.3 nh hng ca tng cation v anion

Nhm nh gi mt cch tng qut chng ti tin hnh kho st nh

hng ca tng cc ion n hp th Abs ca Pb v Cd.

Bng 20: nh hng ca tng ion n tn hiu ph F-AAS

Nng (ppm)

Na+ 0 50 100 200 500 1000

K+ 0 50 100 200 500 1000

Mg2+ 0 50 100 200 500 1000

Ca2+ 0 50 100 200 500 1000

Ba2+ 0 50 100 200 500 1000

Mn2+ 0 10 20 50 80 100

Ni2+ 0 10 20 50 80 100

Zn2+ 0 10 20 50 80 100

Al3+ 0 10 20 50 80 100

Fe3+ 0 10 20 50 80 100

Cr3+ 0 10 20 50 80 100

SO 24 0 50 100 150 200 500

H2PO 4 0 50 100 150 200 500

Abs- Pb 0,0762 0,0762 0,0770 0,0777 0,0778 0,0784

Abs- Cd 0,1514 0,1528 0,1513 0,1519 0,1513 0,1509

Cc kt qu trn chng t rng: Cc ion trong vng nng

kho st khng nh hng n php xc nh Pb v Cd.

Hn na, trong mu thc t th hm lng ca cc ion trn

nh hn hm lng kho st rt nhiu nn c th khng nh

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chc chn l chng khng nh hng. y cng chnh l mt

u im ni bt ca php o F-AAS so vi phng php khc.

Qua thc nghim trn, chng ti c tng kt cc iu

kin ti u o ph ca Pb v Cd nh sau:

Bng 21: Tng kt cc iu kin o ph AAS xc nh Pb

v Cd

iu kin oNguyn t

Pb Cd

Vch o (nm) 217,0 228,8Khe o (mm) 0,5 0,5

Cng n HCL (mA) 8,0 2,5

Chiu cao n NTH (mm) 6 6

Tc khKhng kh(l/h)

469 469

Axetilen (l/h) 65 65

Thnh phnnn

HNO3 (%) 2 2

NH4Ac (%) 1 1

3.1.4 nh gi chung v phng php ph F-AAS

3.1.4.1 Khong tuyn tnh ca Pb, Cd v phng trnh ng

chun

xc nh khong tuyn tnh ca hai nguyn t

phn tch chng ti pha dy mu chun ca hn hp hainguyn t (trong nn HNO3 2%+ NH4Ac 1%) sao cho nng

tng dn. Sau o, ghi li Abs ( mi mu o ba ln v ly

kt qu trung bnh) thu c kt qu nh sau:

Bng 22: Khong tuyn tnh ca Pb

Nng (ppm) hp th quang Abs-

Pb

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0,05 0,0034

0,08 0,0050

0,10 0,0064

0,50 0,01131,00 0,0215

2,00 0,0405

3,00 0,0614

4,00 0,0779

5,00 0,0979

6,00 0,1180

7,00 0,13868,00 0,1567

9,00 0,1758

10,00 0,1929

11,00 0,2019

13,00 0,2140

Hnh 1: th biu din s ph thuc hp th quang

theo nng Ch

0 2 4 6 8 10 12 14

0.00

0.05

0.10

0.15

0.20

0.25

Abs

C (ppm)

T th ta thy, Pb c khong tuyn tnh t 0,05

10,00 ppm

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Hnh 2: ng chun ca Pb

Phng trnh ng chun: y = 0,0028 + 0,0192 x

0 2 4 6 8 10 12 14

0.00

0.05

0.10

0.15

0.20

0.25

Abs

C (ppm)

Parameter Value ErrorA 0.00286 4.602E-4B 0.01915 8.774E-5

R SD N P0.99987 0.00112 14


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0 1 2 3 4 5

0.0

0.1

0.2

.3

0.4

.5

.

