chuong1.pdf phân tích dư lượng thuốc trừ sâu

7/23/2019 chuong1.pdf phn tch d lng thuc tr su

1/27

9

CHNG 1. TNG QUAN

1.1 Gii thiu v thuc trsu

1.1.1 nh nghaThuc bo v thc vt (gi tt l thuc tr su) l cc cht hay hn hp cht t

nhin hoc tng hp c tc dng kim sot, y li cc loi su v cn trng gy tc

hi n thc phm, pht tn bnh tt. Thuc tr su bao gm ch yu 4 nhm chnh:

nhm clo hu c (organochlorines), nhm ln hu c (organophosphorus), nhm

carbamate v nhm cc (pyrethroid) [17]

1.1.2 c im

* Nhm clo hu c(organochlorine pesticides OC): gm nhng hp cht hahc nh DDT, methoxychlor, heptachlor, aldrin, lindane, mirex, rt bn vng trong

mi trng t nhin v c thi gian bn phn hy di. Nhm thuc tr su ny c

ha tan vo trong cc m mv c tch ly trong mng mbao quanh t bo thn

kinh lm ngn cn s chuyn dch ca cc rung ng thn kinh dc theo nhng axon

(ni lin cc t bo thn kinh). Kt qu l ph hy h thng thn kinh trung ng v

git cht sinh vt cn dit tr.[7]

c trng cho nhm ny l 3 loi hp cht DDT, hexachlorobenzen v cc hpcht cyclodiene. DDT l mt trong nhng cht bn v khng ha tan c trong nc

v p sut hi thp. BHC v cyclodiene s dng rng ri do kh nng tiu dit nhiu

cn trng, nhng do kh phn hy v c tnh cao ca thuc tr su h clo nn hu ht

b cm hoc b hn ch s dng. [7]

* Nhm ln hu c (organophosphorus pesticides-OP) gm nhng hp cht

ester ca acid phosphoric hay acid thiophosphoric vi cc gc ca hp cht hu c

khc. V d nh malathion, parathion, diazinon, fenitrothion Nhm ny c thi gian

bn phn hy nhanh hn nhm clo hu c, c c cao hn i vi ngi v ng

vt. Nhm ln hu ctc ng vo thn kinh ca cn trng bng cch ngn cn s to

thnh cholinesteraza, lm cho thn kinh km hot ng, yu c, gy chong vng v


2/27

10

cht. y l nhm vn cn c s dng rng ri hin nay ngoi nhm pyrethroid

(cc) v carbamate. [7]

* Nhm carbamate: gm nhng hp cht ester ca acid carbamic v N-methyl

hay N,N-dimethyl. Mt s cht in hnh l: aldicarb, carbofuran, carbaryl,

methomyl,y l nhng hp cht t bn vng trong mi trng t nhin nhng c

c tnh rt cao i vi ngi v ng vt. Chng tc ng trc tip vo men

cholinesteraza ca h thn kinh. [7]

* Nhm cc: thuc tr su nhm Cc tng hp dn xut t ngun gc thc vt

ca cy h Cc, trong cng thc c cha cht Pyrethrin gy c cho cn trng. Thuc

ny t gy c cp tnh, phn hy nhanh trong mi trng, d chu tc ng ca nhsng v nhit . Tuy nhin, nu p dng lu v lin tc trn ng rung d gy tnh

khng ca cn trng. Nhm ny d bay hi v tng i mau phn hy trong mi

trng v cth ngi. Pyrethrin l loi ho cht c thn kinh, chng tn cng ln h

thng thn kinh ca cn trng. Khi nng khng tiu dit cn trng, chng vn

gy nn hiu lc xua ui i vi cn trng. Pyrethrin v cc cht cc tng hp l

nhng cht gy c ln knh mui (sodium channel) ca mng thn kinh. Cc

pyrethroid c i lc rt cao i vi cc knh mui, to ra nhng thay i nh chcnng ca knh. Cc pyrethroid thc cht l nhng cht gy c chc nng, hu qu xu

ca thuc mang tnh th cp, l hu qu ca s kch thch qu h thn kinh. iu

ny th hin r ch khng tm thy cc du hiu bnh l trong h thn kinh trung

ng, ngay c khi gy c nng nhiu ln cng nh s ch to thnh cc m hoi t

khng c trng v c th phc hi trn cc thn kinh ngoi vi ca ng vt b co git

v th hin cc triu chng ri lon vn ng nghim trng. Sau khi b pyrethroids lm

cho bin i knh mui vn tip tc hot ng bnh thng, vn duy tr c chcnng chn la cc ion mui v ni vi in th mng.

