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Cc phng php chit, tch v lm giu mu

Cc phng php chit, tch v lm giumu

- S dng phng php chit pha rn (SPE) phn tch hm lng thuc tr su, bao gm triazine v cc sn phm phn hy ca n, trong t v b mt nc

- S dng phng php vi chit pha rn (SPME) xcnh thuc dit c c trong mu ly t mi trng

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MC LC

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I. Cc phng php chit, tch v lm giu mu:1. Xc nh vt cc nguyn t (cc tp cht vi lng)

Trong nhng nm gn y, cng vi s pht trin ca cc ngnh cng nghip hini v cc ngnh k thut mi, cn nhng vt liu c tinh khit cao, cc phng phpxc nh vt cc nguyn t (cc cht vi lng) cng c ngha ln. V vy, cc yu cuv chnh xc v nhy ca cc phng php c dng phn tch cc cht cbit tinh khit ngy cng tng ln.

K thut ca cc phng php cng c hin i cho php pht hin hoc xc nhnhng lng nh ca cc cht. V d, bng bung Wilson v my m Gauge-Mule, cth pht hin c khong 10-10 g ca mt cht. Phng php khi ph k cho ta khnng xc nh 10-8, 10-6 g tp cht. Bng cc phng php ng hc, c th pht hin

c 10-19 mol trong 1 ml dung dch, hoc pht hin c 60000 phn t, cn trongtrng hp s dng k thut phn tch siu vi lng, c th xc nh c nhng lngcht nh hn na.

Khong nng ca cc vi cht (c biu th di dng %) c xc nh bngcc phng php khc nhau l:

Phng php Khong nng (%) V dPhng php ph pht x 10-5 10-4 Vi B 10-5

Phng php o mu, so mu 4 x 10-7 10-4 Al 10-6Quang ph ngn la 10-6 10-5 Ca 10-6

phn tch hunh quang 10-6 10-5 Ca 10-6Cc ph 10-8 10-6 In 10-6

phn tch kch hot 10-9 10-8 Au 10-9

xc nh cc tp cht v cc lng nh, ngi ta rt hay dng nhng phngphp khc nhau tch v lm giu nhng lng vt ca cc nguyn t cn xc nh. thc hin iu , ngi ta s dng cc phng php sau:

- Kt ta cc hp cht kh tan v cng kt;- Tch bng in ha;- Chit;- Ct cc cht d bay hi;- Tch bng sc k;- Nng chy vng (kt tinh li vng);

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- S tuyn ni v cc phng php khc.

Trong ha hc phn tch , cc phng php chit, tch v lm giu lng vt ccyu t c ngha cc k quan trng. Cc phng php ny gi vai tr quan trng nhvy, trc ht l v cc phng php phn tch hin c b hn ch bi nhy v tnhchn lc; khi phn tch cc kim loi, cc hp kim, cc vt liu bn dn, cc loi qung,thuc th ha hc bng cc phng php phn tch ha l, nhy v tnh chn lc bgim i do nh hng ca cht c thnh phn ch yu.

S kt hp phng php lm giu vi cc phng php phn tch vt l (v d nhkt hp phng php chit bng cc dung mi hu c vi cc phng php quang phpht x, ph quang ngn la, quang ph hp th nguyn t, trc quang v cc phngphp khc) m ra kh nng xc nh cc vt nguyn t trc tip trong hu c, trnhc giai on tch trc cc nguyn t cn xc nh ra khi phn chit.

S kt hp cc phng php lm giu cc lng vt ca cc tp cht vi ccphng php xc nh ha l (nh cc ph, trc quang, v. v) lm tng nhy cacc phng php ln rt nhiu, cn vic s dng s to phc cho php nng cao tnhchn lc ca cc phng php.

S tch v lm giu cc nguyn t ha hc v cc hp cht ca chng da trn slm chuyn dch cn bng ha hc ng v pha d nh. C ch lm chuyn dch cnbng c s dng, v d nh, i vi cc phn ng:

- Kt ta ha tan;

- Chit gii chit;

- Hp ph gii hp ph;

- Chng ct ngng t; v. v

2. Phng php kt ta cc hp cht t tan v s cng kt:

Trong phn tch ha hc, s kt ta cc hp cht kh tan c ng dng:

a) tch cc hp phn khc nhau ca cc hn hp phc tp;b) pht hin cc cation v cc anion;c) nh lng cc hp phn ca mt cht ring bit hoc hn hp cc cht.

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Cc cht kt ta: cc hp cht ha hc a dng c s dng lm cht kt tanhm phn chia v tch cc cu t ring bit ra khi hn hp phn tch . Trong , cccht thng c dng nht l:

- Hydrogen sulfide, dng kt ta cc ion ca cc nhm phn tch V, IV v mtphn nhm III di dng sulfide v dng phn hy cc anion AsO 33-, AsO43-,VO3-, MoO42-, WO42-, ti nhng pH xc nh;

- Dung dch nc ca ammonium, dng kt ta cc cation ca beryllium, ferrum(III), aluminium, thallium, gallium, indium, niobium, tantalum, uranium, ccnguyn t t him, v. v, cc phosphate kim loi kim v ammonium;

- Sodium acetate;- Cc kim n da;- Ammonium thiosulfate; v. v

Cc cht kt ta hu c: c s dng rt rng ri trong phn tch nh lng.Chng c dng iu ch dung dch chun ( chun ), lm cc cht ch th, cccht che, cht kt ta, v. v

u im ca cc cht kt ta hu c: Cc cht kt ta hu c c mt lot uim so vi cc cht kt ta v c thng thng nh:

- Khi dng cc cht kt ta hu c, c th kt ta v phn tch cc nguyn t khcnhau t nhng hn hp rt phc tp.

- Cc kt ta thu c bng cch dng cc cht kt ta hu c d lc v ra, nh, ta d dng ra cc tp cht c trong dung dch phn tch khi kt ta.

- Cc kt ta thu c khi dng cc cht kt ta hu c cho tc dng vi cc cationhoc anion c phn t lng ln. Do , chnh xc ca php phn tch ctng ln.

