estrategias de cromatografia para analizar pesticidas en agua

7/28/2019 Estrategias de Cromatografia Para Analizar Pesticidas en Agua

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ELSEVIER Journal of Chrom atography A , 754 (1996) 125-135

JOURNAL OFCHROMATOGRAPHYA

Rev i ew

Str a te g i e s fo r c hr o m a to g r a ph i c a na l y s i s o f pe s t i c i de r e s i due s i nw a t e r

Anna BalinovaPlant Protection Insti tute , Kos t inbrod 2230, Bulgaria

Abstract

A r e v i e w i s p re s e n t e d o f t h e m o d e r n t e c h n i q u e s a n d a p p r o a c h e s i n m e t h o d s f o r p e s t ic i d e r e s i d u e a n a l y s is i n w a t e rma t r i c e s . T h e s t a t e o f th e a r t o f th e in d iv id u a l s t e p s ( e x t r a c t io n , c l e a n - u p , s e p a r a t io n , id e n t i f i c a t io n , q u a n t i t a t io n ) o f th ec h r o m a t o g r a p h i c m e t h o d s i s r e v i e w e d w i t h e m p h a s i s l a i d o n e m e r g i n g t e c h n i q u e s w h i c h h a v e g a i n e d p o p u l a r i t y . T h e n e wa p p r o a c h e s a r e d i s c u s s e d wi th r e s p e c t to th e i r r e l e v a n c y to th e r e q u i r e m e n t s f o r in c r e a s in g th e s e n s i t iv i ty o f d e te c t io n a n dr e l i ab i l i t y o f i d e n ti f i c at i o n a n d q u a n t i t a ti o n a t l o w l e v e l s o f c o n c e n t r a ti o n s , a r i s i n g f r o m t h e E u r o p e a n C o m m u n i t y D r i n k i n gW a t e r D i r e c t i v e .K e y w o r d s . " R e v i e w s ; E n v i r o n m e n t a l a n a l y s i s ; W a t e r a n a l y s i s ; E x t r a c t i o n m e t h o d s ; P e s t i c i d e s

C o n t e n t s

1. Intr odu ctio n .................. ................... ................... ................... .................... ................... ................... .................... ................... 1252. Sam ple pretreatm ent ................................................................................................................................................................ 1262.1 . Li qu id -li qu id extractio n .................................................................................................................................................. 1262.2. Solid -phase extractio n ..................................................................................................................................................... 1272.3. Cou pled-co lum n liquid chrom atograp hy ........................................................................................................................... 1292.4. Solid -phase mic roextrac tion ............................................................................................................................................. 1292.5. Supe rcritical fluid extractio n ............................................................................................................................................ 1293. D eterm ina tion ................. .................... ................... ................... ................... .................... ................... ................... ................. 1303.1. Gas chrom atograp hy ....................................................................................................................................................... 1303.2 . HP LC .................. ................... ................... ................... .................... ................... ................... .................... ................... 1313.3. Hig h-perform ance thin-lay er chrom atograp hy ................................................................................................................... 132

4. Co nclu sion s .................. ................... ................... ................... .................... ................... ................... .................... ................... 133Re feren ces .................. .................... ................... ................... .................... ................... ................... ................... .................... ..... 133

I . I n t r o d u c t i o n

T h e M a x i m u m A d m i s s i b l e C o n c e n tr a t io n o f p e s -t i c i d e s in d r i n k i n g w a t e r , d e f i n e d b y E u r o p e a nC o m m u n i t y D r i n k i n g W a t e r D i r e c t i v e a s 0 .1 / z g 1 ~f o r i n d i v i d u a l p e s t i c i d e s a n d a s 0 . 5 / x g 1 - ~ f o r t h e

s u m o f p e s t i c i d e s [ 1 ] p o s e d c e r t a i n d e m a n d s t o t h ea n a l y t i c a l m e t h o d s f o r p e s t i c i d e r e s i d u e d e t e r m i n a -t i o n . I t i n i t i a t e d i n t e n s i v e r e s e a r c h a c t i v i t i e s t oi n c r e a s e t h e s e n s i t i v it y o f th e m e t h o d s a n d t h e i rr e l i a b i l i ty a t l o w l e v e l s o f c o n c e n t r a t i o n s . T h e e f f o r t st o i n c r e a s e t h e v a l i d it Y o f p e a k i d e n t i f i c a t i o n w e r e

0021-9673/96/$15.00 19 96 Elsevier Science B.V. All r ights reservedP I I S 0 0 2 1 - 9 6 7 3 ( 9 6 ) 0 0 4 0 9 - 8


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126 A . B a l in o v a / J . C h r o m a t o g r . A 7 5 4 ( 1 9 9 6 ) 1 2 5 - 1 3 5

es s en t i a l fo r avo i d i ng f a l s e pos i t i ve r e s u l t s . Theneces s i t y t o ex t r ac t l a rge vo l um es o f wa t e r s am p l esg a v e r i s e t o t h e d e v e l o p m e n t o f n e w t e c h n i q u e s f o rs am p l e p re t r ea t m en t . As m a t r i x e f f ec t s f rom t hewat e r can caus e e r ro r s i n de t e rm i na t i on and quan t i t a -t i on , r educ t i on o f t he m a t r i x i n t e r f e rences was a l s oan i m por t an t goa l i n t he e f fo r t s t o deve l op adequa t em e t h o d o l o g y a n d t e c h n i q u e s c a p a b l e o f d e t e r m i n i n gt he env i ronm en t a l l y i m por t an t pes t i c i des i n wa t e rs am p l es .

T h e g o a l o f th e w o r k w a s t o r e v i e w t h e e m e r g i n gt echn i ques and app roaches i n t he bas i c s t ep s o fc h r o m a t o g r a p h i c m e t h o d s f o r p e s t i c i d e a n a l y s e s i nd i f f e ren t t ypes o f wa t e r .

2. Sample pretreatment2.1. Liquid-liquid extraction

Ext rac t i on m e t hods a re con t i nua l l y be i ng r ev i s eda n d i m p r o v e d w i t h n e w t e c h n o l o g i e s . L i q u i d - l i q u i dex t r ac t i on (LLE) i s t he c l a s s i ca l app roach fo r pes -t i c i de ex t r ac t i on f rom wa t e r s am p l es [2 -11 ] . I t i sp e r f o r m e d b y r e p e t i t i v e e x t r a c t i o n o f 5 0 0 - 1 0 0 0 m ls am p l es i n a s epa ra t o ry funne l and d i ch l o rom et hanei s t he m os t popu l a r s o l ven t [3 -9 ] becaus e i t i sc a p a b l e o f e x t r a c ti n g c o m p o u n d s w i t h a w i d e r a n g eo f po l a r i t i e s and i s eas y t o evapo ra t e . There a renum erous exa m p l es on t he app l ica t i on o f t h is s i m p l et echn i que bu t on l y a f ew genera l works w i l l bem e n t i o n e d . D i f f e r e n t e x p e r i m e n t a l p r o c e d u r e s b a s e do n d i c h l o r o m e t h a n e L L E f r o m a q u e o u s m e d i a o fs em i -vo l a t i l e ana l y t e s ( i nc l ud i ng ha l ogena t ed pes -t i c i des ) l i s t ed i n t he EP A Targe t C om pounds L i s thave been eva l ua t ed [12 ] . EP A m et hods 8120 [13 ]and 8140 [14 ] u s e LL E p rocedu re fo r ana l y s i s o f 15o r g a n o c h l o r i n e ( O C ) a n d 2 1 o r g a n o p h o s p h o r u s ( O P )pes t i c i des r e s pec t i ve l y i n wa t e r s am p l es . F o r ex -t r ac t i on o f ac i d i c he rb i c i des f rom aqueous s am p l es ,a d j u s tm e n t t o p H < 2 , f o l l o w e d b y L L E w i t h d ie t h y ie t he r o r d i ch l o rom et hane were u s ed [ 15 ,16 ].