Cc ho cht nhm pyrethroid gy hi cho c, nhng rt t nh hng n chim v

ng vt c v hn nhiu loi ho cht dit cn trng tng hp khc. Chng khng bn

vng, d b phn hu khi tip xc vi nh sng v oxy. Chng thng b phn hu di


3/27

11

nh sng mt tri v trong khng kh trong vng mt vi ngy, v khng nh hng

ng kn cht lng nc ngm. Chng c xem nh l nhng loi ho cht dit

cn trng an ton nht i vi ngi v mi trng.[19]

1.1.3 Tc hi ca thuc trsu

Cc loi thuc tr su tc ng ln h thn kinh, c ch men

acetylcholinesteraza v tc ng ln khong khng gian gia cc t bo thn kinh

(synapsis) ca h thn kinh ca cc c th trng c. Nu quan st, chng ta s thy

nhng hng phn thn kinh i km vi cc hot ng lon nhp, mt thng bng hay

bt nga, cc chi v u co git lin tc, yu dn v cht.

Hp cht OC rt bn vng trong cthng thc vt v c tch ly lu trongm m, lipit, lipoprotein, sa. Hp cht OP v carbamate tng i t hay khng tch

ly lu trong m m, lipit, lipoprotein nhng li ha tan v tn ti rt lu trong dn

xut ester ca acid hu cvng thm.

V bn cht ha hc, thuc tr su c thi gian bn phn hy trong t ko di

tng i lu. Trong mi trng t nhin, di tc dng ca nh sng, nhit , m

v vi sinh vt, cc ha cht ny bt u b phn hy. Sn phm chuyn ha ca OC t

c hn hp cht ban u. Nhng i vi OP, s chuyn ha din ra nhanh v phctp, ng thi xut hin nhiu hp cht trung gian c hn rt nhiu ln dng thuc ban

u vi cn trng v ng vt mu nng.

Thuc tr su c th gy ngc cp tnh cho sinh vt khi tip xc trc tip,

nut nhm hoc ht th. Chng cng c th gy ng c mn tnh cho sinh vt m

khng c triu chng ban u c th no.

D lng thuc tr su cn li trong rau qu, thc phm l nguyn nhn gy ra

nhng bnh nh ung th phi, tiu ng, bt thng v van tim, tiu ha thn kinh.Chng c kh nng lm suy yu h min dch khin cth khng chng li c cc t

bo ung th v cc loi vi sinh vt gy bnh. Ngoi ra, chng cn c th gy mt s

nh hng khc n cth con ngi.


4/27

12

1.1.4 Cng thc cu to ca cc hp cht thuc trsu nghin cu trong ti

DDT, DDD, DDE

Methacriphos Tetradifon

Tribufos

Dichlorodiphenyldichloroethan

Dichlorodiphenyltrichloroethan

Dichlorodiphenyldichloroethylen


5/27

13

Hexaclorobenzen Ethoprophos

Chlorpyriphos methyl Chlorfenvinphos

Tolclofos methyl Pirimifos-methyl

Isofenphos Fenpropimorph


6/27

14

Tefluthrin

Bifenthrin Fenpropathrin

Permethrin Esfenvalerate

Hnh 1.1 Cng thc cu to ca cc hp cht thuc trsu nghin cu trong ti


7/27

15

1.1.5 Yu cu v dlng ca thuc trsu

Do tnh c hi ca thuc tr su nh hng n sc khe con ngi v gy

nhim mi trng nn hin nay cc nc thit lp nhng gii hn cho php ti a

ca cc hp cht thuc tr su trn cc i tng thc phm khc nhau. V gii hn

ny khc nhau ty theo tng hp cht v tng loi thc phm.