- Trong thnh phn cc kt ta l cc hp cht hu c c cc cu t hu c thngcha t tp cht c kt ta theo.

ng dng cc cht kt ta hu c trong phn tch nh lng: trong phn tchnh lng, kt ta v tch nhiu cation, ngi ta dng dithizone, cupferron, pyridine,8-oxyquinoline, dng phenylarsonic acid lm cht kt ta c chn lc cao i viniobium v tantalum, diethyl dithiophosphoric acid v cc ng ng ca n kt ta vtch mt lot nguyn t, 6- hoc 8-methylquinoline kt ta wolfram; 1-8 aminonaphthalene sulfonate ca magnesium kt ta ion sodium khi c mt ion kalium vnhiu ion khc.

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Thc nghim chng t rng, bng cch thay i pH ca dung dch, thng c thtin hnh c s kt ta ln lt v tch c nhiu cation khc nhau bng cng mtcht kt ta hu c. V d: t dung dch cupferron acid (acid mnh) ch kt ta c ccion ca niobium, tantalium, titanium, zirconium, vanadium, iron (III), tin v cho phptch chng khi cc ion khng kt ta trong iu kin l aluminum, chromium,uranium (VI), beryllium, manganese, nickel, cobalt, zinc, phosphorus v boron.

Khi dng tan ca mt s kt ta thu c bng cc cht kt ta hu c trongcc dung mi hu c, c th chit c chng.

Phng php cng kt: nhn chung c cc u im sau: n gin, hiu qu cao,nn mu phn tch c chuyn t phc tp sang n gin hn. Tuy nhin, nhc imchnh ca phng php l mt rt nhiu thi gian, nn cng t c s dng hn so vicc phng php khc.

Kt hp vi s cng kt lm giu cc nguyn t. Dng c cht cng kt v cv hu c, y l mt trong cc phng php hiu nghim dng lm giu cc nguynt.

3. Cc phng php tch in ha:

Cc phng php tch in ha da trn vic tch cht cn xc nh trn in cctr di dng nguyn t hoc kt ta khng tan khi cho mt dng in mt chiu i quadung dch phn tch.

Cc phng php ny rt ph bin khi dng tch cc hp cht ca a s ccnguyn t ha hc, v chng khng i hi phi a cc cht l vo dung dch phn tch .

Khi dng cc phng php kt ta in ha khc nhau vi vic s dng cc ccplatin hoc cc cc khc, cng vi catod thy ngn v dng phng php ni in phn,c th tch c cc cation aluminium, titanium, zirconium, vanadium, uranium khi cccation chromium, iron, cobalt, nickel, zinc, cophng phper, silver, cadung miium,germanium, molybdenum, tin, bismuth v cc nguyn t khc. Cng c th tch cc tpcht khi cc cu t chnh khi phn tch cc kim loi mu, cc hp kim ca chng v v.v

C th tch c cc hn hp phc tp gm cc ion khc nhau, c kh nng b ktta in bng cch chn cht in ly thch hp hoc tin hnh in phn c s iu chnht ng th in cc s kt ta in xy ra.

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Kt ta trn catod thy ngn: l mt dng tch in phn c bit. Trongphng php ny, di tc dng ca dng in, cc kim loi b tch ra trn thy ngn vto thnh hn hng. Do , s kt ta v tch nhiu kim loi xy ra rt nhanh v nhlng. Mt s kim loi khng kt ta c trn catod rn, nh iron, nhng li kt ta trncatod thy ngn. Tuy vy, mt lot nguyn t, nh aluminium, khng b kt ta trncatod thy ngn.

Dng catod thy ngn c th tch c:

- Aluminium khi ferrum, zinc v cophng phper;- Titanium khi indium, rhenium, molybdenum, germanium;- Vanadium khi molybdenum;- Cc hp cht ca phosphorus v arsenic khi tt c cc nguyn t tch c ra

trn catod thy ngn (iron, zinc, cobalt, chromium, silver, cophng phper,cadung miium, mercury, tin, platinum, gold)

Cc phng php in ha khng ch c dng tch v kt ta cc nguyn tm cn lm giu cht cn xc nh.

S lm giu theo loi ny c thc hin theo phng php cc ph hn hng.Bn cht ca phng php ny nh sau: bng cch in phn trong thi gian no thng vi dng gii hn, nguyn t cn xc nh c lm giu di dng hn hng tdung dch long ln cc git thy ngn (c dng vi vai tr vi in cc). Sau ghing cong ha tan hn hng khi bin thin in p tuyn tnh vi thi gian. Khi , trncc ph xut hin cc peak anod, v tr ca chng v phng din th c trng chobn cht ca cht, chiu cao ca peak c trng cho nng .

S kt hp phng php lm giu in ha cc nguyn t cn xc nh trn gitthy ngn tnh vi s phn cc tip theo hn hng thu c lm nhy ca phngphp c nng ln vi bc so vi phng php cc ph thng thng. iu ny c ngha thc tin ln i vi vic phn tch cc kim loi c bit tinh khit, cc thuc thha hc v cc vt liu bn dn.

4. Phng php chit:

Phng php chit da trn s rt cht bng cc dung mi hu c. iu kin chyu tch c cht cn phn tch bng phng php chit l tan ca cht c chitrt trong dung mi hu c.

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Trong thc tin phn tch , cht c chit thng c to thnh do phn ngxy ra trong mi trng nc, trong cc ion cn xc nh tng tc vi cc thuc th,m ch yu l thuc th hu c. Trong trng hp ny, dung mi hu c phi khngc trn ln vi nc. Phng php chit cho php ta tch c nhng lng cht rtnh t nhng lng rt ln cc sn phm em phn tch .

Chit bng cc dung mi hu c c ng dng rt rng ri, khng nhng ch tch m cn lm giu cc nguyn t. Hp cht ca cc nguyn t cn lm giu cchit bng cc dung mi hu c; i khi s lm giu bng cch chit c thc hin bngcch chit cc hp cht ca nguyn t chnh, cn cc tp cht l c gi li trong lpnc.

Trong nhiu trng hp, s lm giu tp cht bng phng php chit c nhiuu im ni bt hn so vi cc phng php lm giu khc. Chng hn, khi so snh nhy ca phng php chit vi phng php cng kt, th phng php chit nhy hn.ng ch l s kt hp phng php chit vi cc phng php xc nh tip theo(nh: phng php quang ph, phng x, cc ph) Trong s cc phng php kt hp, phng php phn tch chit trc quang l phng php c ngha nht, v c nhy v tnh chn lc cao. Trong cc phng php trn, qu trnh thu cdung dchmuc kt hp ng thi vi qu trnh chit, tch cht cn xc nh, do qu trnh xcnh cng khng phc tp.

