Determination of organophosphorus insecticides in natural waters using SPE-disks and SPME followed by GC/FTD and GC/MS

Transcription

1 Fresenius J Anl Chem (2000) 368 : Springer-Verlg 2000 ORIGINAL PAPER D. Lmbropoulou T. Skellrides T. Albnis Determintion of orgnophosphorus insecticides in nturl wters using SPE-disks nd SPME followed by GC/FTD nd GC/MS Received: 10 April 2000 / Revised: 19 June 2000 / Accepted: 23 June 2000 Abstrct Two methods for the nlysis of ten orgnophosphorus insecticides in nturl wters using solid phse extrction disks contining C 18 nd SDB nd solid phse microextrction fibers contining polycrylte (PA) re developed. Bromophos ethyl, bromophos methyl, dichlofenthion, ethion, fenmiphos, fenitrothion, fenthion, mlthion, prthion ethyl nd prthion methyl were determined by GC/MS nd GC/FTD. The SPE-disks require only 1000 ml of smple nd provide method limit of detection in the rnge of µg/l nd recovery rtes from 60.7 to 104.1%. The solid phse microextrction (SPME) technique requires 2-5 ml of wter smple nd provides method limit of detection in the rnge of 0.01 to 0.05 µg/l for ll detectors nd the recoveries compred to distilled wter rnged from 86.2 to 119.7%. The proposed methods were pplied to the trce level screening determintion of insecticides in river wter smples originting from different Greek regions. Introduction D. Lmbropoulou, T. Skellrides, T. Albnis ( ) Deprtment of Chemistry, University of Ionnin, Ionnin 45110, Greece e-mil: tlbnis@cc.uoi.gr The determintion of pesticide residues in wter smples is necessry for solving vrious environmentl nd biologicl problems [1]. EU regultions for drinking wter qulity set limit in concentrtion of 0.5 µg/l for the sum of ll pesticides nd 0.1 µg/l for ech compound, so tht detection limits below 0.1 µg/l re required for monitoring potble wter. The trce determintion of pesticides requires both high performnces from nlyticl instruments nd efficient smple preprtion [2]. The determintion of low concentrtions of orgnophosphorus insecticides in wter by chromtogrphic techniques requires previous concentrtion of the smple, e.g. by liquid-liquid prtition requiring lrge mounts of toxic nd expensive solvents. Solid-phse extrction (SPE) disks nd solid phse microextrtion (SPME) fibers hve been used due to simplicity nd robustness [3-5] in reltion to liquid-liquid extrction [6]. Solid-phse microextrction (SPME) llows the simultneous extrction nd preconcentrtion of nlytes from smple mtrix [7-8]. The nlytes re extrcted by bsorption over the fiber which is directly exposed to the smples or to the hedspce. Finlly, the fiber is introduced into the gs chromtogrph injector where the nlytes re thermlly desorbed. Different sttionry phses, such s polydimethylsiloxne nd polycrylte, provided tht vriety of different groups of nlytes cn selectively be extrcted. The SPME method hs been pplied to the trce determintion of orgnic micropollutnts, including voltile orgnic compounds (VOCs) [9-11], phenol nd its derivtives [12, 13], polycyclic romtic hydrocrbons (PAHs) nd polychlorinted biphenyls (PCBs) [14,15]. More recently, the method ws pplied to ftty cids [16] nd other environmentl pollutnts, such s pesticides of chemicl groups of trizines, trizoles, thiocrbmtes, mides, chlorocetmides, orgnochlorines [8] nd orgnophosphorus pesticides [17]. The process involved in SPME is bsed on prtition process tht cnnot be relted to chromtogrphic dt, thus explining the difficulty involved in predicting the extrction properties of the fibers ccording to the nlyte s properties [8]. Two efficient multi-residue methods for the pre-concentrtion nd chromtogrphic nlysis of 10 selected orgnophosphorus insecticides tht belong to those minly used in the Mediterrnen [18] region nd re included to the list of EU [19] were developed for the monitoring of the selected pesticides in vrious nturl wters. The methods include SPE-disks, SPME nd GC with flme thermionic (FTD) nd MS detector for the determintion of the ten orgnophosphorus insecticides bromophos ethyl, bromophos methyl, dichlofenthion, ethion, fenmiphos, fenitrothion, fenthion, mlthion, prthion ethyl nd prthion methyl in different wters (distilled, underground nd surfce wters). The methods were tested with spiked nturl wter smples (underground, river, lke nd mrine wter). Both methods were pplied for the monitoring of surfce wter in Greece.