Th i s c l a s s i ca l app roach s hows m any d i s advan -t ages . I t i s no t app l i cab l e t o au t om at i on o f t heana l y t i ca l p rocedu re , r equ i r e s l a rge vo l um es o f t ox i cs o l ven t s and i s t i m e cons um i ng . F o rm at i on o f s t ab l e

em u l s i ons o f t en occu r s e s pec i a l l y w i t h h i gh l y po l -l u t ed s u r f ace wa t e r s . S i ng l e con t i nuous LLE hasb e e n r e c o m m e n d e d f o r s a m p l e s w h i c h f o r m e m u l -s i ons o r a r e o t he rwi s e d i f f i cu l t t o ex t r ac t by t hes epa ra t o ry funne l p rocedu re [12 ,17 ] . I t i s pe r fo rm edi n con t i nuous ex t r ac t o r s , des i gned t o ex t r ac t l a rgevo l um e s , fo r i n s t ance 1 1 wa t e r w i th s o l ven t s heav i e rt han wa t e r . The ex t r ac t o r s , a t t ached t o bo i l i ng f l a s kscon t a i n i ng 500 m l d i ch l o rom e t ane a re re f l uxed fo r 18h . The p rocedu re a l l ows fo r chang i ng t he pH o f t heaqueous m a t r i x and co l l ec t i on o f s epa ra t e f r ac t i onso f t h e e x t r a c t . T h e c o n t i n u o u s L L E i s r e c o m m e n d e das an e f f ec t i ve and l abo r s av i ng p rocedu re bu t i t ist i m e and t ox i c s o l ven t cons um i ng and i s u s ed a s ana l t e rna t i ve when LLE i s no t app l i cab l e [18 ] .

A l t hough t he t r ad i t i ona l LLE i s cons i de red ad i s advan t ageous p rocedu re , s om e recen t s t ud i es a r er e p o r t e d o n d e v e l o p m e n t o f n e w m o d i f i c a t i o n s .M i c r o l i q u i d - l i q u i d e x t r a c t i o n ( M L L E ) w a s d e -ve l oped as a s i m p l e a l t e rna t i ve m e t hod fo r ana l y s i so f o rgan i c com p ound s i n wa t e r [19] . Th i s app roachwas app l i ed fo r de t e rm i na t i on o f t he he rb i c i dea l ach l o r and t wo o f i t s m e t abo l i t e s [20 ] . The p r i nc i -p l e o f M L L E i s th e e x t r a c t io n o f a l a rg e v o l u m e o fw a t e r ( 4 0 0 m l ) w i t h a v e r y s m a l l v o l u m e o f s o l v e n t(500 / z l o f to l uene ) t ha t can be d i r ec t l y app l i ed fo rGC ana l y s i s w i t hou t an evapo ra t i on s t ep . Th i s i spa r t i cu l a r l y u s e fu l fo r de t e rm i na t i on o f vo l a t i l e com -pounds . A v i go rous s hak i ng and s a l ti ng ou t o f theana l y t e s and t he o rgan i c s o l ven t f rom wa t e r bys a t u ra t i on wi t h s od i um ch l o r i de was abs o l u t e l yn e c e s s a r y t o a c h i e v e s u f fi c ie n t r e c o v e r y ( 8 0 - 1 0 0 % ) .In com par i s on wi t h s o l i d -phas e ex t r ac t i on (S P E) t h i st e c h n i q u e w a s l e s s e x p e n s i v e a n d t i m e c o n s u m i n g .M L L E w a s r e p o r t e d t o s h o w l es s c o - e x t r a c ti v e s t h a nS P E bu t t h is s t a t em en t i s t o s om e e x t en t i nexp l i cab l et ak i ng i n t o accoun t t ha t a p rope r l y des i gned S P Eprocedu re a l l ows fo r t he pos s i b i l i t y o f s epa ra t i on o fana l y t e s f rom a ce r t a i n pa r t o f i m pur i t i e s . C on f i rm a-t i on wi t h ana l y s i s o f va r i ous t ypes o f wa t e r w i l l beneces s a ry . The l i m i t o f de t e rm i na t i on o f bo t h t ech -n iques was s imi lar . S t i l l , SPE showed bet ter resu l t s ,10 ng 1 - ] was t he m i n i m um de t ec t ab l e concen t r a t i ono f a l a c h l o r b y S P E , a n d 2 5 n g 1 ~ b y M L L E .App l i cab i l i t y o f t h i s app roach t o ex t r ac t i on o f d i f f e r -en t c l a s s es o f pes t i c i des f rom wa t e r has no t beens t ud i ed i n t he l i t e r a t u re known t o u s .


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A . B a l i n o v a / J. C h r o m a t o g r . A 7 5 4 ( 1 9 9 6 ) 1 2 5 - 1 3 5 127

2 . 2 . S o l i d - p h a s e e x t r a c t i o nA s u b s t a n t i a l l y n e w a p p r o a c h t o a q u e o u s s a mp l e

p r e p a r a t i o n t e c h n i q u e s i s SPE . I t o f f e r s a d v a n t a g e ss u c h a s t i me s a v i n g , s o l v e n t r e d u c ti o n , e l i m i n a t i o n o fe mu l s i o n s , t r a c e e n r i c h me n t , a n d a h i g h p o t e n t i a l f o ra u t o ma t i o n . T h e a d v a n t a g e s o f SPE h a v e n o t y e tbeen fu l ly rea l i zed in the i so la t ion o f pes t i c ider e s i d u e s f r o m a l l ma t r i c e s , b u t SPE h a s b e e n a d a p t e dt o e n v i r o n me n t a l w a t e r a n a l y s i s w i t h g o o d r e s u l t s .

Cu r r e n t l y SPE i s p r e d o mi n a n t i n a n a l y t i c a l me t h -o d s u s e d f o r p e s t ic i d e r e s i d u e s i n w a t e r m a t r i c e s.Co n v e n t i o n a l L L E h a s b e e n l a r g e l y r e p l a c e d b yprocedures u t i l i z ing so l id -phase par t i t i on . The bas i cs t e p s a s s o c i a t e d w i t h t h e s e p r o c e d u r e s i n c l u d e c o l -u mn c o n d i t i o n i n g b y r i n s i n g w i t h t h e s o l v e n t u s e d t oe l u t e t h e a n a l y t e s f o l l o w e d b y me t h a n o l a n d w a t e r t oi mp r o v e r e p r o d u c i b i l i t y a n d r e d u c e b a c k g r o u n d c o n -t a mi n a n t s . T h e s o r b e n t i s n o t a l l o w e d t o d r y b e f o r ethe water sample i s added . The samples (1 1 ) a ref o r c e d t h r o u g h t h e c o l u mn u s u a l l y a t f l o w - r a t e sb e t w e e n 5 - 1 0 m l m i n ~ a n d th e c o l u m n i s dr ie du n d e r v a c u u m. W e a k s o l v e n t s a r e u s e d f i r s t f o re lu t ion o f impur i t i es . F ina l ly the ana ly tes a re e lu t edw i t h s t r o n g e r s o l v e n t s d e s i g n e d t o e l u t e c o mp l e t e l yt h e p e s t i c i d e s w h i l e l e a v i n g a s ma n y i mp u r i t i e s a sp o s s i b l e o n t h e c o l u mn . E t h y l a c e t a t e a n d d i c h l o r o -me t h a n e a r e t h e mo s t p o p u l a r e l u t i o n s o l v e n t s f o rSPE . V a r i o u s t y p e s o f s o r b e n t s a n d t e c h n i q u e s h a v eb e e n d e v e l o p e d a n d a p p l i e d . Ch e mi c a l l y b o n d e ds i l i c a - b a s e d s o r b e n t s a r e g e n e r a l l y u s e d i n SPEc o l u mn s . T h e n o n - p o l a r o c t a d e c y l ( C~8 ) i s t h e mo s tc o mmo n s o r b e n t u s e d i n p e s t i c i d e a n a l y s i s . I t h a sb e e n u s e d t o e x t r a c t c o mp o u n d s b e l o n g i n g t o d i f f e r -e n t c h e mi c a l c l a s s e s a n d w i t h i n a w i d e r a n g e o fp o l a r i t i e s - - t r i a z i n e s [ 2 1, 2 2] a s w e l l a s s o me o f t h e irp o l a r d e c o m p o s i t i o n p r o d u c t s - - h y d r o x y - s - t r i a z i n e s[ 2 3 ], u r e a h e r b i c id e s [ 2 0] , N - me t h y l c a r b a m a t e p e s -t i c i d e s a n d t h e i r p o l a r me t a b o l i t e s [ 2 4 - 2 6 ] , O C[27 ,28] and OP insec t i c ides [29 ,30] , t r i azo le andp y r i mi d i n e p e s t i c i d e s [ 3 1 ] . Mu l t i r e s i d u e me t h o d s[ 3 2 - 3 4 ] i n c l u d in g a la r g e n u m b e r o f p e st i c id e s ( u pt o 1 2 8 ) o f d i f f e r e n t c l a s s e s h a v e b e e n d e v e l o p e du s i n g C~ b o n d e d s i l i c a c a r t r i d g e s . Mi x e d s o r b e n t s o fC~8 a n d p h e n y l ( PH ) b o n d e d p h a s e s i n s i n g l ec o l u mn h a v e a l s o b e e n u s e d i n mu l t i r e s i d u e p r o -c e d u r e s t o i n c r e a s e t h e r e t e n t i o n p o w e r a n d t h e r a n g e