Abs

C m

Bng 23: Khong tuyn tnh ca Cd

Nng (ppm) hp th quang Abs- Cd

0,05 0,01230,08 0,0218

0,10 0,0247

0,50 0,0861

1,00 0,1575

1,50 0,2313

2,00 0,3050

2,50 0,36913,00 0,4085

3,50 0,4594

4,00 0,4725

Hnh 3: : th biu din s ph thuc hp th quang theo

nng Cadimi

T th ta thy, Cd c khong tuyn tnh t 0,05

2,50 ppm

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Hnh 4: ng chun ca Cd

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Abs

C (ppm)

Phng trnh ng chun: y = 0,0102 + 0,1457 x

3.1.4.2. Gii hn pht hin, gii hn nh lng ca phng php F-AAS xc

nh Pb v Cd.

Theo l thuyt thng k th:

Gii hn pht hin ( Limit of detection LOD): c xem l nng

thp nht ( XL) ca cht phn tch m h thng phn tch cn cho tn hiu

phn tch ( YL) khc c ngha vi tn hiu ca mu trng hay tn hiu nn.

Gii hn nh lng ( Limit of quantity LOQ): c xem l nng

thp nht ( XQ) ca cht phn tch m h thng phn tch nh lng c vi

tn hiu phn tch ( YQ) khc c ngha nh lng vi tn hiu ca mu trng

hay tn hiu nn.

Cng thc tnh LOD v LOQ nh sau:

YL = Yb + k* Sb

Vi Yb: Tn hiu trung bnh ca mu trng sau nb th nghim

Sb: lch chun tn hiu ca mu trng

Parameter Value ErrorA 0.01017 0.00197B 0.14573 0.0015

R SD N P

0.99968 0.00377 8


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K: i lng s hc c chn theo tin cy mong mun

XL = Xb +b

SK b*

V mu trng c Xb = 0 v vi K = 3 nnLOD =

b

Sb

*3

LOQ =b

Sb*10

Trong :b: H s hi quy tuyn tnh

tm LOD v LOQ, chng ti tin hnh o hp th ca 15 mu

trng trong php xc nh Pb, Cd bng F-AAS. Kt qu nh sau:

Bng 24: Phn tch mu trng

S TT hp th quang ( Abs)

Pb Cd

1 0,0026 0,0025

2 0,0028 0,0030

3 0,0029 0,00234 0,0022 0,0033

5 0,0027 0,0045

6 0,0030 0,0019

7 0,0026 0,0024

8 0,0028 0,0027

9 0,0025 0,0042

10 0,0028 0,001011 0,0029 0,0018

12 0,0024 0,0040

13 0,0031 0,0026

14 0,0025 0,0041

15 0,0021 0,0035

Kt qu tnh bng orgin 6.0 nh sau:

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Bng 25: Gii hn pht hin, gii hn nh

lng ca php o F-AAS xc nh Pb, Cd

Thng s thng kNguyn t

Pb Cd

Trung bnh (Abs) 0,0027 0,0029

sai chun 7,35E-5 2,59E-4

lch chun 2,85E-4 0,0010

Phng sai mu 8,11E-8 1,0E-6

b 0,0192 0,1457

LOD (ppm) 0,04 0,02

LOQ (ppm) 0,15 0,06

3.1.4.3 Sai s v lp li ca php o

* Sai s ca php o:

nh gi sai s ca php o i vi Pb, Cd tin hnh pha 10 mu

chun lp li ca hai nguyn t phn tch nm trong khong tuyn tnh. Sau o hp th ca chng. Tnh sai s ca mi ln o theo cng thc:

X% =2

21

A

AA *100

Trong :

X: Sai s phn trm tng i

A1: Gi tr hp th o c

A2: Gi tr hp th tnh theo ng chun

Bng 26: Sai s ca php o F-AAS xc nh Pb, Cd

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Nguyn t Pb Cd

Nng (ppm) 5.0 1.0A2 0.0988 0.1559

Ln o A1 X% A1 X%

1 0,0973 1,52 0,1525 2,19

2 0,0981 0,71 0,1524 2,24

3 0,0961 2,73 0,1498 3,92

4 0,0953 3,54 0,1506 3,40

5 0,0974 1,42 0,1527 2,05

6 0,0975 1,32 0,1508 3,27

7 0,0945 4,35 0,1527 2,05

8 0,0967 2,13 0,1506 3,40

9 0,0959 2,94 0,1509 3,21

10 0,0959 2,94 0,1506 3,40

TB 0,0965 2,36 0,1513 2,91

Cc kt qu trn cho thy sai s ca php o i vi hai nguyn t

tng i nh v u thp hn mc sai s cho php ca phng php phn

tch cng c xc nh lng vt (15%).

