as_aas

I HC QUC GIA H NI

TRNG I HC KHOA HC T NHIN -----X-----

Nguyn th thu hng

Nghin cu cc iu kin xc nh cc dng

asen bng phng php ph hp th nguyn t

Lun vn thc s khoa hc

CHUYN NGNH: HO PHN TCH

M S: 1.04.03

CN B HNG DN KHOA HC: TS. T TH THO

H Ni, 2008

Nguyn Th Thu Hng li cm n

Khoa Ha hc Trng HKHTN http://www.ebook.edu.vn

LLii ccmm nn

Vi lng bit n su sc, ti xin chn thnh cm n TS. T Th Tho

giao ti v tn tnh hng dn, to iu kin cho ti hon thnh lun vn ny.

Ti cng xin chn thnh cm n PGS. TS. Chu Xun Anh v cc thy c trong b

mn Ho phn tch ht lng gip ti trong qu trnh hc tp v nghin cu.

Cui cng, ti xin gi li cm n gia nh v cc bn hc vin, sinh vin

b mn Ho Phn tch gip ti trong thi gian lm lun vn.

H Ni, ngy 25 thng 7 nm 2008

Hc vin

NNgguuyynn TThh TThhuu HHnngg

Nguyn Th Thu Hng CC K HIU VIT TT

Khoa Ha hc Trng HKHTN http://www.ebook.edu.vn

BBNNGG KK HHIIU NHNG CH VIT TT

Bnh phng ti thiu nghch o (inverse least

squares) ILS

Hi qui cu t chnh (Principal component

regression) PCR

Cu t chnh (Principal component)

PC

Phng php o ph hp th nguyn t s dng k

thut hidrua ho HVG - AAS

Nguyn Th Thu Hng Mc lc

Khoa Ha hc Trng HKHTN Lun vn thc s

MMCC LLCC M U ........................................................................................................... - 1 -

CHNG 1. TNG QUAN ............................................................................. - 3 -

1.1. TRNG THI T NHIN, NGUN GC NHIM V CC DNG TN TI TRONG DUNG DCH CA ASEN ................................................ - 3 -

1.1.1. Trng thi t nhin v ngun gc nhim As ............................................. - 3 -

1.1.2. Cc dng tn ti trong dung dch ca As ....................................................... - 4 -

1.2. C TNH CA CC DNG ASEN ...................................................... - 5 -

1.3. S PHN TN, DI CHUYN V CHUYN HA LN NHAU TRONG MI TRNG CA CC DNG ASEN ...................................................... - 7 -

1.4. HIN TRNG NHIM ASEN VIT NAM...................................... - 8 -

1.5. PHNG PHP XC NH NG THI CC DNG ASEN ......... - 10 -

1.5.1. Cc phng php xc nh c s dng k thut hidrua ha (HVG) ....... - 10 -

1.5.2. Phng php s dng h tch HPLC kt hp vi mt detector .............. - 11 -

1.6.1. Gii thiu phn mm Matlab ......................................................................... - 12 -

1.6.2. C s phng php ton ................................................................................. - 13 -

1.6.3. Xc nh ng thi cc dng As bng phng php HVG AAS s dng Chemometrics .............................................................................................................. - 21 -

CHNG 2. THC NGHIM ...................................................................... - 23 -

2.1. NI DUNG V PHNG PHP NGHIN CU ................................ - 23 -

2.1.1. Phng php nghin cu ................................................................................ - 23 -

2.1.2. Ni dung nghin cu ....................................................................................... - 23 -

2.2. HA CHT V DNG C TH NGHIM ........................................... - 24 -

2.2.1. Ha cht ............................................................................................................. - 24 -

2.2.2. Dng c v trang thit b o ........................................................................... - 25 -

2.2.3. Cc phn mm tnh ton v x l .................................................................. - 25 -

2.3. TIN HNH TH NGHIM ................................................................... - 25 -



2.3.1. Qui trnh phn tch ........................................................................................... - 25 -

2.3.2. Cc thut ton hi qui a bin ....................................................................... - 26 -

CHNG 3. KT QU V THO LUN .................................................. - 28 -

3.1. NGHIN CU CC IU KIN TI U XC NH HM LNG As(III) BNG PHNG PHP HVG AAS .............................................. - 28 -

3.1.1. Kho st cc thng s ca my o AAS ...................................................... - 28 -

3.1.2. Kho st iu kin kh As(III) thnh asin vi h HVG ........................... - 29 -

3.1.3. Kho st khong tuyn tnh v lp ng chun xc nh As(III) ......... - 43 -

3.1.4. Kho st nh hng ca cc ion l ti php xc nh As(III) bng phng php HVG AAS ....................................................................................................... - 45 -

3.2. NGHIN CU NH HNG CA CC CHT KH I VI QU TRNH KH CC DNG As THNH ASIN .............................................. - 51 -

3.2.1. Kh nng kh cc dng As(V) thnh As(III) ca KI ............................... - 51 -

3.2.2. Kh nng kh cc dng As(V) thnh As(III) ca h kh KI/Ascobic ... - 52 -

3.2.3. Kh nng kh cc dng As(V) thnh As(III) ca NaHSO3 ..................... - 54 -

3.2.4. Kh nng kh cc dng As(V) thnh As(III) ca L-cystein .................... - 55 -

3.3. NGHIN CU NH HNG CA MI TRNG PHN NG I VI QU TRNH KH CC DNG As THNH ASIN BNG CHT KH NaBH4 ............................................................................................................. - 56 -

3.4. XC NH NG THI CC DNG As THEO PHNG PHP PH HP TH NGUYN T KT HP VI CHEMOMETRICS .................... - 61 -

3.4.1. ng chun xc nh cc dng As ring r .............................................. - 61 -

3.4.2. Gii hn pht hin v gii hn nh lng.................................................. - 62 -

3.4.3. lp li v ng ca cc php xc nh ring tng dng As .......... - 64 -

3.4.4. Kim tra tnh cng tnh ca cc dng As ..................................................... - 65 -

3.5. NH GI PHNG PHP PHN TCH V NG DNG PHN TCH MU THC T .............................................................................................. - 70 -



3.5.1. nh gi tnh ph hp ca phng trnh hi qui thng qua mu kim chng ............................................................................................................................. - 70 -

3.5.2. ng dng phn tch mu thc t v tnh hiu sut thu hi ca phng php ................................................................................................................................ - 76 -

KT LUN ..................................................................................................... - 83 -

TI LIU THAM KHO ............................................................................... - 85 -

PH LC ................................................................................................................ i

Nguyn Th Thu Hng M U

Khoa Ha hc Trng HKHTN - 1 - Lun vn thc s

M U Cng vi s pht trin nhanh chng ca x hi hin i, vn nhim

mi trng ngy nay ang tr thnh mi quan tm chung ca nhn loi. S lng cc c cht phn tn trong mi trng ngy mt nhiu hn do cc hot ng sn xut v tiu th a dng ca con ngi ngy mt tng. Mt trong s nhng nguyn t gy nhim mang c tnh cao nht l Asen (As) v ang c phn tn nhanh trong mi trng theo nhiu con ng [1, 9, 45]. As c xem l c cht bng A khng ch do tnh c hi ln m cn do n c kh nng tch ly cao trong c th sinh vt v xm nhp vo c th qua nhiu ng, mt khc, y hc hin nay vn cha c phc iu tr hiu qu cho bnh nhn nhim c As. Mc d As v mt s hp cht ca n l tc nhn gy nhiu bnh ung th, t bin v tn thng ni tng nhng i vi qu trnh sinh trng th As l nguyn t vi lng cn thit [1, 27, 40]. Do , hm lng As trong mi trng c qui nh rt nghim ngt. Trong nhng thp k gn y, vn nhim As ang ngy cng tr nn nng bng hn do mc nhim trn din rng ngy mt gia tng nhanh chng theo tc pht trin ca i sng con ngi. Ty theo ngun nhim v iu kin pht tn, As i vo mi trng theo nhiu con ng v tn ti nhiu dng khc nhau, kh nng phn tn v di chuyn trong mi trng, hp ph v tng tc ln c th con ngi ca cc dng cng khc nhau [9, 11]. V vy, vic nh lng cc dng As nh gi mc nhim c v lm tin cho vic kho st ngun nhim, t lp bin php thch hp loi tr v hn ch nhim lan rng l vn cp bch.

Trong nghin cu xc nh lng vt cc dng As, s lng cc cng trnh nghin cu cn hn ch v ch yu tp trung cc nghin cu trn h kt hp sc k lng hiu nng cao (HPLC) kt ni vi b phn pht hin nh AAS, AES, AFS, MS, ...[8, 10, 19, 24, 32]. Cc h o ny cho php tch v nh lng ng thi cc dng As mt cch hiu qu trn nhiu i tng, c bit l i tng sinh hc. Nhng, chi ph cho qu trnh phn tch kh ln do i hi trang thit b t tin nn khng phi phng th nghim no cng c th trang b c. Vn t ra trong thc t th nghim Vit Nam hin nay l cn nghin cu mt phng php c th s dng cc thit b ph bin hn nh dng As m khng cn cng on tch.

Nguyn Th Thu Hng M U


Trong nhng nm gn y, cng vi s pht trin mnh m ca ngnh ton hc thng k v tin hc ng dng, Chemometrics - mt nhnh ca ha hc phn tch hin i - pht trin nhanh chng v c ng dng ngy mt rng hn. Mt mng quan trng trong Chemometrics ang c nghin cu v s dng hiu qu l k thut hi qui a bin thut ton xc nh ng thi nhiu cu t trong hn hp m khng cn tch loi. Thut ton ny c ng dng rng ri gii quyt nhiu bi ton nh dng phc tp. i vi vn xc nh cc dng As trong hn hp, hin nay cha c nhiu cng trnh nghin cu theo hng ny tuy u im ca n l rt ln so vi cc hng nghin cu khc. V vy, chng ti la chn nghin cu gp phn pht trin cc phng php xc nh ng thi cc dng As theo hng ng dng Chemometrics trong phm vi lun vn l nghin cu cc iu kin xc nh cc dng As bng phng php ph hp th nguyn t s dng phng php hi qui a bin tuyn tnh.

Nguyn Th Thu Hng CHNG 1. TNG QUAN


CHNG 1. TNG QUAN 1.1. TRNG THI T NHIN, NGUN GC NHIM V CC DNG TN TI TRONG DUNG DCH CA ASEN

1.1.1. Trng thi t nhin v ngun gc nhim As

As xut hin trong mi trng dng hp cht v c hoc hu c. As phn b rt rng ri trong t nhin, c bit l trong ngun nc nh nc ngm, nc bin, ngun nc khong, nc sng sui. Trong t nhin As tn ti ch yu cc dng hp cht vi O, Cl, S, trong khong vt nh khong st, vi, mui m, reagal As4S4, opriment As2S3, asenopirit FeAsS, qung km, [3, 27, 28].

Vic s dng rng ri As trong nhiu ngnh cng nghip nh dc, sn xut knh, cht nhum, cht c n mn, thuc tr su, thuc dit nm, thuc da, hoc ngnh cng nghip s dng nhin liu ha thch nh cng nghip xi mng, nhit in, cng ngh t cht thi rn cng l ngun gy nhim khng kh, nc bi As [12, 14, 45]. Cc ngnh cng nghip khai thc v ch bin cc loi qung, nht l qung sunfua, luyn kim to ra ngun nhim As do vic khai o cc m nguyn sinh phi l cc qung sunfua, lm gia tng qu trnh phong ha, bo mn v to ra khi lng ln t thi c ln asenopyrit ln cn khu m. Ti cc nh my tuyn qung, asenopyrit c tch ra khi cc khong vt c ch v phi ra khng kh. Asenopyrit b ra tri, dn n hu qu l mt lng ln As c a vo mi trng xung quanh. Nhng ngi khai thc t do khi i qung thm vo axit sunphuric, xng du, cht ty. Asenopyrit sau khi tch khi qung s thnh cht thi v c cht ng ngoi tri v tri vo sng sui, gy nhim trn lan. Bn cnh , cc qu trnh t nhin nh a cht, a ha, sinh a ha, ... lm cho As nguyn sinh c mt trong mt s thnh to a cht (cc phn v a tng, cc bin i nhit dch v qung ha sunphua cha As) tip tc phn tn hay tp trung gy nhim mi trng sng [1, 27, 33, 35].



1.1.2. Cc dng tn ti trong dung dch ca As

Sau khi pht tn vo mi trng, As tn ti nhiu dng khc nhau ty theo bn cht ca ngun pht tn, iu kin pht tn v iu kin ca mi trng tn ti.

Bng 1. Mt s dng As trong cc i tng sinh hc v mi trng

STT Tn gi Cng thc

1. Asin AsH3

2. Asenit AsO33-

3. Asenat AsO43-

4. Axit dimetylasenic, DMAA Me2AsO2H

5. Axit metylasonic, MMAA MeAsO3H2

6. Trimetylasin Me3As

7. Oxit trimetylasin, TMAO Me3As+-O-

8. Ion tetrametylasoni Me4As+

9. Trimetylasoniaxetat Me3As+CH2COO-

10. Asenocholin (2-trimetylasonietanol)

Me3As+CH2CH2OH

11. Dimetylasinoyletanol Me3As+(O-)CH2CH2OH

Cc dng ch yu ca As trong mi trng nc i tng c quan tm nht trong phn tch mi trng l bn dng As(III), As(V), DMA v MMA, trong hai dng v c c c tnh cao hn. Hm lng As trong nc ngm ph thuc vo tnh cht v trng thi mi trng a ha. As tn ti trong nc ngm dng H2AsO4- (trong mi trng pH axit n gn trung tnh), HAsO42- (trong mi trng kim). Hp cht H3AsO3 c hnh thnh ch yu



trong mi trng oxi ha-kh yu [11, 35]. Hnh 1 minh ha cho s tn ti ca cc dng As v c v hm lng As trong dung dch di nh hng tng h ca pH v th oxi ho kh ca dung dch (Eh) mt s vng.

