Nghiên cứu phương pháp trắc quang xác định asen bằng thuốc thử safranine

TRNG I HC KHOA HC T NHIN

I HC QUC GIA H NI

NGUYN L THANH VN

NGHIN CU PHNG PHP TRC QUANG

XC NH ASEN BNG THUC TH SAFRANINE

Lun vn thc s khoa hc

H Ni - 2012

TRNG I HC KHOA HC T NHIN

I HC QUC GIA H NI

NGUYN L THANH VN

NGHIN CU PHNG PHP TRC QUANG

XC NH ASEN BNG THUC TH SAFRANINE

Chuyn ngnh: Ha phn tch

M s: 60.44.29

Lun vn thc s khoa hc

Ng-i h-ng dn khoa hc: GS. TS. Trn T Hiu

H Ni - 2012

DANH MC HNH V BNG HNH Trang

Hnh 1.1: nh hng ca pH n dng tn ti ca asen....................... ...........4

Hnh 1.2: th nh hng ca pH/Eh n dng tn ti ca asen....................4

Hnh 1.3: Bnh ung th da do asen gy ra......................................................11

Hnh 1.4: Biu phn b khu vc nhim asen trn th gii......................13

Hnh 1.5: nhim asen ti Vit Nam.............................................................15

Hnh 1.6: nhim asen ti ng bng chu th sng Hng...........................16

Hnh 3.1: Ph hp th quang ca dung dch Safranin khi c mt As(III);

KIO3 v HCl.....................................................................................................33

Hnh 3.2: S ph thuc ca hp th quang theo thi gian.........................35

Hnh 3.3 : nh hng ca nng KIO3 n hp th quang ca dung dch....37

Hnh 3.4: nh hng ca nng Safranin n hp th quang ca dung

dch..................................................................................................................39

Hnh 3.5. th kho st nh hng ca nng HCl...................40

Hnh 3.6: th kho st khong tuyn tnh xc nh As(III)................49

Hnh 3.7: ng chun xc nh As(III)....................................................49

Hnh 3.8: ng thm chun xc nh As(III) trong mu nc ngm s 852

Hnh 3.9: ng thm chun xc nh As(III) trong mu nc ngm s 1....57

Hnh 3.10: ng thm chun xc nh As(III) trong mu nc ngm s 2..58

Hnh 3.11: ng thm chun xc nh As(III) trong mu nc ngm s 3. 59

Hnh 3.12: ng thm chun xc nh As(III) trong mu nc ngm s 4. 60





BNG

Bng 1.1: Hm lng asen cc vng khc nhau trn th gii..............13

Bng 3.1: nh hng ca nng KIO3 n php phn tch.................36

Bng 3.2: nh hng ca nng Safranin n php phn tch............38

Bng 3.3: nh hng ca nng HCl..........................................40

Bng 3.4: nh hng ca ion NO3- n php xc nh As(III) 6,0ppm.42

Bng 3.5: nh hng ca ion SO42-

n php xc nh As(III) 6,0ppm ........43

Bng 3.6: nh hng ca ion Ca2+ n php xc nh As(III) 2,0ppm .........44

Bng 3.7: nh hng ca ion Ba2+ n php xc nh As(III) 2,0ppm .........45

Bng 3.8: nh hng ca ion Zn2+ n php xc nh As(III) 6,0ppm .........45

Bng 3.9: nh hng ca ion Fe3+ n php xc nh As(III) 2,0ppm ........46

Bng 3.10: nh hng ca ion Cu+ n php xc nh As(III) 2,0ppm 47

Bng 3.11: Kho st khong tuyn tnh xc nh As(III) .......48

Bng 3.12: Xc nh hm lng asen trong mu nc ngm s 8..............52

Bng 3.13: nh gi lp li ca phng php...... ....54

Bng 3.14: Thng tin v cc mu nc ngm... 55

Bng 3.15: Xc nh hm lng As(III) trong mu nc ngm s 1..56

Bng 3.16: Xc nh hm lng As(III) trong mu nc ngm s 2......57

Bng 3.17: Xc nh hm lng As(III) trong mu nc ngm 3.............58

Bng 3.18: Xc nh hm lng As(III) trong mu nc ngm 4.........59



Bng 3.21: Xc nh hm lng As(III) trong mu nc ngm 7.................63

Bng 3.22: Xc nh hm lng As(III) trong mu nc ngm 8.............65

MC LC

M U ........................................................................................................... 1

CHNG 1: TNG QUAN ............................................................................. 3

1.1. Gii thiu chung v asen ............................................................................ 3

1.1.1. Cc dng tn ti v tnh cht l ha hc ca asen (As) .......................... 3

1.1.1.1. Cc dng tn ti ca asen ..................................................................... 3

1.1.1.2. Tnh cht vt l ..................................................................................... 5

1.1.1.3. Tnh cht ha hc ................................................................................. 5

1.1.2. c tnh ca asen v s tch ly trong c th ngi ............................... 9

1.1.3. nhim asen trong nc ngm trn th gii v Vit Nam .................. 12

1.1.3.1. nhim Asen trn th gii ................................................................ 12

1.1.3.2. nhim asen ti Vit Nam ................................................................ 15

1.2. Mt s phng php xc nh Asen ........................................................ 17

1.2.1. Phng php phn tch o quang phn t ............................................. 17

1.2.1.1. Phng php o quang vi bc dietyl ithiocacbamat ...................... 17

1.2.1.2. Phng php xanh molipden ............................................................. 17

1.2.1.3. o quang xc nh asen sau khi hp th asin bng hn hp ............. 18

1.2.1.4. Phng php xc nh asen bng thuc th Leuco crystal violet (LCV) 19

1.2.1.5. Phng php ng hc xc tc .......................................................... 19

1.2.1.6. Xc nh lng vt As(III) bng phng php ng hc- trc quang

da trn nh hng c ch phn ng gia kalibromua v kalibromat

trong mi trng axit ............................................................................ 20

1.2.1.7. Xc nh As(III) da trn h Ce(IV)/Ce(III). .................................... 20

1.2.1.8. Phng php quang ph hp ph nguyn t (AAS) .......................... 21

1.2.2. Phng php hunh quang .................................................................... 23

1.2.2.1. Xc nh As(III) bng thuc th fluorescein ..................................... 23

6

1.2.2.2. Phng php dng chy - hunh quang xc nh axit dimethyl

arsinic(DMAA) trong thuc dit c s dng phn ng quang ha trc tip 24

1.2.2.3. Xc nh Asen bng phng php hunh quang phn t vi h thuc

th murexit Cr(VI) ............................................................................. 24

1.2.2.4. Phng php biosensor s dng vi khun ch th .............................. 25

CHNG 2: THC NGHIM ...................................................................... 27

2.1. Mc tiu, ni dung v phng php nghin cu ..................................... 27

2.1.1. Nguyn tc ca phng php trc quang xc nh hm lng asen bng

Safranin. ................................................................................................... 27

2.1.2. Ni dung nghin cu ............................................................................. 28

2.2. Ha cht, dng c, thit b ....................................................................... 29

2.2.1. Dng c, thit b .................................................................................... 29

CHNG 3: KT QU V THO LUN .................................................. 33

3.1. Nghin cu phng php xc nh As (III) da trn h phn ng oxi ha

kh As(III), KIO3 v Safranin. .................................................................... 33

3.1.1. Nghin cu chn iu kin ti u ca phn ng ch th ....................... 33

3.1.1.1. Ph hp th ca sn phm phn ng ch th ....................................... 33

3.1.1.2. Nghin cu nh hng ca thi gian phn ng ................................. 34

3.1.1.3. nh hng ca nng KIO3............................................................ 36

3.1.1.4. nh hng ca nng thuc th Safranine: ................................... 37

3.1.1.5. nh hng ca nng HCl: ............................................................ 39

3.1.2. nh gi phng php phn tch .......................................................... 41

3.1.2.1. chn lc ca phng php phn tch [21] .................................... 41

3.1.2.2. Kho st khong tuyn tnh ................................................................ 47

3.2. Phn tch mu thc t ............................................................................... 55

3.2.1. Xc nh hm lng As(III) trong mu nc ngm ............................. 55

KT LUN ..................................................................................................... 67

1

M U

Hin nay, mi trng nhim l vn mang tnh ton cu, l h qu t

khai thc m, cng nghip, nng nghip, v cc hot ng qun s Cng

vi nhim hp cht hu c th s c mt kim loi v kim cng l nhng

ngun chnh ca nhim nghim trng c th e da sc khe con ngi

[19]. Trong s cc nguyn t c hi asen (As) - nguyn t c tnh c, chc

nng sinh hc r rng ang c th gii quan tm.

Asen l mt nguyn t vi lng rt cn thit i vi qu trnh sinh trng

v pht trin ca ng thc vt. Asen cng c s dng rng ri trong k

thut v i sng nh trong cng nghip nhum, thuc tr su, dc liu,

Tuy nhin hm lng cao, asen gy tc hi to ln i vi h sinh thi.

Asen cn tr qu trnh quang hp ca cy, gy ra hin tng rng l thc

vt. Asen cng rt c hi i vi con ngi v ng vt. Khi xm nhp vo

c th asen c th gy hng lot chng bnh nguy him nh cc bnh d dy,

ri lon chc nng gan, hi chng en da v ung th da,[9] c tnh ca

asen rt khc nhau, asen (III) c gp 50 ln asen (V), asen dng v c c

hn dng hu c. Do hm lng asen trong mi trng lun c quy

nh nhng nng rt thp. Gii hn cho php ca asen trong nc sinh

hot theo tiu chun ca t chc y t th gii l 0,01 mg/l, theo tiu chun VN

5502 2003 l 0,01mg/l [8].

Ngun gy nhim asen t cng nghip, s t chy cc khong cha

asen v ngun khong trong t nhin giu asen trong c s ha tan cc

khong sunfua ca asen trong t l ch yu. Asen l thnh phn t nhin ca

lp trm tch v tri t nn n thng c mt trong cc tng nc ngm v

nc mt. mt s khu vc trn th gii, nc ngm c hm lng asen rt

cao do lp trm tch c cu trc, thnh phn ha hc thun li cho vic ha

tan asen t t ra nc. Hin tng ny c pht hin ti cc khu vc ng

2

bng chu th thp trng, xy ra lt li hng nm, dng chy thy vn chm,

cc lp bi tch tr thiu oxy (mang tnh kh) thun li cho vic gii phng

asen t t ra nc. nhim asen trong nc ngm dng cho sinh hot v

ti tiu c pht hin trong khong 20 nm qua ti Bangladet, n ,

Trung quc, Vit nam, Campuchia, Achentina, Chile, [18] Vit nam, s

nhim asen c pht hin nhiu ni nh H Ni, H Nam, Hi

Dng, Ph Th, C Mau, Nhiu nghin cu v nhim asen trong nc

ging khoan ti Vit Nam c tin hnh trong nhng nm va qua. Trong

s cc phng php phn tch nh phng php ng hc trc quang,

phng php ph khi plasma cm ng cao tn (ICP - MS), phng php ph

hp th nguyn t (AAS), hoc nhiu phng php khc ...th phng php

trc quang l phng php ang c quan tm nghin cu xc nh asen

v phng php ny c nhy v chnh xc cao, quy trnh phn tch n

gin khng tn nhiu ho cht v khng i hi trang thit b t tin. V vy,

ng gp vo vic pht trin ng dng phng php ny vi i tng

nghin cu l nc ngm chng ti chn ti: Nghin cu phng php

trc quang xc nh asen bng thuc th Safranine.

3

CHNG 1: TNG QUAN

1.1. Gii thiu chung v asen

1.1.1. Cc dng tn ti v tnh cht l ha hc ca asen (As)

1.1.1.1. Cc dng tn ti ca asen

Asen (k hiu As) c s nguyn t l 33, l nguyn t ph bin th 12

trong v tri t chim 1.10-4% tng s nguyn t trong v tri t, khi

lng nguyn t ca n bng 74,92; tn ti ch yu dng asen 3 v 5. Asen

c trong cc khong vt sunfua: reanga (As4S4), oripimen (As2S3). Nguyn t

asen c mt vi dng th hnh, dng kim loi v dng khng kim loi. Dng

khng kim loi ca asen c to nn khi lm ngng t hi ca n, khi

asen c mu vng, dng kim loi ca asen c mu trng bc [3].

Trong t nhin, Asen khng tn ti dng n cht m tn ti di dng

cc hp cht v c (asenit, asenat) v hu c (metyl asen, dimetyl asen).

Asen c mt khp ni trong t nhin, trong t, trong , trong khong,

trong qung, trong cc c th sng

Asen thng c hm lng cao trong cc khong ca st, ng, ch hoc

trong nhng khong sunfua, trong khong asenopyrit c hm lng asen

cao nht.