of ex t rac te d com pou nds [35]. C~8 so rben t s were no te f f e c t i v e f o r e x t r a c t i o n o f v e r y p o l a r c o mp o u n d s :d i me t h o a t , me t o my l a n d a l d i c a r b w e r e p o o r l y r e -c o v e r e d [ 3 0 , 3 2 ] f r o m s p i k e d w a t e r s a mp l e s . A p p l i c a -t io n o f m o r e p o l a r s o r b e n t s - - P H , c y a n o p r o p y l ( C N ) ,d id no t g ive sa t i s fac to ry resu l t s . Hydroxy-dea lky l t r i az ines cou ld no t be en r i ched on C~8 [231 .

I n o r d e r t o r e d u c e t h e b r e a k t h r o u g h o f t h e e a r l ye l u ti n g p o l a r c o mp o u n d s l a r g e r a mo u n t s o f s o r b e n t s -u p t o 2 g h a v e b e e n a p p l i e d , e s p e c i a l l y i n mu l -t i res idue metho ds [22 ,34] . S t i ll , r ecov er i es o f veryp o l a r c o mp o u n d s s u c h a s d e s i s o p r o p y l a t r a z i n e c o u l dn o t b e i mp r o v e d b y t h e u s e o f mo r e c o l u mn ma t e r i a l[22].

A c i d i c c o mp o u n d s s u c h a s p h e n o x y a l c a n o i c a c i d sand o ther ac id ic herb ic ides have been success fu l lyex t rac ted on C~8 bonded s i l i ca car t r idges unders t r o n g a c i d i c ( p H < 2 ) c o n d i t i o n s [ 3 6 - 3 8 ] . A d j u s t i n gt h e p H o f t h e w a t e r s a mp l e b e l o w t h e p K ~ , o f t h eac id ic herb ic ides was es sen t i a l i n o rder to increaset h e r e t e n t i o n c a p a c i t y o f RP s y s t e m t o t h e s e c o m-pounds . S ince the bonded s i l i ca so rben t s a re no ts t ab le a t such cond i t ions , an a l t e rna t ive approachu s i n g i o n - p a i r i n g me c h a n i s m w i t h t r i e t h y l a mi n e a sc o u n t e r i o n w a s r e c e n t l y d e v e l o p e d f o r SPE o f a c i d icc o mp o u n d s u n d e r m i l d c o n d i t i o n s , a t n e a r l y n e u t r a lpH [39].

T h e v o l u me s o f w a t e r s a mp l e s e x t r a c t e d o n c a r -t r idges wi th d i f fe ren t so rben t s have been usua l ly int h e ra n g e o f 0 . 5 - 1 1, b u t l a rg e v o l u me s , u p t o 8 - 1 0 1[ 3 5 , 4 0 ] h a v e b e e n p r e c o n c e n t r a t e d i n s o me c a s e s .T h e s a mp l e v o l u me s s h o u l d b e c o n s i d e r e d c a r e f u l l ywi th respec t t o increas ing the de te rmina t ion l imi t sf r o m o n e s i d e a n d f r o m t h e o t h e r - - w i t h r e s p e c t t othe poss ib i l i t i es o f decreas ing the recover i es , espe-c i a l l y o f t h e e a r l y e l u t i n g c o mp o u n d s , d u e t o t h e i rb reak th rough dur ing p reconcen t ra t ion [41] . Pass ingl a r g e v o l u me s t h r o u g h t h e c a r t r i d g e ma t e r i a l s c o u l dr e s u l t i n p l u g g i n g a n d c h a n n e l i n g ; a s o p t i mu m f l o w -ra t es a re abou t 10 ml min-~ [42] , t he use o f SPEc a r t r i d g e s f o r l a r g e s a mp l e v o l u me s i s a t i me c o n -suming p rocess [38] .

T h e s e s h o r t c o mi n g s o f t h e e x t r a c t i o n c a r t r i d g e sh a v e b e e n o v e r c o m e w i t h a n e w t e c h n i q u e - - S P Ed i s c s . T h e u s e o f SPE d i s c s h a s b e e n d e s c r i b e d i nm o r e r e c e n t s t u d i e s [ 4 3 - 4 6 ] . T h e m e m b r a n e e x -t rac t ion d i scs have been used as an a l t e rna t ive to


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ca r t r i dge S P E . H i gher f l ow- ra t e s can be app l i ed wi t ht he S P E d i s cs and t he ex t r ac t i on t i m e i s m uch s ho r t e r[ 4 7 - 4 9 ] . T h e y d o n o t g e t p l u g g e d a n d c h a n n e l i n gdoes no t occu r . C ~ d i s cs exh i b i t ed be t t e r b l anks t hanC ~ 8 ca r t r i dges [50 ] . The com par i s on o f bo t h S P Et e c h n i q u e s - - c a r t r i d g e s a n d d i s c s s h o w a l s o s o m ed i s advan t ages o f t he la t te r . They r equ i r e 4 - 6 t i m esh i gher cons u m pt i on o f e l uen t s [47] and a re abo u t 4t i m e s m o r e e x p e n s i v e .

Ex t r ac t i on d i s cs can be u s ed i n o f f - l i ne m ode[51 ,52 ] and i n on - l i ne m ode u s i ng a m em braneho l de r [45 ,53 ] .

C ~ 8 s o rben t s s eem t o be i napp rop r i a t e fo r s om epes t i c i des , e s pec i a l l y ve ry po l a r and ve ry non -po l a rc o m p o u n d s . E n r i c h m e n t o n s y n t h e ti c p o l y m e r r e s-i n s - s t y r e n e d i v in y l b e n ze n e c o p o l y m e r s ( S D B ) inca r t r i dges o r i n S P E d i s cs has been app l i ed i n r ecen ts tudies as an a l t ernat ive to C j8 bond ed s i l i ca SPE[38 ,40 ,41 ,48 ] . Im provem en t o f t he r e s u l t s fo r r e -cover i e s , r e l a t i ve s t andard dev i a t i ons and de t e rm i -na t i on l i m i t s w i t h S DB Em pore d i s cs were r epo r t edi n com par i s on wi t h C ~ 8 Em pore d i s cs [38 ,54 ] ,e s pec i a l l y w i t h m ore po l a r com pounds s uch as ac i d i che rb i c i des . The obs e rva t i ons on t he r ecover i e s ob -t a i ned wi t h S DB d i s cs i n com par i s on wi t h C ~ 8 d i s csunder ac i d i c cond i t i ons were con t rove r s i a l . An i m -p r o v e m e n t i n t h e r e c o v e r i e s o f a c i d i c h e r b i c id e s a n dp h e n o l s w i th S D B d i sc s u n d e r p H < 2 w a s r e p o r t e d i nsome ar t i c les [48 ,54 ,55] whi le in o ther s tudies [38]S D B d i sc s s h o w e d w o r s e r e c o v e r y r a te s u n d e r a c i d iccon di t ions in co m par i son wi th C ~8 d i scs .