* lp li ca php o

lp li ca php o c nh gi qua: Phng sai mu ( S2) v h

s bin thin CV%. Mun xc nh hai thng s ny cho php o mi nguyn

t Pb, Cd chng ti lm nh sau:

Pha 10 mu chun lp li ca hai nguyn t phn tch ( nng tng

ng vi Pb, Cd l 5ppm; 1ppm).

o hp th ca chng, sau tnh ton thng k bng phn mm

orgin 6.0 tm ra phng sai mu v h s bin theo cng thc:

S2 =1

)(2

n AA

tbi

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CV (%) =tbA

S*100

Vi: Ai - hp th o c

Atb - hp th trung bnh ca n ln o

n - S ln o lp li

S - lch chun ca mu, v S = 2S

Bng 27: lp li ca php o F-AAS xc nh Pb, Cd

Nguyn t Phng sai (S2) lch chun (S) CV (%)

Pb 1,26E-6 0,00112 1,16Cd 1.18E-6 0.00109 0.72

Qua bng s liu trn thy rng phng sai (hay lch chun) v h

s bin thin ca mu kh nh, chng t lp li ca php o tt.

Nhn xt: Thng qua cc bc nh gi chung ( khong tuyn tnh,

lp li, sai s) chng ti nhn thy phng php ph F-AAS l phng

php phn tch n nh, lp li tt ng thi c chnh xc cao, hon ton

ph hp vi xc nh vi lng kim loi trong mu.

3.2 Kho st cc iu kin lm giu v tch chit bng pha rn XAD7

* Thuc th

Ammoniumpyrrolydineithiocacbamate (APDC) l cht bt mu trng

to phc vi Pb2+, Cd 2+. C cng thc phn t C5H12N2S2 v cng thc cu

to l:

APDC phn ng vi cc kim loi to thnh hp cht phc bn thun li

cho vic nghin cu tch, lm giu bng phng php chit pha rn. Phc ca

APDC vi Pb2+,Cd 2+ ( Me2+) c dng:

CH2

CH2

CH2

CH2

N C S NH4

S

CH2

CH2

CH2

CH2

N C

S

S

MeS

SC N

CH2

CH2

CH2

CH2

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tch lm giu Pb2+, Cd 2+ chng ti tin hnh kho st tm cc

iu kin ti u cho vic tch v lm giu Pb2+, Cd 2+bng XAD-7 v APDC.

y chng ti tin hnh kho st iu kin ng. Qua nh gi tnh

kh thi ca phng php thng qua gi tr hiu sut thu hi.

* Quy trnh chung ca phng php kho st ny nh sau: Dung dch

mu phn tch cha Pb2+

, Cd2+

to phc vi APDC gi tr pH thch hp,c cho i qua ct chit pha rn cha XAD-7 vi mt tc xc nh. Sau

khi i qua ct cht phn tch b gi li trn ct chit. Dng dung mi ra gii

vi nng v th tch thch hp thu hi lng cht phn tch gi li trn

ct chit t nh gi c kh nng tch v lm giu Pb2+, Cd 2+.

Hiu sut thu hi (H) ca Pb, Cd c tnh ton nh sau:

H =0m

m *100 (%) m: Khi lng thu hi

m0: Khi lng ban u

3.2.1 Kho st nh hng ca pH

S to phc ca kim loi nng vi thuc th APDC, s hp thu phc

trn ct chit ph thuc vo rt nhiu yu t. Mt trong nhng yu t quan

trng u tin phi ni n l mi trng to phc (pH), gi tr pH thch hp

s lm cho kh nng hp thu ca cht phn tch trn ct chit t hiu qu cao

nht.

kho st pH chng ti tin hnh nh sau:

Pha 100 ml dung dch chit c cha 5g Cd 2+; 10g Pb2+ thm 5 ml

thuc th APDC 0,1% v 5 ml dung dch m ( pH = 3 8).