Ty theo tng iu kin mi trng m asen c th tn ti nhiu trng

thi oxi ha khc nhau: -3, 0, +3,+5. Trong nc t nhin, asen tn ti ch

yu 2 dng hp cht v c l asenat [As(V)], asenit [As(III)]. As(V) l dng

tn ti ch yu ca asen trong nc b mt v As(III) l dng ch yu ca

asen trong nc ngm. Dng As(V) hay cc arsenate gm AsO43-

, HAsO42-

,

H2AsO4-, H3AsO4; cn dng As(III) hay cc arsenit gm H3AsO3, H2AsO3

-,

HAsO32-

v AsO33-. Asen cn tn ti nhiu dng hp cht hu c nh:

metylasen, imetylasen. Cc dng tn ti ca asen trong nc ph thuc vo

4

pH v th oxi ho kh Eh ca mi trng. nh hng ca pH n dng tn ti

ca asen c trnh by nh trn hnh 1.1 v hnh 1.2 [35].

Hnh 1.1: nh hng ca pH n dng tn ti ca Asen

Th xi-ha kh v pH l cc yu t quyt nh n dng tn ti ca

asen trong mi trng. iu kin xi-ha, v pH thp (nh hn 6,9) dng

H2AsO4- chim a s, trong khi pH cao HAsO4

2- li chim u th (H3AsO4

0

v AsO43-

ch c th tn ti trong mi trng axit mnh v baz mnh).

iu kin kh v pH thp (

5

1.1.1.2. Tnh cht vt l

Asen l nguyn t c mt vi dng th hnh dng kim loi v khng kim

loi. Asen tn ti 3 dng As: l dng bn, tng i cng gin; As: dng v

nh hnh, gin; As: gm nhiu phn t As4 gi bn, mm nh sp, d tan

trong dung mi CS2. As4 l dng khng kim loi, nhit thng di tc

dng ca nh sng n chuyn sang dng kim loi. V tnh cht vt l Asen

mang tnh cht ca kim loi.

T trng: 5,72g/cm3 140C

Nhit nng chy: 8170C 37 atm

Nhit si: 6150C

m in: = 2

M = 74,9216g/mol

Nng lng ion ha t th nht n th 5 l: 10,5; 20,1; 28,0; 49,9; 62,5 eV.

1.1.1.3. Tnh cht ha hc

V mt tnh cht ha hc cc hp cht ca Asen ging nh tnh cht ca

mt s phi kim.

Tnh cht ca asin (AsH3) [4,5,10]

As3-

thng tn ti di dng AsH3 hoc asin hu c. AsH3 c cu to tng

t NH3, PH3.

N c mt s tnh cht vt l sau:

- di lin kt As-H: 1,52Ao, gc lin kt 92o

- Nng lng lin kt trung bnh = 71 kcal/mol

- Nhit nng chy l: -116oC, nhit si l: -62oC

- L cht kh khng mu, nng hn khng kh khong 2,7 ln v c mi

hnh nhn ng hay mi ti.

V ha tnh:

AsH3 l hp cht thu nhit nn d b phn hy khi un nng (300oC),

asen bm ln thnh bnh to mt lp lp lnh nh gng.

6

AsH3 c tnh kh mnh c th bc chy trong khng kh. Chng kh

c mui ca kim loi t Cu tr v sau:

4AsH3 +10H2SO4 3SO2 + 4AsSO4(OH) + 14H2O + 3S

AsH3 + 6AgNO3 + 3H2O 6Ag + 6HNO3 + H3AsO3

AsH3 bc chy trong khng kh to thnh As2O3

2AsH3 + 3O2 As2O3 + 3H2O + 44,2 kcal

AsH3 tc dng vi HgCl2 tm trn giy lc to ra hp cht c mu bin i t

vng nu.

AsH2(HgCl) AsH(HgCl)2 As(HgCl)3 As2Hg3

Tnh cht ny c p dng phn tch bn nh lng bng phng php so

mu. AsH3 tc dng vi I2/KI v I2/ CO32- pH = 8

AsH3 + 4I2 + 4H2O H3AsO4 + 8I- + 8H

+

Tnh cht ha hc ca Asen ha tr (III) [4,7,23]

Ch yu As(III) tn ti dng cc hp cht nh: As2O3, As2S3, AsCl3,

AsO33-

, H2AsO3

* As2O3: L oxit mu trng hay cn gi l asen trng, t tan trong nc

(1,7g trong 100g H2O) 15oC dung dch bo ha cha khong 1,5% As2O3.

Khi tan trong nc to thnh axit asen.

As2O3 + 3H2O 2As(OH)3

As(OH)3 H3AsO3 l cht lng tnh nhng tnh axit tri hn.

Dng oxit ca As2O3 trng thi kh tn ti di dng phn t kp

As4O6.

Trng thi rn tinh th c mu vng. 250oC tan vo nc cho dung

dch 2%. As2O3 tan tt trong kim

As2O3 + 4NaOH 2NaHAsO3 + H2O

Khi un nng, As2O3 b C,H2 kh d dng sinh ra kim loi

As2O3 + 6H2 2As + 3H2O

7

As2O3 (As4O6) th hin tnh kh khi tc dng vi O3, H2O2, FeCl3,

K2CrO7, HNO3 khi ta c:

3As4O6 + 8HNO3 + 14H2O 12H3AsO4 + 8NO

As2O3 tc dng vi kim loi trong mi trng axit

As2O3 + 6Zn + 12HCl 6ZnCl2 +2AsH3 + H2O

Phn ng ny ng dng trong phn tch nh lng.

* AsX3: cng ging nh hp cht As2O3, AsX3 (X l Cl, Br, I, F) l nhng

hp cht d dng thy phn to mi trng axit

AsCl3 + 3H2O H3AsO3 + 3HCl

AsF3, AsCl3 l cht lng khng mu, snh

AsBr3, AsI4 l cht rn d nng chy

* Phn ng ha hc ca AsO33-

H3AsO3 khng iu ch c dng t do m ch tn ti trong dung

dch nc.

Khi c cn bng: H3AsO3 H2O + HAsO2

Kpl = 6.10-10

cn bng chuyn dch mnh v pha phi.

* Tc dng vi Na2S v (NH4)2S

Cc sunfua kim loi kim v sunfua amoni u khng to c kt ta

sunfua vi cc dung dch axit H3AsO3 trc tip m to mui thio tan

H3AsO3 + 3Na2S Na3AsS3 + 3N aOH

H3AsO3 + 3(NH4)2S (NH4)3AsS3 + 3NH4OH

Nhng tc dng gia AsO33-

v Na2S trong mi trng axit HCl 6N to

kt ta vng

2AsO33-

+ 12H+ + 3Na2S As2S3 + 6H2O + 6Na

+

(vng)

C th tch kt ta ra c

* Tc dng vi H2S

8

Tc dng vi H2S trong mi trng axit cho kt ta mu vng:

2H3AsO3 + 6HCl 2AsCl3 + 6H2O

2AsCl3 + 3H2S As2S3 + 6HCl

* Tc dng vi AgNO3

AsO33-

+ 3Ag+ Ag3AsO3 vng

Ag3AsO3 + 6NH4OH 3[Ag(NH3)2]+ + AsO3

3- + 6H2O

* Tc dng vi dung dch CuSO4

Dung dch CuSO4 tc dng vi H3AsO3 khi c mt xt n da cho kt

ta mu vng lc hyroasenit ng

H3AsO3 + CuSO4 CuHAsO3 + H2SO4

NaOH ha tan c kt ta ny v dung dch c mu xanh tm

NaOH + CuHAsO3 CuNaAsO3 + H2O

Phn ng ny c dng trong phn tch nh tnh

* Tc dng vi Cr2O72-

trong mi trng axit

3AsO33-

+ Cr2O72-

+ 8H+ 3AsO4

3- + 2Cr

3+ + 4H2O

* Tc dng vi I2

Phn ng trong mi trng NaHCO3 pH = 8

AsO33-

+ I2 + H2O AsO43-

+2I- + 2H

+

Phn ng ny p dng phn tch nh lng v nh tnh.

Cc hp cht ca Asen (V) [4,7]

As (V) thng tn ti dng cc hp cht nh : As2O5, As2S5, AsCl5,

AsO43-

, As(OH)6, H3AsO4 As (V) c mc oxi ha cao nht ca Asen. Hp

cht As(V) c tnh axit mnh hn tnh baz.

* As2O5: trong cc hp cht As(V) th hp cht As2O5 l cht hnh khi

ging thy tinh.

N khng bn, tan trong nc v b thy phn mnh, c tnh cht tng

t P2O5.

9

As2O5 + 3H2O 2H3AsO4

As2O5 phn hy nhit cao (400oC) thnh oxi v oxit c s oxi ha

thp hn.

2As2O5 As4O6 + 2O2

Tc dng vi HCl

2As2O5 + 8HCl As4O6 + 4H2O + 4Cl2

* As2S5: C mu vng, khng tan trong nc v HCl ch tan trong NaOH

v HNO3 c, nc cng thy.

As2S5 + 6NaOH Na3AsS4 + Na3AsO3S + 3H2O

3As2S5 + 10HNO3 c + 4H2O 6H3AsO4 + 10NO + 15S

* Dng AsO43-

v H3AsO4

- Tc dng vi H2S

Trong mi trng axit HCl 6N ngui, asenic s tc dng vi H2S to ra S

ngay nhng dung dch vn khng mu, ch mt thi gian khi As(V) b kh v

As(III) th kt ta vng mi xut hin.

H3AsO4 + H2S H3AsO3 + S + H2O

2H3AsO3 + 6HCl 2AsCl3 + 6H2O

2AsCl3 + 3H2S As2S3 + 6 HCl

(vng)

- Tc dng vi hn hp MgCl2, NH3 v NH4+

H3AsO4 + MgCl2 + 3NH4OH MgNH4AsO4 + 2NH4Cl + 3H2O

1.1.2. c tnh ca asen v s tch ly trong c th ngi

Asen l cht c mnh c kh nng gy ung th cao, liu LD50 i vi

con ngi l 1 4 mg/kg trng lng c th. Tuy nhin, ty thuc vo cc

trng thi oxi ha ca asen m asen th hin tnh c khc nhau. C As(III) v

As(V) u l nhng cht c, cc hp cht asen v c c hn so vi asen

10

hu c [1]. Tnh c ca asen theo th t: AsH3>asenit> asenat >

monomethyl arsenoic axit (MMAA) > dimethyl arsenic axit (DMAA). C

khong 60 70% asen v c i vo c th v c gii phng ra ngoi bng

ng nc tiu dng DMAA v MMAA [26,28].

- C ch gy c ca As(III)

Khi b nhim c AsO3-, As(III) s tn cng vo nhm hot ng SH

ca enzym, kha cht chc nng hot ng ca enzym lm t lit hot ng

ca enzym. Khi b nhim As(III) nng cao, n s lm ng t protein c

th l do As(III) tn cng vo cc lin kt c nhm sunfua trong protein [14].

- C ch gy c ca As(V) (AsO4-): c tnh cht tng t nh PO4

3-, n

s thc hin phn ng thay th PO43-

gy c ch enzym ngn cn to ra cht

ATP (Adenozin triphotohat) l cht sn sinh ra nng lng cho c th. Khi b

nhim AsO4- s tham gia phn ng th PO4

3-, to ra sn phm khng phi l

ATP, nn khng sn sinh ra nng lng cho c th [14].

Tm li, tc dng c ca asen l do n lm ng t protein, tc dng

vi nhm chc hot ng SH ca enzym lm cho enzym b th ng ha,

mt hn kh nng hot ng sinh ha ca enzym, ph hy qu trnh photphat

to ATP.

Nhng cht c th gii c Asen l nhng hp cht c cha cc nhm chc

SH, v d 2,3- dimecaptopropanol. Hp cht ny c th to phc vi AsO33-

,

nh vy m AsO33-

khng phn ng vi cc nhm SH ca enzyme na.

Asen c xem nh l cht gy ung th i vi con ngi nhng kh

nng gy ung th ph thuc vo cc dng ha hc ca asen nh trng thi oxi

ha. Mt t l nh asen sau khi i vo c th s c tch t trong cc phn

ca c th v sau s c bi tit ra ngoi qua tc, mng, da, phn v m

hi. S tch ly asen trong c th sau 5 10 nm s gy ra bnh v asen [35].

Cc bnh thng gp khi b nhim c asen l ung th da, bng quang v ung

11

th phi v gan... iu ny thng xy ra vng c s phi nhim asen hoc

nhng vng c hm lng asen cao trong nc ung [20,25].

Hnh 1.3: Bnh ung th da do asen gy ra

S phi nhim asen v c xy ra trong c th thng qua ng ht kh

bi cng nghip v qu trnh chuyn ha qua ng thc n v nc ung. S

phi nhim asen hu c xy ra ch yu thng qua chui thc n. Nu mt

ngy ht lng bi asen t 0,1 4 g/ngy v c th hp th mt lng thc

n c hm lng asen khong t 7 330 g/ngy th sau khi i vo c th

c khong 80 100% lng asen c hp th qua d dy v l phi; 50

70% asen c bi tit qua ng nc tiu v mt lng nh c hp ph

qua ng tc, mng tay, mng chn [28].