An a l t e rna t i ve s o rben t , e s pec i a l l y e f f ec t i ve fo rS P E o f ac i d i c pes t i c i des f rom wa t e r i s C arbopack B ,com pos ed o f non -po rous s phe r i ca l g raph i t e pa r t i c l e s .S t ud i es on t he app l i ca t i on o f C arbopack B i n p re -concen t r a t i on o f d i f f e ren t c l a s s es o f pes t i c i des (OP ,t r i az i nes , pheny l u reas , ca rbam at es , phenoxyac i d s ,ace t an i l i des , pheno l s ) a r e des c r i bed by Di C orc i a e ta l. [ 56 - 58 ] . Grap h i t i zed ca rbo n b l ack ca r t r i dgeso f fe r t he advan t age o f be i ng ab l e t o ex t r ac t s i m u l -t a n e o u s l y b a s i c / n e u t r a l a n d a c i d i c c o m p o u n d s . T h e yappea red t o be s upe r i o r t o o t he r s o rben t s fo r ex -t r a c t i o n o f v e r y p o l a r c o m p o u n d s ( p h e n o l s , p o l a rm e t abo l i t e s o f a t r az ine ) . Am ong t he va r i ous ex t r ac -t io n t e c h n i q u e s c o m p a r e d , t h a t e m p l o y i n g 1 gg raph i t i zed ca rbon b l ack ca r t r i dges and r eex t r ac t i onby back - f l u s h i ng had t he h i ghes t ab i l i t y t o r e t a i n

hyd roph i l i c pes t i c i des f rom l a rge wa t e r vo l um es[58 ] . The s o rp t i on m echan i s m i s a l m os t unknownand s om e cas es o f ob t a i n i ng ve ry h i gh s t andarddev i a t i ons and de t e rm i na t i on l i m i t s canno t be ex -p la ined [38] .

A us e fu l t echn i que has been deve l oped i n r ecen tyea r s t o i nc reas e t he e f f ec t i venes s o f pes t i c i deres idues analys i s in water . I t i s based on on- l ineen r i chm en t o f t he ana l y t e s f rom aque ous s am p l es onsmal l car t r idges f i l l ed wi th a su i tab le reversed-phases o rben t and s ubs equen t d i r ec t de t e rm i na t i on u t i l i z ings wi t ch i ng t o ana l y t i ca l HP LC co l um ns [59 ] . Theadvan t ages o f th i s app roach a re t i m e s av i ng and ah i gh po t en t i a l fo r au t om at i on .

O n - l i n e S P E , f o l l o w e d b y H P L C c o u p l e d w i t hd i o d e a r r a y d e t e c t o r ( D A D ) o r M S , r e p r e s e n t s ar ap i d , robus t and ve ry s e l ec t i ve app roach t o i den t i f i -ca t i on and qu an t i t a ti on o f pes t ic i des i n w a t e r m a t r i x .Th i s t echn i que has been app l i ed t o va r i ous pes t i c i dec l as s es i nc l ud i ng ch l o rophenoxyac i d s [48 ,60 ,61 ] , OP[62,63] , OC [64] , carbamates [65] , ch loro t r iazines[66] . I t has been success fu l ly appl ied in mul t i res idueana l y s is o f 51 com p ound s r ep res en t i ng s i x g roups o fpes t ic ides , d i f fer ing s t rongly in polar i t i es [41] . Rela-t i ve l y l ow recover i e s were ob t a i ned on l y wi t h ve rypo l a r com pounds due t o t he i r ea r l y e l u t i on andb reak t h rough d u r i ng en r i chm en t . Th i s e f f ec t wass i m i l a r w i t h a l l s o rben t m a t e r i a l s s t ud i ed - -C ~ 8b o n d e d s i li c a a n d t w o s t y r e n e d i v in y l b e n z e n e c o p o l y -m ers . A t t em p t s t o r educe t he b reak t h rough by u s i ngl a rge r am oun t s o f ad s o rben t s wou l d l ead t o ex t r em epeak b roaden i ng , pa r t i cu l a r l y fo r ea r l y e l u t i ng com -p o u n d s . W h e n h i g h l y h y d r o p h o b i c m a t e r i a l s ( S D B )were u s ed fo r p reconcen t r a t i on , s t rong band b roaden -i ng was obs e rved , l ead i ng t o ove r l app i ng peaks i nt he ch rom at og ram [41 ,62 ] . Th i s e f f ec t m ade t heana l y s i s o f com pl ex m i x t u res i m pos s i b l e . Thecom bi na t i on o f a l m os t i den t ica l m a t e r ia l s ( i . e . , C j 8 /C 8) i n bo t h p reco l um n and ana l y t i ca l co l um n wasc o n s i d e r e d m o r e a d e q u a t e a s t h e b a n d b r o a d e n i n g o fea r l y e l u t i ng com pounds was r educed [41 ] .

A n ega t i ve m a t r i x e f f ec t due m a i n l y t o hum i cs ubs t ances p res en t ed i n r ea l wa t e r s has o f t en beenrepo r t ed [41 ,46 ,48 ,67 ,68 ]. P e ak i n t e r f e renc es andl ow recover i e s were a t t r i bu t ed t o t he fo rm a t i on o fp e s t i c i d e - h u m i c c o m p l e x e s t h a t c o u l d n o t b e s u f f i -c i en t l y ex t r ac t ed by t he ads o rben t s u s ed [67 ] . A


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A . B a l i n o v a / J . C h r o m a t o g r . A 7 . 54 ( 1 9 9 6 ) 1 2 5 - 1 3 5 129

s epa ra t i on o f hum i c ac i d s on F l o r i s i l ca r t r i dges wasa p p l i e d i n a m e t h o d f o r H P L C w i t h U V d e t e c t i o nana l y s i s o f pes t i c i des i n wa t e r [22 ].2 .3 . C ou p le d - c o lum n l i qu id c hrom atograp hy

A pos s i b i l it y fo r i nc reas i ng t he s e l ec t i v it y be t weent he i n t e r f e rences and ana l y t e s by u t i l i z i ng coup l ed -c o l u m n H P L C w i t h c o l u m n s w i t c h i n g h a s b e e nrepo r t ed [69 ] . The bas i c p rocedu re i nvo l ves s eve ra ls teps : the crude sample ex t ract i s in jected on the f i rs tc h r o m a t o g r a p h i c c o l u m n w h e r e a p r e - s e p a r a t i o n i spe r fo rm e d wi t h a ce r t a in vo l um e o f t he f i rs t m ob i l ephas e . Dur i ng t h i s s t ep t he m ore po l a r i n t e r f e rencesa re r em oved . J u s t be fo re t he f i r s t ana l y t e s t a r t s t oe l u t e , t he f i r s t co l um n i s s wi t ched on - l i ne w i t h t hes econd ana l y t i ca l co l um n where t he s epa ra t i on o f t heana l y t e s i s pe r fo rm ed u s i ng a s econd m ob i l e phas e .The advan t ages o f th i s app roach a re s u i tab i l i ty fo rau t om at i on , i nc reas e o f t he s ens i t i v i t y by i n t ro -duc t i on o f l a rge r s am p l e vo l um es under con t ro l l edb a n d b r o a d e n i n g c o n d i t i o n s , i m p r o v e m e n t o f s e l e c -t i v i t y by t r ans fe r r i ng accu ra t e vo l um es con t a i n i ngon l y t he ana l y t e s o f i n t e res t t o t he s econd ana l y t i ca lco l um n . Th i s t echn i que has been app l i ed t o ana l y s i so f s eve ra l pes t i c i des i n aqueous m a t r i ces : ETU [70 ] ,i p rod i one [71 ] , b rom ac i l , d i u ron and 3 ,4 -d i ch l o ro -an i l ine [721 , ben t az one [73 ]. I ts s ucces s fu l pe r fo rm -a n c e d e p e n d s o n t h e o p t i m i z a t io n o f t w o i m p o r t a n tpa ram et e r s - t he cho i ce o f t he f ir s t s epa ra t i on co l um nand t he e l uo t rop i c s t r eng t h o f t he c l ean -up s o l ven t .In o rde r t o ex t end t he app l i cab i l i t y o f t h i s t echn i quet o s i m u l t aneous de t e rm i na t i on o f pes t ic i des w i t hd i f f e ren t po l a r i t i e s , a com pu t e r a i ded ch rom at og rams i m u l a t i on was deve l oped fo r op t i m i z i ng t he con -d i ti o n s o f c o u p l e d - c o l u m n H P L C c o m b i n e d w i ths t ep -g rad i en t e l u t i on [74 ] . The coup l ed -co l um n l i q -u i d ch rom at og raphy i s no t gene ra l l y app l i cab l e i nl abo ra t o ry p rac t i ce becaus e t he op t i m i za t i on o f t hecond i t i ons fo r c l ean -up and s epa ra t i on o f pes t i c i deses pec i a l l y l b r m u l t i r e s i due ana l y s i s r equ i r e s s pec i a ls k i l l s , and s i m u l t aneous de t e rm i na t i on o f ana l y t e swi th d i f ferent polar i t i es i s d i f f i cu l t .2 . 4 . So l id - phase m ic roe x t rac t ion