Hnh 1. nh hng ca Eh v pH n s tn ti ca cc dng As v c (S liu tham kho bn vng: a, Arizona; b, Korea; c, Bangladesh; d, India)

[35] 1.2. C TNH CA CC DNG ASEN

Nh chng ta bit, As l nguyn t vi lng, rt cn thit cho s sinh trng v pht trin ca con ngi v sinh vt. hm lng nht nh, As c vai tr quan trng trong trao i cht nuclein, tng hp protit v hemoglobin. Tuy nhin, khi xut hin hm lng cao hn, As v cc hp cht ca n l tc nhn gy 19 bnh ung thu, t bin v d thai trong t nhin. i vi thc vt, As cn tr qu trnh trao i cht, lm gim mnh nng sut, c bit trong mi trng thiu photpho. S nhim c As c gi l arsenicosis. l mt tai ha mi trng i vi sc khe con ngi. Nhng biu hin ca bnh nhn nhim c As l chng sm da (melanosis), dy biu b (kerarosis), tn thng mch mu, ri lon cm gic v s di ng, ... Ngi b nhim c As lu ngy s xut hin



hin tng sng ha da, gy sm v mt sc t da hay bnh Bowen, ... t dn n hoi th hay ung th da, vim rng, khp, tim mch, ... [12, 17, 28, 40]. c tnh cao ca As v cc hp cht ca n cn do kh nng nhim c qua nhiu con ng: h hp, tiu ho, tip xc qua da, c bit As l tc nhn gy ung th trn mi b phn ca c th [11, 12]. Hin ti trn th gii cha c phng php hu hiu cha bnh nhim c As, cc nghin cu vn ch tp trung vo iu tr triu chng v s dng b sung thm cc thuc tng thi v vitamin c th t o thi As [1, 14].

Hnh 2. Mt s hnh nh v nn nhn nhim c As [45]

Trong s cc hp cht ca As th As(III) v c c hn c. As(III) c c tnh cao hn As(V) khong 50 ln do As(V) v cc hp cht As hu c c o thi qua thn rt nhanh v hu nh ton b. As(III) th hin tnh c v n tn cng vo cc nhm hot ng -SH ca enzim lm v hiu ho enzim:

As(III) nng cao cn lm ng t protein, c l do As(III) tn cng vo cc lin kt c nhm sunfua. Tuy nhin, phn ln As(III) hp th vo c th u nhanh chng b trit tiu qua ng tit niu o thi As cha metyl ha v thng qua hot ng kh c ca gan bng cch metyl ha thnh MMAA hoc DMAA [27, 40].



As(V) dng AsO43- c tnh cht tng t PO43- s thay th PO43- gy c ch enzim, ngn cn qu trnh to ATP l cht sn sinh ra nng lng sinh hc.

Cc dng As hu c c tnh c thp hn rt nhiu, mt s hp cht As(V) v c thm ch khng c [13, 33].

1.3. S PHN TN, DI CHUYN V CHUYN HA LN NHAU TRONG MI TRNG CA CC DNG ASEN

As phn b rng ri trong mi trng di nhiu trng thi khc nhau v i vo cc mi trng sng theo nhiu cch thc v tc khc nhau.

Trong a quyn: As tch ly trong mt s thnh to a cht nh khong vt v qung phong ha lng ln nhng kh phn tn. As c b sung vo t qua tch ly t nc, xm nhp t khng kh v rc thi cng nghip. Lng As trong t di chuyn do cc qu trnh a cht, a ha v sinh a ha khc nhau. Trong t, cc dng As v c tham gia qu trnh oxi ha v metyl ha nh cc vi sinh vt [1, 9, 28, 37].

Trong thy quyn: S phn tn v di chuyn ca As trong mi trng nc c bit quan trng v phn ln cc qu trnh nhim u do nhim nc. As t t c gii phng vo mi trng nc do qu trnh oxi ha cc khong sunfua hoc kh cc khong oxi hidroxit giu As hay qu trnh ra tri v khuch tn t nhin. V c ch xm nhim cc kim loi nng - trong c As - vo nc ngm cho n nay c nhiu gi thit khc nhau nhng vn cha thng nht. Thng qua cc qu trnh thy a ha v sinh a ha, cc iu kin a cht thy vn m As c th xm nhp vo mi trng nc. Hm lng As trong nc ngm ph thuc vo tnh cht v trng thi mi trng a ha. Nc ngm trong nhng vng trm tch ni la, khu vc qung ha ngun gc nhit dch, m du kh, m than, ... thng giu As [17, 35, 41].

Ngoi qu trnh di chuyn t t vo nc, nhim As trong nc cn do qu trnh o thi cng nghip. Lng ln As trong cng nghip v khai thc m c a nhanh vo ngun nc do thi trc tip hoc qu trnh ra tri gy nhim nghim trng mi trng nc trn din rng do kh nng ha tan cao ca cc hp cht As [1, 12, 14].

Trong kh quyn: Lng As i vo khng kh ch yu do hai ngun l kh thi cng nghip hay kh ni la v do vi sinh vt chuyn vo [11].



Trong sinh vt quyn: As i vo c th thc vt qua nc hoc t l ch yu, sau chuyn vo c th ng vt v b hp th, chuyn ha v tch ly mt phn. As xm nhp vo c th sinh vt, c bit l c th ngi theo nhiu con ng, trong ph bin l qua ng tip xc v qua tiu ha. Phn ln lng As i vo c th ng vt b chuyn ha nhanh chng v o thi ra mi trng, tip tc chu trnh vn chuyn ca n trong t nhin [6, 19, 32, 33].

Hnh 3 l s cc qu trnh chuyn ha n gin ca As trong t nhin.

Hnh 3. Qu trnh chuyn ha ca cc dng As trong mi trng [30]

1.4. HIN TRNG NHIM ASEN VIT NAM

Nhng nm gn y, khi trn th gii pht hin nhiu vng nhim As c nh hng nghim trng ti i sng v sc kho ngi dn th vn nhim As Vit Nam cng tr thnh vn thi s. Vic lin tip pht hin nhiu vng nhim As mc nng khin Vit Nam c tn trong bn nhim As ca th gii [39, 41]



Hnh 4. Bn phn b As trong nc ngm cc tnh Thi Bnh, Nam nh, Ninh Bnh nm 2001 [41]

Vn As bt ngun ch yu do a cht. Nc ngm ti cc trm tch cch y 25000 n 80000 nm ang nh hng mnh ti 50% lnh th Bangladesh [28]. Nc ta cng c cu to a tng nh Bangladesh, c bit l lu vc ng bng sng Hng v sng Cu Long, do nguy c nc ngm b nhim As tng i cao [41]. Nhng nghin cu s b ca UNICEF phi hp vi Trng i hc Khoa hc T nhin, Cc a cht Khong sn v Vin Ho hc trong thi gian gn y cho thy nhiu mu nc ngm ti mt s tnh ng bng sng Hng v sng Cu Long c hm lng As vt qu nhiu ln ch tiu cho php ca WHO. Theo c tnh ca UNICEF, ti nc ta hin nay, s ngi c nguy c mc bnh do tip xc vi As ln n 10 triu. Ti im nng H Nam, kt qu xt nghim As trong tc v nc tiu ca 100 ngi dn cho thy hm lng As cao hn c chc ln so vi ngi bnh thng. Cng ti y, 94,4% ging khoan c nghin cu c hm lng As cao hn tiu chun v sinh nc n ung. Ngay ti H Ni, nc ngm b nhim As c pht hin t nm 1996, c bit ti mt s khu vc nh Qunh Li - qun Hai B Trng. Bn phn b hm lng As (hnh 4) ti mt s tnh pha bc trn y cng



cho thy nhiu vng c hm lng As trong nc ngm cao hn mc cho php nhiu ln [1].

1.5. PHNG PHP XC NH NG THI CC DNG ASEN

1.5.1. Cc phng php xc nh c s dng k thut hidrua ha (HVG)

Phng php ny da trn nguyn tc kh cc hp cht As v dng asin v metylasin sau nh lng sn phm sinh ra tnh ngc li hm lng cc hp cht ban u nu mi dn xut ca asin c sinh ra t mt hp cht ban u.

Phng php c in nht xc nh As theo hng ny l phng php Guizeit - s dng Zn v axit HCl kh As v o asin bng php o quang vi bc dietyldithiocacbamat [34]. Nhiu cng trnh sau s dng NaBH4 lm cht kh thay cho h Zn/HCl kt hp vi mt b phn pht hin khc nh lng asin nh AAS, GC AAS, GC MS, ... [36, 37, 39].

Cc nh khoa hc nghin cu nh lng cc dng As theo hng ny a ra mt s vn cn lu cho qu trnh xc nh [32]. Th nht, hiu sut kh cc dng As thnh asin v dn xut asin ph thuc nhiu vo mi trng phn ng v nng NaBH4. Mi dng As c mt mi trng kh ti u ring, y cng l c s chnh ca phng php xc nh ng thi cc dng As trong mu. Th hai, trong qu trnh kh s xut hin s sp xp li phn t cc dng asin, c bit l khi c mt oxi trong dung dch. Th ba, c rt nhiu ion l nh hng ti php o nh cc ion kim loi nng, nitrat, ... ch yu theo hng lm gim tn hiu tc l gim nhy ca phng php v cch thc cc ion ny nh hng ln php o khng nh nhau.

Cc nghin cu gn y pht trin theo hng ny c nhng thnh tu ng k trong vic gp phn nh lng cc dng As v c. Emil A.Cordosa v cc cng s xc nh hm lng As(III) v As(V) trong mu trn h HVG AAS bng cch iu chnh pH ca mi trng phn ng [15]. Nghin cu ny ch ra rng, vi cc iu kin kh nht nh (v tc dng, nng cht kh, ...) th As(V) s hon ton khng b kh ti pH = 2, do c th xc nh ring hm lng As(III), sau s dng L cystein kh hon ton As(V) v As(III) xc nh tng hm lng v suy ra lng As(V). Trong mt cng trnh khc,



Jian-bo Shi v ng nghip [37] chit hai dng As v c ra khi mu t v s dng h HVG AFS xc nh ring tng dng bng cch xc nh As(III) trong mi trng axit citric 0,1M v xc nh tng hm lng As sau khi kh As(V) v As(III) bng L cystein ngay trn dng.

S lng cng trnh p dng k thut hidrua ho xc nh As rt ln v a dng [18, 36, 37] cho thy tnh u vit vt tri ca k thut ny, c bit l khi kt hp s dng mt h sc k v b phn hidrua ho vi mt detector nh MS hay cc detector quang khc.

1.5.2. Phng php s dng h tch HPLC kt hp vi mt detector

Vic kt hp h tch HPLC v mt detector (AAS, AFS, MS, ...) to thnh cc h xc nh dng As hiu dng cao v ang ngy mt tr nn ph bin trong cc phng th nghim hin i. Nhiu cng trnh nghin cu theo hng ny t c nhng thnh tu nht nh trong vic nh lng cc dng As cng nh pht hin v ghi nhn thi gian lu ca cc dng cha bit. Vic s dng cc h xc nh ny cho nhiu tin ch trong vic xc nh hm lng As, c bit l u th s dng lng mu nh nn n ph hp vi yu cu xc nh lng vt nhiu i tng khc nhau [32].

Cc tc gi [10] tin hnh xc nh hm lng cc dng As trong mu nc t nhin vi nhy kh cao (



qu trnh tch v xc nh cc dng As trong mt s loi thc vt trn h HPLC HVG AFS vi pha ng l dung dch NaH2PO4 v dung mi chit l h nc metanol (1:2) v thu c kt qu l trn 73% lng As c chit sau 3 phn on. Kt qu phn tch cc mu l o theo phng php ny cho thy As(V) chim lng ln v khng pht hin c As(III) trong cc mu ny. S dng h HPLC HVG AFS, tc gi [26] cn xc nh kt hp c cc dng As v selen trong i tng nc t nhin vi nhy cao.

Ngoi cc cng trnh trn, s lng cc nghin cu p dng cc h kt hp khc nhau cng b rt a dng. Nhiu nhm tc gi nghin cu so snh kh nng pht hin v nh lng ca cc detector khi kt hp vi h tch HPLC [8, 19, 20, 43] v nhn thy mi loi c u th xc nh cc nhm hp cht As khc nhau, tu theo i tng c th la chn detecter ph hp.

1.6. XC NH NG THI CC DNG ASEN S DNG CHEMOMETRICS

1.6.1. Gii thiu phn mm Matlab

Matlab (Matrix laboratory), theo tn gi ca n, l mt cng c phn mm ca Math Work, ban u c pht trin nhm phc v ch yu cho vic m t cc nghin cu k thut bng ton hc vi phn t c bn l ma trn. Trn c s ban u , cc nh lp trnh pht trin phn mm ny s dng cho nhiu ngnh khoa hc nh c hc, vt l, sinh hc, ho hc, m phng, i vi c d liu ri rc hay lin tc [2, 4, 5, 16].