Ung th da l c tnh ph bin nht ca asen. Vi nhng vng c hm

lng asen trong nc sinh hot < 300 g/l, trung bnh (300 600 g/l), cao

(>600 g/l) th t l ung th da tng ng s l 2,6/1000; 10,1/1000 v

24,1/1000 [29].

Sc khe ca con ngi b nh hng do qu trnh chuyn ha asen v

c trong nc ngm tr nn ph bin. Cc nghin cu gn y cho thy

asen v c c th thc hin qu trnh chuyn ha trong c th bng hai qu

trnh an xen nhau: s kh lin tc v s methyl ha: s kh asen (V) thnh

asen (III), tip theo l oxi ha methylasen (V) [20,23]. Trong mu As(V)

c kh thnh As(III) v c a ti t bo gan ri c methyl ha to

12

thnh methylasonate (MA) v dimethylarsenate (DMA). Cc hp cht c

to thnh sau qu trnh methyl ha t c hn so vi asen v c, do vy qu

trnh chuyn ha ny c xem nh l c ch gii c asen [20]. Mt s

nghin cu gn y ch ra As v c ha tr III c methyl ha trong c

th c tnh c khc nhau trong cc loi t bo ca c th. Trong t bo gan,

axit monomethylarson (MMA) c gp 26 ln so vi As(III), trong mt s

loi t bo (t bo gan, t bo da, t bo cung phi) monomethylarsine

(MMAO) c hn so vi As v c ha tr III [20].

1.1.3. nhim asen trong nc ngm trn th gii v Vit Nam

Hin nay do s bng n dn s th gii, vn cung cp nc sch cho

sinh hot ang l mt vn ln m x hi quan tm. Trong khi ngun nc

b mt: sng, sui, ao, h ang ngy cng b nhim nng bi nc thi sinh

hot, nc thi t cc nh my cng nghip th vic s dng ngun nc

ngm nh l mt gii php hu hiu cho vic cung cp nc sch. Nc

ngm t chu nh hng bi cc tc ng ca con ngi. Cht lng nc

ngm thng tt hn cht lng nc b mt. Trong nc ngm, hu nh

khng c cc ht keo hay cn l lng, cc ch tiu vi sinh trong nc ngm

cng tt hn. Tuy nhin, khi khai thc ngun nc ngm, chng ta phi i

mt vi mt vn rt ng lo ngi, l vic nhim c kim loi nng, c

bit l asen. Ngun asen c trong nc ngm ch yu do s ho tan cc hp

cht c cha asen trong t, do qu trnh phong ho, hot ng ni la v

mt phn do qu trnh sn xut cng, nng nghip to ra.

1.1.3.1. nhim Asen trn th gii

Hin nay trn th gii c hng chc triu ngi b bnh en v rng

mng chn, sng ho da, ung th da do s dng ngun nc sinh hot c

nng asen cao. Nhiu nc pht hin hm lng asen rt cao trong

ngun nc sinh hot nh Canada, Alaska, Chile, Arhentina, Trung Quc,

13

India, Thi Lan, Bangladesh ... S c mt ca asen cc vng khc nhau trn

th gii c tng hp trong bng 1.1 v hnh 1.4 [30].

Bng 1.1: Hm lng asen cc vng khc nhau trn th gii

Hnh 1.4: Bn phn b khu vc nhim asen trn th gii [30]

Trung Quc, trng hp bnh nhn nhim c asen u tin c pht

hin t nm 1953. S liu thng k cho thy 88% nhim qua thc phm, 5%

t khng kh v 7% t nc ung. n nm 1993 mi c 1546 nn nhn mc

cn bnh Asenicosis (bnh nhim c asen) nhng cho n thi im ny

pht hin 13500 bnh nhn, trong s 558000 ngi c kim tra 462 lng

thuc 47 vng b lit vo khu vc nhim asen cao. Trn c nc Trung Quc

14

c ti 13 - 14 triu ngi sng trong nhng vng c ngun nc b nhim

asen cao, tp trung nhiu nht tnh An Huy, Sn Ty, Ni Mng, Ninh H,

Tn Cng. Ti Sn Ty pht hin 105 lng b nhim asen. Hm lng

asen ti a thu c trong nc ung l 4,43 mg/l gp ti 443 ln gi tr asen

cho php ca t chc y t th gii WHO (10g/l).

Khu vc c vn ln nht l vng ng bng chu th sng Ganges

nm gia Ty Bengal ca n v Bangladesh (Theo Chowdhury v cng

s, 1999). Ty Bengal, trn 40 triu ngi c nguy c nhim c asen do

sng trong cc khu vc c nng asen cao. Ti nay c 0,2 triu ngi b

nhim v nng asen ti a trong nc cao gp 370 ln nng cho php

ca WHO. Ti Bangladesh, trng hp u tin nhim asen mi c pht

hin vo nm 1993, nhng cho n nay c ti 3000 ngi cht v nhim c

asen mi nm v 77 triu ngi c nguy c nhim asen. T chc Y t Th

gii phi coi y l "v nhim c tp th ln nht trong lch s".

Con s bnh nhn nhim c asen Archentina cng c ti 20 000

ngi. Ngay c cc nc pht trin mnh nh M, Nht Bn cng ang phi

i ph vi thc trng nhim asen. M, theo nhng nghin cu mi nht

cho thy trn 3 triu ngi dn M c nguy c nhim c asen, mc nhim

asen trong nc ung dao ng t 0,045 0,092 mg/l. Cn Nht Bn,

nhng nn nhn u tin c triu chng nhim asen c pht hin t nm

1971, cho n nm 1995 c 217 nn nhn cht v asen.

15

1.1.3.2. nhim asen ti Vit Nam

Hnh 1.5: nhim asen ti Vit Nam

Do cu to t nhin ca a cht, nhiu vng ca nc ta nc ngm b

nhim asen (thch tn). Theo thng k cha y , nc ta hin c khong

hn 1 triu ging khoan, nhiu ging trong s ny c nng asen cao hn t

20-50 ln theo tiu chun ca B Yt 0,01mg/l, gy nh hng xu n sc

kho, tnh mng ca cng ng. Vng nc b nhim asen ca nc ta kh

rng nn vic cnh bo nhim c t nc ging khoan cho khong 10 triu

dn l rt cn thit. Nhng nghin cu gn y cho thy vng chu th sng

Hng c nhiu ging khoan c hm lng asen cao vt qu tiu chun ca

T chc Y t Th gii (WHO) v vt qu tiu chun B Y t Vit Nam

(0,01mg/l). Nhng vng b nhim nghim trng nht l pha Nam H Ni,

H Nam, Hng Yn, Nam nh, Ninh Bnh, Thi Bnh v Hi Dng.

16

Hnh 1.6: nhim asen ti ng bng chu th sng Hng

ng bng sng Cu Long cng pht hin ra nhiu ging khoan c

hm lng asen cao nm ng Thp v An Giang. S nhim asen min

Bc hin ph bin v cao hn min Nam. Qua iu tra cho thy 1/4 s h

gia nh s dng trc tip nc ngm khng qua x l ngoi thnh H Ni

b nhim asen, tp trung nhiu pha Nam thnh ph (20,6%), huyn

Thanh Tr (41%) v Gia Lm (18,5%). iu nguy him l asen khng gy

mi kh chu khi c mt trong nc ngay c khi hm lng gy cht ngi

nn nu khng phn tch mu m ch bng cm quan th khng th pht hin

c s tn ti ca asen. Bi vy cc nh khoa hc cn gi asen l st th v

hnh. Hin nay c khong 13,5% dn s Vit Nam (10-15 triu ngi ang

s dng nc n t ging khoan nn rt d b nhim asen).

T nm 1999, t chc UNICEF, mt s c quan chnh ph Vit nam, cc

vin nghin cu bt u tp trung nghin cu mt cch nghim tc v asen

v tm hng gim nh.

17

1.2. Mt s phng php xc nh Asen

1.2.1. Phng php phn tch o quang phn t

1.2.1.1. Phng php o quang vi bc dietyl ithiocacbamat

Dng H mi sinh kh asen v c thnh asin v dn kh asin vo ng

hp th cha bc ietylithiocacbamat (AgDDC) trong piridin hoc

cloroform. Khi asin b hp th to dung dch c mu tm v tin hnh

o hp th quang bc sng = 535 nm.

AsH3 + 6AgDDC = AsAg33AgDDC + 3H-DDC

AsAg33AgDDC + 3NR3 + 3 HDDC = 6Ag + As(DDC)3 + 3(NR3HDDC)

Trong NR3 l baz hu c bc 3 cn thit cho sn phm cui cng

hnh thnh cc ht keo bc quyt nh mu tm .

Tp cht AgNO3 ngn cn php xc nh do tng cng mu, c

loi b bng cch ho tan AgDDC trong piridin sau pha long bng nc,

lc tch DDC, ra bng nc trn giy lc.

Trong qu trnh kh, hp cht asen thnh asin ng thi cng to ra cc

hp cht d bay hi: SbH3, PH3, GeH3, H2S. Nhng cht ny sau cng tc

dng vi AgDDC cho mu tng t nh asen. Do , hn ch nh hng

ta phi cho hi i qua ng lm sch cha bng thu tinh c tm

Pb(CH3COO)2. loi tr nh hng ca mt s nguyn t v tng hiu qu

ca qu trnh kh th ngi ta kh trc dung dch bng cch a SnCl2 v KI

vo (KI, SnCl2 s loi tr nh hng ca Pb, mui Ni v lm tng qu trnh

kh asen thnh asin) [11].

1.2.1.2. Phng php xanh molipden

Nguyn tc ca phng php l As(V) phn ng vi molipdat to thnh

axit d a, axit ny b kh bng hidrazin, SnCl2, hydroquinon hay axit

ascorbic to thnh molipden xanh hp th quang max = 840 nm

H3AsO4 + 12(NH4)2MoO4 + 21HNO3 12(NH4)3[AsMo12O40] vng +

21NH4NO3

18

Trc khi xc nh phi chuyn tt c cc dng ca As v As(V). Cc

cht gy nh hng Ge, SiO2, P loi bng chng ct, ion PO43-

, SiO33-

gy cn

tr b loi bng chit clorofom. Phng php ny thng s dng xc nh

asen trong qung c Ge. Gii hn nng asen cho php xc nh bng

phng php ny l 0,01 0,2 ppm [22,34]

1.2.1.3. o quang xc nh asen sau khi hp th asin bng hn hp

AgNO3-PVA-C2H5OH

Mu cha As(III) v As(V) c x l vi KI, NaBH4 trong mi trng

H2SO4 to thnh asin:

2NaBH4 + 6H3O 2H3BO3 + 2Na+ + 14H

+

12H+ + 2As

3+ 2AsH3 + 3H2 (H

+ hidro mi sinh)

Kh asin sinh ra c hp th vo dung dch hn hp AgNO3-HNO3-PVA-

C2H5OH s to ra Ag3As.3AgNO3

AsH3 + 6AgNO3 Ag3As.3AgNO3 +3HNO3

Ban u asin sinh ra phn ng theo phng trnh trn sau b nc

phn hy theo phn ng:

2Ag3As.3AgNO3 + 3H2O 12Ag + As2O3 + 6HNO3

Nhng trong dung mi C2H5OH-H2O th phn ng ny khng xy ra.

Ag3As.3AgNO3 c mu vng, trong mi trng axit nitric rt long n c

th bn t 1 n 2 ngy. Trong dung dch hp th, n c gi n nh bi

ru etylic v axit nitric v c phn tn u trong dung dch khi c mt

PVA. o quang dung dch sn phm phn ng c mu vng bc sng 408

nm. iu kin tin hnh phn ng nhit 20-35oC, dung dch hp th thch

hp pha t cc dung dch PVA 1%, AgNO3 0,012M (trong HNO3 4M),

C2H5OH 96% theo th t v t l th tch tng ng l 1:1:2. Gii hn nh

lng l 1,34 g As, gii hn pht hin l 0,447 g trong mu. Phng php

ny cho php xc nh tng lng vt As trong mu thc t vi nhy v

chn lc cao v qua qu trnh tch v lm giu Asen bng cch ct asin [16]

19

1.2.1.4. Phng php xc nh asen bng thuc th Leuco crystal violet (LCV)

Cc tc gi Omiagrawal, G.Sunita v V.K.Gupta nghin cu mt

phng php xc nh lng vt asen trong mu mi trng v sinh hc bng

thuc th tm tinh th Leuco (LCV). Phng php ny da trn c s phn

ng ca As(III) v KIO3 gii phng I2. I2 tip tc oxi ha chn lc thuc th

LCV hnh thnh sn phm mu l tm tinh th khi c mt NaOH.