Trong ha phn tch , ngi ta chia cc h chit thnh:

- H lng lng;- H lng rn.

Lm giu bng chit: Ngi ta s dng mt s phng php lm giu dng ccdung mi hu c, nh sau:

a) Chit chu k, trong qu trnh ny, cht cn chit c chit bng cch lc vi chtdng chit trong mt phu chia . Khi , mc chit Rn bng:

y: Vn v VH2O th tch ca lp hu c v lp nc, K h s phn b, n sln chit.

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ngha vt l ca phng trnh: Vic chit nhiu ln, mi ln bng nhng lngnh dung mi tt hn chit 1 2 ln bng lng dung mi ln hn. Mc chit ctng ln cng vi s ln chit n khi dng cng mt th tch dung mi cho trc.

b) Chit lin tc c thc hin trong nhng thit b c bit;c) Chit ngc dng.

Ngoi ra, cn mt vi phng php khc.

nh hng ca nhng yu t khc nhau n s tch: Vic tch hn hp hngph phn tch v s lm giu cc tp cht vi lng bng phng php chit ch c kt qukhi thc hin nghim ngt cc iu kin xc nh khi chit. Trong s , cc yu t cnh hng nhiu n kt qu ca vic chit l pH ca mi trng, thnh phn mui cadung dch, s to phc, bc oxy ha ca cc nguyn t cn tch, nhit , v. v kimtra hon ton ca s tch, ngi ta dng cc phng php ha hc, quang ph vphng x.

So snh phng php chit, tch v lm giu vi cc phng php khc:Chit l mt trong nhng phng php ph bin nht trong thc tin phn tch . u imquan trng nht ca phng php chit l: cho php ta khng ch tch c cc lng vtca cc nguyn t i km theo khi cht chnh m cn tch c cht chnh khi cclng vt. Nh vy, ta s dng c hiu qu hn cc phng php quang ph pht x,quang ph hp th nguyn t, cc ph phn tch cc cht c lm giu cha ccnguyn t tp cht.

Mt trong nhng phng php tch v lm giu khc phng php cng kt thng khng th gii quyt trit cc yu cu ra, v c s lm bn kt ta bi cctp cht c hi, hoc v tc kt ta rt chm. Trong trng hp , chit l phngphp khng th thay th c. Trong nhiu trng hp, khi kt hp vi cc phng phplm giu v tch khc (nh sc k, chng ct), phng php chit cn cho nhiu ktqu tt hn na.

Trong s nhng u im ca phng php chit, phi k n tnh vn nng, chn lc cao, s nhanh chng v n gin khi tin hnh v kt hp phng php ny vicc phng php ha hc, ha l v vt l xc nh cc nguyn t, th chit l phngphp ni bt v c ng dng ph bin nht.

Cc phng php chit thng dng: bao gm LLE (chit lng lng), SPE(chit pha rn), v SPME (vi chit pha rn).

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A. Phng php chit lng lng (LLE): [43] Nguyn tc: Phng php da trn s phn b cht tan khi c to thnh dng

phc lin hp hay ion phc vng khng mang in tch gia hai pha khng trnln, thng l cc dung mi hu c v nc.

Mt s h chit thng dng:o Chit lng vt cc ion kim loi nng (Cu, Pb, Cr, Cd, Fe, Zn, Ni, Mn, Co)

t nc bin vo dung mi methyl isobutyl ketone (MIBK) vi thuc thto phc APDC, sau xc nh nguyn t ny bng php o F AAS.

o To phc chelate vi NaDDC (sodium diethyl dithiocarbamate) t dungdch m ammonium citrate pH = 9.5, dung mi chit l MIBK.

B. Phng php chit pha rn (SPE): [43,44,45] Chit pha rn l qu trnh phn b cht tan gia hai pha lng rn. Pha rn c th

l ht silicagen xp, cc polymer hu c hoc cc loi nha trao i ion hay thanhot tnh. Qu trnh chit c th thc hin iu kin tnh hay ng. Cc cht bgi li trn pha rn c th c tch ra bng cch ra gii vi dung mi thch hp.Thng thng, th tch cn thit ra gii hon ton cht phn tch lun nh hnrt nhiu so vi th tch ca dung dch mu ban u, v th, mu cn c lmgiu.

V c bn, c ch chit SPE ging vi c ch tch trong phng php sc k lnghiu nng cao (HPLC), bao gm 3 c ch chnh, l: c ch hp ph pha thng,c ch hp ph pha o v c ch trao i ion. Tuy nhin, SPE khc vi HPLC ch: trong HPLC, s tch cht phn tch ra khi nhau trong h dng chy lin tcca pha ng, cn SPE gi cht phn tch li trn pha rn sau ra gii cht phntch ra khi pha rn vi dung mi ph hp. Cc cht phn tch s c tch khidung dch ban u vi nng m c hn v tinh khit hn.

K thut chit ny c cc u nhc im chnh sau y:o C tnh chn lc cao i vi mt nhm hp cht phn tch;o Cn bng chit nhanh t c v c tnh thun nghch;o Thch hp cho mu lng nh v phn tch lng vt cc cht;o Thao tc n gin v nhanh hn cc k thut chit khc;o Trong qu trnh chit lun c c s lm giu cht phn tch.

V vy, phng php ny c s dng ph bin trong phn tch, c bit l phntch hm lng cc cht vi lng c hi trong mi trng.

5. Phng php chng ct cc hp cht bay hi:

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Phng php ny c s dng rng ri trong trng hp m hp phn cn xcnh ca hn hp phn tch c th b chng ct khi un nng. Ngi ta un nng hn hpphn tch v thu hoc hp th hp phn bay hi c ct.

Phng php chng ct c dng tch:

a) Boron di dng ester d bay hi ca boric acid, v d B(OCH3)3;b) Arsenic di dng AsCl3;c) Germanium di dng GeCl4;d) Iron di dng FeCl3;e) Mercury di dng Hg; v. v

Phng php chng ct cng c s dng khi xc nh vanadium, wolfram,molybdenum, tin, antimony, iodine, fluorine, osmium, sulfur, selenium, tellurium, siliconv mt s nguyn t khc.