Mc pht trin ca Matlab chng t n l phn mm c giao din cc mnh v nhiu li th trong k thut lp trnh gii quyt nhng vn a dng trong nghin cu khoa hc k thut. Trong Matlab, cc cu lnh vit st vi cc m t k thut nn lp trnh trn ngn ng ny thc hin nhanh, n gin hn so vi nhiu ngn ng thng dng khc nh Pascal, Fortran, Nhng hm c sn trong Matlab c cu trc thit lp gn ging ngn ng C, do ngi dng khng mt nhiu thi gian hc hi khi nm c nhng vn c bn ca mt s ngn ng lp trnh thng dng. Bn cnh , Matlab khng ch cho php t vn tnh ton m cn c th x l d liu, biu din ho mt cch mm do, n gin, chnh xc trong khng gian 2D v 3D bng c nhng hm sn c v cc hm ng dng do ngi s dng to lp. c bit hn na, giao din ca



Matlab cho php c, x l v a tn hiu u ra ngay trn cc file Excel - rt tin li cho qu trnh x l tp s liu phc tp. Cui cng, vi u im ci t n gin, c th lin kt vi cc th vin h tr nh Simulink, Fuzzy, Toolbox, DSP (digital signal processing) hay tch hp vi cc ngn ng quen thuc nh C, C++, Fortran,, Matlab thc s tr thnh cng c ph bin c lc trong cc mi trng khc nhau [2, 5].

Vi u th l b chng trnh phn mm ln trong lnh vc ton s v m phng, chng ti la chn phn mm Matlab nghin cu trin khai nhng lp trnh hi qui a bin nhm gii quyt bi ton xc nh ng thi cc dng asen.

1.6.2. C s phng php ton

Chemometrics c nh ngha l vic ng dng cc phng php ton hc, thng k, ho, qui hoch thc nghim, ti u ho cc thng tin ho hc trch ra t tp s liu phn tch v a ra ti a nhng thng tin hu ch t tp s liu ban u [7, 23].

Ra i t nhng nm u ca thp k 70, cho ti nay Chemometrics xc lp c mt v tr quan trng cho mnh trong ngnh ho hc, c bit l trong ho hc phn tch hin i. Mt mng ln trong Chemometrics pht trin nhanh gn lin vi ton hc v tin hc l hi qui a bin k thut a bin c dng rng ri trong phng th nghim ho hc gip gii quyt cc bi ton xc nh ng thi nhiu cu t cng c mt trong hn hp m khng cn tch loi trc. V nguyn tc, ch cn xy dng dy dung dch chun c mt tt c cc cu t cn xc nh vi nng bit trc trong hn hp (cc bin c lp x), o tn hiu phn tch ca cc dung dch ny di dng mt hay nhiu bin ph thuc y v thit lp m hnh ton hc m t quan h gia hm y (tn hiu o) v cc bin c lp x (nng cc cht trong hn hp). Da trn m hnh ny c th tm c nng ca cc cu t trong cng dung dch nh phn khi c tn hiu phn tch ca dung dch [7].

Nu cc cu t c mt trong hn hp cho tn hiu o c tnh cht cng tnh th c th s dng phng php hi qui a bin tuyn tnh thng thng (multiple linear regression- MLR) nh phng php bnh phng ti thiu thng thng hoc hiu qu hn nh bnh phng ti thiu tng phn, phng php



hi qui cu t chnh, . Nhng nu trong hn hp, cc cu t c s tng tc ln nhau lm mt tnh cht cng tnh tn hiu o th phi s dng m hnh hi qui a bin phi tuyn tnh m ph bin l cc phng php kt hp vi mng nron nhn to [31, 38].

Ty thuc vo c im ca hm ph thuc, c th chia cc phng php hi qui a bin tuyn tnh thnh 2 nhm chnh: cc phng php hi qui a bin tuyn tnh s dng ph ton phn nh phng php CLS, PLS, ... v phng php s dng d liu ph ring phn nh ILS. Trong lun vn ny, tn hiu ca cc dung dch cha cc dng As c o 5 im ri rc nn chng ti chn s dng phng php hi qui trn ph ring phn ILS v th nghim nghin cu phng php PCR v phng php ny v l thuyt c th s dng cho c hai trng hp ca hm ph thuc [29, 31, 38].

1.6.2.1. Phng php bnh phng ti thiu nghch o (inverse least squares - ILS)

Phng php bnh phng ti thiu nghch o (ILS) hay cn gi l phung php ma trn P c xy dng trn gi thit rng nng ca tn hiu phn tch l hm ca tn hiu o [7, 29, 31]:

C = P . A

Trong phng php hi qui a bin, phng trnh trn c th khai trin thnh:

C1 = P11A1 + P12A2 + + P1mAm

C2 = P21A1 + P22A2 + + P2mAm

Cx = Px1A1 + Px2A2 + + PxmAm

Trong :

Am : Gi tr tn hiu o thi im m

Pxm : Gi tr h s hi qui ca cu t th x ti thi im m.

Cx : Nng cu t th x.

Cc bc tnh ton trong m hnh ILS bao gm



1. Xy dng cc ma trn d liu chun:

xy dng ng chun s dng k thut ILS ta cn xc nh ma trn h s hi qui P t mu chun c ma trn nng C v ma trn tn hiu o A. P l ma trn cha h s hi qui ca phng trnh, trong mi hng cha h s hi qui ca mt cu t, v vy s hng ca P l s cu t, s ct l s thi im o.

Do trong tp s liu C v A u c cha sai s ngu nhin nn P m t chnh xc quan h gia C v A ta cn xc nh P bng phng php bnh phng ti thiu (tng bnh phng ca sai s gia gi tr tnh theo m hnh v gi tr thc nghim l nh nht).

2. Xc nh cng thc tnh P:

C = A . P

AT . C= AT . A . P

[AT . A]-1 . AT . C = [AT . A]-1 . [AT . A] . P

[AT . A]-1 . AT . C = P

ma trn nghch o ca [AT . A] - nghch o gi ca A - tn ti, A cn c s hng ti thiu bng s ct. Mi hng trong A l tn hiu ca mt mu, mi ct l tn hiu ca cc mu mt thi im nht nh. V vy, trong phng php ILS s mu khng c t hn s thi im o. Do yu cu v s mu ti thiu nh trn nn tin hnh s dng phng php ny, ta cn la chn s thi im o ti thiu c trng nht trn ton di ph, v vy, phng php ILS cn c gi l phng php ph ring phn. Cc im o c trng ny thng l nhng im tha mn cc yu cu sau:

Gi tr tn hiu o ti cc thi im ny ln so vi cc im o khc tng nhy.

Tn hiu ca cc cu t khc nhau ti mi im o c la chn phi bin i khc nhau tc l c s khc bit ln v tn hiu o ti mi im ca cc cu t.

Ti cc im ny, tn hiu ca cc ion cn tr php o l nh nht.



3. D on thng tin ca mu cha bit:

Vi mu cha bit nng , t ma trn tn hiu o Aunk ca mu s xc nh c nng cc cht da vo ma trn P tnh:

Cunk = Aunk . P

u im ca phng php ILS:

- Thch hp vi tp s liu nh, t thng tin.

- Loi tr c sai s nhiu ph v gim thiu c nh hng ca cc cu t l do la chn cc thi im o c trng.

- Khi tn hiu o l cc gi tr nh hn gi tr qui c ca nng th gi tr cc h s trong ma trn P s ln hn h s hi qui ca phng php CLS, iu ny s lm gim sai s trong qu trnh tnh ton.

Nhc im ca phng php ILS:

- Cn la chn ti thiu cc thi im o c trng cho cc cu t. La chn sai lch s dn n sai s ln trong qu trnh tnh ton.

- Phi m bo c tnh cng tnh cao ca cc cu t cc thi im o c la chn.

1.6.2.2. Phng php hi qui cu t chnh (Principal component regression - PCR)

Hi qui a bin, trong trng hp cc bin c tng quan, l vn gy nhiu kh khn khi gii cc bi ton phc tp trong mt s ngnh nh: vt l, ha hc, cc ngnh khoa hc t ng v thit k cng trnh,...

gii quyt by ton ny, cc nh khoa hc thng s dng phng php hi qui cu t chnh (PCR). PCR l phng php bnh phng ti thiu nghch o trn tp d liu mi thu c trong php chiu tp d liu ln cc vect n v ca khng gian mi (PC principal components) [7, 29, 31, 38]

PCR bao gm cc bc tin hnh nh sau:



Cng cn lu rng, do phng php ny pht trin trn c s ca phng php ILS nn s dng c cc phng php ny trong phn tch trc quang chng ta cn s mu chun ti thiu phi bng s thi im s dng trong ng chun m ha, tc l s mu chun khng nh hn s PC la chn. Ly mt v d c th, khi o ph ca 15 dung dch chun ti 100 bc sng, s dng phng php ILS, chng ta cn phi gim kch thc ph xung s bc sng khng qu 15. Cch n gin nht l chn t hn 15 bc sng o hp th nhng sai s s ln nu khng chn c cc bc sng c trng cho ph cc cht. Vi m hnh PCR ta c th s dng ton ph tnh cc PC, sau chn s PC nh hn 15 tnh ton tip. Thng thng, vi mt tp s liu c mc tp trung tt th ch c mt s t cc PC u tin l c ngha (c tng phng sai tch ly ln coi rng chng cha ton b thng tin hu ch c trng ca tp s liu). Nh vy, s dng m hnh PCR c th gim c kch thc tp s liu m khng lm mt thng tin ng thi c th loi c tn hiu nhiu ca d liu gc.

Cc bc chnh ca PCR bao gm:

1. X l ban u (khng bt buc)

Ni dung chnh ca bc ny l chun ha tp s liu.

D liu

Cc x l ban u khng bt buc

Cc x l cn thit

Tnh ton cc vect ring

La chn cc vect c ngha

Phc hi tp s liu c ngha

Xy dng ng chun



2. Cc x l cn thit:

Vi mt tp s liu chun ha hoc cha chun ha, trc khi s dng u cn bc bnh phng ton tp d liu - y l yu cu bt buc i vi hu ht cc hm tnh vect ring.

D = AT . A

Trong A l ma trn s liu biu din hp th quang theo cc thi im o ca cc dung dch chun v AT l ma trn chuyn v ca ma trn A.

3. Xc nh cc vect ring hay cc PC:

C th tnh ton cc vect ring ca tp s liu bng nhiu hm ton hc khc nhau. C 3 hm chnh, thng s dng l hm NIPALS (hm phi tuyn lp s dng k thut bnh phng ti thiu ring phn), hm SVD (hm phn tch cc gi tr ring) v hm Princomp (hm tnh cc cu t chnh). Cn lu rng, tt c cc hm ny u tnh ton v a ra tt c cc cu t nhng thng khng s dng tt c m ch s dng N cu t u xc nh khng gian mi [16, 23, 25].

NIPALS l hm lp thng s dng cho cc tp s liu kch thc ln hoc c a cng tuyn cao. Vi tp s liu c kch thc nh, qu trnh tnh lp trong hm NIPALS s lm khuch i sai s ca tp s liu nn thng thng ngi ta khng s dng hm ny tnh cc PC.

SVD l hm tnh PC s dng phng php tch tp s liu ban u thnh cc nhn t. Cc vect ring v tr ring ca ma trn d liu u l nhng tp con ring ca cc nhn t trong SVD. Hm SVD s dng hnh thc cho ha cho php khng ch thang o mt cch hp l nn gim thiu c sai s do lm trn. V vy hm ny s dng c vi cc kiu tp s liu rng ri hn hm NIPALS.

Princomp l hm tnh ton trc tip cc cu t chnh (PC) c vai tr tng ng cc vect ring. Tuy nhin, so vi hm SVD th vic s dng hm Princomp vi tp s liu ln c u im l phng sai tp trung khng cao nn v tr cc PC s chnh lch khng qu ln, do sai s trong qu trnh lm trn s v chuyn ha tp s liu s nh hn.



Cc hm ton hc trn u a ra mt ma trn ct cha cc vect ring - Vc - l ma trn trong mi ct l mt vect hay nhn t mi - PC - ca ma trn d liu v s hng ma trn l s thi im o. Mi nhn t hay vect ny li l t hp bc nht ca cc im ph ban u, phn ng gp ca cc im ny vo mi vect l khc nhau ty thuc vo gi tr hm ph thuc ti im . Nhng im c gi tr ng gp ln vo cc PC cha phng sai ln s l nhng im o c nh hng quyt nh ti kt qu tnh ma trn h s hi qui v kt qu hi qui sau . Ma trn kt qu th hai cng rt quan trng l ma trn phng sai ca cc PC: l dng ma trn cho i vi hm SVD, l mt vect ct i vi hm NIPALS v hm Princomp.

4. La chn cc vect c ngha

y l bc c nh hng c bit quan trng n bc x l tip theo. Nu gi li nhiu vect hn s cn dng th nhng vect s cha c tn hiu nhiu v nh vy, kt qu hi qui s mc phi sai s. Nu gi li khng s vecto cn thit s lm mt i thng tin c ch t tp d liu, iu ny cng s gy nn sai lch gia m hnh hi qui thu c v m hnh thc. V vy, vic nh gi v la chn cc vect c ngha l rt quan trng. Di y l mt s phng php ph bin xc nh s PC c ngha [25, 29, 44]:

Dng cc hm ch th: C rt nhiu hm ch th khc nhau nh CPV (tnh phn trm phng sai tch ly), hm IEF, ...

Tnh ton PRESS (tng bnh phng sai s d on) nh gi thng tin t d liu.

Phng php nh gi cho

Phng php nh gi Xu Kailath

nh gi theo tiu chun Akaike

Tnh phng sai ca sai s ti lp VRE

Cc phng php ny u c nhng u im ring khi s dng v kt qu nh gi tng i thng nht vi nhau. Phng php c s dng rng ri la chn cc PC c ngha khi cc PC ny c tnh bng hm SVD hay Princomp l phng php tnh v nh gi qua phn trm phng sai tch ly



ca cc PC . Cch tnh ny n gin hn v cc hm tnh PC trn cho sn d liu c th nh gi nhanh.