Cho cc dung dch phn tch qua ct chit pha rn vi tc 2 ml/pht.

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Ra gii bng 15 ml dung dch HNO3 1M/Axeton, c cn lm bay hi

Axetn trong dung dch. Thm HNO3 1M c mt ca NH4Ac 10% n th

tch 5 ml, xc nh lng Pb; Cd thu hi c bng phng php F-AAS kt

qu thu c nh sau:

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Bng 28: nh hng ca pH n hiu sut thu hi Pb; Cd

pH 3 4 5 6 7 8

H(%) Pb 62,45 82,50 96,80 97,75 97,50 95,15H(%) Cd 78,30 97,78 97,50 97,38 94,20 96,80

Qua ta thu c th nh hng ca pH ti hiu sut thu hi Pb; Cd

Hnh 5: nh hng ca pH ti hiu sut thu hi Pb; Cd

3 4 5 6 7 80

30

60

90

120

H(%)

pH

Pb

Cd

Kt qu thc nghim cho thy vng pH ti u lm giu ng thi Pb2+, Cd2+

pH=5-6. Trong cng trnh ny chng ti chn gi tr pH=6 kho st cc th

nghim v sau.

3.2.2 Kho st nh hng ca th tch thuc th

Lng thuc th APDC dng to phc vi Pb2+, Cd 2+ cng l mt

iu kin rt quan trng cho vic hp thu tt Pb2+, Cd 2+ trn ct chit pha rn.

Tin hnh kho st vi cc mu nh mc 3.2.1.1 vng pH ti u chn

pH=6. Nhng vi lng thuc th APDC 0.1% khc nhau. Kt qu thu c

nh sau:

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Bng 29: nh hng ca th tch thuc th

V APDC (ml) 1 2 3 4 5 6 7

H (%) Pb 82,00 97,70 98,50 98,60 98,42 97,80 97,60H (%) Cd 73,10 97,50 98,20 98,55 98,40 97,00 96,80

Hnh 6: nh hng ca th tch thuc th n hiu sut thu hi Pb; Cd

0 1 2 3 4 5 6 70

30

60

90

120

H(%)

V APDC (ml)

Pb

Cd

Kt qu thc nghim ch ra rng c th la chn c vng th tch

APDC 0,1% ti u cho hp thu c hai ion l 2 7 ml. Trong cng trnh ny

chng ti chn:

V APDC = 3 ml kho st cc th nghim v sau

3.2.3 Kho st t l Cd2+/Pb2+ trong hn hp

Tin hnh kho st vi cc mu nh mc 3.2.1.2 cc iu kin ti u

chn. Nhng vi t l hm lng Cd 2+/Pb2+ trong hn hp khc nhau. Kt

qu thu c nh sau:

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Bng 30: Kho st t l Cd2+/Pb2+ trong hn hp

Hm lng (g)T l

1/1 1/2 1/5 1/6 1/8 1/10Cd 2+ 5 5 5 5 5 5

Pb2+ 5 10 25 30 40 50

H (%) Pb 97,90 97,55 97,70 90,45 85,30 80,60

H (%) Cd 98,26 97,47 97,28 95,58 90,63 85,78

Kt qu thc nghim cho thy c th chn t l hn hp Cd 2+/Pb2+ =

1/1- 1/5 . Trong cng trnh ny chng ti chn t l Cd 2+/Pb2+ = 1/2 cho cc

th nghim sau.

3.2.4 Kho st tc np mu

Tc np mu ln ct cng nh hng n kh nng lu gi cht

phn tch trn ct. Nu tc np mu qu nhanh th cht phn tch cha kp

hp thu ln ct b a ra. Ngc li tc np mu qu chm lm tn thi

gian m kt qu t c cng khng ti u. Tc np mu thch hp s

a n lng cht phn tch hp thu ln ct l nhiu nht.