R ou t i ne m on i t o r i ng s t ud i es on pes t i c i de po l l u t i on

o f w a t e r r e q u i r e d e v e l o p m e n t o f r a p i d m e t h o d s o fana l y s i s . R ecen t l y a ve ry s i m p l e and r ap i d t echn i quehas been deve l op ed bas ed on s o l i d -phas e m i c roex -t r ac t i on (S P ME) [75 ,76 ] . The ex t r ac t i on and con -cent ra t ion s teps are focused in one s ingle s tep . I t i saccom pl i s hed on fu s ed - s i l i ca f i be r coa t ed wi t h ani m m ob i l i zed s t a t iona ry phas e (p o l yac ry l a t e o r po l y -d i m e t hy l s i l oxane) fo r t he ex t r ac t i on wi t hou t m ak i ngus e o f any s o l ven t s . The f i be r i s expos ed t o t hes am p l e fo r an op t i m i zed ads o rp t i on t i m e (25 m i n )un t i l equ i l i b r i um i s ach i eved . The t r ans po r t o f t heana l y t e s f rom t he aqueous phas e t o t he po l ym er i cm i c rophas e i s con t ro l l ed by d i f fu s i on and can beenhanced by s t i r r i ng t he wa t e r s am p l e . S m al l s am p l evo l um es (down t o 3 m l ) cou l d be u s ed wi t hou t l o s so f s ens i t i v i t y becaus e t he t o t a l am oun t o f t he ex -t racted sample i s used . The f ibers are d i rect lyin t roduced in to the heated sp l i t -sp l i t l ess in jector ofGC . T he s am e f i be r can be u s ed r epea t ed l y . Theex t r ac t i on e f f i c i ency s t rong l y depends on t he po l a r i tyo f i nd i v i dua l com pounds . The po l yac r i l a t e phas e hash i ghe r a f f i n i t y t o l e s s po l a r com pounds . Add i t i on o fs od i um ch l o r i de t o the aqueous s am p l e co u l d be u s edt o i nc reas e t he ex t r ac t i on e f f i c i ency fo r the po l a rcom pounds . Th i s app roach has been app l i ed t od e t e r m i n a t i o n o f v a r i o u s g r o u p s o f p e s t i c i d e s - - O P ,t r i az i nes , d i n i t roan i l i nes and good accu racy andp rec i s i on were r epo r t ed [76 ] .S P M E p r o c e d u r e h a s b e e n d e v e l o p e d f o r a n a l y s i so f o rgan i c po l l u t an t s i n wa t e r u s i ng penc i l l ead a ss o rben t and s ubs equen t t he rm a l des o rp t i on [77 ] .

2.5 . Sup ercr i t ica l . flu id ex trac t ionSupercr i t i ca l f lu id ex t ract ion (SFE) i s a pr incipal ly

new app roach wh i ch i s ga i n i ng popu l a r i t y a s as am p l e p repa ra t i on t echn i que . One o f t he b i gges tadvan t ages o f S F E over t he s t andard LLE i s t ha t i tcan be done wi t h non po l l u t i ng f lu i d s s uch as C O 2 . I ti s the m os t w i de l y u s ed s uperc r i t ica l s o l ven t wh i ch i sa na t u ra l com ponen t o f t he a i r and a f t e r decom pres -s i on i t can be a l l owed t o e s cape wi t hou t env i ronm en-t a l conce rn . The r em ai n i ng ex t r ac t s a r e c l ean o forganic so lvents [78] .

F l u i d s a re de f i ned as s upe rc r i t i ca l when t hey a rem ai n t a i ned a t t em pera t u res and p res s u res above t he


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130 A . B a li n o v a / J . C h r o m a t o g r . A 7 5 4 ( 1 9 9 6 ) 1 2 5 - 1 3 5

cr i t i ca l po in t . At these cond i t ions the subs tance canno t be l iqu i f i ed regard less the p ressu re exer t ed to i tb u t p o s s e s s e s p r o p e r t i e s o f b o t h l i q u id a n d g a s .Supercr i t i ca l f lu ids exh ib i t severa l un ique p roper t i est h a t ma k e t h e m d e s i r a b l e a s e x t r a c t i o n s o l v e n t s . O n eof the mos t in t e res t ing p ro per t i es i s tha t the so lven ts t reng th o f the supercr i t i ca l f lu id i s d i rec t ly re l a t ed toi t s dens i ty . S ince the dens i ty o f the f lu id i s a func t iono f i t s p r e s s u r e a n d t e mp e r a t u r e , a s o l v e n t w i t hs p e c i fi c s o l v a t i n g s t re n g t h c a n b e o b t a i n e d b y p r e c i s ec o n t r o l o f t h e p r e s s u r e a n d t e mp e r a t u r e . I t l e a d s t ot h e a b i l i t y t o p e r f o r m a v e r y s e l e c t i v e e x t r a c t i o n .H i g h e r m o l e c u l a r w e i g h t c o m p o u n d s c a n b e d i s -so lved as the p res su re o f the f lu id increases . I f thepressu re i s reduced the f lu id losses i t s so lva t inga b i l i t y a n d t h e e x t r a c t e d c o mp o u n d s f a l l o u t o fsolut ion.A n o t h e r a d v a n t a g e o f s u p e r c r i t i c a l f l u i d s i s t h a tthe i r d i f fus iv i t i es a re h igher and the v i scos i t i es a rel o w e r i n c o mp a r i s o n w i t h ma n y o r g a n i c s o l v e n t s .T h e s e p r o p e r t i e s o f s u p e r c r i t i c a l f l u i d s a l l o w t h e m t op r o mo t e r a p i d ma s s t r a n s f e r a n d f a s t e r s o l u t e e x -t rac t ions .

SFE h a s b e e n u s e d f o r a n a l y s i s ma i n l y i n s o i l s ,a n i ma l a n d p l a n t t i s s u e s o f v a r i o u s c l a s s e s o fp e s t ic i d e s : O C [ 7 9 - 8 1 ] , u r e a h e r b i c id e s [ 8 2 ,8 3 ] ,s u l f o n y l u r e a s [ 8 4 ] , c o mp o u n d s w i t h d i f f e r e n tp o l a r i t i e s - - p y r e t h r o i d s , c a r b a m a t e s , u r e a s , O E O C ,t r i az ines [85] , s - t r i az ines [86] , OP and OC [87 ,88] .

A d d i t i o n o f c o - s o l v e n t s ( e n t r a i n e r s o r m o d i f ie r s ) t ot h e p r i ma r y s o l v e n t p r o v e d t o b e u s e f u l f o r e n h a n c -i n g t h e e x t r a c t i o n e f f i c i e n c y o f t h e c o mp o u n d s o fi n t e r e s t . Me t h a n o l i s t h e mo s t c o mmo n c o - s o l v e n ta d d e d t o CO 2. O n e o f t h e r e a s o n s f o r a d d i t i o n o fe n t r a i n e r s i s t o o v e r c o me ma t r i x e f f e c t s . Pe s t i c i d e ss t r o n g l y b o u n d t o t h e ma t r i x ( f o r i n s t a n c e b o u n dres idues in so i l and p lan t t i s sues ) a re no t recoveredb y p u r e CO 2. T h e u s e o f m e t h a n o l o r a c e t o n e i nadd i t ion to CO 2 i s necess ary to ob ta in quan t i t a t ivereco ver i e s [80 ,89] . A secon d reas on i s tha t CO 2 i s ane x c e l l e n t s o l v e n t f o r n o n - p o l a r c o mp o u n d s , b u t i t i sn o t g o o d f o r p o l a r o n e s . A d d i t i o n o f e n t ra i n e r s i sn e c e s s a r y t o i n c r e a s e t h e p o l a r i t y o f t h e p r i ma r ys o l v e n t a n d i t s s t r e n g t h f o r e x t r a c t i o n o f p o l a rc o m p o u n d s [ 8 2 - 8 4 ] .