5. Tnh ton li

Sau khi loi b cc vect ring khng c ngha, chng ta cng loi c tn hiu nhiu ca d liu gc v cn tnh li d liu sau khi loi b sai s. Nh vy, khi tnh ton h ta mi ta loi b c tn hiu nhiu trong tp d liu ban u.

6. Xy dng ng chun

Khi xy dng ng chun PCR theo phng php ILS, im khc bit duy nht l tp s liu s dng.

Cc bc tin hnh bao gm:

+ Xc nh php chiu trong h ta mi:

Aj = A . Vc

Trong :

Aj: ma trn s liu h ta mi

A: ma trn gc

Vc: ma trn cc vect ring c ngha

+ Thay th A bng Aj trong phng trnh hi quy

C = Aj . F , trong F c tnh theo cng thc:

F = (AjT . Aj)-1 . AjT . C

Nng cht phn tch trong mu cha bit c tnh theo cng thc:

Cx = Ax . Vc . F

= Ax . Fcal

vi Fcal = Vc . F ng vai tr tng t ma trn P trong phng trnh ca ILS

u im ca phng php PCR:



- Hi t y cc u im ca phng php ILS ng thi khc phc c cc nhc im ca phng php ILS do tin hnh tnh ton trn ton ph.

- Phng php ny cho php loi b sai s nhiu ph v sai s ngu nhin trong qu trnh o khi la chn c s PC ph hp.

- i vi trng hp s dng ph ton phn, khi dng cc phng php khc nh CLS, kt qu tnh cui cng l kt qu tnh trung bnh trn ton ph nn km chnh xc hn trng hp dng ph chn lc. Khi s dng m hnh PCR, tuy kt qu vn tnh trn tt c cc im nhng ng gp ca cc im o s khc nhau ty theo lng ng gp ca tng im ny vo cc PC c chn m lng ng gp ny li c phn tch da trn tn hiu o ti tng im ca cc mu chun. Do c s phn bit v chn lc trong nh gi mi im o nn kt qu thu c s chnh xc hn phng php tnh trung bnh trn ton ph cc phng php ph ton phn khc.

1.6.3. Xc nh ng thi cc dng As bng phng php HVG AAS s dng Chemometrics

Nhm tc gi [42] pht trin mt phng php xc nh ng thi 4 dng As l As(III) v c, As(V) v c, DMA(V) v MMA(V) bng ph hp th nguyn t s dng k thut bnh phng ti thiu nghch o xy dng ng chun a bin. Phng php ny xy dng trn c s 4 dng As ny cho tn hiu hp th khc nhau khi o trn h quang AAS sau khi kh bng NaBH4. Vi 4 bin c lp, phng php ny cn s im o tn hiu ti thiu cng l 4 im. Cc tc gi nghin cu v la chn o tn hiu cc dng As ny ti 6 mi trng phn ng l mi trng HCl 6M, 1M, 0,5M, axit axetic 1M, mi trng m citric/citrat c pH = 2 v 4. trong cc mi trng khc nhau, tn hiu thu c ca cc dng As nghin cu cng khc nhau cho thy chng c s ph thuc ln vo pH, bn cht axit v nng axit s dng lm mi trng kh. tc gi s dng ng chun a bin xy dng theo phng php ILS kim tra cc mu chun v nhn thy phng php xc nh ny c hiu sut thu hi tng i cao, hon ton ph hp ng dng nh lng mu thc t. Gii hn pht hin ca phng php ny rt thp, i vi As(III), As(V), MMA v DMA th gi tr LOD ln lt bng hoc thp hn 2,7ng/ml, 0,8ng/ml, 3,0ng/ml,



4,9ng/ml. Trn c s phng php xc nh ny, chng ti xy dng mt phng php xc nh ng thi cc dng As s dng cc m hnh ng chun xy dng trn k thut ILS v pht trin thm phng php PCR.

Nguyn Th Thu Hng CHNG 2. THC NGHIM


CHNG 2. THC NGHIM 2.1. NI DUNG V PHNG PHP NGHIN CU

2.1.1. Phng php nghin cu

C s ca phng php l da trn s chnh lch hiu sut phn ng khi kh cc dng As thnh asin bng NaBH4 trong cc mi trng c nng H+ khc nhau. Cc phn ng xy ra khi kh 4 dng As kho st (As(III) v c, As(V) v c, DMA(V) v MMA(V)) nh sau [33, 43]:

AsO43- + BH4- + H+ AsO33- + H2 + BO3-

AsO33- + BH4- + H+ AsH3 + H2 + BO3-

(CH3)nAs(O)(OH)3-n + BH4- + H+ (CH3)nAs(OH)3-n + H2 + BO3-

(CH3)nAs(OH)3-n + BH4- + H+ (CH3)nAsH3-n + H2 + BO3-

Trong , n l s nhm th metyl trong hp cht.

Dng kh mang Ar s dn AsH3 v cc hp cht metylasin khc sang vng nguyn t ha:

(CH3)nAsH3-n 0t nC + As + (3 + 2n)H

nh lng As sinh ra bng phng php ph hp th nguyn t ti bc sng c trng ca As l = 193,7nm.

Ti mi mi trng phn ng, cc dng As khc nhau s b kh vi tc khc nhau nn lng As sinh ra l khc nhau, tn hiu o c cng khc nhau. Da trn chnh lch tn hiu gia cc dng As trong cc mi trng phn ng la chn thit lp ma trn chun cho m hnh xc nh ng thi ILS v PCR.

2.1.2. Ni dung nghin cu

xy dng qui trnh xc nh ng thi cc dng As bng phng php ph hp th nguyn t kt hp vi vic s dng chemometrics, trong lun vn ny chng ti tp trung nghin cu cc vn sau:

1. Ti u ha qui trnh xc nh As(III) v c trn h o HVG AAS.



2. Nghin cu nh hng ca mt s cht kh i vi qu trnh kh cc dng As thnh asin.

3. Nghin cu nh hng ca mi trng kh cc dng As thnh asin bng cht kh NaBH4 lm c s la chn cc mi trng phn ng o tn hiu cc dng As.

4. Kho st khong tuyn tnh ca cc dng As, kh nng cng tnh v xy dng ng chun a bin xc nh ng thi cc dng As trong dung dch.

5. Da trn c s cc phng php ILS v PCR, s dng phn mm Matlab lp chng trnh tnh h s trong phng trnh hi qui t mu gi. nh gi kh nng ng dng ca hai phng php v la chn phng php thch hp xc nh hm lng cc dng As trong mu nc ngm.

2.2. HA CHT V DNG C TH NGHIM

2.2.1. Ha cht

Cc loi ho cht c s dng l loi tinh khit phn tch (P.A) v cc dung dch c pha ch bng nc ct 2 ln.

Chun b cc dung dch chun:

Dung dch chun As(III) dng v c 0,1M (7500ppm): Cn 0,9902g oxit As2O3, ha tan trong 50ml dung dch NaOH 5%, chuyn vo bnh nh mc 100ml, thm nc ct n khong 70ml, lc u. Thm tip 10ml dung dch HCl 2M, nh mc ti vch bng nc ct v lc u. chun ca dung dch Na3AsO3 trn c xc nh li bng phng php bromat vi ch th metyl da cam trong mi trng HCl 6M 70 800C.

Dung dch chun gc As(V) dng v c 1000ppm.

Dung dch chun gc DMA(V) 1000ppm trong HCl 1M: pha t axit (CH3)2HAsO2.

Dung dch chun gc MMA(V) 1000ppm trong HCl 1M: pha t mui CH3NaHAsO3.1,5H2O.



Dung dch NaBH4 1% pha trong NaOH 0,5%: Cn 1,0g NaBH4, ha tan trong 10ml dung dch NaOH 5%, chuyn vo bnh nh mc 100ml, nh mc ti vch v lc u.

Cc dung dch HCl 6M, HCl 1M: Pha t HCl c 37%(Merck).

Cc dung dch m tactric tactrat 1M c pH = 2, 3, 4: pha ch t axit tactric v mui kali natri tactrat v hiu chnh bng my o pH.

Cc dung dch H2SO4, HNO3 v cc dung dch cha cc ion cn thit cho cc kho st khc c chun b t cc dung dch c v mui dng tinh th c tinh khit cao.

2.2.2. Dng c v trang thit b o

-Bnh nh mc thy tinh loi 10ml, 25ml, 50ml, 100ml, 250ml

-Cc loi pipet vch, pipet bu

-Phu, cc, bnh tam gic, a thy tinh

-My quang ph hp th nguyn t (AAS) Model AA-6800 ghp ni h thng HVG, hng Shimadzhu, Nht Bn.

-Cn phn tch v cn k thut.

-My o pH HANNA Instrument 211

2.2.3. Cc phn mm tnh ton v x l

-X l thng k trn phn mm Origin 6.0 v MINITAB 14

-Lp trnh tnh ton theo phng php hi qui a bin trn phn mm Matlab 7.0

2.3. TIN HNH TH NGHIM

2.3.1. Qui trnh phn tch

2.3.1.1. Qui trnh phn tch ring As(III)

Chun b cc dung dch cha As(III) c nng trong khong 0,2 10 ppb, iu chnh bng dung dch HCl hoc NaOH sao cho pH ca dung dch nm trong khong 1,5 2. Bm mu As vi tc 6ml/pht, cc dng cht kh



NaBH4 1%/NaOH 0,5% v dng HCl 6M c tc 2ml/pht. Cc iu kin nguyn t ha v o tn hiu hp th quang nguyn t ca dng cht nh sau:

- Vch ph: 193,7nm

- Cng dng n: 7mA

- Chiu cao n nguyn t ha: 16mm

- Tc dng kh chy: 1,8L C2H2/8L khng kh/pht

Tn hiu thu c di dng hp th quang nguyn t A

2.3.1.2. Qui trnh phn tch ng thi cc dng As

Pha cc dung dch chun cha cc dng As (As(III), As(V), DMA, MMA) c nng trong khong tuyn tnh, o tn hiu cc dung dch ny cc iu kin kh v nguyn t ha nh trn trong 5 mi trng phn ng l HCl 6M, HCl 1M, mi trng m tactric/tactrat 1M c pH = 2, 3, 4.

Nhp s liu ma trn nng cc cht v ma trn tn hiu o vo phn mm Matlab, chy chng trnh tnh ton ma trn h s hi qui trn phn mm v s dng ma trn ny tm nng cc dng trong mu.

2.3.2. Cc thut ton hi qui a bin

2.3.2.1. Phng php bnh phng ti thiu nghch o (ILS)

Thut ton ILS gii trong Matlab nh sau:

- Nhp ma trn nng C (40x4) ca 40 dung dch chun cha 4 dng As phn tch vo phn mm

- Nhp ma trn hp th quang A (40x5)

- Tnh ma trn h s hi qui theo cng thc:

P = inv(A'*A)*A*C

- Nhp ma trn gi tr Ax (k*5) ca k mu cn nh phn

- Tnh nng cc dng theo cng thc

Cx = Ax*P



2.3.2.2. Phng php hi qui cu t chnh (PCR)

Thut ton PCR gii trong Matlab nh sau:

- Nhp ma trn nng C (40x4) v ma trn tn hiu o A ca 40 dung dch chun cha 4 dng As cn phn tch

- Bnh phng tp s liu cha bin ph thuc:

D = A*A

- S dng mt trong 3 hm tnh PC xc nh cc PC. Cu lnh sau s dng hm SVD:

[V S] = svd(D)

- Tnh ma trn phn trm phng sai ca cc PC

d = diag(S)/sum(diag(S))*100

- T gi tr phn trm phng sai ca cc PC, cn c vo yu cu c th ca bi ton quyt nh chn s PC lm c s cho khng gian mi ca tp s liu (n):

f = V(:,1:n)

- Chuyn i tp s liu ban u v tnh ma trn h s hi qui:

Aj = A*f

F = inv(Aj'*Aj)*Aj'*C

Fj=f*F

- Nhp ma trn bin ph thuc ca k mu cn nh phn Ax(k*5) v tnh nng cc dng As trong mu theo cng thc:

Cx=Ax*Fj

Cc thao tc tnh sai s v hiu sut thu hi s dng cc cu lnh tnh ton thng thng trn ma trn trong phn mm.

Nguyn Th Thu Hng CHNG 3. KT QU V THO LUN


CHNG 3. KT QU V THO LUN 3.1. NGHIN CU CC IU KIN TI U XC NH HM LNG As(III) BNG PHNG PHP HVG AAS

3.1.1. Kho st cc thng s ca my o AAS

* Chn vch o ph:

Mi nguyn t c kh nng hp th nhng bc x m bn thn n pht ra trong qu trnh pht x. V vy, nhng bc x ny l yu t c trng ca mi nguyn t. Cc nguyn t thng c vi vch ph vi nhy khc nhau, tuy nhin, theo cc ti liu [27, 30, 32], vch ph ng vi bc sng 193,7nm l vch c trng v nhy ca As. V vy, chng ti nh lng As qua tn hiu ca vch ph ny.

* Cng dng n catot rng (HCL):

HCL l ngun pht x cng hng ch pht ra tia pht x nhy ca nguyn t kim loi c dng lm catot. Mi n u c dng in gii hn cc i ca n. L thuyt v thc nghim u khuyn co ch nn s dng cng dng trong khong 60 85% dng gii hn cc i ca n m bo lp li v nhy ca php o cng nh tui th ca n. Mt khc, cng dng lm vic ca HCL v cng vch ph c mi quan h cht ch vi nhau. V vy, chng ti kho st tm cng dng n lm vic ph hp sao cho c th t c nhy v n nh tt nht. Cc th nghim c tin hnh vi dung dch As(III) 4ppb, mi mu o ba ln ri ly kt qu trung bnh. Kt qu hp th quang thu c sau khi tr tn hiu mu trng thu c bng 2.