Cht mu to thnh c cc i hp th 592 nm. Mt s kt qu ca

phng php ny: khong tuyn tnh theo nh lut Lambert-Beer l 0,1 g

1 g/ 25ml dung dch cui (0,004-0,04 ppm), gii hn pht hin l 0,002 g

As/ml, gi tr hp th mol phn t l 1,49.106 Lmol-1cm-1, phng php

loi tr c nh hng ca hu ht cc ion thng thng c mt trong nc.

Cc tc gi p dng phng php ny xc nh As(III) trong cc mu

mi trng v sinh hc nh mu tc, mu mng, mu huyt thanh, nc tiu

v cc mu nc ging, nc thi, mu thc vt Cc kt qu c thu hi

cao v ng nht vi kt qu kim nh ca phng php chun[31].

1.2.1.5. Phng php ng hc xc tc

Phng php ny da trn tc dng ca cht phn tch vi phn ng ch

th. o tc phn ng ch th khi nng cht nh phn trong phn ng l

hng s. Ta c phn ng tc :

Dx/dt = k.(a-x).C.c

k: hng s tc

a: nng ban u ca cht A

a-x: nng cht asen thi im t

c: nng cht nh phn

c: tng nng cht cn li v l hng s

Phng php ng hc xc tc l phng php n gin, t tn km, c

th xc nh As(III) da trn tc dng xc tc ca n vi phn ng oxy ha

20

natri pyrogallol-5sunphonate bng icromat, bng cch o s thay i hp

th quang ca sn phm mu = 436.8 nm.Phng php cho php xc nh

lng nh As trong nc nh tc dng ca ezym glyceraldegyde- 3phonate

dehydrogenaza vi nng As t 0,02-2 g/ml.

1.2.1.6. Xc nh lng vt As(III) bng phng php ng hc- trc

quang da trn nh hng c ch phn ng gia kalibromua v

kalibromat trong mi trng axit

Bromat b kh bi ion Br- trong mi trng axit theo phn ng:

BrO3- + 5Br

- + 6H

+ 3Br3 + 3H2O (1)

Br2 to thnh phn ng vi metyldacam v lm mt mu metyldacam

-O3S-C6H4-N=N-C6H4-N(CH3)2 + Br2 + H2O HO-C6H4-N(CH3)2 + Br-

C6H4-SO3H + N2 + Br- (2)

S gim mu ca metyldacam ph thuc vo tc phn ng (1), tc

phn ng xy ra cng nhanh, s gim mu ca metyldacam din ra cng

nhanh v ngc li. Khi c mt ca As(III) trong h, asen c tc dng c ch

lm phn ng mt mu metyldacam chm li so vi khi khng c mt ca n,

As(III) tc dng vi Br2 theo phn ng:

As(III) + Br2 As(V) + 2Br- (3)

Phn ng (3) c tc dng c ch phn ng (1) lm chm tc gim mu

ca metyldacam trong phn ng (2). o s thay i hp th ca dung dch ti

bc sng 525 nm ti t=100s. Phng php xc nh As(III) trong khong 10-

100 g/l xc nh As(III) trong mu nc t nhin [15].

1.2.1.7. Xc nh As(III) da trn h Ce(IV)/Ce(III).

Cc tc gi [27] ni v mt s ng dng trong phn tch hunh quang

ca h Ce(IV)/Ce(III) nh xc nh As(III), Ce(IV), Fe(II), oxalat, I2, C

s xc nh As(III) da trn phn ng:

As(III) + 2Ce(IV) 2Ce(III) + As(V)

21

Theo phng trnh c 1 phn t As(III) phn ng vi Ce(IV) to 2 phn

t Ce(III). Phn ng xy ra chm iu kin thng nhng khi c mt OsO4

phn ng xy ra nhanh hn, As(III), Ce(IV), As(V) khng c tnh cht pht

quang. Ring Ce(III) l mt trong s t nhng ion c tnh cht pht quang

bc sng 350 nm khi b kch thch bc sng 260 nm. ng chun xc

nh As(III) c xy dng trong khong nng 0,07- 0,4 ppm. Cc yu t

gy nh hng cng c nghin cu: cc ion NO3-, Fe

3+ gy nh hng

do chng hp th nh sng bc sng 260 nm hoc 350 nm lm gim cng

hunh quang. Cc cation Hg(I), Sn(II), Ti(III), V(IV) cng cho phn ng

tng t nh As(III) lm tng lng Ce(III) sinh ra, do cng hunh

quang tng ln. Citrat, tatrat, EDTA to phc vi Ce(IV) gy cn tr php xc

nh. Vi lng mol gp 200 ln As(III), cc catrion Al3+, Be2+, Ca2+, Cd2+,

Cu2+

, K+, Na

+, Mg

2+, NH4

+, Ni

2+,Sr

2+, Zn

2+ v mt s nguyn t t him

khng nh hng n h nhit phng.

1.2.1.8. Phng php quang ph hp ph nguyn t (AAS)

Ngy nay phng php ph hp th nguyn t l phng php c s

dng rt ph bin phn tch hm lng cc kim loi nng trong cc i

tng khc nhau: nc sinh hot, nc thi, hoa qu, thc phm Phng

php ny n gin, c nhy v chnh xc cao, trang b ca n khng qu

cng knh, thch hp cho vic phn tch hng lot.

Phng php AAS l phng php ph bin xc nh tng lng asen

c trong mu. Phng php AAS s dng k thut hyrat ha (HG - AAS) c

nhy cao, kt qu phn tch n nh v loi c nhiu nh hng ca

matrix vn thng rt phc tp. Phng php ny cho php xc nh asen

hm lng thp (vi ppb) m khng cn lm giu. Mun xc nh ring l

As(III) v As(V) ngi ta da vo kh nng kh khc nhau ca As(III) v

As(V) i vi NaBF4 cc pH khc nhau. Qu trnh kh pH t 0 n 7 ca

22

As(III) l d hn As(V). As(V) ch b kh trong mi trng c nng axit

ln. Ngi ta tin hnh hydrua ha trc khi nguyn t ha mu bng ngn

la n kh. Mu sau khi v c ha c kh thnh asin bng NaBF4 trong

mi trng HCl sau c dn vo ng thch anh t vng n nh ngn

la n kh. Kh AsH3 to thnh c o bc sng = 197,3 nm. Tuy

nhin nu c mt lng d cc nguyn t: Sb, Sn, Bi, Hg, Se, Te s gy tr

ngi cho vic xc nh asen bng phng php ny do chng c th bay hi

trong iu kin trn. Phng php ny c nhy vi As(III) cao hn As(V).

Bng phng php ny chng ta c th xc nh tng As(III) v As(V)

trong cng mt dung dch. As(V) c kh thnh As(III) bng cht kh thch

hp (KI 20% - Na2SO3 5%, KI 10% - axit ascorbic 5% - HCL 2M). Nh tc

dng ca cht kh mnh NaBF4 ton b As(III) c chuyn thnh kh AsH3 .

Kh ny c chuyn ti b phn nguyn t ha nh dng kh tr (Ar, N2 hoc

He). Trong b phn ny kh AsH3 c nguyn t ha thnh As nhit 900

1000oC, sau cc nguyn t As c o bc sng = 197,3 nm.

Tc gi L T Thnh v cng s ng dng phng php HG AAS

xc nh tng As trong mu nghu c x l bng hn hp HNO3 +

H2O2, kt qu thu c c n nh cao, hiu sut thu hi 92,6 105,9 %.

Nguyn t ha khng ngn la (ETA AAS) thng dng mt l nung

nh bng graphit (cuvet graphit) hay thuyn Tatan nguyn t ha mu nh

ngun nng lng nhit ca dng in c th thp (nh hn 12V) nhng c

dng rt cao (50- 800A), cho nhy cao t n 0,1 ppb v c ng dng

kh ph bin hin nay. u im ca k thut nguyn t ha mu ny l tiu

tn rt t mu, ch t 20 50 l. V nguyn tc, y l qu trnh nguyn t

ha tc khc trong thi gian rt ngn nh nng lng ca dng in c cng

sut ln v trong mi trng kh tr. Qu trnh nguyn t ha xy ra trong

vng t 60 80 giy, theo bn giai on tip nhau: sy kh, tro ha luyn

23

mu, nguyn t ha v lm sch cuvet. Ngun nng lng thng c dng

hin nay l dng in c cng dng rt cao (t 50 600A) v th thp

(di 12V) hoc nng lng ca dng cao tn cm ng. Khi dng k thut

nguyn t ha khng ngn la nhy ca phng php tng ln rt nhiu

nh hiu sut nguyn t ha cao, tuy nhin nh hng ca nn n cng

hp th l rt ln. As trong nc c th c nh lng trc tip hoc c

to hi asin ri c kh mang Ar a vo cuvet graphit [12].

1.2.2. Phng php hunh quang

Phng php hunh quang gm hunh quang tia-X, hunh quang phn

t, hunh quang nguyn t Tuy nhin, hunh quang phn t l phng

php c ch do kh nng ng dung rng ri, n gin, t tn km,

nhy v chn lc cao, c nhiu nghin cu ca nhiu tc gi a ra.

1.2.2.1. Xc nh As(III) bng thuc th fluorescein

Cc tc gi [37] a ra phng php hunh quang xc nh gin tip

As(III) da trn h phn ng I2- fluorescein. Bn thn fluorescein l mt cht

pht quang mnh bc sng 516 nm (bc sng kch thch l 495 nm), I2

phn ng vi fluorescein to ra hp cht hunh quang yu bc sng ny.

Khi c mt As(III), As(III) s tc dng vi iot lm gim lng iot phn ng

vi fluorescein, dn ti thay i lng fluorescein cn li trong dung dch.

Nh vy lng asen s t l vi lng d fluorescein trong dung dch.

AsO3- + I2 + H2O AsO4

3- + 2I

- + 2H

+

AsH3 + 4I2 + 4H2O AsO43-

+ 8I- + 11H

+

Cc tc gi nghin cu v tm ra c nhng iu kin ti u cho

php xc nh l pH= 6,1 (khong pH nghin cu 5,7- 7); 0,8 ml I2 20 l/ml

(khong nghin cu t 0,5-0,9 ml); 0,8 ml fluorescein 10-4 M (khong nghin

cu t 0,6- 0,9 ml).

24

Gii hn xc nh ca phng php l 0,4 ppb. Nu coi sai s > 5% mi

c ngha th cc ion K+, Na+, PO43-

khng gy nh hng, cc ion Mg2+, Cl-,

I-, Br

-, F

-, SO4

2-, CO

2-3 gp 200 ln As(III); As(V), Al3

+, Mn

2++, Hg

2+, Zn

2+,

Ca2+

, Ba2+

, Fe3+

gp 100 ln, Cu2+ gp 50 ln, CN- gp 2 ln; Sb3+ v Bi3+ gp

0,5 ln c nh hng. Tuy nhin CN- c th tch bng chng ct, Sb3+ v Bi3+

c th tch bng chit. Mu trc khi phn tch c tch bng chng ct

di dng AsCl3 v lm giu cch chit vi dung mi benzen. Phng php

ny ng dng xc nh As(III) trong nc sng v nc sinh hot.

1.2.2.2. Phng php dng chy - hunh quang xc nh axit dimethyl

arsinic(DMAA) trong thuc dit c s dng phn ng quang ha trc tip

Nguyn tc ca phng php l dng peroxidisunfat di bc x t

ngoi oxi ha DMAA ti asenat. Asenat sinh ra s phn ng vi molipdat

sinh ra asenomolipdat. Sau cht ny s tc dng vi thiamin to ra sn

phm c tnh hunh quang l thiochrom. Da vo cng pht quang ca

thichorom bc sng 440 nm ( = 375 nm) ta c th xc nh c nng

DMAA, c th: khong tuyn tnh 0,14- 14 ppm, gii hn xc nh 0,014

ppm, tc phn tch 60 mu/hp th. Bng cch tch v lm giu vi nha

trao i cation Dowex AG 50W- X8 dng H+ cc tc gi c th xc nh c

DMAA trong khong nng 5,6- 560 ppb, gii hn xc nh l 0,6 ppb.