D i r e c t SFE h a s b e e n u s e d o n l y i n a f e w c a s e s t oe x t r a c t a n a l y t e s f r o m a n a q u e o u s ma t r i x [ 9 0 , 9 1 ] . T h emo d e r a t e s o l u b i li t y o f w a t e r i n s u p e r c r it i c a l CO 2 c a n

l e a d t o p r o b l e ms s u c h a s r e s t r i c t o r p l u g g i n g d u e t oi c e f o r ma t i o n a n d d i f f i c u l t i e s i n r e mo v a l o f w a t e rf rom the ex t rac t s [92] . A success fu l approach too v e r c o m i n g t h e s e p r o b l e m s h a s b e e n d e v e l o p e d b yc o m b i n i n g S PE w i t h SF E [ 9 3 - 9 5 ] . C 18 E m p o r e d i s c shave been used to t rap ana ly tes p r io r to e lu t ion wi ths u p e r c r it i c a l f lu i d. T h e e f f e c t i v e n e s s o f CO 2 s e l e c -t i v i t y t o p o l a r a n d n o n - p o l a r p e s t i c i d e s h a s b e e nd e mo n s t r a t e d i n s e p a r a t i o n o f O P f r o m O C p e s t i c i d e sunder d i f fe ren t ex t rac t ion cond i t ions [95] .

An in te res t ing app l i ca t ion o f SFE i s repor t ed [96]f o r t h e i s o la t i o n a n d t r a c e e n r i c h m e n t o f p e s t ic i d e s i nf r e e z e - d r i e d w a t e r s a mp l e s u s e d i n i n t e r l a b o r a t o r ys tud ies . The SFE wi th C O 2 resu l t ed in be t t e r re -c o v e r y a n d s e l e c t i v i t y t h a n L L E . T h e e x t r a c t i o ne f f i c i e n c y d e p e n d e d o n s o l u b i l i t y o f t h e a n a l y t e s i nthe supercr i t i ca l f lu id and in the water mat r ix .A subs tan t i a l reduc t ion o f ana lys i s t ime i s ano thera d v a n t a g e o f SFE a s n o c l e a n - u p o f t h e e x t r a c t s i sn e c e s s a r y .

T h e a v a i l a b i l i t y o f SFE i n s t r u me n t a t i o n i s al imi ta t ion fo r app l i ca t ion o f th i s t echn ique in l abora-to ry p rac t i ce .

3 . D e t e r m i n a t i o n

C h r o m a t o g r a p h i c m e t h o d s a r e m o s t w i d e l y u s e dfo r ana ly t i ca l separa t ion , iden t i f i ca t ion and quan t i t a -t ion o f pes t i c ide res idues in d i f fe ren t mat r i ces inc lud-i n g w a t e r . A p p l i c a t i o n o f s e l e c t i v e a n d h i g h l y s e n s i -t ive de tec t ion sys tems i s es sen t i a l i n water ana lys i sb e c a u s e o f t h e v e r y l o w l e v e l o f a d mi s s i b l e c o n -cen t ra t ions o f pes t i c ide res idues in water .

3 ,1 . G a s c h r o m a t o g r a p h yG C i s p r e f e r a b l y u s e d f o r a n a l y s i s o f v o l a t i l e a n d

t h e r mo s t a b l e p e s t i c i d e s . I n c o mb i n a t i o n w i t h s e l e c -t i v e d e t e c t o r s s u c h a s N PD a n d E CD i t b e c a me arou t ine t echn ique in pes t i c ide ana lys i s in water[ 6 ,9 , 3 0 ,3 1 , 4 7, 9 7 ,9 8 ] . Ca p i l l a r y a n d m e g a b o r e c a p i l -l a r y c o l u mn s h a v e r e p l a c e d t h e t r a d i t i o n a l p a c k e dc o l u mn s . Fu s e d c a p i l l a r y c o l u mn s w i t h b o n d e dp h a s e s o f d i f f e r e n t p o la r i ti e s ( n o n - p o l a r H P - 1 , U l t ra -l ; l o w p o l a r SE - 5 4 , H P- 5 , D B- 5 , U l t r a - 2 , CP S i l 8 ;


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A . B a l i n o v a / J. C h r o m a t o g r . A 7 5 4 ( 1 9 9 6 ) 1 2 5 - 1 3 5 131

me d i u m p o l a r D B- 1 7 0 1 , CP S i l 1 9 ; o r p o l a r CPW a x ) ; i n te r n a l d ia me t e r s ( 0 . 2 - 0 . 5 3 mm ) ; fi l m t h i c k -n e s s ( 0 . 1 2 - 1 / x m ) ; l e ng t hs ( 1 5 - 3 0 m ) o r o t h er s w e r er e p o r t e d . I o n i c c o mp o u n d s , s u c h a s p h e n o x y a l c a n o i ca c i d s a l s o c a n b e d e t e r mi n e d b y G C w i t h E CD a f t e rder iva t i za t ion to the i r methy l - , 2 -ch lo roe thy l - , 2 ,2 ,2 -t r i c h l o r o e t h y l - a n d p e n t a f l u o r o b e n z y l - ( PFB) e s t e r s[ 9 9 ] . Fo r w a t e r a n a l y s i s PFB e s t e r s w e r e p r e f e r a b l ebecause o f the h igher sens i t iv i ty [36 ,99] .

A s c h r o ma t o g r a p h y i s a p o o r i d e n t i f i c a t i o n t e c h -n i q u e , h y p h e n a t e d t e c h n i q u e s h a v e b e e n d e v e l o p e da n d h a v e g a i n e d p o p u l a r i t y f o r i n c r e a s i n g t h e s e l e c -t i v it y a n d c e r ta i n t y o f i d e n ti f ic a t io n . G C - M S h a sb e c o me t h e p r e f e r r e d a n a l y t i c a l t e c h n i q u e . I n mu l -t i res idue pes t i c ide de te rmina t ion in water i t i s usede i t h e r f o r c o n f i r ma t i o n o f t h e r e s u l t s o b t a i n e d w i t hG C - E C D , N P D [ 31 ,9 6 ] o r a s a p r i m a r y m e t h o d[ 1 00 l. T h r e e m o d e s o f G C - M S o p e r a ti o n a re g e n e r-a l l y a v a i l a b l e : e l e c t r o n i mp a c t ( E l ) , p o s i t i v e c h e mi -c a l i o n i z a t i o n ( PCI ) a n d n e g a t i v e c h e mi c a l i o n i z a t i o n( N C I ) [ 1 0 1] . G C - M S i n E l m o d e u s i n g se l e ct e d i onmo n i t o r i n g ( S I M) i s c o mmo n l y u s e d i n d e t e r mi -na t ion o f d i f fe ren t c l as ses o f pes t i c ides in water[ 2 3 , 3 5 , 1 0 0 , 1 0 2 ] . N CI a n d PCI a r e g o o d a l t e r n a t i v ei o n i z a t i o n me t h o d s , w h i c h o f f e r , d e p e n d i n g o n t h ec o mp o u n d s , b e t t e r s e l e c t i v i t y a n d / o r s e n s i t i v i t y t h a nE l . G C - M S w i th N C I i s a s el e c ti v e a p p r o a c hp a r t i c u l a r l y s u i t a b l e f o r c o n f i r mi n g t h e p r e s e n c e o fO C a n d O P i n e n v i r o n m e n t a l s a m p l e s . G C - M S - P C Ihas been app l i ed fo r conf i rming t r i az ines [103] andOP wi th the i r su lphox ides and su lphones [104] inw a t e r s a m p l e s . G C - M S w i t h P C I o r N C I a n d S 1 M o ft w o o r t h r e e c h a r a c t e r i s t i c f r a g me n t i o n s a r e s t r o n g l yr e c o mm e n d e d f o r d e t e r mi n a t i o n o f t r ia z i n e s a n d O Prespec t ive ly in d i r ty ex t rac t s s ince d iagnos t i c ions a rea t h igher m / z v a l u e s a n d c o n s e q u e n t l y l e s s i n t e r f e r -e n c e f r o m t h e ma t r i x w i l l a p p e a r [ 1 0 5 ] . A d r a w b a c kof th i s approach i s t ha t on ly a few l ib rar i es o fs t a n d a r d m a s s s p e c t r a f o r P C I a n d N C I G C - M S a r ea v a i l a b l e a n d t h e y mu s t b e b u i l t i n e a c h l a b o r a t o r y .