Bng 2. nh hng ca cng dng HCL n hp th quang ca As (Imax=10mA)

I, mA 6 7 8

Abs 0,1307 0,1278 0,1252

RSD(%) 6,08 2,47 2,02



Kt qu trn cho thy chn cng dng lm vic ca n l 7mA s cho kt qu o c nhy v lp li tt. Kt qu kho st cng ph hp vi hng dn s dng ca n ny. V vy, chn cng dng lm vic ca n HCL l 7mA cho cc th nghim sau.

* Chiu cao n nguyn t ha mu:

y l mt thng s quan trng trong php o AAS. Chiu cao n nguyn t ha mu phi ph hp sao cho ton b chm tia sng pht ra t n HCL u c chiu gn vo ca s ca cuvet o. Nu khng chn ng chiu cao n ph hp, gi tr o s c nhy v n nh km.

kho st nh hng ca chiu cao n nguyn t ha n hp th quang ca dung dch As(III), t ch qut t ng cho my vi khong kho st chiu cao n l 12 20mm, dung dch o c hm lng As(III) l 4ppb. Kt qu kho st cho thy gi tr ti u ca chiu cao n nguyn t ha mu l 16mm v gi tr ny c s dng cho cc th nghim tip theo.

* Thnh phn hn hp kh chy C2H2/khng kh:

Vi php o AAS, y l mt i lng rt quan trng. Thnh phn ca hn hp kh chy s quyt nh nhit ngn la nguyn t ha v do quyt nh qu trnh nguyn t ha mu. V vy, chn c thnh phn hn hp kh chy (t l th tch ca C2H2 v khng kh trong hn hp kh chy) ph hp, chng ti kho st vi dung dch o cha 4ppb As(III), tc dng khng kh c nh l 8L/pht, tc dng kh C2H2 thay i trong khong 1 2,4(L/pht), t ch t ng kho st cho my. Kt qu thc nghim cho thy khi tc dng kh C2H2 l 1,8L/pht s thu c gi tr hp th quang tt nht, tn hiu o n nh nht.

3.1.2. Kho st iu kin kh As(III) thnh asin vi h HVG

Qu trnh kh As(III) thnh asin bng cht kh NaBH4 trong mi trng axit chu nh hng ca rt nhiu yu t, trong cc yu t c bn l:

Nng axit, loi axit v tc bm dng dung dch axit

Nng v tc ca dng dung dch cht kh NaBH4

Tc dng mu



Nng cc cht v tc bm cc dng dung dch s quyt nh qu trnh pha long mu, qu trnh trn mu, phn ng v vn chuyn mu ti cuvet o. V vy, chng ti ln lt kho st tng yu t trn nhm tm ra iu kin ti u cho qu trnh kh As(III) thnh asin trong h HVG s dng cht kh l NaBH4.

3.1.2.1. Nng v bn cht ca dung dch axit

i vi dng axit, chng ti ch kho st nh hng ca nng v bn cht axit s dng, khng kho st tc dng ny do dng axit v dng NaBH4 c cng tc bm nn ch kho st tc dng khi nghin cu iu kin ti u cho dng NaBH4.

* nh hng ca nng axit (nng H+) ti qu trnh kh As(III) thnh asin:

xc nh c nng H+ ti u cho qu trnh phn tch, chng ti tin hnh th nghim vi cc iu kin sau:

- Dng mu: As(III) 4ppb, tc dng 5ml/pht

- Dng cht kh NaBH4 cha NaBH4 1% trong NaOH 0,5%, tc dng 2ml/pht

- Dng axit: s dng HCl c nng bin thin trong khong 1M 10M, c cng tc vi dng cht kh.

Cc dung dch c o 3 ln ly kt qu hp th trung bnh; dung dich so snh l mu trng. Kt qu kho st hp th quang v lch chun tn hiu o thu c nh trong bng 3 v biu din trn th hnh 5.

Bng 3. nh hng ca nng H+ ti hp th quang ca As

CH+, M 1 4 5 6 8 10

Abs 0,1089 0,1225 0,1263 0,1275 0,1294 0,1311

RSD(%) 4,12 2,57 3,40 2,15 2,24 3,51



0 2 4 6 8 100,105

0,110

0,115

0,120

0,125

0,130

0,135

Abs

CH+, M

Hnh 5. S ph thuc ca hp th quang ca As vo nng H+

Kt qu kho st cho thy, nng H+ cng ln th hiu sut kh cng cao, qu trnh kh As(III) thnh asin xy ra cng hon ton. Khi tip tc tng nng H+ trn 5M th hp th quang tng chm. C th ni, nng H+ cng cao th cng c kh nng tng nhy ca php o, tuy nhin nng qu cao s gy kh khn cho qu trnh tin hnh th nghim v tn nhiu ha cht m nhy tng khng ng k. Kt hp gia cc yu cu th nghim, chng ti la chn dung dch c nng H+ 6M tin hnh hidrua ha As(III).

* nh hng ca loi axit ti qu trnh kh As(III) thnh asin:

Tin hnh kho st vi mt s axit khc nhau chn axit thch hp nht cho qu trnh xc nh As(III), chng ti vn s dng dung dch mu c cha 4ppb As(III), cc iu kin o nh chn. Kt qu nghin cu trn 4 loi axit thu c bng 4.

Nh vy, nu xem hiu sut hirua ha khi dng dung dch HCl l 100 % th khi dng H2SO4 vi nng H+ gn nh nhau s t c hiu sut kh l 98%. Nu dng dung dch HNO3 lm mi trng vi cng nng H+ cho kt qu thp hn hn. iu ny c th do ion NO3- phn ng vi mt lng NaBH4 trong hn hp kh nn khng cn kh As(III) thnh asin, gy sai s m. Chng ti cng tin hnh kho st kh nng kh As(III) thnh asin



trong cc mi trng phn ng c nng CH3COOH t 5M ln ti 10M nhng hiu sut kh vn di 60%. Nh vy ch c th dng dung dch axit HCl 6M hoc H2SO4 3M lm mi trng phn ng cho qu trnh kh As(III) thnh asin bng cht kh NaBH4. Tuy nhin, thc t cc mu nc phn tch thng c axit ha bng HCl thay v dng H2SO4 nn chng ti la chn axit HCl 6M lm mi trng kh trong php o As.

Bng 4. nh hng ca bn cht axit n hp th quang ca dung dch As(III)

Dung dch HCl 6MH2SO4 3M

([H+] = 6M) HNO3 6M

H3PO4 6M

([H+] 6M)

Abs 0,1281 0,1257 0,0713 0,1071

RSD(%) 1,14 2,37 4,05 1,22

%Abs 100 98 56 84

3.1.2.2. nh hng ca nng , tc bm NaBH4 v tc bm mu n kh nng kh As(III) thnh asin

3.1.2.1.1. nh hng ca nng NaBH4 ti kh nng kh As(III) thnh asin

Trong mi trng thch hp, NaBH4 ng vai tr l cht kh a cc dng As t nhng trng thi oxi ha cao v dng asin hay cc dn xut metylasin tng ng [32]. V vy, nng NaBH4 trong dng cht kh l mt yu t nh hng khng nh ti kt qu o hp th quang ca dung dch.

tm nng thch hp cho qu trnh kh As(III) thnh asin bng cht kh NaBH4, chng ti kho st nh hng ca nng cht ny trong khong gi tr 0,1 4% ln kt qu o tn hiu dung dch As(III) 4ppb, cc iu kin o gi nguyn nh chn trn, tc dng NaBH4 v dng mu ln lt l 2ml/pht v 5ml/pht. Kt qu o c trnh by trong bng 5 v biu din trn th hnh 6.



Bng 5. nh hng ca nng NaBH4 ti hp th quang ca dung dch As(III)

Kt qu o

Nng NaBH4, % (trong NaOH 0,5%)

0,1 0,25 0,5 1 2 4

Abs 0,0861 0,1126 0,1268 0,1274 0,1277 0,1250

RSD% 4,2 5,5 2,8 3,5 4,9 7,2

0 1 2 3 40,08

0,09

0,10

0,11

0,12

0,13

Abs

CNaBH4, % trong NaOH 0,5%

Hnh 6. th biu din s ph thuc ca hp th quang ca dung dch As(III) theo nng NaBH4

3.1.2.1.2. nh hng ca tc dng NaBH4 ti kh nng kh As(III) thnh asin

Nh cp trn, tc bm cc dng cng c nhng nh hng phc tp ti kt qu o tn hiu dung dch. Dng cht kh NaBH4 v dng axit c cng tc nn nh hng ca tc dng ny ti kt qu o rt ng c quan tm.

xc nh tc ti u cho dng ny bng phng php n bin, chng ti kho st kh nng kh dung dch As(III) 4ppb thnh asin trong cc



dng NaBH4 1% pha trong NaOH 0,5% c tc bin thin trong khong 1 3,5ml/pht, tc dng mu c nh 5ml/pht. Kt qu o c cho trong bng 6 v biu din trn th hnh 7.

Bng 6. nh hng ca tc dng NaBH4 ti hp th quang ca dung dch As(III)

Kt qu o

Tc dng NaBH4, ml/pht

1 1,5 2 2,5 3 3,5

Abs 0,1121 0,1254 0,1268 0,1271 0,1262 0,1241

RSD% 1,5 4,4 3,9 2,2 5,7 3,1

1,0 1,5 2,0 2,5 3,0 3,5

0,112

0,116

0,120

0,124

0,128

Abs

Tc dng NaBH4, ml/pht

Hnh 7. th biu din s ph thuc ca hp th quang ca dung dch As(III) theo tc dng NaBH4

Nhn thy, trong khong gi tr tc dng NaBH4 t 2 2,5ml/pht, tn hiu o As n nh v cao, khi tng tc ln cao hn thy c hin tng gim nh tn hiu o nhng khng ng k. Cn c vo kt qu ny, c th kt lun rng vi tc dng NaBH4 khong 2 2,5ml/pht s cho kt qu o As(III) tt v tit kim c ha cht.



3.1.2.1.3. nh hng ca tc dng mu ti kt qu o hp th quang ca dung dch

Tc dng mu cng c vai tr quan trng i vi kt qu o v y l dng cung cp cht phn ng. kho st chn tc dng mu ti u cho qu trnh o, chng ti tin hnh xc nh nh hng ca yu t ny trong khong 3 8ml/pht ln kt qu o dung dch As(III) 4ppb trong dng NaBH4 1% (trong NaOH 0,5%) c tc bm 2ml/pht. Kt qu c a ra bng 7 v biu din trn th hnh 8.

Bng 7. nh hng ca tc dng mu ti kt qu o tn hiu dung dch As(III)

Kt qu o

Tc dng mu, ml/pht

3 4 5 6 7 8

Abs 0,1102 0,1211 0,1264 0,1271 0,1277 0,1258

RSD% 4,7 5,1 1,2 4,6 4,2 6,5

3 4 5 6 7 80,108

0,112

0,116

0,120

0,124

0,128

Abs

Tc dng mu, ml/pht

Hnh 8. th biu din s ph thuc ca hp th quang ca dung dch As(III) theo tc dng As(III)



Vi kt qu kho st trn c th nhn thy rng, tng cao tc dng mu hn 7ml/pht s lm gim nh tn hiu do hin tng pha long dng v gy tn mu, tc nh hn s cho tn hiu thp hn v thi gian o ko di hn gy tn cc ha cht o khc. V vy, tc dn mu nn gi c nh trong khong 5,5 6,5ml/pht trong qu trnh o s cho kt qu o c nhy cao nht.

3.1.2.1.4. S dng m hnh bc 2 tm xoay kho st ng thi nh hng ca nng , tc dng NaBH4 v tc dng mu ti tn hiu o ca dung dch As(III)

V mt l thuyt, chng ti nhn thy c mi quan h qua li cht ch gia nng NaBH4, tc bm NaBH4 v tc bm mu n qu trnh hirua ha nn tin hnh tm iu kin ti u bng cch kho st ng thi nh hng ca 3 i lng ny, s dng m hnh thc nghim bc hai tm xoay 3 yu t. Trn c s cc kho st n bin thc hin, chng ti xc nh khong kho st cc yu t ny nh trong bng 8.

Bng 8. Khong bin thin ca cc yu t cn kho st

Yu t K hiu

Mc thp

Mc cao

Khong bin thin ()

Tc bm NaBH4 (ml/pht) v1 1,5 3,5 2

Tc bm mu(ml/pht) v2 3,0 10,0 7

Nng NaBH4 (%) / NaOH 0,5%

C 0,2 2 1,8

Khi mi quan h gia tn hiu phn tch v cc yu t cn kho st c c trng bng phng trnh bc hai nh sau:

Y=b0 + b1v1 + b2v2+ b3C + b1,1v12 + b2,2v22 + b3,3C2 + b1,2v1v2 +b1,3v1C+ +b2,3v2C + b1,2,3v1v2C

Trong b0 c trng cho phn tn hiu nhiu ca m hnh, cc h s bi, bi,j v bi,i l h s c trng cho chiu hng v mc nh hng bc mt, bc hai ca cc yu t n tn hiu phn tch.



S dng phn mm MINITAB thit lp bng qui hoch thc nghim vi cc iu kin nh trn v tin hnh cc th nghim theo bng ny. Kt qu hp th quang thu c khi tin hnh thay i ng thi cc yu t bng 9.