Phng php ng dng xc nh DMAA trong nc ti v thc vt. [36]

1.2.2.3. Xc nh Asen bng phng php hunh quang phn t vi h

thuc th murexit Cr(VI)

Phng php da trn phn ng oxi ha ca As(III) vi Cr(VI) vi xc

tc iot. Lng d Cr(VI) sau phn ng vi As(III) s lm tt hunh quang ca

murexit trong mi trng axit H2SO4 0,45M. Tn hiu hunh quang c o

bc sng kch thch v pht x ln lt l 336 nm v 424 nm vi mu trng;

336 nm v 428,8 nm khi c mt As(III). Bc sng kch thch v pht x

25

ca murexit trong mi trng axit khng c Cr(VI) ln lt l 353,6 v 444,8

nm. Php o c lp li khi cho thm As(III) v o cng hunh quang

s xc nh c nng As(III) theo 2 ng chun:

F = 611 + 816C(g/ml) ( r = 0,9999 vi gii hn nng t 5 100

ng/ml)

F = 391 + 141C(g/ml) ( r = 1 vi gii hn nng t 100 ng/ml 1

g/ml)

xc nh tng lng As(III) v As(V) c trong mu, kh As(V) v

As(III) bng natri metabisulphite, un nng 90- 100oC ui lng d

cht kh.

Hn 35 cation, anion v mt vi phc c nghin cu v kt lun: vi

lng d gp 1000 ln nng As(III) ca EDTA, tartrate, sulphate,

phosphate, nitrate, clorua, ion kim loi kim v kim th, 500 ln Zn2+, Cd2+,

Ni2+

, Co2+

, Al3+, 100 ln Mn2+, Th4+, Cr3+, Os8+, 50 ln Bi3+, Hg2+ khng gy

nh hng ti php o. Khi c mt ca EDTA, lng d Fe3+, Cu2+ 100 ln

khng gy nh hng. nh hng ca Fe2+ c loi tr bng ct trao i

cation Amberlite IR 120 v loi Sb3+ bng kt ta vi antimony pyrogallate.

Gii hn pht hin l 1,5 ppb. Phng php c ng v tin cy cao c

ng dng xc nh Asen trong nhng nn phc tp, mu c nhiu nguyn t

nh hng ( hp kim), mu mi trng v sinh hc. [33]

1.2.2.4. Phng php biosensor s dng vi khun ch th

Phng php da trn kh nng khng ca vi khun trong mi trng

c asen. Biosensor hot ng ty thuc vo nng ca asen trong mi

trng m n to ra tn hiu in t t l vi nng ca asen. Phn ng pht

hin c th l hot ng ca mt enzym hay lin kt ca cht phn tch vi

mt khng th hay mt cht nhn Cc tn hiu thu c c th l tn hiu

quang hc hoc in ha tuyn tnh vi mt hay nhiu cht phn tch. Thnh

26

phn quan trng ca vi khun ch th asen l plasmit, trong t bo vi khun c

cha gen khng asen t nhin v gen ch th, hai on gen ny c ni vi

nhau cng hot ng di s iu khin ca mt promoter. Khi vi khun tip

xc vi mi trng c cha asen, asen c thm qua mng t bo vi khun

thng qua con ng hp th, vn chuyn tch cc hay th ng n s lin kt

vi protein iu ha dn n hot ha s phin m ca gen ch th. Gen ch th

m ha to ra ezym luciferase xc tc cho phn ng pht quang:

n-decanal + FMNH2 + O2 Axit decanoic + FMN + hv

Phn ng pht sng ca luciferase vi khun bao gm s oxy ha kh

monolucleotit flavin v 1 aldehyt chui di lm c cht phn ng vi ezym

v kt qu l sn sinh ra nh sng mu xanh bc sng 490 nm. [32]

Kt lun: Cn c vo cc ti liu tham kho c, vic xc nh asen

n gin, c kh nng kh thi trong cc phng th nghim, chng ti chn

phng php xc nh asen bng phng php trc quang vi thuc th

Safranin.

27

CHNG 2: THC NGHIM

2.1. Mc tiu, ni dung v phng php nghin cu

2.1.1. Nguyn tc ca phng php trc quang xc nh hm lng

asen bng Safranin.

Safranin T (Tolusafranin; 3,6- diamino- 2,7- dimetyl-10 phenyl phenazin

clohidrat (I); 3- 6- diamino- 2,7- dimetylphenazin (II)).

N+

N CH3

NH2

H3C

H2N

Cl-

(I)

M=350,8

N+

N CH3

NH2

H3C

H2N

Cl-

(II)

M=364,9

CH3

Safranin T l hn hp ca hai cht I v II

Safranin T l cht bt mu , rt c, tan trong nc cho dung dch mu

[2]. Dung dch trong ru etylic c mu , pht hunh quang mu

vng. Trong dung dch ru etylic hp th cc i vi nh sng c = 539 v

503,2 nm

Phn ng:

- Khi thm HCl c vo dung dch safranin trong nc s c dung

dch c mu tm xanh.

- Safranin tc dng vi NaOH s to kt ta mu nu

- Trong dung dch H2SO4 c cho dung dch mu xanh l cy, pha long

dung dch bng nc th dung dch s chuyn thnh xanh sau c mu .

28

Safranin l cht ch th oxi ha kh (c Eo = 0,289 V), khi b oxi ha th

n to sn phm khng mu

S lm mt mu ca safranin khi c mt iodate trong mi trng axit xy

ra theo c ch nh sau [21]:

+ As(III) phn ng vi KIO3 trong mi trng axit gii phng ra I2

theo phn ng:

2AsO2- + 2IO3

- + 2H

+ 2AsO3

- +I2 + 4H2O

+ I2 sinh ra s oxi ha lm mt mu thuc th safranin to ra sn phm

khng mu:

N+

N CH3

NH2

H3C

H2N

I2,H+

N

HN CH3

NH2

H3C

H2N

Mu khng mu

V vy, bng cch theo di s gim hp th quang ca Safranin theo

nng As(III) th c th nh lng c As(III) trong mu theo phng

php thi gian n nh hoc phng php tg.

2.1.2. Ni dung nghin cu

Ni dung nghin cu ca lun vn gm:

- Ti u ha cc iu kin ca php xc nh gm nghin cu nh

hng ca cc yu t sau n phn ng ch th:

+ Ph hp th ca dung dch cht mu v chn cc i hp th o

hp th quang.

+ nh hng ca thi gian phn ng. Theo di bin thin tc phn

ng chn phng php tg hay phng php thi gian n nh.

29

+ nh hng ca nng u cc tc nhn phn ng nh KIO3,

Safranine n tc phn ng.

+ nh hng ca mi trng phn ng .

- Nghin cu nh hng ca cc ion l n php xc nh.

- nh gi phng php phn tch : gm kho st gii hn pht hin,

gii hn nh lng, khong tuyn tnh; nh gi chm v chnh xc

ca phng php phn tch, tnh hiu sut thu hi ca phng php phn tch.

- Xy dng qui trnh phn tch v ng dng phn tch mu thc t.

2.2. Ha cht, dng c, thit b

2.2.1. Dng c, thit b

* Bnh nh mc thy tinh loi A c dung tch 25, 50, 100, 250, 500 ml.

* Cc thu tinh chu nhit dung tch 100, 250 ml.

* Bnh nn dung tch 250 ml, buret 25 ml.

* Cc loi pipet chia vch: 0,1; 0,2; 0,5; 1; 2; 5; 10; 25 ml.

* My trc quang UV - VIS 1601 PC - Shimadzu (Nht Bn), bc sng

lm vic t 190- 900 nm , cuvet thy tinh chiu dy l = 1cm.

* Cn phn tch Scientech SA 210 chnh xc 0,0001g.

* My iu nhit.

* ng h bm gi.

* My o pH.

2.2.2. Ha cht

Cc ha cht cn dng l loi tinh khit phn tch (p.a. v tinh khit

thuc th (p.R.). Cc dung dch c pha ch bng nc ct hai ln.

Pha cc dung dch tiu chun:

+ Pha 100,00 ml As(III) 1000ppm t t As2O3 tinh th

Cn chnh xc 0,1320 gam As2O3 tinh th trn cn phn tch, ha tan lng

cn ny bng dung dch NaOH long, sau un nng dung dch cho As2O3 tan

30

ht, chuyn vo bnh nh mc 100,00 ml, trng ra cc cn vi ln bng nc

ct hai ln ri chuyn vo bnh nh mc trn, thm nc ct ti vch mc, sc

trn u dung dch ta c 100,00 ml dung dch As(III) 1000ppm.

+ Thit lp li nng As(III) bng dung dch Iot tiu chun

- Pha 100,00 ml dung dch I2 0,0127 M t Iot tinh th

Cn 0,32g Iot trn cn k thut. Ha tan s b lng cn ny bng nc

ct, sau khi iot tan ht thm khong 10g KI. Thm nc ct ti vch mc, sc

trn u dung dch c dung dch I2 c nng sp s 0,0127 M. Dung dch

va pha bo qun trong chai thy tinh mu nt nhm.

- Pha 100,00 ml dung dch Na2S2O3 0,025M t Na2S2O3 tinh th

Cn 0,62g Natri thiosunfat trn cn k thut, ha tan s b bng nc

ct, chuyn vo bnh dnh mc 100,00 ml, trng ra cc cn, thm nc ct

ti vch mc c 100,00 ml dung dch Na2S2O3 c nng sp s 0,025 M.

- Pha 100,00 ml dung dch K2Cr2O7 4,17x10-3

M

Cn chnh xc 0,1227 0,0001g Kali dicromat loi tinh khit ha hc

trn cn phn tch, ha tan s b bng nc ct chuyn vo bnh nh mc

100ml, trng ra cc cn nhiu ln chuyn vo bnh trn, thm nc ct n

vch mc, sc trn u dung dch c 100,00 ml dung dch K2Cr2O7

4,17x10-3

M.

- Thit lp li nng dung dch Na2S2O3 theo K2Cr2O7

Phng trnh chun :

K2Cr2O7 + 6KI + 7H2SO4 Cr2(SO4)3 + 3I2 + 4 K2SO4 + 7H2O

I2 + 2Na2S2O3 htb 2NaI + Na2S4O6

Ht chnh xc 10,00ml dung dch K2Cr2O7 4,17x10-3M va pha vo bnh

nn nt mi, thm 10,0ml KI 10%; 5,0ml H2SO4 , pha long dung dch bng

nc ct ti khong 150,0 ml. bng ti 5 pht, ly ra em chun bng

dung dch Na2S2O3 va pha ti mu vng nht, thm khong 1,0 ml h tinh

31

bt chun n mt mu xanh. Lm th nghim song song, sai s gia hai ln

chun khng qu 0,1ml.

- Thit lp li nng dung dch I2 theo Na2S2O3

Phng trnh chun :

I2 + 2Na2S2O3 htb 2NaI + Na2S4O6

Ht chnh xc 10,00 ml dung dch I2 vo bnh nn, thm mt lng nh

nc ct, em chun bng dung dch Na2S2O3 ti vng nht, thm 1,0 ml h

tinh bt 1% chun tip ti mt mu xanh. Lm th nghim song song, sai s

gia hai ln chun khng qu 0,1ml.

- Thit lp li nng dung dch As(III) bng I2

Phng trnh chun :

Na3AsO3 + I2 + H2O Na3AsO4 + 2HI

Ht chnh xc 10,00 ml dung dch asenit vo bnh nn 250ml, thm 2

git dung dch phenolphtalein, dung dch c mu hng, thm tng git dung

dch H2SO4 2M cho n khi mt mu hng. Cho tip vo bnh chun

khong 1 gam NaHCO3, lc u (nu dung dch li c mu hng th thm tip

H2SO4 2M cho ti khi mt mu ). Thm 1 2 ml h tinh bt, chun mu

va chun b bng dung dch iot cho ti khi xut hin mu xanh nht. Lm th

nghim song song, sai s gia hai ln chun khng qu 0,1ml.

+ Pha 100,00 ml As(III) 100ppm t dung dch As(III) 1000ppm

Ht chnh xc 10,00 ml dung dch As(III) 1000ppm chuyn vo bnh

nh mc 100 ml, thm nc ct ti vch mc, sc trn u dung dch ta c

100,00 ml dung dch As(III) 100ppm.

+ Pha 100,00 ml As(III) 10ppm t dung dch As(III) 1000ppm

Ht chnh xc 1,00 ml dung dch As(III) 1000ppm chuyn vo bnh nh

mc 100 ml, thm nc ct ti vch mc, sc trn u dung dch ta c

100,00 ml dung dch As(III) 10ppm.

32

+ Pha 100,0 ml dung dch Safranine 0,02 %

Cn 0,02 gam Safranine, ha tan bng nc ct ti th tch 100 ml,

khuy u ta c 100,0 ml dung dch Safranine 0,02 %.

+ Pha 500,0 ml dung dch HCl 1M

ong khong 42,0 ml dung dch HCl c 37% chuyn vo bnh cha c

dung tch 500 ml c cha sn 1/3 nc ct, thm nc ct ti th tch

500,0 ml, khuy u ta c 500,0 ml dung dch HCl 1M.

+ Pha 250,0 ml dung dch KIO3 2%

Cn 5 gam tinh th KIO3, ha tan bng nc ct ti th tch 250,0 ml,

khuy u ta c 250,0 ml dung dch KIO3 2%.