Tin hnh kho st vi cc mu nh mc 3.2.1.3 cc diu kin ti u

chn. Nhng tin hnh kho st cc tc np mu khc nhau tm ra

tc ti u. Kt qu thu c nh sau:

Bng 31: nh hng ca tc np mu

Tc np mu(ml/pht)

1,0 1,2 1,5 2,0 2,5 3,0

H (%) Pb 97,82 97,50 97,30 97,00 90,04 80,06

H (%) Cd 97,30 97,00 97,15 96,80 85,07 70,85

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Hnh 7: th biu din s ph thuc

ca hiu sut thu hi vo tc np mu

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0

30

60

90

120

H(%)

Toc do nap mau (ml)

Pb

Cd

Da vo kt qu thc nghim thy rng duy tr tc np mu t 1 2

ml/ph l thch hp. Tuy nhin, tc chm qu th tn nhiu thi gian. V vy

chng ti la chn tc np mu l 1,5 ml/ph cho cc nghin cu v sau.3.2.5 Kho st kh nng ra gii

* ra gii Pb2+- APDC; Cd 2+- APDC ra khi ct cht hp thu c th

s dng cc tc nhn ra gii khc nhau. Chng ti nghin cu cc tc

nhn ra gii nh: Axit HNO3, HCl, H2SO4 trong cc dung mi khc nhau,

vi cc nng khc nhau.

Tuy nhin qua mt qu trnh nghin cu chng ti thy axit HNO3 l

dung mi ra gii tt nht. V vy chng ti kho st kh nng ra gii ca

axit ny trong cc dung mi khc nhau.

Vic chn c dung mi ra gii thch hp l rt quan trng i vi

phng php chit lm giu cc nguyn t kim loi nng. Dung mi c la

chn phi tho mn cc iu kin sau:

Dung mi phi c hiu sut ra gii cao

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Dung mi phi khng ph hu vt liu hp thu

Dung mi phi ph hp vi php o xc nh kim loi nng (F-AAS)

sau khi lm giu cc iu kin ti u chn.

Cng tin hnh vi cc mu nh trn. Sau ra gii vi cng mt th

tch l 15 ml, nhng vi cc h dung mi khc nhau. Kt qu thu c nh

sau:

Bng 32: Kho st nng HNO3 trong cc dung mi ra gii

[HNO3]/dm 0,25 M 0,5 M 1,0 M 1,5 M 2,0 M

H(%) Pb/H2O 46,44 52,30 83,62 82,00 81,24H(%) Cd/H2O 32,50 43,60 56,50 56,00 55,30

H(%) Pb/Axeton 94,36 97,20 97,75 97,30 97,64

H(%) Cd/Axeton 94,00 96,00 97,50 97,00 97,80

T kt qu kho st trn chng ti chn HNO3 1M/Axeton lm dung

dch ra gii cho cc nghin cu v sau.

* Xc nh th tch ra gii: Sau khi xc nh c nng axit HNO3

trong dung mi thch hp chng ti tin hnh kho st th tch dung dch ra gii:

- Pha 100 ml dung dch mu phn tch cha 5 g Cd 2+ v 10g Pb2+,

thm 3 ml thuc th APDC 0,1% v 5 ml m pH=6

- Cho cc dung dch mu phn tch chy qua ct chit vi tc 1,5

ml/pht. Sau ra ct bng 5ml dung dch m pH=6

- Ra gii bng dung dch HNO3 1M/Axeton vi cc th tch khc nhau

tc 0,6 0,8 ml/pht. C cn lm bay hi Axeton trong dung dch, thm

HNO3 1M c mt ca NH4Ac 10% n th tch 5 ml. Xc nh Pb, Cd thu hi

c bng phng php F-AAS kt qu thu c nh sau:

Bng 33: nh hng ca th tch dung dch ra gii n hiu sut thu hi

VHNO31M/Axeton(ml) 5 8 10 15 20

H (%) Pb 75,45 94,50 97,60 97,80 97,00

H (%) Cd 70,80 93,65 96,40 96,55 96,30

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Da vo kt qu thc nghim, chng ti nhn thy rng, ch cn dng 10

ml dung dch HNO31M/Axeton c th gii hp c Pb, Cd hp thu trn ct vi

hiu sut cao. Nn chng ti chn th tch dung dch ra gii l 10 ml cho cc

nghin cu sau.