6. Cc phng php phn tch sc k:

Cc phng php phn tch sc k c s dng rng ri trong phn tch nhlng tch v lm giu cc cu t ring bit ca cc hn hp phc tp ca cc cht v

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c v hu c. Cc cu t tch c xc nh bng cc phng php ha hc thngthng, cc phng php phn tch vt l hoc ha l. Trong phn tch nh lng,phng php c s dng ph bin nht tch cc hp phn ca cc cht phn tch lphng php sc k trao i ion:

a) Tch cc cation khi mt s anion;b) Tch cc cation;c) Tch cc anion;d) Tch tp cht v iu ch cc dung dch tinh khit ha hc;e) Xc nh nng tng ca cc cht in ly c trong dung dch;f) Lm giu cc loi ion ca cht vi tp cht t cc dung dch7. Phng php nng chy vng (kt tinh li vng):

L mt trong cc phng php tch v lm sch cc cht mc cao c sdng trong ha phn tch. Phng php nng chy vng, hoc tnh ch vng (kt tinh livng) l mt vt l tinh th dng tinh luyn cc kim loi, cc vt liu bn dn, cchp cht v c v hu c.

Phng php da trn s nng chy mt phn nh (vng) ca cht cn tinh ch vchuyn vng nng chy dc theo mt thanh ti. Khi , trn mt b mt phn chiathnh hai lp rn v lng, c gi l mt kt tinh, xy ra s kt tinh cht, cn trn mtkhc, gi l mt nng chy phn mi ca vt liu, ngi ta cho chy lin tip mt svng nng chy.

Nh vy, s lm sch xy ra c l do s phn b cc cht gia cc pha rn vpha lng tip xc vi nhau, tan ca cc tp cht trong khc nhau: trn b mt nycht tinh khit c kt tinh, trong khi trn b mt khc, tp cht c tch t, cc tpcht c di chuyn bi cc vng chy theo hng chuyn ng ca chng hoc theo

hng ngc li ty thuc vo h s phn b K. H s phn b l thc

o s phn b ca cc cht v c biu th bng t s nng ca tp cht trong pha rnv pha lng.

- Khi K < 1: tp cht c lm giu trong vng chy v do kt qu ca vic nngchy nhiu ln, tp cht c chuyn v cui thanh.

- Khi K > 1: tp cht c lm giu trong pha rn v di chuyn theo hng ngcli v pha u thanh.

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Tc di chuyn ca cc vng, theo quy lut, khng vt qu 1 2 mm/pht. Cth t c s lm sch cao bng cch cho di chuyn nhiu ln cc vng theo cngmt pha. Cht c lm sch c tch khi khng kh ca kh quyn. Cc vng nngchy c to nn do s chuyn dng ca cht cn lm sch hoc bng dng c t nng(dng cao tn, n kh, tia in).

Phng php nng chy vng c kh nng thu c cc cht c bit tinh khit,ch cha 10-7 10-9 % tp cht.

8. Phng php tuyn ni:

Phng php tuyn ni l phng php tch cht da trn vic s dng s khcnhau ca cc tnh cht ha l thuc cc phn t trong cu t. V d, cc ht sulfide cckim loi k nc, khng b thm nc, do nu cho vo nc qung c nghinnh th cc phn t qung silica thm nc, c t trng ln, s b chm, cn cc phn tsulfide kim loi c nghin nh khng b thm nc nn khng chm. Nu ta lm sibt hn hp cn tch bng mt lung khng kh hoc bng mt phng php khc, thcc phn t ca huyn ph qung c tuyn b li cun bi bt v c tch t lnmt nc to thnh bt qung. S tuyn ni xy ra khi trn hn hp cc cht rn cnghin nh khng ch vi nc m cn vi cc loi du, cc loi thuc th c bit

Phng php tuyn ni m ra kh nng lm giu cc hp cht c cha cc nguynt khc nhau bng cch tch cc tp cht km theo chng. Phng php tuyn ni c tnhchn lc, cho php ta khng ch tch nhng hp cht cn ly ra khi m cn c khnng tch tt cc hp cht ring bit. Bng phng php tuyn ni, ngi ta tch ccc loi khong ring bit ra khi qung a kim, lm giu c cc loi tinh qung cawolfram, tin, titanium v cc kim loi khc, tch cc loi qung sulfide, lead oxyt, zinc,cophng phper, molybdenum, v. v khi nhau. Phng php tuyn ni ngy cng c ngha ln trong vic tch cc mui hu c v cc hp cht hu c.

Cc cht tuyn ni: lm thay i tnh cht ha l b mt cc phn t qung,ngi ta dng cc cht v c v hu c c bit cc cht tuyn ni, nh cc acid hu cv cc mui ca chng, cc xanthogenate tan trong nc, cc dithiophosphate Bngcc cht tuyn ni, ngi ta tch c cc khong liu v cc mui a dng nht thngkhn tch c bng cc phng php thng thng.

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II. ng dng ca phng php solid-phase microextraction (SPME) trongvic xc nh thuc dit c trong nhng mu mi trng:

1. S dng phng php chit pha rn (SPE) phn tch hm lng thuc trsu, bao gm triazine v cc sn phm phn hy ca n, trong t v b mtnc: [36]

S chun b mu cho k thut chit pha rn ln u tin c gii thiu vo gia nhng nm 70 [23]. N c thng mi ha vo nm 1978, thay th cho k thut chit lng lng LLE [24]. Ct chit pha rn v a chit pha rn gi y c cung ng bi nhiu nh cung cp v c dng rng ri trong ha hc.

Trong qu trnh chit pha rn thng thng, cht lng c a qua cht hp th c nn trong l thy tinh hoc c nhi trong ct chit bng nha P.P hoc c nn dng a. Kt qu l cht phn tch c gi li trn cht hp th. Cht hp th sau c ra (gii hp) vi 1 lng nh dung mi ct t mi lin kt gia cht phn tch v cht hp th. Phng php chit pha rn c la chn da trn s nh gi thuc tr su v nng v lng nc c s dng cho qu trnh gii hp [25]. Vic s dng dung mi ca qu trnh chit pha rn khi s dng a chit l 90%, t hn khi dng k thut chit lng lng, v ln n 20%, t hn khi dng ct chit pha rn. Hn na, vic chit pha rn khi s dng a chit cn loi tr c cc vn m khi s dng ct chit khng gii quyt c [26]. l vic s dng dung mi vi lu lng khc nhau trong qu trnh hp th/gii hp. V theo nghin cu, vic dng a chit vi ng knh ln cth b tr cho s khc nhau ny. Tht ra, lng dung mi c dng i vi a chit c th tng ng hay thm ch cn cao hn i vi ct chit, tt c ch ph thuc vo khilng ht dng lm cht hp th c nhi trong ct chit v ng knh ca a chit docc ht hp th nn li. i vi phng php quy chun, ph p dng k thut ct chit pha rn cho mi mu c d on l r hn ph khi p dng a chit pha rn v LLE ln lt l 30 v 50%. [25]. T l ny c th cao hn nu chit vi s lng ln.

