Determination of Pesticides in Food and Environment

8/2/2019 Determination of Pesticides in Food and Environment

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Review

Current trends in solid-phase-based extraction techniques for thedetermination of pesticides in food and environment

Yolanda Pic, Mnica Fernndez, Maria Jose Ruiz, Guillermina Font

Laboratori de Bromatologia i Toxicologia, Facultat de Farmcia, Universitat de Valencia, Av. Vicent Andrs Estells s/n, 46100 Burjassot, Valencia, Spain

Received 30 May 2006; accepted 27 October 2006

Abstract

Solid-phase extraction (SPE) procedures for pesticide residues in food and environment are reviewed and discussed. The use of theseprocedures, which include several approaches such as: matrix solid-phase dispersion (MSPD), solid-phase micro-extraction (SPME) and stir-barsorptive extraction (SBSE), represents an opportunity to reduce analysis time, solvent consumption, and overall cost. SPE techniques differ fromsolvent extraction depending on the interactions between a sorbent and the pesticide. This interaction may be specific for a particular pesticide, asin the interaction with an immunosorbent, or non-specific, as in the way a number of different pesticides are adsorbed on apolar or polar materials.A variety of applications were classified according to the method applied: conventional SPE, SPME, hollow-fiber micro-extraction (HFME),MSPD and SBSE. Emphasis is placed on the multiresidue analysis of liquid and solid samples. 2006 Elsevier B.V. All rights reserved.

Keywords: Solid-phase extraction; Solid-phase micro-extraction; Hollow-fiber micro-extraction; Stir-bar sorptive extraction; Matrix solid-phase dispersion; Food

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1172. Solid-phase-based extraction techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

2.1. Solid-phase extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1182.2. Solid-phase micro-extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1192.3. In-tube solid-phase micro-extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1212.4. Matrix solid-phase dispersion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1212.5. Stir-bar sorptive extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

3. Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1284. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

1. Introduction

The analysis of pesticide residues in food and environmentalsamples has received increasing attention in the last few de-cades, as can be deduced from the great number of papers

published dealing with this subject[14]. These compounds areusually determined by gas chromatography (GC), liquidchromatography (LC) or capillary electrophoresis (CE),depending on their polarity, volatility, and thermal stability[59]. Regulatory authorities provide assurance that any

pesticide remaining in or on the food is within safe limitsthrough monitoring programs or random sampling and analysisof raw or processed food on the market. In response to thisrequirement a number of methods have been developed and

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Corresponding author. Tel.: +34 96 3544295; fax: +34 96 3544954. E-mail address: [email protected] (G. Font).

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applied routinely for the control of pesticide residues in foodand environment [4,10,11].

In general, food and environmental samples cannot beanalyzed without some preliminary sample preparation, becausecontaminants are too diluted and the matrix is rather complex[2,4]. Due to the low detection levels required by regulatory

bodies and the complex nature of the matrices in which thetarget compounds are present, efficient sample preparation andtrace-level detection and identification are important aspects ofanalytical methods [4]. Sample preparation, such as extraction,concentration, and isolation of analytes, greatly influences thereliability and accuracy of their analysis [2]. In recent years,many innovations in the analytical processes that can be appliedto prepare food and environmental samples for extractionand determination of pesticide residues have been developed[1220]. This has resulted in the recognition that classicalmethods can now be replaced with procedures that are faster,less expensive, and equal to or better than classical methods.

Although most officially methods for the analysis of pesti-cides use liquid/liquid extraction (LLE), solid-phase extraction(SPE) has been developed as an alternative, owing to itssimplicity and economy in terms of time and solvent needs[21,22]. This technique has gained wide acceptance because ofthe inherent disadvantages of LLE, e.g., it is unable to extract

polar pesticides, it is laborious and time-consuming, expensive,and apt to form emulsions, it requires the evaporation of largevolumes of solvents and the disposal of toxic or flammablechemicals. In addition, recent regulations pertaining to the useof organic solvents have made LLE techniques unacceptable.Alternative solid-phase-based extraction techniques, whichreduce or eliminate the use of solvents, can be employed to

prepare samples for chromatographic analysis. These includeSPE, solid phase micro-extraction (SPME), matrix solid-phasedispersion (MSPD), and stir-bar sorptive extraction (SBSE)[15,1720]. The ideal sample preparation methodology should

be fast, accurate, precise, and consumes little solvent. Further-

more, this sample preparation should be easily adapted for fieldwork and employs less costly materials [2]. The solid-phase-

based extraction techniques could be the isolation techniquescapable of meeting these expectations.