Bng 1.2 Gii hn cho php ca mt vi hp cht theo quy nh chu u

(Regulation EC No 396/2005)

STT Thuc trsuTri cy

ti (ppb)Tht c(ppb)

Rau(ppb)

1 Methacrifos 50 10 50

2 Ethoprophos 20 10 203 Hexaclorobenzen 10 200 104 Tefluthrin 50 50 505 Tolclofos methyl 50 50 50-1006 Chlorpyrifos methyl 50-500 50 507 Pirimiphos methyl 50 50 508 Fenpropimorph 50 10-300 509 Chlorfenvinphos 20 10 2010 Bifenthrin 50-300 50-100 50

11 Fenpropathrin 10 - 1012 Tetradifon 20 50 2013 Permethrin 50 50 5014 Esfenvalerate 20-50 200 20

Phn ln cc hp cht c gii hn ti a khong 10ppb n 50ppb, iu i

hi pht trin phng php phn tch lm sao c nhy tng i tt c th kim

sot tt d lng thuc tr su trong thc phm.

1.2 Gii thiu mt s phng php chit thuc trsu

Mc ch chnh ca cc quy trnh chit l c th tch c cc hp cht thuc

tr su t nn mu bng quy trnh chit thch hp. C nhiu phng php chit thuc

tr su nh chit rn lng SLE (solid liquid extraction) , chit lng lng LLE (liquid-


8/27

16

liquid extraction) , chit pha rn SPE (solid phase extraction) v chit vi lng pha rn

SPME (solid phase micro extraction). Vic chit thuc tr su t mu lng (v d mu

nc) th k thut chit thch hp l chit pha rn SPE hoc chit lng lng LLE. i

vi mu mi trng hoc mu thc phm dng rn th vic dng dung mi v h tr

bng k thut lc khuy trn hoc vi sng l thch hp. Trong cc quy trnh th u cn

lm sch bng chit pha rn hoc chit lng lng loi bt tp cht bn t nn mu.

1.2.1 Chit rn lng SLE (solid liquid extraction)

Phng php chit ny l phng php s dng rng ri phn tch thuc tr

su t nn mu rn. u tin dung mi chit len li su vo gia cc thnh phn mu

tip xc vi cht phn tch, sau cht phn tch khuch tn i vo dung mi chit.Yu t quan trng nht ca k thut chit rn lng ny l la chn dung mi thch hp.

Tuy nhin nhng yu t khc nh p sut, nhit cng c nh hng quan trng ln

hiu qu chit. Khi tng p sut s lm tng kh nng phn tn ca dung mi i su vo

nn mu rn, tng nhit s lm tng kh nng ha tan ca cc cht phn tch vo

dung mi. Cc k thut h tr trong chit rn lng l lc, chit soxhlet, nh siu

m, microwave. Mi k thut u c nhng u nhc im ring.

Lc : l cch n gin v thun tin thng s dng chit thuc tr su t tricy v rau qu. Ch cn cho dung mi thch hp ri lc trong mt khong thi gian xc

nh. Dung mi thng s dng l acetone v acetonitrile v kh nng trn vi nc

ko cht phn tch t nn mu ra dung dch lng, ngoi ra dichloromethane hay hexan

cng c dng cho nhng hp cht thuc tr su km phn cc.

K thut lc vi dung mi n gin v thun tin nhng khng hiu qu trong

nhng trng hp cht phn tch c lin kt cht ch vi nn mu. Trong trng hp

ny nh siu m l cch h tr tt, gip cho s khuch tn ca dung mi vo mu,tng thm s tip xc qu trnh chit c hiu qu hn, gim c lng dung mi

v thi gian chit.

Chit soxhlet : khi qu trnh lc khng tt chit, lc cn h trbng

cch gia nhit. Chit soxhlet l mt k thut chit nhit cao, k thut ny ra i t


9/27

17

nm 1879, n nay vn cn c s dng. Dung mi chit c chng ct, sau

ngng t v mu c chit nhiu ln vi dung mi sch .

u im ca chit soxhlet l hiu qu chit tt nhng cng c nhc im v

thi gian chit lu, s dng mt lng ln dung mi.

Chit bng microwave : k thut ny c pht trin trong vi nm qua. Mu

v dung mi chit c gia nhit bng vi sng, c s kim sot v p sut, nhit v

nng lng. K thut ny cho hiu qu chit tng t nh chit soxhlet tuy nhin gim

c thi gian chit (thi gian chit khong 15 pht) v gim c dung mi chit so

vi k thut chit soxhlet (dung mi s dng 25-50ml) v c p dng trong nhiu

phng th nghim.1.2.2 Chit lng lng LLE (liquid-liquid extraction)

c s dng rng ri chit thuc tr su t mu lng. Chit lng lng da

trn s phn b ca cht phn tch gia hai pha lng. Hiu qu ca vic chit lng lng

ph thuc i lc ca cht phn tch vi dung mi chit, t l th tch mi pha. Chit

lng lng thng c s dng chit thuc tr su t mu nc trong mi trng,

hexane v ciclohexane l dung mi hu cthng dng chit cc cht khng phn

cc nh thuc tr su clo hu c, phosphor hu c. Dichloromethane , chloroform ldung mi chit cc cht phn cc va.