Methanol thng c dng hot ha ct C18 v to ra hng lot chui k nc lm tng tnh hiu qu ca din tch b mt v loi tr s nhim bn gy ra bi Benzylsulphonic acid [27,28]. Mu nc cng c tng cng ti thiu 1% methanol tip tc lm t pha tnh. iu ny c th ci thin t l hon lu i vi lng ln thuc tr su, bao gm c triazine. Ngc li, i vi nhng sn phm phn hy, l nhng sn phm thng phn cc nhiu hn hp cht ban u to ra n, c l khng c gi li lm cht i din cho s hot ha hu hiu [29]. Gn y s pht trin phong ph cht

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hp th mi cho K thut chit pha rn i hi khng cn iu kin chit tch trc [30]. S ng dng vt liu ny, vt liu m tit kim thi gian v thit thc hn cho vic chit tch ngoi cng trng, c mong i s c ng dng vo nc ngm trong thi gianti.

Nc ngm v nc mt thng phi c qua lc trc khi chit tch thuc tr su bng k thut chit pha rn. Vic lc trc khi chit thng qua mng lc Teflon c kch thc l 0.45 m c khuyn co khi s dng ct chit C8 [31] hoc a chit Empore [32]. Vic lc trc khi chit s khng nh hng n vic xc nh Triazine v cc sn phm thoi bin ca chng, k t khi nhng hp cht ny c logarit ca h s phn b gn bng 2, ng ngha vi vic chng phn b 99.5 % trong nc [33,34].

Bng 3 din t phn ln k thut SPE v SPME, c dng cho vic xc nh a d lng ca thuc tr su, bao gm Triazine v nhng sn phm thoi bin ca chng, k c trong nc ngm v nc mt.

a. Cht hp th:

S tng tc gia cht hp th v cht phn tch c chia lm 3 loi: khng cc, c cc, v ion. Cht hp th khng cc thng c la chn vic chit tch triazine t nc. Ngc li, cc sn phm phn hy, c cha nhng nhm chc phn cc nh -OH,

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-C=O, -NH2, v -C-SH, cn nhng cht hp th phn cc. Nhng cht hp th phn cc c khuynh hng to lin kt hydro bn. Vic cht hp th phn cc gi c nhng hpcht phn cc c thc thi ha bng dung mi khng phn cc. Cht phn tch hnh thnh cation (ion mang in tch dng) bao gm nhm NH2 , cht phn tch hnh thnh anion (ion mang in tch dng) bao gm COOH, -SO3H, PO43-. Vic xy ra tng tc ion th cht hp th mang ion m s kt hp vi ion dng cn li, v cht hp th mang ion dng s kt hp vi ion m cn li. vic lu gi c ti u, gi tr pH ca hn hp phi l 2 thp hn hng s phn li ca cation v bng 2 cao hn hng s phn li ca anion [35].

Cc chng loi cht hp th c dng trong k thut chit pha rn chit tch triazine v nhng sn phm phn hy ca chng trong nc. V s dng rng ri nht trong lin kt ha hc gia C8 v C18 vi SiO2, C en v nha polymer (v d nh PLRP-S). Nhng hp cht phn cc nht, v d nh DIA, DEA, HA v metribuzin, cn nhng cht hp th c lu lng rt thp, ngoi tr vt liu carbon, v 1 vi nhm mch thng styrene-divinylbenzene (Envi-Chrom P). Trong vi nm tr li y, nha polymer bin i ha hc vi nhm chc phn cc pht trin v c ng dng trong chit pharn p dng cho cc hp cht ny, v th tch ca nhng cht hp th cao hn hn nhng hp cht phn cc nht vi nhng tn hiu khng i. Nhng vt liu cha nhm mch thng styrene-divinylbenzene mi, nh LiChrolut EN, Styrosob and Macronet Hypersol, Isolute ENV v HYSphere-1 c a vo s dng. Nhng cht hp th ny c lin kt gia cc mch cao v v vy, vic m cu trc (i vi nhng vt liu xp cao) s lm tng din tch b mt v cho php xy ra tng tc - gia cht phn tch v cht hp th. iu ny c ngha, khi nhng cht hp th mch thng c dng th lu lng th tch dng s cao hn. Ba cht hp th cho php vic hi lu atrazine v simazine (80 - 86%) trong nc l nh nhau.

Cht hp th N Alkyl silica th thng thch hp trong vic chit tch a d lng i vi nhng cht phn tch c h s phn b ln hn 103. S ng dng i vi N Alkyl silica c ci thin bng vic tng tng tc k nc v s dng din tch b mt silica cao. Tuy nhin, nh th vn cha gi li cc hp cht phn cc nh polymer SDB lm.

Phng php a d lng da trn hnh thc chit pha rn off-line vi GC-MS, LC-UV-DAD and LC-MS c u tin pht trin Chu u trong vic iu khin thuc tr su. Nhng cht hp th khc c kim tra: Isolut C18, LiChrolut, Envi 18, SDB,OASIS, Envichrom and Envi-carb. Nhng cht hp th nh SDB, OASIS, Envichrom

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and Envi-carb xut hin nh l 1 iu ha hn cho vic chit tch cc hp cht phn cc, bao gm c triazine v cc sn phm phn hy ca chng.