33

CHNG 3: KT QU V THO LUN

3.1. Nghin cu phng php xc nh As (III) da trn h phn

ng oxi ha kh As(III), KIO3 v Safranin.

3.1.1. Nghin cu chn iu kin ti u ca phn ng ch th

3.1.1.1. Ph hp th ca sn phm phn ng ch th

Chun b 04 bnh nh mc dung tch 25 ml, ly vo 02 bnh nh mc 3

v 4 cc lng As (III) c ly t dung dch As (III) 100,00 ppm nh sau:

Bnh 1-2: mu trng

Bnh 3: 1,25 ml dung dch As (III) 100,00 ppm.

Bnh 4: 2,50 ml dung dch As (III) 100,00 ppm.

Thm vo cc bnh t 1- 4 mi bnh 2,50 ml dung dch KIO3 2%, thm

vo tt c cc bnh, mi bnh 2,50 ml dung dch HCl 1M; cui cng thm vo

cc bnh 2, 3 v 4 mi bnh 1,50 ml dung dch safranine 0.02 %. Sau nh

mc bng nc ct n vch mc. Sc trn u dung dch, em o hp th

quang ca cc dung dch trong khong bc sng t 400 700 nm vi dung

dch so snh l dung dch trong bnh 1. Kt qu thu c nh hnh 3.1.

Hnh 3.1: Ph hp th quang ca dung dch Safranine khi c mt As(III), KIO3, HCl

(Nng cui ca cc tc nhn trong dung dch ln lt l: Safranine

0,0012%, KIO3 0,2%, HCl 0,1M)

34

ng 1: Ph hp th ca dung dch c Safranine, KIO3, HCl

ng 2: Ph hp th ca dung dch c As(III) 5ppm,Safranine, KIO3, HCl

ng 3: Ph hp th ca dung dch c As(III) 10ppm, Safranine, KIO3, HCl

Safranine l thuc th c mu , c bc sng hp th cc i bc

sng = 519 nm trong mi trng axit mnh (ng 1). Khi gi nguyn nng

KIO3 2% v cho thm As (III) vi nng khc nhau 5,0 ppm (ng 2),

As (III) 10,0 ppm (ng 3) th thc nghim cho thy, cng tng nng ca

As (III) th hp th quang A ca dung dch phn ng cng gim m khng

lm chuyn dch cc i. iu chng t khi c As(III) v khi nng

As(III) cng ln th phn ng gia As(III) v KIO3 trong mi trng axit xy

ra cng trit , gii phng ra cng nhiu I2 v I2 oxi ha safranin to ra sn

phm khng mu. Do trong cc th nghim tip theo chng ti chn bc

sng = 519 nm kho st.

3.1.1.2. Nghin cu nh hng ca thi gian phn ng

Chun b 03 bnh nh mc dung tch 25 ml, ly vo bnh 2 v 3 ln lt

th t thuc th nh sau:

Bnh 1: Mu trng

Bnh 2-3: 1,25 2,5 ml dung dch As (III) 100,0 ppm

Thm vo cc bnh t 1-3 mi bnh 2,50 ml dung dch KIO3 2%; 2,50 ml

dung dch HCl 1M; 1,50ml dung dch Safranine 0,02 %, nh mc bng nc

ct ti vch mc. Sc trn u dung dch. Kho st s gim hp th quang

sau 2 pht tnh t khi nh git Safranin cui cng vo h phn ng, bc

sng = 519 nm trong khong 60 pht vi dung dch so snh l mu trng .

Kt qu thu c nh hnh 3.2.

35

Hnh 3.2: S ph thuc ca hp th quang theo thi gian

(Nng cui ca cc tc nhn trong dung dch ln lt l: Safranine

0,0012%, KIO3 0,2%, HCl 0,1M)

ng 1: Dung dch phn tch khi c KIO3, HCl, Safranine.

ng 2: Dung dch phn tch khi c As(III) 5ppm, KIO3, HCl, Safranine.

ng 3: Dung dch phn tch khi c As(III) 10ppm, KIO3, HCl,

Safranine.

T th kho st thi gian ta thy khi khng c mt As(III) hp th

quang ca dung dch phn tch khng thay i theo thi gian. Khi c mt As

(III) th hp th quang ca dung dch phn tch gim so vi khi khng c

mt As (III) nhng cng khng thay i theo thi gian. Nng As (III) cng

cao th hp th quang ca dung dch phn tch cng gim, c ngha l khi

nng As(III) cng cao th phn ng gia n vi KIO3 trong mi trng axit

gii phng ra cng nhiu I2, do cng mu ca thuc th safranin cng

b gim.

36

3.1.1.3. nh hng ca nng KIO3

nh hng ca nng KIO3 c kho st trong khong nng t

0,04% n 0,36%

Chun b 27 bnh nh mc 25,0 ml, ly vo cc bnh th t cc thuc

th sau:

Bnh 1 - 9: 0,50 4,50 ml KIO3 2%; 2,50 ml HCl 1M.

Bnh 10 - 18: 0,50 4,50 ml KIO3 2%; 2,50 ml HCl 1M; 1,50 ml

Safranine 0,02 %.

Bnh 19 - 27: 1,50 ml As(III) 100 ppm ; 0,50 4,50 ml KIO3 2%;

2,50 ml HCl 1M; 1,50 ml Safranine 0,02 %.

nh mc bng nc ct ti vch mc, sc trn u dung dch. em o

hp th quang ca dung dch bc sng 519 nm, vi dung dch so snh

l dung dch trong cc bnh 1- 9. Kt qu thu c biu din di bng 3.1:

Bng 3.1: nh hng ca nng KIO3 n php phn tch

(Nng cui ca Safranin l 1,2x10-3%; HCl l 0,1M; As(III) l 6ppm)

Nng

KIO3 (%) 0,04 0,08 0,12 0,16 0,20 0,24

A nn 0,948 0,952 0,952 0,954 0,953 0,949

A mu 0,655 0,637 0,608 0,607 0,607 0,605

A 0,286 0,315 0,344 0,347 0,346 0,344

37

Hnh 3.3: nh hng ca nng KIO3 n hp th quang ca dung dch

Ann l hp th quang ca dung dch phn tch khi c KIO3, HCl, Safranine.

Amu l hp th quang ca dung dch phn tch khi c As(III), KIO3, HCl,

Safranine.

T th kho st nh hng ca nng KIO3 ta thy hp th quang

ca phn ng nn gn nh khng thay i khi ta c nh nng ca HCl v

Safranine, tng dn nng ca KIO3. Khi c mt As(III) cng vi s tng

nng ca KIO3- t 0,01 n 0,36% th hp th quang ca hn hp phn

ng ban u gim nh, sau gn nh khng i lm cho hiu s hp th

quang gia tn hiu o ca phn ng nn v tn hiu o ca phn ng c

As(III) cng gn nh khng thay i khi nng KIO3 trong khong nng

t 0,12 0,24 %. iu ny ph hp vi c ch ca phn ng cho rng khi

tng nng As(III) th phn ng gii phng ra nhiu I2 dn n hp th

quang ca h phn ng gim.V vy ta chn nng KIO3 l 0,16 % kho

st cc th nghim tip theo.

3.1.1.4. nh hng ca nng thuc th Safranine:

nh hng ca nng thuc th Safranine c kho st trong khong

nng t 0,4x10-3 n 4x10-3.

38

Chun b 21 bnh nh mc 25 ml, ly vo cc bnh th t cc thuc th sau:

Bnh 1: 2,00 ml KIO3 2%; 2,50 ml HCl 1M (dung dch so snh )

Bnh 2- 11: 2,00 ml KIO3 2%; 2,50 ml HCl 1M; 0,50 5,00 ml

Safranine 0,02 % (dung dch nn )

Bnh 12-21: 1,50 ml As(III) 100 ppm ; 2,00 ml KIO3 2%; 2,50 ml HCl

1M; 0,50 5,00 ml Safranine 0,02 % (dung dch mu )



l dung dch trong bnh 1. Kt qu thu c biu din di bng 3.2:

Bng 3.2: nh hng ca nng Safranine n php phn tch

(Nng cui ca KIO3 l 0,16%; HCl l 0,1M; As(III) l 6ppm)

Nng Safranine (x10-3 %) 0,4 0,8 1,2 1,6 2,0

A nn 0,325 0,641 0,945 1,229 1,489

A mu 0,234 0,420 0,572 0,752 0,920

A 0,091 0,221 0,373 0,477 0,569

Nng Safranine (x10-3 %) 2,4 2,8 3,2 3,6 4,0

A nn 1,753 1,995 2,214 2,482 2,709

A mu 1,089 1,240 1,419 1,601 1,761

A 0,701 0,755 0,795 0,881 0,948

39

Hnh 3.4: nh hng ca nng Safranine n hp th quang ca dung dch

T bng kt qu thu c hnh trn ta thy vi phn ng nn, khi c

nh nng KIO3 v HCl , thay i nng ca Safranine th hp th

quang phi tng tuyn tnh vi nng ca Safranine. Khi c mt As(III),

theo c ch phn ng s gii phng ra I2, khi tng nng Safranine th s

gim hp th quang xy ra t l thun vi nng Safranine v hp th

quang A ca dung dch gim nn ng biu din c h s gc thp hn

ng 1 (phn ng nn). Hiu s ca ng Ann v ng Amu biu th tc

phn ng oxi ha kh cho thy nng Safranin 0,8 x10-3 1,2 x10-3%

th tn hiu o A rt ln v hiu s hp th quang l cao nht. V vy nng

cui ca Safranine c chn cho cc th nghim tip theo l 1,2 x10-3 %.

3.1.1.5. nh hng ca nng HCl:

nh hng ca nng dung dch HCl c kho st trong khong nng

t 0,04 n 0,2M.

Chun b 30 bnh nh mc 25,0 ml, ly vo cc bnh th t cc thuc

th sau:

Bnh 1-10: 2.00 ml KIO3 2%; 1,00 5,00 ml HCl 1M.

Bnh 11- 20: 2.00 ml KIO3 2%; 1,00 5,00 ml HCl 1M; 1,5 ml Safranine 0,02 %.

40

Bnh 21-30: 1.50 ml As(III) 100 ppm ; 2.00 ml KIO3 2%; 1,00 5,00 ml

HCl 1M; 1,5 ml Safranine 0,02 %.



l dung dch trong cc bnh 1- 10. Kt qu thu c biu din di bng 3.3:

Bng 3.3: nh hng ca nng HCl

(Nng cui ca KIO3 l 0,16%; Safranin l 1,2x10-3

%; As(III) l 6ppm)

Nng HCl (M) 0,04 0,06 0,08 0,10 0,12

A nn 0,948 0,947 0,945 0,941 0,939

A mu 0,573 0,574 0,574 0,557 0,568

A 0,375 0,373 0,371 0,371 0,371

Nng HCl (M) 0,14 0,16 0,18 0,20

A nn 0,928 0,925 0,924 0,922

A mu 0,566 0,568 0,571 0,569

A 0,362 0,357 0,353 0,353

Hnh 3.5: nh hng ca nng HCl n hp th quang ca dung dch

41

T th kho st nh hng ca nng HCl ta thy khi c nh nng

KIO3, Safranine, tng nng ca HCl th hp th quang ca c 2 phn

ng c mt As(III) v khng c mt As(III) u gn nh khng thay i. Hiu

s hp th quang gia 2 phn ng cng n nh v hu nh khng thay

i. V vy nng ca HCl c chng ti chn cho cc th nghim tip

theo l 0,08 M.

Nh vy sau khi kho st chng ti chn nng cc cht khi tin hnh

phn tch l: KIO3 l 0,16%; Safranin l 1,2x10-3

% v HCl l 0,08M.

3.1.2. nh gi phng php phn tch

3.1.2.1. chn lc ca phng php phn tch [21]

Theo ti liu m chng ti tham kho c th php xc nh As(III) b

nh hng bi cc ion Ca2+, Fe3+, Cu2+, Ni2+, Cd2+, Ba2+, Bi3+, Al3+, Co3+, V5+,

Zn2+

, PO43-

, SO42-

, NO3-..... do chng c kh nng tham gia phn ng oxi ha

kh vi cc cht trong h hoc n gin ch lm thay i lc ion ca dung

dch. Tuy nhin, vi mc ch xc nh hm lng As(III) trong mu mi

trng (nc ngm) chng ti ch kho st nh hng ca cc ion ch yu

nh: Fe3+, Ca2+, Ba2+, Zn2+, SO42-

, NO3-, Cu

2+.