2 617 Experimentl Chemicls. HPLC-grde wter, methnol, dichloromethne nd ethyl cette from Pestiscn (Lbscn Ltd, Dublin, Irelnd) were pssed through 0.45 µm filter before use. Sodium sulfte nd sulfuric cids were from Merck (Merck Drmstdt, Germny). Bromophos ethyl, bromophos methyl, dichlofenthion, ethion, fenmiphos, fenitrothion, fenthion, mlthion, prthion ethyl, prthion methyl nd dizinon were purchsed from Riedel-de- Hën (Seelze, Germny). The properties of selected orgnophosphorus insecticides re shown in Tble 1. Phosphte buffer employed for ph djustment of the smples ws prepred from 100 ml solution of 0.1 M dipotssium hydrogen phosphte (Merck) dding the pproprite mounts of 0.1 KOH nd/or 0.1 NH 4 Cl solutions (Merck). Tble 1 Chemicl structure, moleculr weight, solubility in wter nd soil sorption coefficient Koc (ml/g) of selected insecticides Insecticides Chemicl Cs No/ Moleculr Wter LogK ow Soil structure weight solubility sorption (mg/l) (Koc) b Dichlofenthion [ ] c Prthion methyl [ ] Fenittrothion [ ] Mlthion [ ] Fenthion [ ] Prthion ethyl [ ] Bromophos methyl [ ] c Bromophos ethyl [ ] c Fenmiphos [ ] Ethion [ ] Log K ow, octnol wter prtition coefficients [20] b Koc, sorption coefficient normlized to orgnic crbon content [21 23] c Estimtion by using the eqution log Koc = 0.62 log S (r 2 = 0.86, n = 107) (where S is the solubility in mg/l), suggested for non-polr compounds [24]

3 618 SPE disks nd SPME fibers. The Empore extrction disks were mnufctured by 3 M nd distributed by Vrin (Hrbor City, CA). The disks used were 47 mm in dimeter nd 0.5 mm thick. Ech disk contined bout 500 mg of C18 nd SDB bonded silic (92 + 2%) nd % PTFE. Empore filter Aid 400 glss beds (St. Pul, USA) were used s filtrtion id when extrcting smples with prticulte content using extrction disks. SPME holder nd fiber ssemblies for mnul smpling were obtined from Supelco (Bellefonte, PA, USA) nd used without modifiction. Polycrylte 85 µm (PA) ws used s the sttionry phse in SPME for the extrction of insecticides. Before mesurements the fiber ws conditioned in the injector for 3 h t 220 C, with the split vent open, to fully remove ny contminnt which might hve cused very high bseline noise nd lrge ghost peks. Then the fiber ws repetedly injected into the GC until interfering peks disppered. During this desorption process the GC column oven temperture ws mintined t 220 C. Wter smples. Wter smples were collected, from river Archthos, lke Pmvotis nd Ionin se in September Ground wter ws obtined from the min re of Ionnin (Greece). Distilled wter ws lso used. The wter smples were nlyzed prior to spiking, to ensure tht they were free of interfering compounds. Their chrcteristics re shown in Tble 2. River wter smples from Klms, Archthos nd Louros were collected in September The smples were stored in drkness t 4 C nd were nlyzed within 48 h fter collection. SPE-disk nlyticl procedure. Empore extrction disks were conditioned with 10 ml cetone for 2 h. Nturl wter smples (n = 3) of 1 L ech were spiked with mixture of the 10 selected pesticides to the finl concenttions of 0.1, 0.2, 0.5, 1, 2, 5, nd 10 µg/l. Methnol modifier (5 ml) ws dded to 1 L wter smples to llow better extrction [25]. The optimum vlues of ph for orgnophosphorus insecticides extrction with SPE ws reported in the rnge of [26]. The ph of the wter smples (Tble 1) were between 6.1 nd 7.8, therefore, the ph of the smples ws not djusted. C 18 nd SDB disks lredy plced in six sttion extrction mnifold nd covered with thin lyer (1 cm) of Empore filter id 400 were wshed with 10 ml of dichloromethne:ethyl cette (1 :1, v/v) with the vcuum on nd with 10 ml of methnol for 3 min with the vcuum off. The disks were not llowed to become dry, s recommended [27, 28]. The wter smples were llowed to percolte through the disks with flow rte of 50 ml/min under vcuum. After smple extrction, the pesticides trpped in the disks were collected by using 2 10 ml of the solvent mixture dichloromethne:ethyl