S kt hp ca dung mi v pH lm tng kh nng chit nhiu thuc tr su t

nn mu, l u im ca phng php chit lng lng. Tuy nhin phng php ny

chi ph cao tn nhiu thi gian v khng tng ha c.

1.2.3 Chit pha rn SPE (solid phase extraction)

Ging nh chit lng lng, chit pha rn da trn i lc khc nhau ca cht phn

tch gia hai pha. Trong chit pha rn, mu c cho qua cht hp ph rn (c nhiuloi cht hp ph rn phn cc, khng phn cc, trao i ion) nhi trong ct. Nhng

cht phn tch c i lc ln vi pha rn hp ph sc gi li trn ct, trong khi

nhng cht khc si qua ct. Tp cht c ra vi dung mi loi b nhng cht


10/27

18

phn tch vn gi li, sau cht phn tch b gi trn ct c ra gii bng mt

lng nh dung mi thch hp chn lc vi cht phn tch.

Vi k thut chit SPE, mu c th lm giu nhiu ln tng nhy cho phn

tch cc hp cht. Vn quan trng trong chit SPE l la chn pha rn hp ph thch

hp, hiu c mi tng quan gia cht phn tch v cht hp ph l vn quan

trng.

1.2.4 Chit vi lng pha rn SPME (solid phase micro extraction)

Arthur v Pawliszyn gii thiu phng php chit vi lng pha rn SPME

vo nm 1989. Phng php chit ny n gin, khng dng dung mi hu cc hi,

v thc hin nhanh vi nhiu loi si chit c lm sn vi nhiu loi cht hp thukhc nhau ph ln si chit. Si chit silica c ph ln mt lp pha tnh tng t

nh ct sc k, si chit c t bn trong mt cy kim bo v. Tng t nh chit

pha rn, chit SPME cng da trn s phn b ca cht phn tch gia nn mu v pha

tnh. Chit vi lng pha rn gm hai bc chnh l chit v gii hp, ngoi ra cn c

th thc hin thm bc ra nu cn.

Chit : qu trnh chit c th thc hin bng cch chit phn khong khng

(i vi cc hp cht d bay hi t nn mu lng hoc mu rn), hoc a trc tip sichit tip xc vi mu. u tin mu c b vo l kn, cm cy kim vo l ri y

si chit ra hp thu cht phn tch ln pha tnh ph bn ngoi si chit. Sau si

chit c ko vo bn trong kim bo v v rt ra khi mu.

Vic la chn si chit vi thnh phn pha tnh hp l l yu t chnh ca k

thut ny. B dy pha tnh ph bn ngoi si chit v xp ca pha tnh cng l yu

tnh hng n hiu qu chit, bn cnh mt s yu t nh nhit , thi gian

chit, pH cng cn ti u t c hiu qu chit tt nht.Gii hp : cc cht phn tch b hp thu vo pha tnh ca si chit c gii

hp ra phn tch. C th gii hp trc tip bng cch gia nhit bung tim mu

sc k kh hoc ra gii bng dung mi thch hp. Gn y c h thng kt ni trc


11/27


12/27

20

Mc d c th s dng dung mi khng cha clo nh acetone hay ethylacetate

nhng trong phng php QuEChERS la chn dung mi acetonitrile v khi thm hn

hp mui dung mi v nc d dng tch khi nhau hn l acetone. Ethylacetate c th

ha trn mt phn vi nc nhng li chit lun c bo v sp t nn mu, cho thu

hi thp i vi thuc tr su dng acid- baz. Dung mi acetonitrile chit khng tt

vi cc cht d tan trong m, nhng vi nhng mu c hm lng ng cao th

acetonitrile v nc d dng hnh thnh hai pha chit thuc tr su ln pha hu c.

So vi acetone th acetonitrile d loi nc hn khi thm MgSO4. Dung mi

acetonitrile thch hp cho c sc k lng v sc k kh. Do vy trong phng php

QuEChERS la chn dung mi acetonitrile chit cc hp cht thuc tr su. Tuynhin dung mi ny c mt nhc im l kh bay hi hn nn thi gian c quay lm

giu mu s lu hn.