3.2.6Kho st nh hng ca tc ra gii

- Cho cc dung dch cht phn tch trn qua ct chit pha rn vi tc

1,5 ml/pht, sau khi cht phn tch qua ht ct ra ct bng 5 ml dung dnh

m pH=6.

- Ra gii lng Pb, Cd c lm giu trn ct bng 10 mlHNO31M/Axeton cc tc khc nhau. Kt qu thu c nh sau:

Bng 34: nh hng ca tc ra gii n hiu sut thu hi

Tc ra gii(ml/pht)

0,4 0,6 0,8 1,0 1,5 2,0

H (%) Pb 97,81 97,45 97,30 97,20 85,20 69,50

H (%) Cd 97,40 96,80 96,60 96,25 80,00 70,50

Hnh 8: th biu din s ph thuc ca hiu sut thu hi vo tc ra gii

0.0 0.4 0.8 1.2 1.6 2.0 2.4

0

30

60

90

120

H(%)

Toc do rua giai (ml/phut)

Pb

Cd

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Nhn vo kt qu ta thy, vi tc 0,4 1,0 ml/pht th hiu sut thu

hi cao. Tuy nhin, tc chm qu th tn thi gian m hiu sut cng

khng tng, nn trong cc qu trnh sau chng ti chn tc ra gii l 0,6

0,8 ml/pht.

3.2.7 nh hng ca th tch mu th

kho st nh hng ca th tch mu th, chng ti thay i th tch

dung dch phn tch, nhng vi hm lng Pb2+ v Cd2+ khng thay i. Tin

hnh kho st cc iu kin ti u chn, xc nh hm lng Pb, Cd thu

c bng phng php F-AAS. Kt qu thu c nh sau:Bng 35: nh hng ca th tch mu n hiu sut thu hi

V mu (ml) 100 250 500 750 1000 1500 2000

H (%) Pb 98,60 98,25 97,15 96,55 95,40 85,45 82,30

H (%) Cd 98,40 98,00 97,30 95,85 95,58 80,79 75,21

Hnh 9: th biu din s ph thuc ca hiu sut thu hi vo th tch mu

0 500 1000 1500 2000 2500

0

30

60

90

120

H(%

)

V mau (ml)

Pb

Cd

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Nhn xt: th trn cho thy vic hp thu Pb2+ -APDC, Cd2+-

APDC ln XAD-7 vi lng 70 mg khng b nh hng nhiu bi th tch

mu 1000 ml. Bng vic s dng 10 ml dung dch ra gii h s lm giu

ca ct chit t c gi tr cao.

F =10

1000= 100 (ln)

Nh vy phng php lm giu Pb2+, Cd2+ trn l tt v h s lm giu

tng i cao.

3.2.8 nh hng ca mt s ion n kh nng hp thu ca Pb2+, Cd2+

Trong thc t, ngoi hai nguyn t kho st c th gp mt s cc ion

khc cng c mt trong thnh phn mu,c th nh hng n kh nng hp

thu ca Pb2+- APDC, Cd2+- APDC ln XAD-7. c th chng ti tin hnh

kho st nh hng ca mt s cation nh Ca2+, Mg2+, Na+, K+, Ni2+, Zn2+,

Mn2+, Cr3+, Fe3+ v mt s anion nh Cl-, NO3-. Di y l cc kt qu thu

c:

3.2.8.1 nh hng ca nhm kim loi kim v kim loi kim th

- Chun b cc mu (vi th tch 100 ml) cha hn hp 5 g Cd2+ v 10 g

Pb2+.

- Thm vo mu 3 ml APDC 0,1%, v cc cation kim loi kim v kim

loi kim th vi nng thay i theo bng di y. iu chnh pH ca

dung dch hn hp cc ion kim loi l 6.