cette (1:1, v/v) s eluting solvent. The frctions were evported to 4 ml on rotry evportor (35 C). After creful evportion of solvent to 0.5 ml in gentle strem of nitrogen, extrct residues were dissolved in 2 ml isooctne nd evported to finl volume of 1 or 0.1 ml for GC injections. Tble 2 Chrcteristics of selected nturl wters Origin of ph Conduc- Totl TOC b wter smple tivity suspended (mg/l) µmhos/cm mtter (mg/l) Distilled wter b.d.l. c Underground wter Archthos river Pmvotis lke Ionin se Totl suspended mtter ws mesured by filtrtion through 0.45 µm PTFE filter (millipore), b TOC = totl orgnic crbon, c b.d.l. = below detection limit (0.01 mg/l) Fig. 1 SPME bsorption-concentrtion profiles for the tested insecticides in wter fter 45 min extrction time, by using PA 85 µm fiber (desorption time 5 min t 240 C) SPME nlyticl procedure. 3 ml volume of stndrd solution or smple ws plced in 4 ml vils, seled with hole-cps nd PTFEline sept. The smples were stirred before nd during extrction. The fiber ws then exposed to the queous phse for n pproprite time period of 45 min, with stirring t room temperture (25 ± 2 C). After extrction, the fiber ws directly exposed to the hot injector of the GC systems for nlysis. Therml desorption of insecticides ws crried out for 5 min. After this period no significnt blnk vlues were observed. The overll methnolic concentrtion during these experiments ws lwys less thn 0.5% (v/v). An extrction time of 45 min ws used for ll experiments. The bove described extrction conditions were employed in producing the bsorption-concentrtion curves in Fig. 1 for ech pesticide tht exhibited bsortion by SPME PA 85 µm fiber. Quntifiction of smples ws mde using clibrtion curve of queous stndrds (between µg/l using HPLC-grde wter) extrcted in the sme wy s the smples nd using pek re mesurements. Gs chromtogrphic conditions. GC-FTD. Single pesticide stndrds nd the extrcts from the Empore disk preconcentrtion step were injected in Shimdzu 14A cpillry gs chromtogrph equippped with flme thermionic detector (FTD) t 250 C. The DB-1 column, 30 m 0.32 mm i.d., contined dimethylpolysiloxne (J & W Scientific, Folsom, CA). The column ws progrmmed from 100 C (2 min) to 210 C (30 min) t 5 C/min nd to 270 C (4 min) t 20 C/min. The injection temperture ws 22 C. The injection volume ws 1.5 µl in the splitless mode with the vlve opened for 60 s. Helium ws used s the crrier nd nitrogen s mke-up gs. The detector gses were hydrogen nd ir, nd their flow rtes were regulted ccording to results given by the simplex optimiztion of the nlyticl vribles, in this instnce ir nd hydrogen flow-rtes in the detector. The ion source of FTD ws n lkli metllic slt (Rb 2 SO 4 ) bonded to 0.2 mm spirl of pltinum wire. GC-MSD. A GC-MSD, QP 5000 Shimdzu equipped with cpillry column DB-225, 15 m 0.25 mm 0.5 µm, contining 50% cynopropylphenyl-methylpolysiloxne (J & W Scientific, Folsom, CA) ws used t the following chromtogrphic conditions: Injector temperture 220 C, column progrm of tempertures C (5 C/min), C (1 C/min), 210 C (12 min), C (20 C/min), 270 C (5 min). Helium ws used s the crrier gs t 96.5 KP. The ion source nd trnsfer line were kept t 200 C nd 240 C, respectively. The spectr were obtined t 70 ev. The splitless mode ws used for injection of 1 µl volume, with the vlve opened for 30 s. Chrcteristic ions of the selected insecticides were chosen for screening nlysis in selected ion monitoring (SIM) mode (Tble 3). The ion trces were divided into three groups tht were recorded sequentilly during the injection, on the bsis of the re-