Mc ch ca vic thm mui bc 3 l tch nc v dung mi hu c

thnh hai pha. Thm mt lng mui MgSO4 bo ha gim lng nc tng s

phn b ca thuc tr su vo pha hu c. Mui NaCl kim sot phn cc ca

dung mi chit, tuy nhin nhiu mui ny qu lm gim s phn b ca thuc tr su

khng phn cc ln pha hu c.Trc y bc lm sch thc hin da trn vic nhi cht hp thu ln ct.

Nhng trong chit pha rn phn tn, phn dung dch chit c cho vo ng nh c

cha mt lng nh PSA (amine bc 1 bc 2), lc u sau ly tm tch phn dung

dch v cht rn hp thu. Cht hp thu ch gi li thnh phn nn mu, khng gi cc

hp cht thuc tr su. Trong trng hp mu cha nhiu bo th thm bt C18 vo

cht hp thu loi bo, mu cha nhiu cht mu trong thc vt th thm GCB

(graphite carbon black). Cc lm sch ny so vi chit SPE th d thc hin hn, khngphi hot ha ct, v dng t dung mi.

Thm acid acetic v cht bo v mc ch cc hp cht thuc tr su c

bn hn, hn ch phn hy khi vo h thng sc k. Thng cht bo v s dng l

sorbitol, gulonolactone and ethylglycerol.


13/27

21

1.3 Gii thiu phng php sc k kh xc nh thuc trsu

1.3.1 Slc v sc k kh [4]

Sc k kh l phng php tch da trn hai qu trnh hp ph v gii hp

ph xy ra lin tc gia hai pha: pha tnh rn hoc lng v pha ng l kh. Sc k kh

khi ni vi cc u d cho php nh tnh v nh lng cc cht da vo thi gian lu

v din tch mi sc k.

Hnh 1.3. S khi ca my sc k kh

H thng bao gm cc b phn cbn nh sau:- Ngun cung cp kh mang thng l bnh kh hoc my sinh kh

- H thng iu khin p sut hoc tc dng kh mang

- Bung bm mu

- L ct iu khin nhit ct tch

- Ct tch l ni xy ra qu trnh tch cht. Cc loi ct gm ct nhi, ct mao

qun

- u d c nhiu loi khc nhau ty theo mc ch phn tch, dng pht hincht v nh lng: FID, ECD, MS, NPD, TCD

- H thng ghi nhn v x l tn hiu: thu thp v tnh ton kt qu.

Trong sc k kh th quan trng nht l ct sc k v kh mang. Kh mang thng phi

trkhng phn ng vi cc hp cht phn tch v pha tnh, kh khng cha oxi, kh


14/27


15/27

23

yu t hiu nng tch v dung lng ct. Hiu nng tch ca ct mao qun th hin

sa l thuyt (N), sa l thuyt tng khi ng knh ct gim. Dung lng

ct tng khi tng ng knh ct, khi phn tch cc cht nng cao hoc nhiu

nng tri rng th nn chn ct c ng knh ln. phn cc ca pha tnh

cng nh hng n dung lng ct, pha tnh khng phn cc cho dung lng cao

hn i vi hp cht phn cc v ngc li. Thng th chn ng knh ct

0.25mm ph hp cho nhiu trng hp phn tch, cho sa l thuyt ca ct v

dung lng trong khong chp nhn c.

- B dy lp pha tnh: chn b dy lp pha tnh nh th mi sc k s hp li, v

gim chy mu ct, nhit s dng ti a ca ct cng tng ln. S dng ct clp pha tnh mng gim c thi gian lu ca cc hp cht ngay ci vi trng

hp phn tch nhit thp. Nhng li c khuyt im l lm cho dung lng ct

gim khi chn b dy pha tnh nh. Ct c lp pha tnh mng (0.1m n 0.25 m)

thng dng phn tch cc hp cht c nhit si cao (nh cc hp cht thuc

tr su, phthalate esters, polychlorinated biphenyls).