Kho st nh hng ca ion NO3- n php xc nh As(III) 6ppm

Chun b 10 bnh nh mc dung tch 25 ml, nh s th t t 1 10,

cho vo cc bnh t bnh 3 n bnh 10 mi bnh 1,5 ml As(III) 100ppm; ri

thm vo cc bnh 4 n bnh 10 t 0,25 12,50 ml dung dch NO3- 100ppm

tng ng vi nng NO3- thay i t 1 50 ppm. Sau thm vo tt c

cc bnh th t cc thuc th sau:

Bnh 1: 2,00 ml KIO3 2%; 2,00 ml HCl 1M

Bnh 2: 2,00 ml KIO3 2%; 2,00 ml HCl 1M; 1,50 ml Safranine 0,02%

Bnh 3 10: 2,00 ml KIO3 2%; 2,00 ml HCl 1M; 1,50 ml Safranine 0,02%

42


hp th quang ca cc dung dch bc sng 519 nm, vi dung dch so

snh l dung dch trong bnh 1. Kt qu thu c nh trong bng 3.4:

Bng 3.4: nh hng ca ion NO3- n php xc nh As(III)(CAs(III)= 6 ppm)

CNO3- (ppm) 1 3 6 10 20 30 40 50

A nn 0,943 0,943 0,943 0,943 0,943 0,943 0,943 0,943

A mu 0,573 0,573 0,573 0,573 0,573 0,573 0,573 0,573

A ion cn 0,575 0,579 0,583 0,592 0,602 0,616 0,638 0,670

Sai s (%) -0,54 -1,62 -2,70 -5,14 -7,84 -11,62 -17,57 -26,22

Nhn xt: Vi sai s ca phng php xc nh khong 15% th

ngng nh hng l khi hm lng ca ion NO3- gp 7 ln As(III), nhng

hm lng ca ion NO3- trong mu cha t n ngng nh hng hoc

b loi tr khi x l mu.

Kho st nh hng ca ion SO42-

n php xc nh As(III) 6ppm



thm vo cc bnh 4 n bnh 10 t 0,25 12,50 ml dung dch SO42-

100ppm

tng ng vi nng SO42-

thay i t 1 50 ppm. Sau thm vo tt c


Bnh 1: 2,00 ml KIO3 2%; 2,00 ml HCl 1M

Bnh 2: 2.00 ml KIO3 2%; 2,00 ml HCl 1M; 3,50 ml Safranine 0,02%

Bnh 3 10: 2.00 ml KIO3 2%; 2,00 ml HCl 1M; 1,50 ml Safranine 0,02%




43

Bng 3.5: nh hng ca ion SO42-

n php xc nh As(III)(CAs(III)= 6 ppm)

CSO42-

(ppm) 1 3 6 10 20 30 40 50

A nn 0,943 0,943 0,943 0,943 0,943 0,943 0,943 0,943

A mu 0,573 0,573 0,573 0,573 0,573 0,573 0,573 0,573

A ion cn 0,559 0,561 0,570 0,580 0,594 0,635 0,723 0,891

Sai s (%) 3,78 3,24 0,81 -1,89 -5,68 -16,97 -40,54 -85,95


ngng nh hng l khi hm lng ca ion SO42- gp 5 ln As(III), nhng

hm lng ca ion SO42- trong mu cha t n ngng nh hng hoc

b loi tr khi x l mu.

Kho st nh hng ca ion Ca2+ n php xc nh As(III) 2ppm



thm vo cc bnh 4 n bnh 10 t 0,05 7,50 ml dung dch Ca2+ 1000 ppm

tng ng vi nng Ca2+ thay i t 6 300 ppm. Sau thm vo tt c


Bnh 1: 2,00 ml KIO3 2%; 2,00 ml HCl 1M






44

Bng 3.6: nh hng ca ion Ca2+ n php xc nh As(III)(CAs(III)= 2 ppm)

CCa2+

(ppm) 2 25 50 100 150 200 250 300

A nn 0,951 0,951 0,951 0,951 0,951 0,951 0,951 0,951

A mu 0,846 0,846 0,846 0,846 0,846 0,846 0,846 0,846

A ion cn 0,842 0,844 0,845 0,850 0,854 0,858 0,861 0,866

Sai s (%) 3,81 1,91 0,95 -3,81 -7,62 -11,43 -14,29 -19,05

Nhn xt: Vi sai s ca phng php xc nh khong

15% th ngng nh hng l khi hm lng ca ion Ca2+ gp 150 ln

As(III), nhng hm lng ca ion Ca2+ trong mu cha t n ngng nh

hng hoc b loi tr khi x l mu.

Kho st nh hng ca ion Ba2+ n php xc nh As(III) 2ppm



thm vo cc bnh 4 n bnh 10 t 0,05 7,5 ml dung dch Ba2+ 1000 ppm

tng ng vi nng Ba2+ thay i t 2 300 ppm. Sau thm vo tt c


Bnh 1: 2,00 ml KIO3 2%; 2,00 ml HCl 1M






45

Bng 3.7: nh hng ca ion Ba2+ n php xc nh As(III)(CAs(III)= 2 ppm)

CBa2+

(ppm) 2 25 50 100 150 200 250 300

A nn 0,951 0,951 0,951 0,951 0,951 0,951 0,951 0,951

A mu 0,846 0,846 0,846 0,846 0,846 0,846 0,846 0,846

A ion cn 0,845 0,844 0,843 0,847 0,849 0,851 0,852 0,854

Sai s (%) 0,95 1,90 2,86 -0,95 -2,86 -4,76 -5,70 -7,62

Nhn xt: Vi sai s ca phng php xc nh khong 15% th hm

lng ca ion Ba2+ khong nng kho st khng nh hng n mu.

Kho st nh hng ca ion Zn2+ n php xc nh As(III) 6ppm



thm vo cc bnh 4 n bnh 10 t 0,15 2,00 ml dung dch Zn2+ 1000ppm

tng ng vi nng Zn2+ thay i t 6 80 ppm. Sau thm vo tt c


Bnh 1: 2,00 ml KIO3 2%; 2,00 ml HCl 1M






Bng 3.8: nh hng ca ion Zn2+ n php xc nh As(III)(CAs(III)= 6 ppm)

CZn2+

(ppm) 6 10 20 30 40 50 60 80

A nn 0,908 0,908 0,908 0,908 0,908 0,908 0,908 0,908

A mu 0,554 0,554 0,554 0,554 0,554 0,554 0,554 0,554

A ion cn 0,553 0,547 0,543 0,552 0,553 0,599 0,611 0,698

Sai s (%) 0,28 1,98 3,11 0,56 0,28 -12,71 -16,10 -40,68

46


ngng nh hng l khi hm lng ca ion Zn2+ gp 10 ln As(III), nhng

hm lng ca ion Zn2+ trong mu cha t n ngng nh hng hoc b

loi tr khi x l mu.

Kho st nh hng ca ion Fe3+ n php xc nh As(III) 2ppm



thm vo cc bnh 4 n bnh 10 t 0,05 5,00 ml dung dch Fe3+ 1000 ppm

tng ng vi nng Fe3+ thay i t 2 200 ppm. Sau thm vo tt c


Bnh 1: 2,00 ml KIO3 2%; 2,00 ml HCl 1M






Bng 3.9: nh hng ca ion Fe3+ n php xc nh As(III)(CAs(III)= 2 ppm)

CFe3+

(ppm) 2 20 40 60 80 100 150 200

A nn 0,945 0,945 0,945 0,945 0,945 0,945 0,945 0,945

A mu 0,838 0,838 0,838 0,838 0,838 0,838 0,838 0,838

A ion cn 0,835 0,839 0,841 0,845 0,849 0,856 0,863 0,882

Sai s (%) 2,80 -0,93 -2,80 -6,54 -10,28 -16,82 -23,36 -41,12


ngng nh hng l khi hm lng ca ion Fe3+ gp 50 ln As(III), nhng

hm lng ca ion Fe3+ trong mu cha t n ngng nh hng hoc b

loi tr khi x l mu.

47

Kho st nh hng ca ion Cu2+ n php xc nh As(III) 2ppm



thm vo cc bnh 4 n bnh 10 t 0,05 5,00 ml dung dch Cu2+ 1000 ppm

tng ng vi nng Cu2+ thay i t 2 200 ppm. Sau thm vo tt c


Bnh 1: 2,00 ml KIO3 2%; 2,00 ml HCl 1M






Bng 3.10: nh hng ca ion Cu2+ n php xc nh As(III)(CAs(III)= 2 ppm)

Ccu2+

(ppm) 2 20 40 60 80 120 150 200

A nn 0,945 0,945 0,945 0,945 0,945 0,945 0,945 0,945

A mu 0,838 0,838 0,838 0,838 0,838 0,838 0,838 0,838

A ion cn 0832 0,834 0,836 0,837 0,840 0,844 0,848 0,857

Sai s (%) 5,61 3,74 1,87 0,93 -1,87 -5,61 -9,35 -17,76


ngng nh hng l khi hm lng ca ion Cu2+ gp 100 ln As(III), nhng

hm lng ca ion Cu2+ trong mu cha t n ngng nh hng hoc b

loi tr khi x l mu.

3.1.2.2. Kho st khong tuyn tnh

Chun b 15 bnh nh mc dung tch 25 ml, nh du t 1- 15, Ln lt

cho vo cc bnh th t cc thuc th sau:

Bnh 1: 2.00 ml KIO3 2%; 2,00 ml HCl 1M

48


Bnh 3 15: 0,125 3,00 ml dung dch As (III) 100,0 ppm tng ng vi

nng As (III) thay i t 0,5 12 ppm; 2.00 ml KIO3 2%; 2,00 ml HCl

1M; 1,50 ml Safranine 0,02%.



snh l dung dch trong bnh 1. Kt qu thu c nh trong bng 3.11 v biu

din trn hnh 3.6:

Bng 3.11: Kho st khong tuyn tnh xc nh As(III)

(Nng cui ca KIO3 l 0,16%; Safranin l 1,2x10-3; HCl l 0,08M)

Nng

As(III) (ppm)

A

A

0.0 0,946 ------

0.5 0,927 0,019

1 0,886 0,06

2 0,844 0,102

3 0,766 0,18

4 0,709 0,237

5 0,647 0,299

6 0,585 0,361

7 0,528 0,418

8 0,480 0,466

9 0,447 0,499

10 0,418 0,528

11 0,405 0,541

12 0,389 0,557

49

Hnh 3.6: th kho st khong tuyn tnh xc nh As (III)

S dng phn mm Origin ta dng c ng chun nh hnh 3.7.

Hnh 3.7: ng chun xc nh As (III)

Nh vy hiu s hp th quang ph thuc tuyn tnh vo nng As

(III) n 8 ppm . Nu xy dng ng chun trong khong nng As (III )

l 0,5 8 ppm th phng trnh hi quy dng y = ax + b c cc gi tr a = -

0,0076; Sa = 0,00497 v b = 0,06048; Sb = 0,00104

Do sau khi x l phng trnh theo phng php bnh phng ti

thiu ta c phng trnh hi quy biu th s ph thuc hiu s hp th

50

quang ca dung dch Safranine khi khng c v c As (III) c dng y

nh sau:

y = (- 0,0076 0,00497) + (0,06048 0,00104) CAs(III) Kim tra s sai khc ca a vi gi tr 0:

Phng trnh hi quy c dng

A = (-0,0076 0,00497) + (0,06048 0,00104) CAs(III)

Nu coi a = 0 ta c phng trnh A = b CAs(III), thay cc gi tr A,

CAs(III) tng ng vo tnh c btb= 0,056

3

)(

3

)( 2'2'2'

n

xby

n

yyS

iiiiy = 4,15.10

-4

Ta c Ftnh=

4

5

2

'

2

10.15,4

10.57,5

y

y

S

S 0,1342

F(0,95;7;6) = 3,866

Nh vy, Ftnh < Fbng nn khng c s khc nhau c ngha thng k

gia a v 0, tc l phng php khng mc sai s h thng.

Tnh gii hn pht hin v gii hn nh lng

Gii hn pht hin (LOD): l nng thp nht ca cht phn tch m h

thng phn tch cn cho tn hiu phn tch khc c ngha vi tn hiu mu

trng hay tn hiu nn.

Gii hn nh lng (LOQ): l nng thp nht ca cht phn tch m

h thng phn tch nh lng c vi tn hiu phn tch khc c ngha

nh lng vi tn hiu ca mu trng hay tn hiu ca nn

+ Gii hn pht hin (LOD):

522

210.57,5

2

)(

2

)(

n

bxay

n

yyS

iiii

y

51

LOD = b

S A3

Trong : AS =

1

1

2

N

AAN

i

i

= 2,8610-4

Vi h s trong phng trnh hi qui b = 0,06048

Do : LOD = 06048,0

1086,23 4xx= 0.01 (ppm)

+ Gii hn nh lng (LOQ):

LOQ=b

S A10 = 0,05(ppm)

Nh vy, khong tuyn tnh khi xc nh Se(IV) l 0,05 8,00 ppm.