4 619 Tble 3 Retention times (t R ) nd chrcteristic ions (% bundnce) of ll trget insecticides nlyzed with GC- EI-MS Compounds (t R ) GC-EI-MS Reltive (min) itensity m/z ions (%) 1. Dichlofenthion [M-Cl] [(OH) 2 PS] Prthion methyl [M] [(CH 3 O) 2 PO] Fenitrothion [M] [(CH 3 O) 2 PS] Mlthion [C 2 H 5 OOC-CH 2 -CHCOOC 2 H 5 ] [173 C 2 H 5 O] Fenthion [M] [(CH 3 O) 2 PS] Prthion ethyl [M] [(C 2 H 5 O)PSH] Bromophos methyl [M-Cl] [(CH 3 O) 2 PS] Bromophos ethyl [M-Cl] [(OH) 2 PS] Fenmiphos [M] [CH 3 S-C 6 H 3 -CH 3 OH] Ethion [(HO) 2 PS] [M (C 2 H 5 O) 2 PS] Dizinon [M] [OH-C 4 H 4 -CH 2 -C-CH-CH 3 ] Tble 4 Anlyzed insecticides, retention times (t R ) in system GC-FTD, limits of detection, linerity dt nd RRF vlues in the GC-FTD, GC-MS systems by using SPE-disks C18 RRF = reltive response fctor, b LOD = limit of detection, c I.S. = internl stndrd, d R.S.D. = reltive stndrd devition Pek No./ t R RRF Linerity GC-FTD GC-MS compounds (min) (Dizinon) LOD b R.S.D. d LOD b R.S.D. d (µg/l) (µg/l) 1. Dichlofenthion Prthion methyl Fenitrothion Mlthion Fenthion Prthion ethyl Bromophos methyl Bromophos ethyl Fenmiphos Ethion Dizinon (I.S.) c tention times of the single substnces. In this wy, different compounds which give common frgment ions belong to different retention time group nd could be esily identified. Results nd discussion Clibrtion curves nd LODs SPE method. The quntittive determintion ws performed with FTD by internl clibrtion using uthentic stndrds. GC-FTD hs frequently been the instrumentl technique of choice for determintion of orgnophosphorus insecticides for resons of selectivity nd sensitivity [29]. Smple nlyses were run in triplicte. Ech stndrd solution contined 1 µg/l dizinon s internl stndrd (I.S.). Tble 4 gives the retention times nd reltive response fctors (RRF) for the internl stndrd dizinon s well s for 10 selected insecticides in GC-FTD with DB-1 column. Limits of detections (LODs) were clculted by compring the signl to noise rtio (S/N) t the lowest concentrtion to S/N 3. SPME method. Series of seven levels were obtined by spiking HPLC-grde wter with ll the insecticides in concentrtion rnge of 0.1 to 10 µg/l. The response of FTD system ws clibrted for ech nlyte by direct injection in the splitless mode of stndrd insecticide mixtures. Ech solution ws run in triplicte. In ll cses, there ws liner regression (p < 0.05) for the nlyte concentrtion rnge tested (Fig. 1). The regression line prmeters

5 620 Tble 5 Anlyzed insecticides, limits of detection nd linerity dt in the GC-FTD, GC-MS by using SPME PA 85 µm fiber Pek No./ Lin- GC-FTD GC-MS compounds erity LOD R.S.D b LOD R.S.D b (µg/l) (µg/l) 1. Dichlofenthion Prthion methyl Fenitrothion Mlthion Fenthion Prthion ethyl Bromophos methyl Bromophos ethyl Fenmiphos Ethion LOD = limit of detection b R.S.D. = reltive stndrd devition A B Fig. 3 GC-FTD chomtogrm obtined by PA 85 µm fiber, c. 2 µg/l of 10 selected insecticides in spiked river wter (A), nd wter smple of Klms river under the sme experimentl conditions (B). DB-1 column, 30 m long contining dimethylpolysiloxne ws progrmmed from 100 C (2 min) to 210 C (30 min) t 5 C/min nd to 270 C (4 min) t 20 C/min. For pek numbers see Tble 3 A B Fig. 2 GC-FTD chomtogrms obtined by C18 disks, c. 2 µg/l of 10 selected insecticides in spiked river wter (A) nd wter smple of Klms river under the sme experimentl conditions (B). DB-1 column, 30 m long contining dimethylpolysiloxne ws progrmmed from 100 C (2 min) to 210 C (30 min) t 5 C/min nd to 270 C (4 min) t 20 C/min. For pek numbers see Tble 3 re shown in Tble 5. Figures 2 nd 3 show typicl gs chromtogrms obtined fter extrction of the tested insecticides with C 18 disks nd PA fiber t 2 µg/l level wter smples of river Archthos. Due to the selectivity of the detector, no interference ws noticed in the GC-FTD retention time dt of these compounds. The dt of Tbles 4 nd 5 show tht both techniques (SPE, SPME) llow the detection of the insecticides in wter t concentrtions lower thn 70 ng/l, but SPME shows lower LODs nd better linerity for lmost ll the nlytes. The precision obtined, expressed s R.S.D, ws lower thn 10% in SPME method with the exception of ethion. The chromtogrphic seprtion nd the precision of the method could be improved by utomting the whole process due to the fct tht the extrction efficiency is bsed on equilibrium, directly