16/27


17/27

25

1.3.2 Sc k kh vi u d ECD (Electron capture detector) [5]

u d ECD l loi u d chn lc, n ch nhy vi mt s hp cht c

cha cc nguyn t c m in ln nh: O, N, F, Cl, Py l loi u d ph bin

nht xc nh thuc tr su v cc hp cht halogen trong mu mi trng, mu

nng thy sn, mu thc phm

u d ECD bao gm mt bung ion ha cha ngun phng x (Ti3H,

Sc3H, hay a chung l 63Ni) pht ra tia . Trong qu trnh phn tch, mt dng kh

Nithay Argon trn vi 5-10% metan i vo trong t bo ni khc ion ha bi

tia , v gii phng cc in t nhit t do. in cc dng thu nhn cc in t, dovy hu nh lun c mt dng in nh cnh c xem nh dng chun. Nu hp

cht cha nguyn t c m in ln nh F, Cl, O,i vo trong t bo, n s nhn

cc in t nhit t do, v vy dng chun s gim xung. Tn hiu u ra c ghi

nhn bi s khuch i v o ngc ca dng chun.

Tc dng kh vo trong u d ty thuc vo cu trc hnh hc ca t

bo, nhng thng khong 10ml/pht. Do , i vi ct mao qun, cn c kh mang

l Nithoc Argon/metan h trcho s ion ha.u d ECD c th phn tch hm lng thuc tr su nh khong 0.01ppb,

nhng ch chn lc cho cc thuc tr su h clo, km nhy phn tch cc thuc tr

su h phospho, carbamate.


18/27

26

Hnh 1.4 S ca u d ECD

1.3.3 Sc k kh vi u d NPD (Nitrogen-phosphorus detector) [5]

u d NPD l loi u d chn lc, nhy vi hp cht cha nit, phosphor.

Cu trc cng tng tu d FID, khc bit l c thm mt vin mui kim loi kim

(mui Rubidi hay Cesi) ni vo cc m t gia ngn la thiu t ha cht v b thu

ion. Khi bt nng, vin tinh th ny (gi s l mui Rubidi) phng thch Rb*. Cc

Rb* phn ng vi cc gc t do CN t hp cht c ni C-N hay cc gc PO2 t hpcht c P ln lt cho ra CN- v PO2

- v tr thnh Rb+ b ht tr li vin tinh th.

Cc ion CN- tip tc phn ng vi gc t do H hay OH c trong ngn la cho HCN

hay HCNO v phng thch in t to ra dng in. Tng t PO2- phn ng vi gc

t do OH cho HPO2 v phng thch in t to dng in. Nu khng c hp cht c

C-N hay P th Rb* cng phn ng vi gc t do H,OH trthnh Rb+ v phng thch

in t to dng in nh. S khc bit gia dng in nn v dng in trong trng

hp c hp cht N hay P c khuch i v biu din di dng mi sc k. Hin

tng c tip tc xy ra nh th. Trn nguyn tc, vin mui Rubidi khng b hao ht

nhng thc cht sau mt thi gian hai ba nm th phi thay, nht l trong iu kin

kh hu m t.


19/27

27

Hnh 1.5 S ca u d NPD

1.3.4 Sc k kh ghp u d khi ph ba ln tcc MS/MS

Sc k kh thch hp phn tch cc hp cht t phn cc, d bay hi v bn

nhit. Phng php sc k kh kt hp u d MS rt hu hiu trong vic nh danh v

nh lng, phn tch ng thi rt nhiu hp cht thuc tr su trong cc nn mu

phc tp. Phng php ny c ng dng rt rng ri do u im phn tch ng thi

nhiu hp cht, cc cht c thi gian lu ging nhau khng phn tch c bng sc k

thng thng, nhy v chn lc cao. Tuy nhin mt vi hp cht kh bay hi

nh carbamate th phng php ny khng phi l th mnh, trong trng hp ny sc

k lng c dng nhiu.

Cu to ca h khi ph ba ln t cc gm c: ngun to ion, b phn phn

tch khi lng , bung bn ph ion , u d ghi nhn tn hiu.

Nguyn tc hot ng ca u d khi ph ba ln t cc


20/27

28

- Cht phn tch sau khi ra khi b phn GC c ion ha bung ion, sau i qua

b phn MS1. y ion mc chn sau b va p phn mnh bung bn ph

(collision cell) vi kh va p l argon, to ra cc mnh ion con. Cc ion con ny tip

tc i qua b phn MS2, ti y cc mnh c lc ra v i n u d ghi nhn tn

hiu.