Bng 9. Th t v kt qu th nghim tin hnh theo m hnh bc hai tm xoay

STT Th t thc

nghim v1 v2 C Abs

1 1 1,5 3,0 0,2 0,0812

6 2 3,5 3,0 2,0 0,0877

8 3 3,5 10,0 2,0 0,0998

9 4 1,0 6,5 1,1 0,1105

18 5 2,5 6,5 1,1 0,1277

3 6 1,5 10,0 0,2 0,0514

16 7 2,5 6,5 1,1 0,1259

4 8 3,5 10,0 0,2 0,0952

15 9 2,5 6,5 1,1 0,1272

2 10 3,5 3,0 0,2 0,0784

14 11 2,5 6,5 2,6 0,1251

20 12 2,5 6,5 1,1 0,1269

17 13 2,5 6,5 1,1 0,1271

11 14 2,5 2,5 1,1 0,0822

12 15 2,5 12,0 1,1 0,0986

7 16 1,5 10,0 2,0 0,1104

10 17 4,0 6,5 1,1 0,1022

19 18 2,5 6,5 1,1 0,1259

13 19 2,5 6,5 0,2 0,0952

5 20 1,5 3,0 2,0 0,1102



X l s liu trn phn mm MINITAB vi cc d liu thc nghim thu c trn cho kt qu nh bng 10.

Bng 10. Bng h s hi qui ca phng trnh hi qui

H s Gi tr Sai s gi tr chun t Tr s P

b0 -0,0132 0,0267 -0,496 0,631

b1 0,0403 0,0154 2,612 0,026

b2 0,0130 0,0042 3,082 0,012

b3 0,0611 0,0142 4,309 0,002

b1,1 -0,0086 0,0027 -3,153 0,010

b2,2 -0,0014 0,0002 -5,671 0,000

b3,3 -0,0119 0,0036 -3,261 0,009

b1b2 0,0021 0,0009 2,380 0,039

b1b3 -0,0103 0,0034 -3,015 0,013

b2b3 0,0010 0,0010 1,029 0,328

lch chun S = 0,0087, h s tng quan R = 91,2%, R2 = 83,3%

T bng 10, nhn thy gi tr hi qui vi tin cy 95% th nh hng ca nhiu nn v nh hng tng h ca tc bm mu vi nng NaBH4 (v2*C) l khng ng k (do tr s P>0,05), nn c th b qua trong qu trnh tnh ton. Bng cch tnh li h s hi qui sau khi loi b yu t nh hng khng c ngha ta thu c bng h s hi qui 11 v bng phn tch phng sai 12.

Gi tr R2 = 0,832 t bng h s hi qui 11 cho thy m hnh tm c phn nh tng i ng thc nghim, c th s dng m hnh ny tm iu kin ti u theo phng php o hm hoc phng php ng dc nht. Cng c th kim tra kt lun ny thng qua bng sai s gia kt qu thc nghim vi kt qu tnh gi tr A t m hnh (bng 13).



Bng 11. Bng h s hi qui ca A sau khi loi b yu t khng c ngha

S hng H s Sai s T Tr s P

b0 -0,02039 0,02581 -0,790 0,446

b1 0,04029 0,01547 2,605 0,024

b2 0,01412 0,00409 3,448 0,005

b3 0,06761 0,01271 5,318 0,000

b1,1 -0,00858 0,00273 -3,144 0,009

b2,2 -0,00140 0,00025 -5,656 0,000

b3,3 -0,01189 0,00365 -3,252 0,008

b1b2 0,00209 0,00088 2,374 0,037

b1b3 -0,01029 0,00342 -3,007 0,012

S = 0,0087 R = 90,3% R2 = 83,2%

Bng 12. Bng phn tch phng sai ca A sau khi loi b yu t khng c ngha

Ngun sai s DF Seq SS Adj SS Adj MS F P

Phng trnh hi qui 8 0,00773 0,00773 0,000967 12,73 0,000

Bc 1 3 0,00182 0,00347 0,001156 15,23 0,000

Bc 2 3 0,00479 0,00479 0,001598 21,04 0,000

Ni tng tc 2 0,00111 0,00111 0,000557 7,34 0,009

Sai s tuyt i 5 0,000003 0,000003 0,000001

Tng 19 0,00857

Trong , Seq SS l gi tr tng bnh phng tch ly, Adj SS l gi tr tng bnh phng ph hp, Adj MS l gi tr trung bnh bnh phng ph hp.



Bng 13. Sai s gia kt qu thc nghim vi kt qu tnh gi tr A t m hnh

TN TT chun Abs Abstnh Sai s tnh lch Sai s

1 1 0,081 0,070 0,007 0,011 2,18*

2 6 0,088 0,083 0,007 0,005 0,89

3 8 0,100 0,106 0,007 -0,006 -1,00

4 9 0,111 0,106 0,007 0,004 0,76

5 18 0,128 0,125 0,003 0,003 0,34

6 3 0,051 0,063 0,007 -0,012 -2,22 *

7 16 0,126 0,125 0,003 0,001 0,11

8 4 0,095 0,096 0,007 -0,001 -0,10

9 15 0,127 0,125 0,003 0,002 0,27

10 2 0,078 0,073 0,007 0,005 1,03

11 14 0,125 0,122 0,007 0,003 0,72

12 20 0,127 0,125 0,003 0,002 0,24

13 17 0,127 0,125 0,003 0,002 0,26

14 11 0,082 0,098 0,005 -0,016 -2,29 *

15 12 0,099 0,089 0,007 0,010 1,90

16 7 0,110 0,110 0,007 0,000 0,04

17 10 0,102 0,105 0,007 -0,003 -0,52

18 19 0,126 0,125 0,003 0,001 0,11

19 13 0,095 0,101 0,005 -0,006 -0,83

20 5 0,110 0,117 0,007 -0,007 -1,19

Nh vy, bng phng php qui hoch ha thc nghim m hnh bc hai tm xoay tm c m hnh m t gi tr tn hiu phn tch ( hp th quang Abs) ph thuc cc yu t nh sau:



A= -0,0204 + 0,0403vNaBH4 +0,0141vmu + 0,0676CNaBH4 0,0086v2NaBH4 0,0014v2mu 0,0119C2 + 0,0021vNaBH4*vmu 0,0103vNaBH4*CNaBH4

Cc yu t gy nh hng dng (lm tng tn hiu phn tch) bao gm nh hng bc nht ca cc yu t v nh hng tng h ca tc bm cc dng. Cc nh hng cn li u c xu hng lm gim gi tr hm mc tiu. Trong , tng nng v tc bm NaBH4 lm tng nhanh tn hiu phn tch hn so vi tng tc bm mu.

Nu c nh gi tr tc bm mu l gi tr mc gc biu din s ph thuc ca tn hiu phn tch vo hai yu t c nh hng nhiu nht l nng v tc bm NaBH4 trong khng gian ba chiu s thu c th hnh 9. Hnh 10 l cc ng ng mc biu th hp th quang ph thuc vo nng v tc bm NaBH4.

2

A

0.08

0.10

0.12

C

0.14

11 2 3 04v1

Hold Valuesv2 6.5

Surface Plot of Abs vs C, v1

Hnh 9. th biu din mt mc tiu Abs theo gi tr ca nng NaBH4 v tc bm NaBH4



v1

v2

4.03.53.02.52.01.51.0

4.03.53.02.52.01.51.0

12

11

10

9

8

7

6

5

4

3

12

11

10

9

8

7

6

5

4

3Hold Values

C 1.1

A

0.072 - 0.0840.084 - 0.0960.096 - 0.1080.108 - 0.120

> 0.120

< 0.0600.060 - 0.072

Contour Plot of Abs vs v2, v1

Hnh 10. Cc ng ng mc biu din gi tr Abs theo tc bm mu v tc bm NaBH4

V nh hng ca cc yu tc c nhiu hng tri ngc nhau nn cn tm iu kin ti u nht ca cc yu t sao cho tn hiu phn tch nhy nht.

M hnh thit lp c trn ph hp vi thc nghim nn c th s dng m hnh ny xc nh iu kin ti u cho php o As theo phng php mt mc tiu (bng cch o hm v tm cc tr). Kt qu ti u ha theo m hnh thu c l:

Tc bm NaBH4: 2-2,5pht

Tc bm mu: 6-7ml/pht

Nng dung dch NaBH4: 1%

Kt qu ny tng i ph hp vi kt qu kho st n bin tin hnh trn. Da vo cc kt qu kho st ny, chng ti chn cc iu kin v tc v nng cc dng cho qu trnh kh As(III) thnh asin nh sau:

Tc dng mu: 6ml/pht

Tc dng NaBH4 v dng axit: 2ml/pht

Nng dng NaBH4(trong NaOH 0,5%): 1%



Nng dng axit HCl: 6M

Chng ti s dng nhng iu kin kh ny tin hnh cc php o xc nh ring cc dng As, ch thay i nng v bn cht dng axit trong cc php o xc nh ng thi sau .

3.1.3. Kho st khong tuyn tnh v lp ng chun xc nh As(III)

Chun b cc dung dch chun As(III) c nng bin thin trong khong 0,2 18ppb, cc iu kin o gi nh chn. Gi tr hp th quang ca cc dung dch chun sau khi tr tn hiu mu trng thu c bng 14 v biu din trn th hnh 11.

th 11 cho thy, khong tuyn tnh ca As(III) l t 0,2 10ppb. Trong khong tuyn tnh ny, kt qu xy dng ng chun thu c hnh 12 v phng trnh ng chun xc nh nng As(III) (ppm) c dng:

Abs = (0,00153 0,00116) + (0,0319 0,00023)CAs(III)

Bng 14. hp th quang ca cc dung dch As(III)

CAs(III), ppb 0 0,2 0,5 1 2 3 4

0 0,0072 0,0171 0,0334 0,0655 0,0952 0,1281

CAs(III), ppb 5 7 8 10 12 15 18

bs 0,162 0,2341 0,2571 0,315 0,3542 0,3841 0,4102

0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 00 , 0

0 , 1

0 , 2

0 , 3

0 , 4

0 , 5

A b s

C A s ( I I I ) , p p b

Hnh 11. S ph thuc ca Abs theo nng As(III)



0 2 4 6 8 100,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

ng chun xc nh As(III):Y = A + B * XThng s Gi tr Sai s t-Value Prob>|t|---------------------------------------------------------------------------A 0,00153 0,00201 0,760 0,4699B 0,03193 0,00039 82,406 0,05 nn c th kt lun rng: Vi tin cy 95%, gi tr hng s t do ca phng trnh khc 0 khng c ngha nn c th b qua bn cnh gi tr h s cn li, iu cng c ngha phng php xc nh ring As(III) qua phng trnh ny khng mc sai s h thng.

c kt lun chnh xc v khong tuyn tnh, chng ti tin hnh o lp li tn hiu ca 8 mu trng vi cc iu kin nh trn. Kt qu o tn hiu cc mu trng nh sau: 0,0017; 0,0021; 0,0023; 0,0011; 0,0018; 0,0025; 0,0014; 0,0015. Sau khi tnh ton LOD, LOQ ca php o theo cng thc 3 v 10 chng ti thu c kt qu:

Gii hn pht hin: LOD = BSb.3 = 0,04(ppb)

Gii hn nh lng: LOQ = BSb.10 = 0,15(ppb)

Trong : Sb l lch chun ca php o lp tn hiu 8 mu trng

B l h s gc ca phng trnh hi qui



Tm tt kt qu: Sau khi kho st cc iu kin ti u xc nh As(III) bng phng php HVG - AAS, chng ti la chn c iu kin cho php o As(III) nh sau:

Bng 15. Tm tt cc iu kin ti u xc nh As(III) bng phng php HVG-AAS

Yu t Khong kho

st Gi tr la

chn Yu t

Khong kho st

Gi tr la chn

Vch ph 193,7nm Mi trng khHCl 1M - HCl 10M

HCl6M

Cng dng n

6 - 8mA 7mA Nng cht kh NaBH4

0,2 - 2% 1%

Chiu cao n nguyn t ha

12 - 20mm 16mm Tc dng

NaBH4 1,5-

3,5ml/pht 2ml/pht

Tc dng kh C2H2

1- 2,4L/pht 1,8L/pht Tc dng

mu 3-10ml/pht 6ml/pht

Tc dng khng kh

8L/pht Khong tuyn

tnh 0,2-18ppb 0,2-10ppb

3.1.4. Kho st nh hng ca cc ion l ti php xc nh As(III) bng phng php HVG AAS

i vi phng php AAS xc nh mt nguyn t bt k, cc ion l trong dung dch mu gy nh hng ti kt qu o nh lng nguyn t theo nhiu cch khc nhau. Ring i vi cc phng php HVG AAS, qu trnh hidrua ho As thnh asin va l phng php lm giu cht v cng l phng php loi tr nh hng ca nhiu ion l trong dung dch. Sau khi tham kho mt s ti liu nghin cu v vn ny, chng ti nhn thy c mt s ion vn gy nh hng nht nh ti php xc nh As theo phng php ny ch yu do kh nng cng b hirua ha. V vy, sau khi kho st s b, chng ti la chn nghin cu nh hng ca mt s ion tiu biu v nghin cu kh nng loi tr nh hng ca chng n php o ny.



3.1.4.1. nh hng ca mt s ion kim loi thng gp ti qu trnh xc nh asen

Cc ion thng gp c kh nng gy nh hng ln ti qu trnh xc nh As nh Cu2+, Pb2+, Cr3+, Ni2+, Mn2+, Fe3+ s c kho st trong mc ny. Cc cht c kho st nhng khong nng khc nhau v da vo sai s gia kt qu o c ion l v khng c ion l khi o dung dch As(III) 4ppb lm c s kt lun ngng nh hng ca cc ion ny. Kt qu kho st c ch ra trong bng 16.