ffected by the time [17]. Prmeters influencing the SPME process. The different prmeters tht cn ffect the SPME (the pproprite time period for the extrction, ph, stirring rte, solvent content nd the time for the desorption of the nlytes) were optimized. An extrction time of 45 min ws selected lthough t this time equilibrium concentrtions were not yet chieved for most pesticides. For routine nlysis it is not necessry to rech complete equilibrium s long s the exposure time of the fiber is kept exctly constnt [17]. The effect of the ph ws nlyzed using different smples in the rnge from 2 to 10 by dding phosphte buffer, respectively. Vrying the ph from 2 to 10 no significnt effect ws observed on the extrction of the nlytes by

6 621 Tble 6 Men recovery of 10 selected orgnophosphorus insecticides in nturl wter smples by using C18 nd SDB Empore extrction disks Pek No./compounds Men Recoveries (%) Distilled Underground Archthos Pmvotis Ionin wter wter river Lke Se (Ionnin) Disk C Dichlofenthion Prthion methyl Fenitrothion Mlthion Fenthion Prthion ethyl Bromophos methyl Bromophos ethyl Fenmiphos Ethion spiking levels of 0.1, 0.2, 0.5, 1, 2, 5, 10 µg/l, N = 3 Disk SDB 1. Dichlofenthion Prthion methyl Fenitrothion Mlthion Fenthion Prthion ethyl Bromophos methyl Bromophos methyl Fenmiphos Ethion the fiber, therefore further nlyses were crried out without djusting the ph. Furthermore, the ph of the nturl wter smples ws in the neutrl region (round 7) nd the nlytes hve n cceptble response t this vlue. The optimum stirring rte ws determined by nlyzing smples contining 10 µg/l of trget insecticides t different stirring rtes. The obtined results show tht with no gittion very poor extrction level ws chieved nd tht the extrction efficiency incresed s the stirring rte incresed. However, the mount of extrcted nlytes decreses for gittion over 1250 rpm becuse t the mximum speed the stirring br begins to vibrte nd gittion of the smple becme worse. Thus, the selected optimum stirring rte ws found to be 960 rpm. In order to study the crry over effect of the fiber blnk desorption experiment ws run. After extrction of ten studied insecticides, no crry over from previous run ws observed, indicting tht these compounds re redily desorbed from the fiber during the 5 min injector desorption for GC-FTD nlysis. Recoveries The results of men recoveries in the SPE method of the selected orgnophosphorus insecticides in nturl wter smples by using extrction disks re given in Tble 6. Recoveries were clculted by using the internl stndrd method; recoveries obtined for distilled wter smples with both disks (C 18 nd SDB) were higher thn 80% for ll the compounds, thus indicting tht the use of the disks does not pose ny problem to the nlysis of such type of wter. The recoveries obtined re within the EPA recommendtions (from 65 to 115%) for these levels of detection in wter smples. The recoveries of ll insecticides were higher in distilled wter compred to underground nd surfce wters (river, lke nd mrine wter). The min differences mong the studied surfce wters re the high conductivity nd the totl suspended mtter in Ionin se s well s the higher concentrtion of the totl orgnic crbon in Archthos river wter. The studied orgnophosphorus compounds were recovered with C 18 disks from underground wter smples in reltively high levels ( %), lso from river ( ) nd mrine wters ( %) compred to lke wter ( %). The recoveries with SDB disks vried from 60.7 to 83.5% in underground wter, from 60.7 to 71.8% in river wter, from 70.9 to 82.5% in mrine wter nd from 70.6 to 89.7 in lke wter. Similr recoveries nd detection limits in the rnge of µg/l for pesticides were reported elsewhere [30, 31]. The SPME technique shows higher recoveries in comprison to SPE disks for ll the nlytes in lmost ll the types of wters. The men recoveries compred to distilled wter obtined for the 10 selected insecticides spiked in four different types of wter re shown in Tble 7.