Knutsson et al. [37] tin hnh trn k thut chit qua mng lc nc h tr; v iu ny c xem l s la chn tt hn vic dng k thut chit pha rn s dng ct chit C18. Trong vn mng lc nc h tr c bao gm lun mng teflon c ph ybng dung mi khng ho tan vo nc. C hai knh, knh cho (mu) v knh nhn (cht hp th), chng c hnh thnh mt trong hai bn ca mng lc, cho cht phn tch thm qua. Cht nhn mang tnh acid c p dng cho propazine v simazine, cht c hng s phn ly thp [37], nhng phng php vn cn phi c ci tin lin tc. Mc d k thut SLM c th chit cc hp cht phn cc, nhng d sao n c giihn trong vic hnh thnh nhng loi ion ho.

Nhng tnh nng ca cc loi cht hp th c dng trong k thut SPE cho vic xc nh a d lng ca thuc tr su, bao gm triazine v cc sn phm phn hy, trong nc ngm v nc mt c miu t trong bng 3.

b. Ct chit rn:

Ct chit pha rn c ng dng vi nhiu loi kch c, vi lu lng t thp hn 1 mL n hn 50 mL. Khi la chn kch thc ti u cho ct chit, yu t cn quan tm l kh nng gi li tt c cht phn tch trong mu, lu lng mu, v th tch nc dng lm sch mu sau khi ra gii. Tng qut, khi lng ca cht phn tch v nhng hpcht gy nh hng c gi li bi cht hp th s phi nh hn 5% khi lng cht hp th. Theo quy tc, th tch gii hp phi bng 2 5 ln n v th tch c s ca ct chit pha rn [35]. Th tch ny c th cao hn, tuy nhin, ph thuc vo tnh cht ca thuc tr su c chn, bn cht ca cht hp th, loi cht gii hp, v k thut phn tch c s dng.

Vic chit pha rn s dng ct chit cho vic xc nh a d lng ca thuc tr su, bao gm triazine v nhng sn phm phn hy, c trong nc ngm v nc mt, s c miu t trong bng 3.

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18


19


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c. a chit pha:

Dng khc ca ct chit pha l a chit trong cht hp th ( dng polymer hay l silica) c nn thnh dng li teflon hoc si thy tinh. a chit dng si thy tinh s dy hn, cng hn, s cung cp dng chy cao hn l khi dng mng teflon, v s tt hn nu a chit c ghp vo nhau thnh mt khi thng nht. Nhng phn t hp th c nn li thnh dng a s nh hn dng ct chit (ng knh 8 m so vi 40 m).ng hp th mu ngn v kch thc cu t nh cho php vic gi li cht phn tch hu hiu hn vi dng chy cao i qua cht hp th, c th so snh vi ct chit. achit c dng lm gim thi gian phn tch i vi lu lng mu ln cn phn tch. a chit c nhiu ng knh khc nhau (4.6 mm, 47 mm, 93 mm), vi lu lng ln cho php tc dng chy nhanh hn. 47 mm l ng knh a chit thng dng, v n ph hp vi cc phng php tiu chun (th tch mu nc 0.5 11). a chit c ng knh nh (4.6 mm) s dng kt hp trc tip vi h thng LC [38].

Barcelo et al. [38] cho thy vic hon lu ca a chit dng Empore C18 (1 41) i vi lng ln thuc tr su s cao hn, bao gm atrazine, simazine, v cyanazine: 80 125%, nhng sn phm phn hy (DEA v DIA): 3 17%. a chit nu so vi ct chit khi dng chung cng mt vt liu s c dng chy cao hn do khng c cht cho, cht nhn v lu lng chuyn s nhanh hn c cung cp bi kch thc ca nhng cu t nhm [38]. Viana et al. [39] chng minh rng a chit C8 s hon lu atrazine,prometryn v propazine cao hn vic dng a chit C18, c th (87 93%) so vi (66 67%). Pichon et al. [40] thc hin phng php a d lng bng vic s dng a chit ghp kt hp vi LC v Baker Speedisk DVB i vi nhng hp cht phn cc v a Silica C18 cho nhng hp cht khng phn cc. Vic thc hin trn 1 L mu vi khong cho php DLs t 0.01 n 0.05 g/L.

d. Vi chit pha rn (SPME):

Vi chit pha rn (SPME) ln u tin c cc nh nghin cu a vo phn tch vo nm 1989. K thut gm c 2 bc: Bc 1, hp th cht phn tch t hn hp cht lng bng cch ngm si SPME vo trong hn hp, bc 2, gii hp cht phn tch t lppolymer, c mang i t dng kh c thi t vi nng GC. K thut SPME d dng kt hp vi sc k kh v sc k lng bng cch s dng thit b c bit. Vi phun nng

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c r nhnh/khng r nhnh, vi phun c lp trnh c vch ngn (SPI) hay ct sc k kh c cng pha trn ct c th c s dng cho vic gii hp nhit ca cht phn tch t si SPME. Vic s dng vi phun GC trong gii hp nhit ca k thut SPME ch dnh cho nhng hp cht bn nhit. Ngc li, nhng cht phn tch khng bn nhit c th c phn tch bi SPME-LC hay SPME-GC (vic chit tch s din ra sau khi cc dn xut trong cht lng c thc thi). Nhng chng loi si SPME c mt trn th trng u ang c s dng cho vic xc nh cc hp cht khc nhau: 100 m polydimethylsiloxane (PDMS), 30 m PDMS, 7 m PDMS, 65 m Carbowax-divinylbenzene (CW-DVB), 85 m polyacylate (PA), 65 m PDMS-DVB, v 75 m Carboxen-polydimethylsiloxane (CX-PDMS). PDMS, c lin quan n khng phn cc, c s dng thng xuyn. i vi triazine, tuy nhin, lp ph polyacylate 85 m thchhp hn khi n l si a nc [162]. Vi k thut ny, DL c th thp c 0.1 g/L (gii hn c thit lp bi EU ch dnh cho thuc tr su c trong nc ung) nu c kt hp vi vi phun GC dng dng kh nitrogen-phosphorus. SPME l k thut chit tch cn bng hn l k thut chit tch y , v n khng th hon nguyn 100% cht phn tch c trong mu v n cng khng phn nh li ton b qu trnh chit. Vic hp thc ho phng php c l v kt qu c so snh vi kt qu dng k thut chit tch tham kho trn cng mt mu, cng mt cht phn tch. Nhng s thay th v thm chun vo cn iu khin hiu sut ca hn hp.