A so p h i st ic a t e d t e c h ni q u e u s in g G C - M S - M S h a sb e e n r e p o r t e d t o e n a b l e a n a l y s i s o f p e s t i c i d e s a n dthe i r metabo l i t es a t t race l eve l i n the p resence o fma n y i n t e r f e r i n g c o mp o u n d s . A l i m i t e d n u mb e r o fe x a mp l e s a r e p r e s e n t i n t h e l i t e r a t u r e o n a p p l i c a t i o no f t hi s te c h n i q u e . I n PCI mo d e i t ha s b e e n e m p l o y e df o r t h e d e t e r mi n a t i o n o f t r i a z i n e a n d a c e t a n i l i d eherb ic ides in water [103] .

3 . 2 . H PL C

H PL C i s t h e me t h o d o f c h o i c e f o r t h e r ma l l yu n s t a b l e a n d i o n i c c o mp o u n d s w h i c h a r e n o t a me n -a b l e t o G C. E n v i r o n me n t a l l y i mp o r t a n t p e s t i c i d e ss u c h a s c a r b a ma t e s , u r e a - a n d p h e n o x y a c i d h e r -b i c i de s , p o l a r me t a b o l i t e s o f t r i a z in e s , b e n z i mi d a z -o l e s a n d o t h e r s a r e a mo n g t h e s e c o mp o u n d s . RP-H P L C c o l u mn s c o n t a i n i n g m a i n l y CL ~ b o n d e d s i li c aso rben t s [4 ,21 ,22 ,32 ,37 ,106] and in som e cases C8[24 ,41] and CN- [37] bonded s i l i ca a re used fo ra n a l y t i c a l s e p a r a t i o n . N a r r o w - b o r e , 3 mm I . D . c o l -u mn s 1 4 1 ] a n d 3 / z m p a r t ic l e s [ 2 2 ,3 8 ] h a v e b e e napp l i ed in recen t s tud ies . Grad ien t e lu t ion wi th al a r g e c h a n g e i n mo b i l e p h a s e s c o mp o s i t i o n i s u s e dfo r mul t i res idue ana lys i s . Buffer so lu t ions wi th pHa d j u s te d b e l o w t h e p K a v a l u e s o f t h e a c i d i c c o m -p o u n d s ( p H < 2 ) a r e c o m m o n l y u s e d i n o r d e r t oincrease the re t en t ion capac i ty o f RP so rben t s fo rH P L C s e p a r a t io n o f a c i d i c h e r b ic i d e s [ 4 8 ,1 0 7 ]. Aposs ib i l i t y to increase the separa t ion e f f i c i ency andr e t e n t i o n c a p a c i t y f o r a c i d i c h e r b i c i d e s i n RP- H PL Cunder mi ld cond i t ions , a t near ly neu t ra l pH u t i l i z inga n i o n - p a i r i n g me c h a n i s m h a s b e e n r e p o r t e d 1 3 9 ] .

U V - d e t e c t i o n w i t h v a r i a b l e w a v e l e n g t h h a s b e e nthe rou t ine ly used t echn ique , enab l ing su f f i c i en tsens i t iv i ty (0 .1 ng ml -~ o r l es s ) fo r mos t pes t i c idesto be ach ie ved [ 37 ,106 ,108] . The p ro b lem of iden t if i -c a t i o n , t y p i c a l o f c h r o ma t o g r a p h i c me t h o d s , c a n n o tbe so lved wi th the app l i ca t ion o f UV-detec to rs . Ani n c r e a s e o f c o n f i r ma t i o n a b i l i t y h a s b e e n a c h i e v e dw i t h D A D . T h i s t e c h n i q u e h a s b e e n r e p o r t e d mo s to f t e n i n mu l t i r e s i d u e H PL C a n a l y s i s o f p e s t i c i d e s i naqueou s sam ples [4 ,21 ,22 ,32 ,38 ,48] , In o rder toincrease the va l id i ty o f iden t i f i ca t ion , t he absorp t ions p e c t r a o f t h e c o m p o u n d s h a v e b e e n c o m p a r e d t oreference subs tances [21 ,22] . Subs tance de tec t ion a ts e v e r a l d i f f e r e n t w a v e l e n g t h s h a s b e e n p e r f o r me d f o rb e t t e r i d e n t i f i c a t i o n . L o w r e c o v e r i e s f o r s o me s u b -s t a n c e s h a v e b e e n o b s e r v e d w i t h D A D c a u s e d b y t h emat r ix in t e r fe rences ]46 ,481 . App l i ca t ion o f DADc a p a b l e o f a u t o ma t i c a l l y i d e n t i f y i n g c o mp o u n d s b yu t i l i z ing a mul t ip l e spec t ra l compar i son t echn iquee n h a n c e s a t t a i n me n t o f c o r r e c t r e s u l t s i n a u t o ma t i cs y s t e ms f o r p e s t i c i d e me a s u r e me n t i n d r i n k i n g w a t e r[ 1 0 9 ] . Mu l t i - c o mp o n e n t a n a l y s i s h a s b e e n r e p o r t e di n t h e s a me a r t i c l e t o p r o v i d e q u a n t i t a t i v e a c c u r a c yfo r peaks tha t co -e lu te due to inadequate reso lu t ion .


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R e c e n t l y D A D h a s b e e n a p p l i e d i n a f u l ly a u t o m a t e dH P L C s y s t e m f o r t r a c e - l e v e l d e t e r m i n a t i o n o f p o l a rpo l l u t an t s i n wa t e r u s i ng an au t om at ed ca r t r i dge -exchange s y s t em fo r on - l i ne t r ace en r i chm en t , g ra -d i e n t e l u ti o n a n d o p t i m i z e d H P L C p a r a m e t e r s f o r 1 8po l l u t an t s i n va r i ous t ypes o f wa t e r s [110 ] .T h e c o m b i n a t io n o f H P L C w i t h M S p r o v i d e spos s i b i l i t i e s fo r ove rcom i ng t he p rob l em s a r i s i ng ou to f t he m a t r i x i n t e r f e rences . D i f f e ren t t ypes o f i n t e r -f a c e s f o r c o n n e c t i o n o f M S t o H P L C a r e p o s s i b l e( i nc l ud i ng t r ans po r t s y s t em s , d i r ec t l i qu i d i n t ro -duc t i on , a t m os pher i c p res s u re i on i za t i on , pa r t i c l ebeam , con t i nuous f l ow- fas t a t om bom bardm en t , t he r -m o s p r a y , e l e c t r o s p ra y ) [ 1 1 1 ]. T h e r m o s p r a y ( T S P ) i st h e m o s t w i d e l y u s e d i n t e r f a c e i n H P L C - M S r e -po r t ed i n pes t i c i de r e s idue m e t hod o l ogy becaus e t heTS P i on i za t i on i n gene ra l l eads t o s i m p l e m as ss pec t r a , r e s u l t i ng i n h i gh s ens i t i v i t y when t i m es chedu l ed S IM i s app l i ed . Th i s t echn i que has beene m p l o y e d i n m e t h o d s f o r d e t e r m i n a t i o n o f a v a r i e t yo f i nd i v i dua l c l a s ses o f pes t ic i des s uch as ca rbam at es[112 ] , OP [113 ,114 ] , u reas [115 ] , ac i d i c he rb i c i des[48] , fungicides [46] , t r i azines [116,117] , su l -fony l u reas [118 [ and o t he r s , bu t cu r ren t l y t he re a refew m u l t i r e s i due m e t hods bas ed on t h i s t echn i que[ 3 4 , 4 1 , 1 1 9 ] . T w o M S m o d e s a r e a p p l i e d r o u t i n e l y - -pos i t i ve i on (P I ) and nega t i ve i on (NI ) . The cho i ceb e t w e e n t h e m d e p e n d s o n t h e c o m p o u n d s d e t e r -m i ned , t he l a t t e r appea r i ng t o be m uch m ore s ens i -t i ve t o e l ec t ronega t i ve com poun ds [48 ,105 ] . De t e r -m i na t i on o f 128 pes t i c i des under d i f f e ren t HP LCcond i t i ons has been r epo r t ed [34 ] when opera t i ng i nP I a n d N I m o d e s . F o r i m p r o v e m e n t o f s e l e c ti v it y a n ds ens i t i v i t y pos t co l um n t echn i ques have been app l i eds uch as add i t i on o f aqueous bu f fe r s o l u t i on andex t e rna l i on i za t i on m ed i a [120 ] . Iden t i f i ca t i on andd e t e r m i n a t io n o f c o - e l u t in g c o m p o u n d s h a s b e e npos s i b l e by com par i s on o f t he i r d i f f e ren t cha rac t e r i s -t i c i ons . In c r i t i ca l cas es d i f f e ren t con f i rm a t o ryt echn i ques have been s hown t o be adequa t e t od i s t i ngu i s h be t ween ana l y t es : va r i a t i on o f i n t e r f acet e m p e r a tu r e s , M S - M S t e c h n i q u e s [ 34 ] , u s e o f e x t e r -na l i on i za t i on m ed i a [ 121 ] , r epe l l e r - i nduc ed s pec t r a lchange s [122 ] , add i t i ona l c l u s t e r ions wi t h s o l ven t o ra d d i t i v e m o l e c u l e s , c o m p l e m e n t a r y P | a n d N I s p e c -tra [34].