7 622 Tble 7 Men recovery of 10 selected orgnophosphorus insecticides in nturl wter smples by using solid phse microextrction fiber PA 85 µm spiking levels of 0.1, 0.2, 0.5, 1, 2, 5, 10 µg/l, N = 3 Pek No./compounds Men Recoveries (%) Underground Archtos river Pmvotis Lke Ionin Se wter (Ionnin) 1. Dichlofenthion Prthion methyl Fenitrothion Mlthion Fenthion Prthion ethyl Bromophos methyl Bromophos ethyl Fenmiphos Ethion Tble 8 Concentrtions (µg/l) of insecticides detected in wter smples from Greek rivers using SPE (C18 disks) nd SPME (PA 85 µm) bdl: below detection limit Compounds Klms river Louros river Archthos river (pek number) SPE SPME SPE SPME SPE SPME 1. Prthion methyl (2) Mlthion (4) bdl Prthion ethyl (6) Ethion (10) The recovery of ll insecticides ws over 86.2% nd reched 119.7%, in river wter from 86.2% to 102.1%, in lke wter from 89.8% to nd in mrine wter from to 116.7%. The linerity ws checked lso in nturl wter smples nd the obtined equtions show correltion coefficients from to for both proposed methods. Environmentl levels Nturl wter smples, collected from rivers Archthos, Klms nd Louros ner Ionnin (Greece), were nlyzed by both proposed methods using SPE-C18 disks nd SPME, PA fiber (Tble 8). The corresponding GC-FTD chromtogrm obtined by SPE nd SPME for river wter smples re shown in Fig. 2 nd Fig. 3. The obtined chromtogrms show lso the presence of severl non-identified compounds in the smple. However, these peks do not interfere with the retention times of the trget nlytes. The identity of these insecticides ws confirmed in the SPE-C18 extrct by GC-MS ccording to the procedure described previously. The concentrtions of insecticides detected re similr to those reported for surfce wters in the Mediterrnen region [3]. Some differences could be explined by considering tht SPME technique shows higher recoveries in comprison with SPE for most of the nlytes in ll the types of wter. The effect of orgnic nd prticulte mtter on the SPME fiber is unknown, but it ppers to reduce the fiber s life nd the dsorption cpcity fter severl extrctions possibly by covering the fiber surfce irreversibly resulting in crry over effect or ltertion of the fiber surfce. As finl result the fiber sorptive cpcity nd efficiency is reduced. Ech fiber cn be re-used mny times with nturl wters, e.g times depending on the wter content of orgnic nd prticulte mtter. Fibers hve been used more thn 100 times with distilled wter nd 27 times in run-off wter s reported elsewhere [32-34]. Conclusions The combined use of GC-FTD nd GC-MS with the use of Empore extrction disks of C18 nd SDB bonded silic provides rpid, efficient nd reproducible method for the simultneous determintion of vrious insecticides in wters. The use of C18 nd SDB Empore disks ws found to be n effective procedure for trce pre-concentrtion of these insecticides for nturl wters. Limit of detection ws t lest 10 times below the drinking wter permissible level (0.1 µg/l) for individul pesticides. SPME