- Cho cc dung dch i qua ct chit pha rn (cha 70 mg XAD-7) vi

tc c nh 1,5 ml/pht. Sau khi dung dch i qua ht ct ra ct bng 5 ml

dung dch m pH=6.

- Ra gii bng 10 ml dung dch HNO3 1M trong Axeton. Dung dch

thu c em c cn c ho tan bng HNO3 1M c mt ca NH4Ac 10%

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n th tch 5 ml, xc nh lng Pb; Cd thu hi c bng phng php F-

AAS kt qu thu c nh sau:

Bng 36: nh hng ca kim loi kim v kim th

n hiu sut thu hi ca Pb v Cd

Hm lng cacc ion (mg)

Mu s

1 2 3 4 5 6

Na+ 0 5 10 50 80 100K+ 0 5 10 50 80 100

Mg2+ 0 5 10 50 80 100

Ca2+ 0 5 10 50 80 100

H (%) Pb 97,80 97,72 96,68 98,38 96,42 96,12

H (%) Cd 97,65 97,45 98,95 100,15 98,85 97,30

Kt qu bng 36 cho thy: Kim loi kim v kim loi kim th vi

nng kho st khng nh hng n kh nng hp thu ca phc Pb2+-

APDC v Cd2+- APDC ln nha XAD-7.

3.2.8.2 nh hng ca mt s kim loi nng nhm II

* nh hng ca Zn2+

Bng 37: nh hng ca Zn2+n hiu sut thu hi ca Pb v Cd

Hm lng cacc ion (g)

Mu s1 2 3 4 5 6

Cd2+ 5 5 5 5 5 5

Pb2+ 10 10 10 10 10 10

Zn2+ 0 10 25 50 100 500

H (%) Pb 98,00 97,40 96,65 51,10 43,70 36,85

H (%) Cd 98,53 98,25 94,27 47,60 33,18 21,30

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Hnh 10: nh hng ca Zn2+n hiu sut thu hi ca Pb v Cd

0 2 4 6 80

40

80

120

H(%)

Mau so

Pb

Cd

* nh hng ca Ni2+

Bng 38: nh hng ca Ni2+n hiu sut thu hi ca Pb v Cd

Hm lng cacc ion (g)

Mu s

1 2 3 4 5 6

Cd2+ 5 5 5 5 5 5

Pb2+ 10 10 10 10 10 10

Ni2+ 0 10 25 50 200 500

H (%) Pb 98,70 98,40 90,25 86,80 60,35 42,20

H (%) Cd 97,70 98,74 87,53 80,22 70,86 30,85

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0 2 4 6 80

40

80

120

H(%)

Mau so

Pb

Cd

Hnh11: nh hng ca Ni2+n hiu sut thu hi ca Pb v Cd

* nh hng ca Mn2+

Bng 39: nh hng ca Mn2+n hiu sut thu hi ca Pb v Cd

Hm lng cacc ion (g)

Mu s

1 2 3 4 5 6Cd2+ 5 5 5 5 5 5

Pb2+ 10 10 10 10 10 10

Mn2+ 0 5 10 25 100 500

H (%) Pb 97,90 96,55 97,05 88,00 75,25 29,35

H (%) Cd 96,51 96,42 96,37 57,25 36,00 23,18

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1 2 3 4 5 6

0

40

80

120

H

(%)

Mau so

Pb

Cd

Hnh 12: nh hng ca Mn2+ n hiu sut thu hi ca Pb v cd

3.2.8.3 nh hng ca mt s kim loi nng nhm III

* nh hng ca Fe3+

Bng 40: nh hng ca Fe3+ n hiu sut thu hi ca Pb v Cd

Hm lng cacc ion (g)

Mu s

1 2 3 4 5 6

Cd2+ 5 5 5 5 5 5

Pb2+ 10 10 10 10 10 10

Fe3+ 0 10 25 50 200 500

H (%) Pb 97,45 97,30 96,40 75,25 54,55 36,40H (%) Cd 98,00 97,96 97,35 80,42 67,54 40,20