3.1.2.3. nh gi chnh xc ( ng, chm ) ca phng php

Mu tht (mu nc ngm s 8)

Chun b 10 bnh nh mc dung tch 25ml:

Bnh 1: 2,00 ml dung dch KIO3 2%; 2,00 ml dung dch HCl 1M

Bnh 2: 2,00 ml dung dch KIO3 2%; 2,00 ml dung dch HCl 1M; 1,50

ml dung dch safranin 0,02%

Bnh 3- 4: 5,00 ml mu nc N8; 2,00 ml dung dch KIO3 2%; 2,00 ml

dung dch HCl 1M; 1,50 ml dung dch safranin 0,02%.

Bnh 5- 6: 5,00 ml mu nc N8; 1,25 ml dung dch As(III) 1ppm; 2,00

ml dung dch KIO3 2%; 2,00 ml dung dch HCl 1M; 1,50 ml dung dch

safranin 0,02%.

Bnh 7- 8: 5,00 ml mu nc N8; 2,50 ml dung dch As(III)1ppm; 2,00

ml dung dch KIO3 2%; 2,00 dung dch ml HCl 1M; 1,50 ml dung dch

safranin 0,02%.

52


ml dung dch KIO3 2%; 2,00 dung dch ml HCl 1M; 1,5 0ml dung dch

safranin 0,02%.

nh mc tt c cc bnh bng nc ct n vch mc, sc trn u

dung dch. em o hp th quang ca dung dch bc sng 519 nm, vi

dung dch so snh l dung dch trong bnh 1. Kt qu thu c nh bng 3.12:

Bng 3.12: Xc nh hm lng As trong mu nc ngm s 8

V (ml) A nn A mu A A

5,00 ml mu nc N8 0,946 0,945 0,001

0,001 0,946 0,945 0,001

5,00 ml mu nc N8, thm 1,25 ml As(III)

1,00 ppm

0,946 0,942 0,004 0,004

0,946 0,942 0,004


1,00 ppm

0,946 0,937 0,009 0,008

0,946 0,938 0,008


1,00 ppm

0,946 0,934 0,012 0,0115

0,946 0,935 0,011

Hnh 3.8 : ng thm chun xc nh As(III) trong mu nc ngm s 8

53

T hnh ta c nng As(III) l:

X1 = 0,011 (ppm)

Tng ng vi hm lng A(III) trong mu nc ngm s 8 l:

5

25011,0 = 0,055 g/ml.

Khi thm mt lng As(III) chun vo mu nc ngm s 8

Chun b 12 bnh nh mc dung tch 25,0 ml, ly vo cc bnh th t

cc thuc th sau:

Bnh 1: 2,00 ml KIO3 2%; 2,00 ml HCl 1M

Bnh 2: 2,00 ml KIO3 2%; 2,00 ml HCl 1M; 1,50 ml Safranine

Bnh 3 - 7: 5,00 ml mu nc ngm s 8; 1,00 ml dung dch As(III)

100ppm; 2,00 ml KIO3 2%; 2,00 ml HCl 1M; 1`,50 ml Safranine

Bnh 8 - 12: 5,00 ml mu nc ngm s 8; 1,50 ml dung dch As(III)

100ppm; 2,00 ml KIO3 2%; 2,00 ml HCl 1M; 1,50 ml Safranine


hp th quang ca cc dung dch bc sng 519 nm vi dung dch so

snh l dung dch trong bnh 1. Kt qu thu c nh bng 3.13:

54

Bng 3.13: nh gi lp li ca phng php

As(III)

4,0ppm

A nn 0,946 0,946 0,946 0,946 0,946

A mu 0,709 0,714 0,712 0,701 0,721

A 0,237 0,232 0,234 0,245 0,225

Hm lng As(III) pht hin (X2) 4,04 3,96 3,99 4,18 3,85

X2 X1 3,93 3,85 3,88 4,07 3,74

x (ppm) 3,89

lch chun S 0,121

H s bin thin CV (%) 3,11

Sai s tng i (%) 2,75

ttnh 0,91

As(III)

6,0ppm

A nn 0,946 0,946 0,946 0,946 0,946

A mu 0,601 0,594 0,582 0,594 0,580

A 0,345 0,352 0,364 0,352 0,366

Hm lng As(III) pht hin (X3) 5,83 5,95 6,14 5,95 6,18

X3 X1 5,72 5,84 6,03 5,84 6,07

x (ppm) 5,90

lch chun S 0,146

H s bin thin CV (%) 2,47

Sai s tng i (%) 2,50

ttnh 0,685

Kim tra s sai khc gia gi tr trung bnh tm c v gi tr thc theo

chun student (t) tin cy thng k 95% v bc t do f= 4 (tbng = 2,571),

55

chng ti thy c hai mc nng As(III) (4,0 ppm v 6,0 ppm) u c ttnh

< tbng, ngha l tin cy thng k ca ttnh nh hn tin cy thng k ca

tbng. iu c ngha l s khc nhau gia gi tr trung bnh v gi tr thc l

khng ng tin cy, ni cch khc phng php c ng chp nhn c.

H s bin thin (CV%) khi xc nh mu gi trn nn mu tht hai mc

nng ny u di 5% chng t phng php c chm tt.

3.2. Phn tch mu thc t

3.2.1. Xc nh hm lng As(III) trong mu nc ngm

*Quy trnh ly mu v bo qun mu: Mu nc c ly vo chai nha,

ri thm vo khong 5 ml dung dch axit HCl 1/1, lc u ri y np kn.

Nu c cn phi em lc b cn. Sau em i phn tch ngay.

Cc mu nc ngm N1 N8 c ly cc ging khoan v ging khi

thuc Tnh Ph Th. Thng tin v cc mu nc ny c ghi trong bng 3.14:

Bng3.14 : Thng tin v cc mu nc ngm

Stt Tn

mu a im ly mu

Ngy ly

mu

su

ging (m)

1 N1 Phm Th Duyn - Khu 2 - oan H - Thanh Thy 9/7/2011 30

2 N2 Phan nh Tun Khu 10 Thch Sn LmThao 11/7/2011 10

3 N3 UBND Khu 10 - Hin Quan Tam Nng 10/7/2011 12

4 N4 Trn S Hi - Khu 2 - oan H - Thanh Thy 9/7/2011 30

5 N5 Nguyn Th Sch - Khu 10 Thch Sn Lm Thao 11/7/2011 10

6 N6 H c Lim - Khu 3 - iu Lng - Cm Kh 10/7/2011 7

7 N7 L Th Ht - Khu 3 - oan H - Thanh Thy 9/7/2011 36

8 N8 Nguyn Xun Hp - Khu 4 - oan H - Thanh Thy 9/7/2011 10

56

Mu nc ngm s 1 (N1):



Bnh 2: 2,00 ml dung dch KIO3 2%; 2,00 ml dung dch HCl 1M; 1,5 ml

dung dch safranin 0,02%





safranin 0,02%.

Bnh 7- 8: 5,00 ml mu nc N1; 1,00 ml dung dch As(III)10ppm; 2,00 ml

dung dch KIO3 2%; 2,00 dung dch ml HCl 1M; 1,5 ml dung dch safranin 0,02%.

Bnh 9- 10: 5,00 ml mu nc N1; 1,50 ml dung dch As(III) 10ppm;

2,00 ml dung dch KIO3 2%; 2,00 dung dch ml HCl 1M; 1,5 ml dung dch

safranin 0,02%.






5,00 ml mu nc N1 0,945 0,943 0,002

0.002 0,945 0,943 0,002


10,00 ppm

0,945 0,934 0,011 0.012

0,945 0,932 0,013


10,00 ppm

0,945 0,919 0,026 0.025

0,945 0,921 0,024


10,00 ppm

0,945 0,908 0,037 0.037

0,945 0,908 0,037

57

Hnh3.9 : ng thm chun xc nh As(III) trong mu nc ngm s 1

T hnh ta c nng As(III) l: Cx = 22,03 (ppb)


5

2510

03,223

= 0,11 g/ml

Mu nc ngm s 2 (N2):

Cc bc tin hnh th nghim tng t vi mu nc ngm s 1, ta c:



5,00 ml mu nc N2 0,945 0,9441 0,0009

0.0009 0,945 0,9441 0,0009


10,00 ppm

0,945 0,933 0,012 0.011

0,945 0,935 0,010


10,00 ppm

0,945 0,920 0,025

0.024 0,945 0,922 0,023


10,00 ppm

0,945 0,9091 0,0359

0.0361 0,945 0,9087 0,0363

58


T hnh ta c nng As(III) l: Cx = 3,54 (ppb)


5

2510

54,33

= 0,018 g/ml

Mu nc ngm s 3 (N3):




5,00 ml mu nc N3 0,948 0,947 0,001

0.001 0,948 0,947 0,001


10,00 ppm

0,948 0,937 0,011 0.012

0,948 0,935 0,013


10,00 ppm

0,948 0,921 0,027 0.025

0,948 0,925 0,023


10,00 ppm

0,948 0,909 0,039 0.038

0,948 0,911 0,037

59



Cx = 6,45 (ppb)


5

2510

45,63

= 0,03 g/ml

Mu nc ngm s 4 (N4):



V (ml) A nn A mu A

5,00 ml mu nc N4 0,946 0,945 0,001

5,00 ml mu nc N4, thm 1,25 ml

As(III) 10,00 ppm 0,946 0,915 0,031


As(III) 10,00 ppm 0,946 0,885 0,061


As(III) 10,00 ppm 0,946 0,8515 0,0945

60



Cx = 4,83(ppb)


5

2510

83,43

= 0,02 g/ml

Mu nc ngm s 5 (N5):




5,00 ml mu nc N5 0,946 0,9451 0,0009

0.0008 0,946 0,9453 0,0007


10,00 ppm

0,946 0,936 0,010 0.011

0,946 0,934 0,012


10,00 ppm

0,946 0,925 0,021 0.023

0,946 0,921 0,025


10,00 ppm

0,946 0,9103 0,0357 0.0355

0,946 0,9107 0,0353

61



Cx = 2,76(ppb)

Tng ng vi hm lng As(III) trong mu nc ngm s 5 l:

5

2510

76,23

= 0,01 g/ml

Mu nc ngm s 6 (N6):









safranin 0,02%.

62



safranin 0,02%.



safranin 0,02%.




Bng3.20: Xc nh hm lng As trong mu nc ngm s 6


5,00 ml mu nc N6 0,945 0,944 0,001

0,001 0,945 0,944 0,001


1,00 ppm

0,945 0,942 ,003 0.0025

0,945 0,943 0,002


1,00 ppm

0,945 0,941 0,004

0.004 0,945 0,941 0,004


1,00 ppm

0,945 0,939 0,006

0.0055 0,945 0,940 0,005

63


T hnh ta c nng As(III) l: Cx = 10(ppb)


5

2510

103

= 0,05 g/ml

Mu nc ngm s 7 (N7):




5,00 ml mu nc N7 0,946 0,945 0,001

0,001 0,946 0,945 0,001


1,00 ppm

0,946 0,944 0,002 0.002

0,946 0,944 0,002


1,00 ppm

0,946 0,943 0,003

0.003 0,946 0,943 0,003


1,00 ppm

0,946 0,942 0,004

0.004 0,946 0,942 0,004

64



Cx = 20 (ppm)


5

2510

203

= 0,10 g/ml

Mu nc ngm s 8 (N8):









safranin 0,02%.

65



safranin 0,02%.


ml dung dch KIO3 2%; 2,00 dung dch ml HCl 1M; 1,5 0ml dung dch

safranin 0,02%.

nh mc tt c cc bnh bng nc ct n vch mc, sc trn u dung

dch. em o hp th quang ca dung dch bc sng 519 nm, vi dung

dch so snh l dung dch trong bnh 1. Kt qu thu c nh bng 3.22:



5,00 ml mu nc N8

0,946 0,945 0,001

0,001

0,946 0,945 0,001


1,00 ppm

0,946 0,942 0,004

0.004

0,946 0,942 0,004


1,00 ppm

0,946 0,937 0,009

0.008

0,946 0,938 0,008


1,00 ppm

0,946 0,934 0,012

0.0115

0,946 0,935 0,011

66



C x = 11 (ppb)


5

2510

113

= 0,055 g/ml.

67

KT LUN

Vi mc ch t ra cho lun vn l xc nh hm lng Asen trong

mu mi trng (nc ngm) bng phng php trc quang vi thuc th

Safranin, chng ti tham kho cc ti liu v tin hnh kho st cc th

nghim la chn cc iu kin thch hp ri tin hnh phn tch mu thc

t kt qu thu c nh sau:

1. kho st c cc iu kin ti u ca phn ng ch th xc nh

As(III) da trn tc dng xc tc ca n vi phn ng gia axit hydrochloric,

Kali iodate v Safranin. Nng cui ca cc tc nhn phn ng KIO3,

Safranin, HCl ln lt l 0,16 %; 1,2x10-3 %; 0,08M. Nng As(III) c

xc nh da

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