with PA coting is precise, reproducible technique for both qulittive nd quntittive determintion of priority of insecticide residues in nturl wter (surfce nd underground) smples. The fiber cn be used repetedly (in contrst to the solid phse extrction (SPE) where the disks re used only once). The smll smple volume necessry (2-5 ml) my be ttrctive for mny pplictions where the smple volume is limited. Combined to gs chromtogrphy with mss spectrometry nd flme thermionic detectors very low detection limits cn be reched. Thus, the mximum level set by the Europen

8 Union for pesticides nd drinking wter cn be verified without difficulty. Acknowledgements This work ws supported by IAEA-Reserch Contrct No 8470/R 2 /UN. References 1. Brcelo D (1991) Anlyst 116: Font G, Mñes J, Moltó JC, Picó Y (1993) J Chromtogr A 642: Albnis TA, Hel DG (1995) J Chromtogr A 707: Slou JS, Alonso A, Btllo G, Brcelo D (1994) Anl Chim Act 293: Crespo C, Mrcé RM, Borrull F (1994) J Chromtogr A 670: Hu R, Bertion JM, Bordereu I, Fournier J (1996) Chromtogrphi 43: Arthur CL, Pwliszyn J (1990) Anl Chem 62: Dugy J, Miege C, Hennion MC (1998) J Chromtogr A 795: Potter DW, Pwliszyn J (1992) J Chromtogr A 625: Zhng Z, Pwliszyn J (1995) Anl Chem 67: Sntos FJ, Clcern MT, Frisse D (1996) J Chromtogr A 742: Bucholz KD, Pwliszyn J (1993) Environ Sci Technol 27: Brtk P, Cp L (1997) J Chromtogr A 767: Potter DW, Pwliszyn J (1994) Environ Sci Technol 28: Chen J, Pwliszyn J (1995) Anl Chem 67: Pn L, Adms M, Pwliszyn J (1995) Anl Chem 67: Eisert R., Levsen K (1995) Fresenius. J Anl Chem 351: Redmn JW, Albnis TA, Brcelo D, Glssi S, Tronczynski J, Gbrielides GP (1993) Mrine Pollution 26: Fielding M, Brcelo D, Helweg A, Glssi S, Torstensson L, Vn Zoonen P, Wolter R, Angeletti G (1992) Pesticides in ground nd drinking wter, Wter Pollution Reserch Report 27, Commission of the Europen Communities, Brussels 20. Noble A (1993) J Chromtogr A 642: Jury WA, Focht DD, Frmer WJ (1987) J Environ Qul 16: Wuchope RD, Buttler TM, Hornsby AC, Augustijn-Beckers PWM, Burt JP (1992) Rev Environ Cont Toxicol 123: Mills MS, Thurmn EM (1994) Environ Sci Technol 28: Hsset JJ, Bnwrt WJ (1989) The sorption of nonpolr orgnics by soils nd sediments. In: Rections nd movement of orgnic chemicls in soils. SSAA Specil Publiction Number 22, (eds) BL Swhney nd K Brown, Mdison, Wisconsin, USA 25. Brouwer ER, Lingemn H, Brinkmn UATh (1990) Chromtogrphi 29: Krmfilov VK, Filemn TW, Evns KM, Mntour RFC (1996) Anl Chim Act 335: Lcorte S, Molin C, Brcelo D (1993) Anl Chim Act 281: Brcelo D, Durnd G, Vreeken RJ, De Jong GJ, Brinkmn UATh (1990) Anl Chem 62: Htrík Š, Tekel J (1996) J Chromtogr A 733: Sennert S, Volmer D, Levsen K, Wünsch G (1995) Fresenius J Anl Chem 351: Cule M, Fenesn I, Cobzc S, Gosn S, Chiric M, Plibrod N (1996) Fresenius J Anl Chem 355: Grhm KN, Srn LP, Webster GRB, Gynor JD, Ng HYF (1996) J Chromtogr 725: Rogers HR, Comber SDW (1998) Chemosphere 8: Dugy J, Miege C, Hennion MC (1998) J Chromtogr A 195: 27 42