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0 2 4 6 8

0

40

80

120

H(%)

Mau so

Pb

Cd

Hnh 13: nh hng ca Fe3+ n hiu sut thu hi ca Pb v Cd

* nh hng ca Cr3+

Bng 41: nh hng ca Cr3+ n hiu sut thu hi ca Pb v Cd

Hm lng cacc ion (g)

Mu s

1 2 3 4 5 6

Cd2+ 5 5 5 5 5 5

Pb2+ 10 10 10 10 10 10

Cr3+ 0 10 25 50 200 500

H (%) Pb 97,25 97,00 95,45 82,40 75,60 45,20

H (%) Cd 98,85 98,00 97,80 90,48 70,25 60,20

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1 2 3 4 5 6

0

40

80

120

H(%)

Mau so

PbCd

Hnh 14: nh hng ca Cr3+ n hiu sut thu hi ca Pb v Cd

3.2.8.4 nh hng ca mt s anion

*nh hng ca Cl-

Bng 42: nh hng ca Cl- n hiu sut thu hi ca Pb v Cd

Hm lng cacc ion (mg)

Mu s

1 2 3 4 5 6

Cd2+ * 10-3 5 5 5 5 5 5

Pb2+ * 10-3 10 10 10 10 10 10

Cl- 0 5 10 50 100 150

H (%) Pb 98,55 97,90 98,65 98,70 97,60 97,00H (%) Cd 98,20 97,86 97,72 98,45 97,50 97,20

Nhn xt: Anion Cl- vi nng kho st hu nh khng nh hng

n kh nng hp thu ca phc Pb2+- APDC; Cd2+- APDC ln nha XAD-7.

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* nh hng ca NO3-

Bng 43: nh hng ca NO3- n hiu sut thu hi ca Pb v Cd

Hm lng cacc ion (mg) Mu s1 2 3 4 5 6

Cd2+ * 10-3 5 5 5 5 5 5

Pb2+ * 10-3 10 10 10 10 10 10

NO3- 0 5 10 50 100 150

H (%) Pb 98,40 98,20 97,55 96,25 97,40 97,25

H (%) Cd 98,65 98,70 97,85 97,42 97,30 97,00

Nhn xt: Anion NO3-

vi nng kho st hu nh khng nh hngn kh nng hp thu ca phc Pb2+- APDC; Cd2+- APDC ln nha XAD-7.

3.2.8.5 nh hng ca tng Cation v Anion

Bng 44: nh hng ca tng Cation v Anion n hiu sut thu hi ca

Pb v Cd

Ion l T l ion l/ Pb

(g)

T l ion l / Cd

(g)

Na+, K+ * 103 10 10 20 20

Ca2+,Mg2+ * 103 10 10 20 20

Ni2+, Mn2+ 1 2,5 2 5

Zn2+ 2,5 5,0 5 10

Fe3+, Cr3+ 2,5 5,0 5 10

Cl-, NO3- * 103 15 15 30 30

H (%) 96,50 79,15 97,03 65,26

Sai s (%) 0,57 18,44 1,45 33,72

Khi c mt mt lng ln cc ion kim loi kim, kim loi kim th,

anion vi nng ln khng nh hng n php xc nh Pb v Cd. Nhng

khi c mt cc ion kim loi nng vi t l trn th hiu sut thu hi ca Pb v

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Cd gim. S gim thu hi ny l do s hp thu cnh tranh ca cc phc ion

kim loi khc.

3.3 Phn tch mu giTrong thc t, cc mu nc cha nhiu cc ion kim loi khc nhau.

nh gi phng php tch v lm giu ny, chng ti tin hnh th nghim

cc mu gi c thnh phn tng t mu thc.

Pha cc mu gi c th tch 1 lt, thnh phn mu gi nh sau:

Bng 45: Nng cc cation kim loi trong mu gi

Cation kim loi N

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Tách, làm giầu, xác định lượng vết Pb và Cd trong một số đối tượng bằng kỹ thuật chiết pha rắn và phương pháp quang phổ