Bng 16. nh hng ca cc cation ti kt qu o As(III)

Ion, ppm Aion l Aion l + As(III)Sai s

(%)Ion, ppm Aion Aion+ As(III)

Sai s (%)

As(III) 4 ppb Abs = 0,1281

Cu2+

1 0,0014 0,1272 -1

Ni2+

5 0,0027 0,1262 -2

4 0,0021 0,1248 -4 10 0,0023 0,1251 -3

10 0,0019 0,1105 -14 50 0,0016 0,1201 -6

20 0,0025 0,1002 -22 100 0,0035 0,1117 -13

Pb2+

5 0,0032 0,1194 -7

Mn2+

5 0,0015 0,1252 -3

7 0,0017 0,1168 -9 10 0,0017 0,1271 -1

10 0,0022 0,1067 -12 50 0,0031 0,1246 -3

20 0,0012 0,1053 -18 100 0,0037 0,1242 -3

Cr3+

5 0,0031 0,1261 -2

Fe3+

5 0,0052 0,1239 -4

10 0,0025 0,1220 -5 10 0,0036 0,1211 -6

50 0,0012 0,1104 -14 50 0,0029 0,1112 -13

100 0,0019 0,1027 -20 100 0,0012 0,1027 -20

Hg2+ (ppb)

10 0,0032 0,1257 -2

Fe2+

5 0,0026 0,1219 -5

50 0,0025 0,1167 -9 10 0,0032 0,1169 -9

100 0,0037 0,1115 -13 50 0,0013 0,1092 -15

200 0,0014 0,1066 -17 100 0,0041 0,1021 -15



Cc ion kim loi kho st trn u lm gim tn hiu phn tch khi c mt trong dung dch. Vi php xc nh cc nguyn t mc nng ppb, nu sai s cho php l 10-15% th ngng nh hng ca hu ht cc ion kim loi (tr Hg) ti kt qu o As(III) u kh ln (gi tr in m trong bng 16) so vi hm lng thng gp trong cc mu nc. Mn2+ khng gy nh hng hm lng 100ppm nn c coi l khng nh hng ti kt qu o. Tuy nhin i vi mt s i tng thc t vn c th gp trng hp c cc ion ny hm lng ln. V vy chng ti tip tc nghin cu kh nng loi tr nh hng ca cc ion ny bng dung dch L-cystein pha trong HCl 0,1M. Kt qu kho st kh nng loi tr nh hng ca cc cation ny bng L-cystein cc nng khc nhau c trnh by trong bng 17.

Bng 17. Kho st kh nng s dng L-cystein lm cht loi nh hng ca cation (AAs(III) = 0,1275)

Ion CL-cystein, %

0,1 0,25 0,5 1 5 10

Cu(II) 50ppm 0,1235 0,1241 0,1246 0,1248 0,1242 0,1240

Pb(II) 50ppm 0,1224 0,1238 0,1237 0,1242 0,1245 0,1241

Cr(II) 100ppm 0,1234 0,1258 0,1252 0,1253 0,1248 0,1235

Ni(II) 100ppm 0,1228 0,1238 0,1231 0,1234 0,1242 0,1245

Fe(II) 100ppm 0,1228 0,1227 0,1232 0,1237 0,1224 0,1229

Fe(III) 100ppm

0,1225 0,1231 0,1237 0,1230 0,1235 0,1221

Hg(II) 200ppb 0,1211 0,1225 0,1228 0,1225 0,1210 0,1212

Tt c cc ion trn

0,1201 0,1223 0,1227 0,1230 0,1224 0,1221



Nh vy, khi c mt L-cystein 0,25% th sai s php o As(III) khi c mt tt c cc ion nng cao hn ngng nh hng di 10%. Do c th ni dng L- cystein 0,25-0,5% loi c nh hng ca cc cation n kt qu o As(III) bng phng php HVG-AAS.

3.1.4.2. nh hng ca mt s ion c kh nng hidrua ho v mt s hp cht hu c thng gp trong dung dch

Cc nghin cu trc y u ch ra rng: cc nguyn t phn nhm V gy nh hng ng k ti kt qu o As bng phng php HVG-AAS [32, 39]. Trong lun vn ny, chng ti kho st li nh hng ca cc nguyn t ny cng vi mt s anion hu c lm c s cho vic la chn h m trong cc nghin cu tip theo. Kt qu kho st c ch ra trong bng 18.

Kt qu nghin cu cho thy, cc ion S2-, Se(IV), Bi(III) v Sb(III) khi nng thp c nh hng r rt ti kt qu o As(III) l do cc ion ny c kh nng to hp cht hidrua khi tng tc vi cht kh NaBH4 trong mi trng axit, cc hp cht ny s c nhng tng tc khc nhau ti qu trnh nguyn t ha ca AsH3 hoc qu trnh hp th nh sng ca nguyn t As. Tuy nhin, theo nghin cu trc y ca chng ti [39], nh hng ca cc ion nh Se(IV), Bi(III) v S2- c th b loi b bng bng tm dung dch Pb(CH3COO)2 t trn ng dn kh ti bnh phn ng hoc cuvet trc khi nguyn t ho. Do khng c php sa cha trc tip lm thay i kt cu ca thit b o, chng ti khng th th nghim lp t b phn loi tr ny vo my. V vy, cha c kt qu nghin cu loi tr nhng nh hng ny trong phm vi nghin cu ca lun vn.

Ring i vi Sb(III), trong nhng cng trnh nghin cu m chng ti c bit, cha c bin php no loi tr c hon ton nh hng ca ion ny ti kt qu o As bng phng php AAS. Chng ti nghin cu th nghim kh nng loi tr nh hng ca Sb(III) bng cch cho to phc vi tactrat hn ch kh nng tham gia cc phn ng khc ca Sb(III). Kt qu nghin cu c a ra trong bng 19.



Bng 18. nh hng ca mt s ion c kh nng hidrua ho v mt s hp cht hu c thng gp trong dung dch ti kt qu o As(III) (AAs=0,1275)

Ion Aion Aion+As Sai

s,%Ion Aion Aion+As

Sai s,%

S2-, ppm

0,5 0,0018 0,1291 +0,5

NO3-, ppm

10 0,0022 0,1245 -3

1 0,0025 0,1181 +2 20 0,0015 0,1149 -11

5 0,0057 0,1445 +13 50 0,0017 0,1108 -14

10 0,0078 0,1682 +31 100 0,0021 0,1042 -19

Se(IV), ppb

5 0,0012 0,1243 -3

NO2-,

ppm

5 0,0023 0,1251 -3

10 0,0032 0,1181 -8 10 0,0038 0,1201 -6

50 0,0025 0,1127 -12 20 0,0029 0,1125 -14

100 0,0028 0,0708 -45 50 0,0034 0,1058 -18

Bi(III), ppb

5 0,0024 0,1301 +1

SO32-,

ppm

10 0,0027 0,1278 0

10 0,0029 0,1325 +3 20 0,0035 0,1352 +5

50 0,0035 0,1412 +10 50 0,0045 0,1427 +11

100 0,0026 0,1658 +29 100 0,0081 0,1465 +14

Sb(III), ppb

1 0,0018 0,1259 -2

Citrat, (M)

0,1 0,0012 0,1277 0

5 0,0026 0,1117 -13 0,5 0,0014 0,1289 0

10 0,0015 0,0976 -24 1 0,0024 0,1268 -1

20 0,0017 0,0783 -39 2 0,0025 0,1258 -2

Tactrat, M

0,1 0,0025 0,1277 -1

Axetat (M)

0,1 0,0031 0,1255 -2

0,5 0,0011 0,1258 -2 0,5 0,0028 0,1261 -2

1 0,0013 0,1261 -2 1 0,0016 0,1242 -3

2 0,0032 0,1282 0 2 0,0036 0,1238 -4

SO42-, ppm

10 0,0018 0,1258 -2

PO43-, ppm

10 0,0040 0,1255 -2

50 0,0014 0,1261 -1 50 0,0035 0,1266 -1

100 0,0026 0,1284 0 100 0,0015 0,1281 0

500 0,0032 0,1277 -1 1000 0,0021 0,1295 +1



Bng 19. Kh nng loi tr nh hng ca Sb(III) bng tactrat (AAs(III) = 0,1277)

CSb(III), ppb Ctactrat, M

0,01 0,05 0,1 0,5

10 0,1125 0,1131 0,1135 0,1134

50 0,1112 0,1138 0,1141 0,1136

100 0,1145 0,1128 0,1130 0,1149

H% trung bnh 88%

Khi tip tc tng nng tactrat ln 2M, chng ti nhn thy vn khng c s thay i c ngha trong hiu sut thu c As. Nh vy, tuy khng th loi tr hon ton nh hng ca Sb(III) nhng vi vic s dng tactrat 0,5 M to phc vi Sb(III) ta c th hn ch c nh hng ny xung mc sai s cho php ca php o.

Tm tt kt qu: Sau khi nghin cu nh hng ca mt s ion trong dung dch ti kt qu php o As(III) trn h HVG-AAS, ngng nh hng v chiu hng nh hng ca cc ion l c tm tt bng 20.

Bng 20. nh hng ca cc ion l ti php o As(III)

STT Ion Ngng nh hng

Chiu hng nh

hng

STT Ion Ngng nh hng

Chiu hng nh

hng

1 Mn2+ Khng nh hng 12 SO42- Khng nh hng

2 Cu2+ 10ppm m 13 NO3- 50ppm m

3 Pb2+ 10ppm m 14 NO2- 20ppm m

4 Cr3+ 50ppm m 15 PO43- Khng nh hng

5 Ni2+ 100ppm m 16 Sb(III) 5ppb m

6 Fe2+ 50ppm m 17 Se(IV) 50ppb m

7 Fe3+ 50ppm m 18 Bi(III) 50ppb Dng

8 Hg2+ 100ppb m 19 axetat Khng nh hng

9 S2- 5ppm Dng 20 Citrat Khng nh hng

10 SO32- 50ppm Dng 21 tactrat Khng nh hng



3.2. NGHIN CU NH HNG CA CC CHT KH I VI QU TRNH KH CC DNG As THNH ASIN

Mt s cng trnh nghin cu trc y kho st nhiu h kh As(III) thnh asin v kt lun l h kh NaBH4/HCl cho kt qu tt hn c [32, 39]. Cc nghin cu ny cng ch ra rng qu trnh kh trc tip As(V) thnh asin khng th t c hiu sut 100% so vi qu trnh kh As(III) v cn thit phi c qu trnh kh s b ban u chuyn cc dng As khc nhau thnh As(III) bng cc cht kh nh KI, KI/ascobic, KI/Sn2+, KI/Sn2+/ascobic, K2S2O5/H+, Na2S2O4/H+, [32]. Kt qu thc nghim khi kho st hiu sut kh cc dng khc nhau ca As thu c bng 21. Hiu sut c tnh da trn s chnh lch hp th quang so vi dung dch As(III).

Bng 21. Hiu sut kh cc dng As trong mi trng HCl 6M

Dng asen Nng (ppb) Abs Hiu sut kh

(%)

As(III) 5 0,1625 100

As(V) 5 0,0414 25

DMA 5 0,0532 30

MMA 5 0,1204 70

Nh vy, xc nh tng hm lng As cn thc hin qu trnh kh cc dng As(V) thnh As(III) trc khi tin hnh hidrua ha.

3.2.1. Kh nng kh cc dng As(V) thnh As(III) ca KI

Vi dung dch KI 0,1% - 5%, tin hnh kho st kh nng kh cc dng As(V) v so snh hiu sut kh (H%) cc dng bng cch so snh kt qu so vi As(III) c cng nng v khng c KI. Thi gian kh s b bng KI l 30 pht trc khi tin hnh phn tch theo phng php HVG- AAS. Kt qu thu c bng 22.

Nhn thy dung dch KI tuy c nng kh ln so vi cc dng As trong dung dch nhng hiu sut kh cc dng As(V) vn thp, c bit i vi dng



DMA do hp cht ny kh bn. V vy, xc nh tng hm lng As khng th s dng dung dch KI lm cht kh cc dng As(V) v As(III) trc khi hidrua ha.

3.2.2. Kh nng kh cc dng As(V) thnh As(III) ca h kh KI/Ascobic

y chng ti s dng cc dung dch KI c nng t 0,1% - 5% pha trong dung dch axit ascobic 5% kho st kh nng kh ca h ny, thi gian phn ng vn gi 30 pht trc khi phn tch bng thit b HVG-AAS. Kt qu thu c bng 23.