Trong nh gi vic s dng si CW-DVB 65 m kt hp vi SPME-GC-NPD, ni ln rng si ny nhy vi 12 thuc tr su, bao gm atrazine, prometon, v terbutryn. PDMS-DVB, CW-DVB v PA th thch hp vi nhng cht phn cc, thuc dit c c cha nitrogen. Vic th nghim trong ni b phng LAB, bao gm vic phn tch triazine v nhng sn phm phn hy chng minh tnh hp l ca phng php SPME khi s dng si CW-DVB kt hp vi vic thm NaCl v kt ni vi h thng GC. Kt qu t c vi nhng phng php ny chng minh rng SPME l phng php thch hp cho vic phn tch mt s thuc tr su. Nhng vic s dng k thut ny li b gii hn trong vic chit tch nhng thuc tr su phn cc do loi si dng phn tch.

S ci tin c thc hin trong qu trnh ci thin k thut SPME. Giao din LC-SPME c ci thin, v pha mi c da trn s hp th rn-lng (CW-DVB v PDMS-DVB) c pht trin vi nm tr li y trong vic phn tch hp cht bng LC. Vic thay i, lm mi ph kin ca h thng LC, c gi l SPME trong ng, gn y cng c pht trin. K thut phun kh v phun mu trong kim tim v tr phun, khi

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gii hp cho dung mi kh trong tnh trng b tc ng. Tr li hnh thc t vn n vi phun chuyn cht phn tch vo ct phn tch.

e. Chit min dch:

K thut chit min dch bao gm vic s dng ct chit SPE c lm y bng cc vt liu khng th, c lin kt vi nhng cht hp th nn Silica. Nhng loi vt liu ny, c gi l min nhim i lc vi nhng cht hp th, c s dng chit triazine t mu nc [130]. Chng c lm r i vi tng hp cht ring; v vy,DIA khng hi lu c nhng cht hp th min dch vi s khng atrazine, trong khi HA v prometon khng hi lu c nhng cht hp th min dch vi s khng simazine.

Vic so snh gia cht hp th min dch vi s khng atrazine v cht hp th PLRP-S trong vic chit triazine t sng Seine (50 mL) bng vic s dng k thut SPE chng minh rng cht hp th min dch c tnh chn lc v hiu sut cao. Thi gian gn y, Dalluge et al. [41] bo co v vic s dng phi hp trc tip k thut chit pha rn da trn nhng loi vt liu min nhim i lc vi nhng cht hp th v sc k kh cho vic xc nh s-triazine c trong mu nc. Nhng cht hp th c mong i l x l tt i vi mi loi thuc tr su. iu ny s cho php vic chit tch mt vi hp cht phn cc t nc do s tip xc gia khng nguyn khng th khng cn da trn qu trnh k nc.

f. Polymer ng du phn t (MIP):

Ni dung ca k thut ny c truyn cm hng bi hc thuyt hnh thnh khngth Pauling, trong khng nguyn c dng nh l mt mu h tr trong vic sp xp li nhng chui khng th polypeptide v vy khng th c cu hnh 3 chiu b sung cho phn t khng nguyn. K thut ng du phn t c n lc thc hin u tin vonm 1949 bng cch ng du thuc nhum ln silicagel. Tuy nhin, vn cha thnh cng cho n na u nhng nm 70 vic ng du thnh cng ln polymer hu c tng hp. K thut MIP tr nn ph bin khng ngng nhng nm tr li y. N c ng dng nhiu lnh vc khc nhau nh h dn truyn thuc, trong thuc enantioseparation, v nh vt liu dng chit pha rn trong lnh vc chit hydroxycoumarin, c tim nng l phng php chit c tnh chn lc. N c mong i l c li cho vic chit tch v lm sch cc loi thuc tr su phn cc t hn hp khng ng nht. ng dng phn tch trn triazine c tin hnh, bng cch s dng h thng off-line. Bng cch kt hp trc tip ct MIP-SPE vi ct C18, Bjarnason et al.

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[42] phn bit triazine t axit humic, t c nhn t lm giu ln n 100 vi s hon nguyn l 74 77%. Lanza v Sellergren [177] kim tra monomer 6 chc bng MIP methacrylic acid (MAA), methyl methacrylate (NMA), hydroxyethyl methacrylate(HEMA), N-vinyl-a-pyrrolidone (NVP), (trifluoromethyl)acrylic acid (TFM), v 4-vinylpyridine v pht hin ra rng MAA thch hp cho vic chit tch chlorotriazine hn.

Vic ti u ha MIP c th dn u trong vic phn bit hn hp cc cht v cho php vic chit tch mt vi cu t phn cc t nc nh tng tc gia polymer phn t khng cn da trn qu trnh k nc.

g. Kt lun:

Vic s dng qu nhiu thuc tr su dn n vic nhim ngun t v nc mt. Do , nhiu phng php a ta c pht trin xc nh hm lng thuc tr su, bao gm triazine v nhng sn phm phn hy ca n, trong cc nn. K thut SPE c chng minh l k thut tch cc hp cht ny trong nc tt nht. u im ca n l: nhanh chng, chnh xc, tn t dung mi, d dng a vo thc a, v khng tn nguyn liu. Vic phn tch thuc tr su, nh , tr nn d dng hn. Hin nay, c nhiu cht hp th c sn trong hp hoc a, bao gm cc cht khng phn cc, phn cc, cc ion, cc cht min dch v MIP. Nhng phng php t ng ha s dng k thut SPE kt hp vi nhiu cht hp th khc nhau hin ang c s dng kh rng ri,dn n vic khi lng mu nh (ch vi mL) v DLs thp (ng/L). Vi vic s dng SPE, mt lng ln cc thuc tr su, bao gm triazine v cc sn phm phn hy ca n, c xc nh hm lng mt cch d dng v hiu qu hn, vi lng mu nc t hn v dng dung mi t c hn.

2. S dng phng php vi chit pha rn (SPME) xc nh thuc dit c ctrong mu ly t mi trng: [22]

LLEGC hay SPMEGC hay sc k lng hiu nng cao (HPLC) l nhng phngphp phn tch truyn thng dng phn tch hm lng thuc dit c c trong mi trng. Phng php phn tch vi chit pha rn (SPME) khng cn dung mi, nhanh chng, nhy v thch hp phn tch hm lng thuc dit c, c ng dng rng ri trong nhiu loi mi trng.

a. Gii thiu:

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LLE v SPE l nhng phng php truyn thng c s dng trong phn tch hm lng thuc dit c trong cc mu mi trng. Phng php LLE cn mt lng lndung mi v thi gian chun b mu di. Ngc li, SPE cn lng dung mi t hn v thi gian chun b mu cng ngn hn so vi LLE. Nhng hn ch ca LLE v SPE cgim thiu ng k trong SPME.