T h e o t h e r i n te r f a c e t e c h n i q u e s h a v e b e e n s c a r c e l yus ed i n pes t i c ide ana l y s is . E l ec t ro s p ray (E S P ) i on i za -

t i on has been app l i ed r ecen t l y i n h i gh - f l ow m ode fo rde t e rm i na t i on o f OP pes t i c i des [123 ] . An advan t ageo f t h i s t echn i que i n com par i s on wi t h TS P i s t ha t nodeg rada t i on occu r s under ES P cond i t i ons t hus i t i sv e r y u s e f u l f o r d e t e r m i n a t i o n o f c o m p o u n d s w h i c ha re eas i l y t he rm odeg raded s uch as t r i ch l o r fon . Ani m por t an t f ea t u re o f ES P i s t ha t i t g i ves be t t e rs t ruc t u ra l i n fo rm at i on t han TS P and can be u s ed fo ri d e n t i f i c a t i o n o f u n k n o w n c o m p o u n d s . H i g h e r s e n -s i t iv i t i es (about 100 t imes) have been repor ted wi thL C - E S P - M S f o r s e v e r a l O P i n s e c t i c i d e s a s c o m -p a r e d t o L C - T S P - M S .

P ar t i c l e beam i n t e r f ace g i v i ng e l ec t ron i on i za t i ons pec t r a has been r epo r t ed t o have an advan t age ove rt h e T S P t e c h n i q u e f o r H P L C - M S d e t e r m i n a t i o n o fch l o r i na t ed phenoxy ac i d he rb i c i des becaus e i t p ro -v i d e d a n e x c e l l e n t c o n f i r m a t i o n b a s e d o n n u m e r o u sand h i gh l y r ep roduc i b l e d i agnos t i c f r agm en t a t i onions [124] .

L i m i t a t i ons fo r gene ra l app l i ca t i on o f t hes e ad -vanced t echn i ques a re t he h i gh cos t s o f the i n s t ru -m en t a t i on and t he com pl ex i t y o f i t s exp l o i t a t i on .

3.3. High-p erforman ce thin-layer chromatographyHi gh-pe r fo rn~ ance t h i n - l aye r ch rom at og raphy

( H P T L C ) i s n o t t h e m e t h o d o f c h o i c e f o r p e s t i c i d eres i due ana l y s i s i n wa t e r . As com pared t o t headvanced t echn i ques des c r i bed above i t i s no t con -s i de red as p ro s pec t i ve . In r ecen t yea r s t he re a re ave ry l i m i t ed num ber o f a r t i c l e s on t he app l i ca t i on o ft h i s t echn i que i n pes t i c i de r e s i due ana l y s i s andpar t i cu l a r l y i n wa t e r s am p l es . An exam pl e wi l l beg i ven t o s how t he pos s i b i l i t i e s o f HP TLC u t i l i z i ngm odern t echn i ques fo r i nc reas i ng app l i cab i l i t y fo rt h i s pu rpos e [125 ] . The m i g ra t i on d i s t ances o f 275ac t i ve s ubs t ances have been de t e rm i ned u t i l i z i ngau t om at ed m u l t i p l e deve l opm en t wi t h a s t andard i zede l u t i on g rad i en t and a s econd g rad i en t fo r ve r i f i ca -t i on . The UV-s pec t r a i n r e f l ec t ed l i gh t , m eas u red ont he HP TLC p l a t e , have been s t o red i n a l i b ra ryp rog ram . Th i s t echn i que has been r epo r t ed t o besui tab le for rout ine ident i f i cat ion and quant i t a t ivede t e rm i na t i on o f pes ti c i des i n wa t e r s am p l es andes pec i a l l y o f t he rm al l y uns t ab l e com pounds s uch aspheny l u reas , ca rbam at es and o t he r s , no t am enab l e t oGC . As t he com p ound s s t ud i ed d i f f e r i n the i r UV


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A . B a l in o v a / J . C h r o m a t o g r . A 7 5 4 ( 1 9 9 6 ) 1 2 5 - 1 3 5 13 3

a b s o r b a n c e , t h e r a n g e o f s e n s i t i v i t i e s i s w i d e . S o m ep e s t i c i d e s l a c k a s t r o n g c h r o m o p h o r e i n t h e U Vr e g i o n f o r s e n s i t i v e d e t e c t i o n . H e n c e U V d e t e c t i o n i sn o t w e l l s u i t e d f o r u n i v e r s a l a p p l i c a t i o n . T h e e q u i p -m e n t u s e d i n t h e H P T L C m e t h o d d e s c r i b e d i s n o tm u c h s i m p l e r o r c h e a p e r i f c o m p a r e d t o H P L C o rG C b u t t h e p o s s i b i l i t i e s f o r d e t e r m i n a t i o n o f m u l -t i r e s i d u e s a t l o w c o n c e n t r a t i o n s a r e m o r e l i m i t e d .

4 . C o n c l u s i o n sT h e m a i n c o n t e m p o r a r y g o a l i n p e s t i c i d e r e s i d u e

a n a l y s i s o f e n v i r o n m e n t a l w a t e r s i s i n c r e a s i n g t h es e n s i t i v i t y o f d e t e c t i o n i n c o m p l i a n c e w i t h t h e h i g hd e m a n d s f o r d r i n k i n g w a t e r q u a l i t y . I m p r o v e m e n t o ft h e s e l e c t i v i t y a n d d e v e l o p m e n t o f r e l i a b l e c o n f i r m a t -o r y t e c h n i q u e s a r e a d e q u a t e a p p r o a c h e s f o r e l i m i n a t -i n g f a l s e p o s i t i v e r e s u l t s . T h e n e c e s s i t y t o e n h a n c et h e c o n t r o l o f w a t e r p o l l u t i o n g i v e s r i s e t o d e v e l o p -m e n t o f t e c h n i q u e s a n d m e t h o d s l e a d i n g t o m i n i m i -z a t i o n o f t h e a n a l y s i s t i m e b y s i m p l i f i c a t i o n o fs a m p l e p r e p a r a t i o n p r o c e d u r e s a n d i n c r e a s i n g t h es a m p l e t h r o u g h p u t b y a u t o m a t i o n . E f fo r t s h a v e a l s ob e e n f o c u s e d o n r e d u c i n g t h e c o n s u m p t i o n o fh a z a r d o u s s o l v e n t s a s t h i s i s e s s e n t i a l f o r e n v i r o n -m e n t a l s a f e t y .T h e p r e s e n t e d r e v i e w c l e a r l y i n d i c a t e s t h a t t h e r e i sa r a p i d l y d e v e l o p i n g r e s p o n s e o f a n a l y t i c a l c h e m i s t st o r e s i d u e p r o b l e m s . T h e e n o r m o u s g r o w t h i n t e c h -n i q u e s a n d i d e a s i s s t r o n g e v i d e n c e t h a t t h e d i f f ic u l ta n a l y t i c a l p r o b l e m s r e l a t e d t o d e t e r m i n a t i o n o f p e s -t i c i d e r e s i d u e s i n w a t e r c a n b e s o l v e d b y e x p e r i e n c ea n d i n v e n t i v e i m a g i n a t i o n .

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