- Ngun to ion: trong ti ny thc hin ion ha theo ch ion ha in t EI

(Electron Impact Ionization)

Ion ha in t: xy ra trong mi trng chn khng p th 70V, dng electron

c nng lng cao khong 70eV pht ra t si dy tc (filament), di chuyn gn hi

phn t ca cht cn phn tch M, v lm bin dng m my in t ca phn t. Dong nng electron cao nn khi bao quanh m my electron ng thi truyn ng

nng cho electron ca m my in t, khi ng nng ln chng tch ra hnh thnh

ion phn t M.+ v ng thi qu trnh tip xc va p ca electron vi hi phn t ca

cht phn tch cng to thnh ion con A+, B+ . Cc ion ny c nh hng v i vo

b lc khi (quadrupole). Do trong ion ha in t, cc electron c nng lng rt ln

nn sau khi va p cn li t ion phn t, v vy khng thu c nhiu thng tin v khi

lng phn t, tuy nhin t cc mnh ion nh c th thu thp c nhiu thng tin vcu trc phn ti vi nhng hp cht mi.


21/27

29

Hnh 1.6 S ion ha EI

B phn tch t cc (quadrupole): c cu to gm bn thanh in cc song song

b tr cch u mt trung tm. Thin t c tn s tnh hay bin i c p vo 2

cp thanh song song i din to ra in trng. Cc ion m hay dng t ngun

ion si vo dc theo mt trc trung tm ca t cc. Do in trng c cng v

tn s c th nn ch cho nhng ion c khi lng thch hp i qua c b t cc

n b phn pht hin (detector). Thng thng ngi ta gi tn s khng i v thay

i th p vo gip cho vic la chn ion.


22/27

30

Hnh 1.7 S b tcc

Hnh 1.8 S khi ph3 ln tcc (MS/MS)

BphnMS1

BphnMS2

B phn bnph ion sau khiqua MS1(collision cell)


23/27

31

Nhng ch s dng ca u d khi ph ba ln t cc: phn tch mt cht

cn c hai cp mnh ion c cng thi gian lu, hai cp c th l mt mnh m v

hai mnh con hoc hai cp mnh khc nhau khng cng mnh m. tm c cc cp

phn mnh ion cn c cc ch qut khc nhau tm v xc nhn thng tin chnh

xc ca cc cp phn mnh ion ca mt cht

- Ch qut mnh ion con (product ion mode): mt ion mc chn MS1

sau qua bung bn ph ion, ti y ion m b phn mnh thnh nhiu ion con

khc nhau, vi ch qut mnh ion con s cho tt c cc mnh ion con i

qua c t cc n b phn pht hin (detector). Sau khi c c tng

mnh con vi cng khc nhau, chn hai mnh con c nhy tt nht v n

nh nht chy ch MRM (multiple reaction mornitoring) nh lng

cc hp cht ny.

- Ch qut mnh m (precursor ion mode): nhiu mnh m ca cc hp cht

khc nhau c th b bn ph v cho ra cng mt mnh con, khi b phn pht

hin o tn hiu cng ca ion con v tnh ra hm lng ca cht phn

tch s b sai s dng, l yu t cn nhiu ca u d khi ph. Do xc nhn li mnh con c phi l ca hp cht cn phn tch hay khng th s

dng ch qut mnh m xc nhn li thng tin.

- Ch MRM: S dng nh lng cc hp cht. ch ny, b phn t

cc MS1 ch cho mt ion mi qua c v n bung bn ph phn mnh


24/27

32

Hnh 1.9 Cc ch phn tch ca u d khi phba ln tcc

- Ngoi ra vi h thng khi ph ba ln t cc cng c th s dng ring b phn t

cc MS1 hoc MS2 thc hin ch SCAN qut nhiu ion hay chn lc tng ion

SIM (single ion mornitoring) nh trong sc k kh ghp khi ph GC-MS mt ln.

ch SCAN, b t cc c p th thay i trong mt khong xc nh, v ghi nhn


25/27

33

li tt c cc ion tng ng trong khong p th. Lc bung bn ph khng hot

ng. Tuy nhin mt phn ion s mt mt trong qu trnh di chuyn qua ba b phn

MS1, bung bn ph v MS2 nn lng ion n c b phn pht hin ion s gim i

so vi h khi ph MS mt ln, nn nhy s khng bng.

u im ca u d khi ph MS/MS:

Phng php c chn lc cao, kh nng nhn danh cao, t bnh hng ca

nhiu nn. Phng php x l mu cng n gin hn. Khng mt nhiu thi gian

tch mi sc k ca hn hp nhiu hp cht, c th phn tch cng lc vi trm hp

cht thuc tr su, trong khi phng php phn tch thuc tr su khc nh sc k khu d ECD, NPD phn tch c t hn nhiu.