Bng 22. Kh nng kh cc dng As(V) ca KI

Nng cht, ppb

CKI, %

0,1% 0,5% 1% 2% 5%

H% H% H% H% H%

As(III)

1 0,0332 107 0,0327 105 0,0335 107 0,0317 103 0,0339 107

4 0,1285 105 0,1284 105 0,1274 104 0,1267 104 0,1287 105

10 0,3241 100 0,3192 100 0,3195 100 0,3235 101 0,3248 102

As(V)

2 0,0259 38 0,0357 55 0,0429 65 0,0499 75 0,0568 84

10 0,1289 40 0,1795 55 0,2117 65 0,2481 77 0,2892 85

15 0,1929 40 0,2682 55 0,3151 64 0,3749 77 0,4322 82

MMA

1 0,0236 70 0,0244 72 0,0256 75 0,0252 75 0,0272 80

4 0,0895 70 0,0929 74 0,0958 77 0,0954 76 0,1031 82

10 0,2272 70 0,2339 72 0,2405 74 0,2438 75 0,2604 80

DMA

1 0,0101 30 0,0118 35 0,0138 40 0,0138 40 0,0141 40

4 0,0413 32 0,0464 36 0,0517 40 0,0533 42 0,0519 40

10 0,1012 30 0,1135 35 0,1392 43 0,1327 41 0,1362 42



Bng 23. Kh nng kh cc dng As(V) thnh As(III) ca h KI/Ascobic

Nng cht,ppb

CKI/axit ascobic 5%

0,1% 0,5% 1% 2% 5%

H% H% H% H% H%

As(III)

1 0,0325 101 0,0314 98 0,0329 103 0,0338 106 0,0339 106

4 0,1281 105 0,1255 102 0,1271 104 0,1262 103 0,1277 105

10 0,3248 102 0,3204 100 0,3221 101 0,3209 100 0,3197 100

As(V)

2 0,0324 50 0,0454 70 0,0552 85 0,0550 85 0,0561 87

10 0,1685 52 0,2269 70 0,2722 84 0,2691 83 0,2754 85

15 0,2431 50 0,3500 72 0,4133 85 0,4121 85 0,4228 87

MMA

1 0,0238 70 0,0272 80 0,0271 80 0,0278 82 0,0270 80

4 0,0899 70 0,1040 80 0,1065 83 0,1029 80 0,1027 80

10 0,2205 68 0,2591 80 0,2531 78 0,2626 81 0,2659 82

DMA

1 0,0103 30 0,0137 40 0,0135 40 0,0138 40 0,0136 40

4 0,0417 32 0,0534 41 0,0522 40 0,0548 42 0,0538 41

10 0,1015 30 0,1288 38 0,1455 43 0,1459 43 0,1452 43

Nh vy, hiu sut kh tng r rt hai dng MMA v As(V) v c (t ti 85% khi s dng dung dch KI 1%), nhng hiu sut kh dng DMA vn kh thp (40%). Nh vy vi h kh ny ch c th xc nh tng hm lng As v c khi khng c mt cc dng hu c trong mu ch khng th xc nh chnh xc tng hm lng As v c nu khng tin hnh v c ha mu.



3.2.3. Kh nng kh cc dng As(V) thnh As(III) ca NaHSO3

Tng t nh trn, chng ti kho st kh nng kh ca cht kh NaHSO3 trn cc dng As(V) trong vng nng NaHSO3 t 0,01 1%. Dung dch trc khi o bng phng php HVG-AAS cn ui ht NaHSO3 bng cch un si k dung dch trong 15 pht. Kt qu kho st c a ra trong bng 24.

Bng 24. Kh nng kh cc dng As(V) thnh As(III) ca NaHSO3

Nng cht, ppb

CNaHSO3, %

0,01 0,05 0,1 0,5 1

H% H% H% H% H%

As(III)

1 0,0332 104 0,0314 98 0,0321 101 0,0317 99 0,0332 104

4 0,1277 104 0,1261 103 0,1254 102 0,1272 104 0,1281 105

10 0,3244 102 0,3231 101 0,3209 100 0,3198 100 0,3224 101

As(V)

2 0,0259 80 0,0292 90 0,0290 90 0,0298 92 0,0292 90

10 0,1031 81 0,1127 88 0,1153 90 0,1168 91 0,1179 92

15 0,2529 78 0,2945 91 0,2985 92 0,2981 92 0,2920 90

MMA

1 0,0227 70 0,0245 75 0,0258 80 0,0262 81 0,0259 80

4 0,0899 70 0,0945 74 0,1024 80 0,1049 82 0,1051 82

10 0,2333 72 0,2399 74 0,2625 81 0,2641 81 0,2575 80

DMA

1 0,0130 40 0,0133 41 0,0148 45 0,0145 45 0,0143 44

4 0,0513 40 0,0511 40 0,0560 44 0,0563 44 0,0549 43

10 0,1233 38 0,1361 42 0,1455 45 0,1427 44 0,1450 45

Kt qu cho thy, NaHSO3 kh As(V) thnh As(III) tt hn KI/axit ascobic. Hiu sut kh hai dng MMA v As(V) v c (t ti 80-90%), nhng



hiu sut kh dng DMA vn kh thp (45%). Nh vy vi h kh ny cng ch c th xc nh tng hm lng asen v c khi khng c mt cc dng hu c trong mu ch khng th xc nh chnh xc tng hm lng asen v c nu khng tin hnh v c ha mu.

3.2.4. Kh nng kh cc dng As(V) thnh As(III) ca L-cystein

L-cystein l tc nhn loi tr nh hng ca cc ion kim loi rt hiu qu. Nu c th s dng L-cystein lm cht kh trc cc dng As(V) v As(III) th tc nhn ny hon ton c th s dng trong thc t phn tch mu. Tin hnh th nghim vi nng L-cystein thay i t 0,05 5%. Cc kt qu kho st trong bng 25 cng cho cng kt lun nh vi cc cht kho kho st trn.

Bng 25. Kh nng kh cc dng As(V) thnh As(III) ca L-cystein

Hp cht,ppb

CL-cystein, %

0,05 0,1 0,5 1 5

H% H% H% H% H%

As(III)

1 0,0330 103 0,0317 99 0,0321 101 0,0335 105 0,0327 103

4 0,1279 104 0,1252 102 0,1261 103 0,1231 100 0,1280 105

10 0,3242 102 0,3211 101 0,3192 100 0,3258 102 0,3301 103

As(V)

1 0,0227 70 0,0292 90 0,0296 91 0,0291 90 0,0292 90

4 0,0922 72 0,1165 91 0,1178 92 0,1175 92 0,1163 90

10 0,2268 70 0,2916 90 0,2948 91 0,2921 90 0,2940 90

MMA

1 0,0229 70 0,0237 73 0,0253 78 0,0259 80 0,0262 81

4 0,1253 70 0,0946 74 0,1023 80 0,1030 80 0,1048 82

10 0,3201 71 0,2398 74 0,2592 80 0,2624 81 0,2599 80

DMA

1 0,0113 35 0,0133 41 0,0146 45 0,0143 44 0,0145 45

4 0,0454 35 0,0537 42 0,0577 45 0,0575 45 0,0589 46

10 0,1104 34 0,1367 42 0,1455 45 0,1462 45 0,1466 45



Cc kt qu kho st kh nng kh cc dng As(V) thnh As(III) bng cht kh L-cystein cng cho kt lun tng t nh i vi cht kh NaHSO3 kho st trn: Dung dch L-cystein nng 0,5 5% s cho hiu sut kh dng As(V) v c thnh As(III) t xp x 100% nhng s dng cht kh ny cng khng cho php xc nh c tng hm lng As trong mu do cc qu trnh o dng As(V) hu c ch cho hiu sut thp.

Nhn xt chung: S dng cc cht kh l L-cystein 1%, NaHSO3 0,5% hay h KI 1%/ascobic 5% u cho kt qu tt khi kh dng As(V) v c v As(III). Vi c 3 h kh ny, chng ti nhn thy ch c th xc nh tng hm lng As v c mt cch chnh xc khi khng c mt cc dng hu c trong mu, ngha l mun xc nh chnh xc tng hm lng As phi tin hnh v c ha mu hoc tch loi cc dng hu c v xc nh tng hm lng As v c.

Kt qu kho st trn cho thy khng th tin hnh phn tch chnh xc hm lng As v c khi c mt cc dng hu c nu khng qua giai on tch loi nhng ng thi cng m ra kh nng xc nh ng thi chng theo phng php HVG- AAS da trn hiu sut kh cc dng ny nu s dng cc thut ton hi qui a bin tuyn tnh.

3.3. NGHIN CU NH HNG CA MI TRNG PHN NG I VI QU TRNH KH CC DNG As THNH ASIN BNG CHT KH NaBH4

Nh cp trn, nu hiu sut kh cc dng As trong cc mi trng phn ng khc nhau l khc nhau th cc d kin ny c th s dng nghin cu kh nng xc nh ng thi cc dng As trong cng mt mu bng cch s dng thut ton bnh phng ti thiu nghch o. Da trn mt s yu t nh n nh ca tn hiu o cc mi trng, kh nng loi tr nh hng ca nguyn t Sb bng h m tactrat v c bit l s khc nhau r rt ca tn hiu o cc mi trng khc nhau ca cc dng As khi kho st s b la chn im o thch hp, chng ti chn 5 mi trng l HCl 6M, HCl 1M, m axit tactric tactrat c pH = 2, 3, 4 lm cc im thc nghim xc nh hi sut kh cc dng As ny. Cc kt qu iu kin khc v thng s my, nng NaBH4, tc dng c gi nguyn iu kin ti u kho st. Kt qu



nghin cu kh nng kh cc dng As trong 5 mi trng ny thu c bng 26 v tm tt bng 27.

Bng 26. Kt qu kho st kh nng kh cc dng As trong cc mi trng khc nhau

Hp cht

Nng ,ppb

HCl 6M HCl 1M m pH=2 m pH=3 m pH=4

A H% A H% A H% A H% A H%

As(III)

1

0,0325 101,9 0,0278 87,1 0,0234 73,4 0,0172 53,9 0,0104 32,6

0,0316 99,1 0,0268 84,0 0,0225 70,5 0,0177 55,5 0,0112 35,1

0,0331 103,8 0,0274 85,9 0,0235 73,7 0,0169 53,0 0,0098 30,7

0,0310 97,2 0,0265 83,1 0,0229 71,8 0,0165 51,7 0,0095 29,8

0,0328 102,8 0,0281 88,1 0,0221 69,3 0,0171 53,6 0,0108 33,9

3

0,0952 99,5 0,0834 87,1 0,0702 73,4 0,0516 53,9 0,0312 32,6

0,0975 101,9 0,0825 86,2 0,0714 74,6 0,0509 53,2 0,0302 31,6

0,0958 100,1 0,0827 86,4 0,0691 72,2 0,0512 53,5 0,0324 33,9

0,0949 99,2 0,0838 87,6 0,0689 72,0 0,0525 54,9 0,0317 33,1

0,0942 98,4 0,0819 85,6 0,0705 73,7 0,0517 54,0 0,0322 33,6

5

0,1625 101,9 0,1391 87,2 0,1174 73,6 0,0864 54,2 0,0524 32,9

0,1612 101,1 0,1379 86,5 0,1158 72,6 0,0857 53,7 0,0535 33,5

0,1637 102,6 0,1378 86,4 0,1172 73,5 0,0881 55,2 0,0518 32,5

0,1611 101,0 0,1412 88,5 0,1161 72,8 0,0851 53,4 0,0511 32,0

0,1608 100,8 0,1386 86,9 0,1152 72,2 0,0866 54,3 0,0527 33,0

As(V) 2

0,0175 27,4 0,0112 17,6 0,0084 13,2 0,0068 10,7 0,0036 5,6

0,0171 26,8 0,0105 16,5 0,0081 12,7 0,0061 9,6 0,0031 4,9



0,0168 26,3 0,0108 16,9 0,0075 11,8 0,0059 9,2 0,0042 6,6

0,0179 28,1 0,0115 18,0 0,0072 11,3 0,0064 10,0 0,0034 5,3

0,0164 25,7 0,0103 16,1 0,0088 13,8 0,0066 10,3 0,0028 4,4

6

0,0514 26,9 0,0332 17,3 0,0267 13,9 0,0181 9,5 0,0112 5,9

0,0504 26,3 0,0328 17,1 0,0249 13,0 0,0175 9,1 0,0105 5,5

0,0519 27,1 0,0319 16,7 0,0251 13,1 0,0184 9,6 0,0117 6,1

0,0521 27,2 0,0335 17,5 0,0247 12,9 0,0184 9,6 0,0114 6,0

0,0492 25,7 0,0314 16,4 0,0242 12,6 0,0192 10,0 0,0102 5,3

12

0,0826 25,9 0,0552 17,3 0,0441 13,8 0,0291 9,1 0,0182 5,7

0,0821 25,7 0,0548 17,2 0,0426 13,4 0,0285 8,9 0,0186 5,8

0,0835 26,2 0,0559 17,5 0,0433 13,6 0,0299 9,4 0,0175 5,5

0,0838 26,3 0,0535 16,8 0,0419 13,1 0,0312 9,8 0,0171 5,4

0,0817 25,6 0,0531 16,6 0,0411 12,9 0,0324 10,2 0,0168 5,3

DMA

1

0,0105 32,9 0,0245 76,8 0,0361 113,2 0,0275 86,2 0,0175 54,9

0,0114 35,7 0,0228 71,5 0,0348 109,1 0,0258 80,9 0,0161 50,5

0,0101 31,7 0,0231 72,4 0,0355 111,3 0,0262 82,1 0,0174 54,5

0,0095 29,8 0,0241 75,5 0,0337 105,6 0,0281 88,1 0,0171 53,6

0,0112 35,1 0,0226 70,8 0,0358 112,2 0,0277 86,8 0,0166 52,0

3

0,0301 31,5 0,0725 75,8 0,1145 119,6 0,0812 84,8 0,0511 53,4

0,0309 32,3 0,0721 75,3 0,1101 115,0 0,0802 83,8 0,0508 53,1

0,0295 30,8 0,0711 74,3 0,1112 116,2 0,0786 82,1 0,0489 51,1

0,0311 32,5 0,0734 76,7 0,1085 113,4 0,0821 85,8 0,0524 54,8



0,0299 31,2 0,0716 74,8 0,1071 111,9 0,0844 88,2 0,0529 55,3

5

0,0522 32,7 0,1221 76,6 0,1902 119,2 0,1357 85,1 0,0825 51,7

0,0534 33,5 0,1245 78,1 0,1878 117,7 0,1377 86,3 0,0861 54,0

0,0515 32,3 0,1218 76,4 0,1859 116,6 0,1362 85,4 0,0843 52,9

0,0524 32,9 0,1225 76,8 0,1872 117,4 0,1335 83,7 0,0881 55,2

0,0506 31,7 0,1207 75,7 0,1852 116,1 0,1374 86,1 0,0827 51,8

MMA

1

0,0228 71,5 0,0308 96,6 0,0206 64,6 0,0133 41,7 0,0104 32,6

0,0233 73,0 0,

as_aas

Documents