SPME c bo co u tin bi Pawliszyn v ng s nm 1990 [1,2]. l phng php gm hai giai on thun li cho c vic chit v tin c c nn mu. Tronggiai on mt, si silica nng chy c ph ngoi bi mt pha polymer n nh s c tip xc vi nn mu ti vng cn phn tch gia nn v pha polymer n nh ni trn. giai on hai, si/cht phn tch c a vo dng c phn tch gii hp, tch v nhlng.

Vic ng dng phng php SPME phn tch d lng thuc dit c c bo co u tin vo nm 1995 bi Boyd-Boland v Pawliszyn [3] xc nh ng thi cc cht dit c c cha nitrogen trong cc mu t, nc v ru. T 1995, phng php SPME c s dng phn tch 81 hp cht t 15 h thuc dit c trong nhiu loi nn mi trng (t v nc) v nn sinh hc (mu, nc tiu v huyt thanh).

Nhng u im vt tri ca SPME so vi cc phng php phn tch truyn thng dng phn tch d lng thuc dit c khc l: SPME nhanh chng, n gin, khng cn dung mi, d dng t ng ha cho c thit b GC v HPLC, cho ph tuyn tnh cao v nhy cao.

b. Pha polymer n nh:

dy ca pha polymer v pha hn hp trong thng mi c lit k trong bng1.

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26


c. Ti u ha SPME:

C nhiu yu t nh hng n hiu qu ca SPME v chng c nh gi khi tin hnh pht trin phng php. Vi chit pha rn c ti u ha bng cch iu chnh cc thng s nh hng n cht hp th v gii hp. Cc thng s chnh nh hng n cht hp th trong pha n nh l loi si, thi gian chit, lc ion, pH, nhit , th tch mu, v s khuy trn. i vi phng php SPME-GC, cht gii hp l hm s ca thi gian v nhit . Trong khi , loi dung mi v th tch hay thi gian l rt quan trng trong cc ch SPME-HPLC.

d. ng dng trong phn tch:A. Cc mu t:

T nm 1995, nng trong t ca 21 hp cht t 5 h thuc dit c khc nhau c xc nh da vo k thut SPME (bng 2). C 3 phng php xc nh c bn: Mt l, s dng h huyn ph t/nc m c ly mu bng c phng php DI- ln HS-SPME [3,13,16,19]. Hai, Zambonin et al. s dng phng php tng t [10], trong huyn ph t/nc c ly tm, v nng thuc dit c trong pha nc c xc nh bi DI-SPME. Ba, cc ti liu ch ra rng DI-SPME ca phn hu c long thu c bng cch chit lng rn thng thng l phng php phn tch t SPME ng tin cy nht [18,20].

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B. Cc mu nc:

Nhiu phng php SPME c pht trin xc nh d lng thuc dit c trong cc mu nc. Cho n nay, c 36 bi bo khoa hc m t li nh lng ca 81 hp cht t 14 h thuc dit c khc nhau (Bng 3). c nhiu bo co v vic chit tch thuc dit c t nhiu mu nc khc nhau bao gm dung dch nc ngm, nc trn b mt, nc ct, nc Milli-Q, nc t lp tuyt trn cng tan ra, li bng, ru, nc cam p, v nc my. Dng phng php SPME, c th xc nh ng thi cc thuc dit c phenylurea [5], triazine [4,10,11], phenoxy [8,21], carbamate [6], v dinitroaniline [7]. Tng t, cc phng php m t li s pht hin cng lc cc hp cht t nhiu h thuc dit c khc nhau cng c bo co [3,12-17].

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Ti liu tham kho:[1] R. G. Berladi, J. Pawliszyn, Water Pollut. Res. J. Can. 24 (1989) 179.

[2] C. L. Arthur, J. Pawliszyn, Anal. Chem. 62 (1990) 2145.

[3] A.A. Boyd-Boland, J.B. Pawliszyn, J. Chromatogr. A 704 (1995) 163.

[4] I.J. Barnabas, J.R. Dean, I.A. Fowlis, S.P. Owen, J. Chromatogr. A 705 (1995) 305.

[5] A.C. Gerecke al et. J. Chromatogr. A 930 (2001) 9.

[6] Y. Gou, R. Eisert, J. Pawliszyn, J. Chromatogr. A 873 (2000) 137.

[7] F. Guan al et. J. Chromatogr. B 714 (1998) 205.

[8] M. Lee al et. Anal. Chem. 70 (1998) 1963.

[9] T. Nilsson al et. J. Chromatogr. A 826 (1998) 211.

[10] C.G. Zambonin, F. Catucci, F. Palmisano, Analyst 123 (1998) 2825.

[11] C.G. Zambonin, F. Palmisano, J. Chromatogr. A 874 (2000) 247.

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39

I. Cc phng php chit, tch v lm giu mu:1. Xc nh vt cc nguyn t (cc tp cht vi lng)2. Phng php kt ta cc hp cht t tan v s cng kt:3. Cc phng php tch in ha:4. Phng php chit:A. Phng php chit lng lng (LLE): [43]B. Phng php chit pha rn (SPE): [43,44,45]

5. Phng php chng ct cc hp cht bay hi:6. Cc phng php phn tch sc k:7. Phng php nng chy vng (kt tinh li vng):

II. ng dng ca phng php solid-phase microextraction (SPME) trong vic xc nh thuc dit c trong nhng mu mi trng:1. S dng phng php chit pha rn (SPE) phn tch hm lng thuc tr su, bao gm triazine v cc sn phm phn hy ca n, trong t v b mt nc: [36]a. Cht hp th:b. Ct chit rn:c. a chit pha:d. Vi chit pha rn (SPME):e. Chit min dch:f. Polymer ng du phn t (MIP):g. Kt lun:

2. S dng phng php vi chit pha rn (SPME) xc nh thuc dit c c trong mu ly t mi trng: [22]a. Gii thiu:b. Pha polymer n nh:c. Ti u ha SPME:d. ng dng trong phn tch:

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