Nhc im:

nhy so vi cc phng php chuyn dng thng thng khng bng.

Thng xuyn phi lm sch b phn MS v nh hng nhiu n nhy ca

phng php.

Gi thnh t.

1.4 Gii thiu phng php sc k lng xc nh thuc trsu

Rt nhiu hp cht thuc tr su t phn cc, d bay hi c xc nh bng

phng php sc k kh rt hiu qu. Kt hp vi cc hu d khc nhau nh ECD,

FID hay u d MS, sc k kh phn tch c nhiu thuc tr su trong thc phm

v trong mi trng. Tuy nhin cc hp cht khng bn nhit, km bay hi th li l th

mnh ca sc k lng.

1.4.1 Phng php sc k lng u d hunh quang

Phng php ny c bit chn lc cho vic phn tch cc hp cht thuc tr

su h carbamate sau khi to dn xut.[6]


26/27

34

Nguyn tc ca phng php HPLC to dn xut sau ct l da vo c tnh

khng bn ca nhm carbamate trong mi trng kim. Sau khi tng loi carbamate

tch trn ct sc k pha o, c thy phn trong mi trng baz sinh ra methyl

amin, sau methyl amin phn ng vi thuc th O-phthalaldehyde (OPA) v 2-

mercaptoethanol to ra dn xut hunh quang 1-hydroxytylthio-2-methylisoimdol.

Phn ng phn hy ca carbamate trong mi trng baz (phn ng xy ra

nhanh hn di tc dng ca nhit )

Phn ng ca methyl amin vi thuc th sinh ra hp cht hunh quang 1-

hydroxytylthio-2-methylisoimdol. Cht ny c cc i hp thu khong 340nm v cc

i pht x 440-460nm.

Mu c ng nht v chit vi dung mi MeOH, lm sch bng ct C18, sau

mu c ra gii bng CH2Cl2, thi kh v ha tan li bng MeOH

Phng php ny rt nhy v chn lc cho phn tch thuc tr su carbamate

trong mu t, nc, thc phm. Gii hn pht hin 0.51-5.0ppb, gii hn nh lng

1.69-9.09ppb. Tuy nhin ch chn lc cho phn tch thuc tr su h carbamate, khng

thch hp phn tch thuc tr su thuc h khc.

1.4.2 Phng php sc k lng ghp u d khi ph (LC-MS/MS)

Phng php sc k lng kt hp vi u d khi ph MS/MS rt chn lc v

hiu qu xc nh ng thi nhiu thuc tr su nh carbamate, phenylureas, thuc

tr su phospho hu c, triazines m khng cn cc k thut to dn xut phc tp.


27/27

35

u d khi ph cn cho nhiu thng tin v cu trc phn t gip don c tn

hp cht trong vic nh danh cc cht.

Nguyn tc hot ng ca h sc k lng ghp khi ph: mu sau khi tim c

pha ng li ko i v cc hp cht c tch ra trong ct sc k, sau mu c ha

hi v chuyn v dng ion bung ion ha. B phn MS1 s chn ion m tip tc

bn ph thnh ion con v MS2 s lc ra cc mnh con . Da vo cc cp phn mnh

nh tnh v nh lng cc cht.

u im ca phng php sc k lng u d khi ph l nhy v chn

lc cao, kh nng nh tnh v nh lng tt. Khi tim vi th tch ln c th h thp

gii hn pht hin ca cc cht phn tch. Thi gian phn tch nhanh hn so vi sc kkh. Qu trnh ti u ha cc thng s nh nng lng bn ph mnh ion m, mnh ion

con thc hin nhanh chng hn phng php sc k kh, c th nhn thy c mnh

ion con c nhy v bn ngay trong lc tim chun ti u m khng cn chy

th, do vy tit kim c thi gian tm phng php chy my thch hp cho mt

hp cht mi.

Tuy nhin vi phng php sc k lng cng c nhc im l cn thi gian

cn bng dung mi pha ng trc khi chy khng bnh hng thi gian lu cacc hp cht.

Documents

chuong1.pdf phân tích dư lượng thuốc trừ sâu