The extraction of analytes from solid matrices is an activedevelopment area in sample preparation technology [21]. More-

over, there has been an increasing demand for new extractiontechniques amenable to automation with shortened extractiontimes and reduced organic solvent consumption [23]. Severalother sample preparation methods for organic compounds aresupercritical-fluid extraction (SFE) [13] and solidfluidfluidizing series extraction procedures, named fluidized-bedextraction (FBE) [23]. However, the application of SPEtechnology to the isolation of pesticides and related compoundshas grown enormously [15,17,21].

The aim of this review is to describe the current trends ofSPE of pesticides with special emphasis on articles published inthe last three years. The solid-phase-based extraction proce-

dures developed to isolate and pre-concentrate pesticide resi-dues as well as the principles and relative merits of each procedure are summarized and discussed. Isolation and pre-treatment steps in SPE of pesticide residues in food andenvironmental matrices are outlined. An overview of practicalapplication is given for SPE, SPME, in-tube SPME, MSPD, andSBSE methods.

2. Solid-phase-based extraction techniques

2.1. Solid-phase extraction

The SPE technique was first introduced in the mid-1970s

[16]. It became commercially available in 1978, and now SPEcartridges and disks are available from many suppliers. Con-ventional SPE is generally performed by passing aqueoussamples through a solid sorbent in a column. Pesticides areeluted from the solid medium with an appropriate organic

Fig. 1. GC/MS chromatogram of pesticide-spiked lemon essential oil (from Barrek et al. [43]).

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solvent. One highly important aspect in SPE is the selection ofthe sorbent. C-18 bonded silicas and styrene/divinyl benzeneco-polymers are the most frequently used. This technique iswidely applied to water samples [14,16,22,2439]. For liquidfoods, such as fruit juices, wine, and milk, acceptable recoveriescan be obtained. Before SPE can be applied to a solid matrix

(soil, vegetables and fruits), a separate homogenization stepand, often, filtration, sonication, centrifugation, and liquid/liquid clean-up are required [34,4056]. However, the presenceof interfering substances, such as salts, humic acids, and otherhumic substances in water; or proteins, lipids, and carbohy-drates in food; makes the determination of polar or early-eluted

pesticides, difficult or impossible. The use of selective solid phases, such as immunosorbents or molecularly imprinted polymers (MIPs) can solve these problems. MIPs are usedpreferentially, because of their low cost compared with im-munosorbents [25,57].

Compatibility of reversed-phase (RP) LC systems with

aqueous samples allows on-line coupling of SPE with theanalytical system. This on-line system is generalized for watersamples and typically handles the pre-concentration of analytesfrom 50- to 250-ml aqueous samples on a small cartridge,

packed with a suitable sorbent. Subsequent gradient elution ofthe trapped analytes into an analytical column or detectionsystem is carried out. Automated SPE on-line sample handlingcan be performed with commercially available equipment, withhand-made cartridges, and six-port switching valves [31,58,59].The advantages of on-line systems are: analyte enrichment,automated sample preparation and analysis, and minimizedlosses. The disadvantages of the on-line pre-concentration arethe reduced sample throughput, since only small sample

volumes can be processed, and lack of versatility of the system.The direct coupling of SPE with GC is more difficult, because itrequires effective elimination of traces of water. There are someanalytical methodologies that use automated SPE, followed bylarge-volume injection (LVI) by injectors with programmabletemperature vaporization (PTV), in combination with GC/MS[28]. This system provides a fast, reproducible, and sensitivetechnique for pesticide determination in drinking water.

The use of fully automated on-line RPLC/GC has also beenreported, mainly for the determination of pesticide residues inolive oil. This procedure, in conjunction with the through-oventransfer adsorption/desorption (TOTAD) interface can be car-

ried out without any other sample pre-treatment than a simplefiltration [44]. Automated, coupled on-line LC/GC systemshave numerous advantages, especially when a large number ofsamples is to be analyzed. High sample throughput, as practicedroutinely in pharmacokinetic screening, is now expandingrapidly in other sectors, such as environmental and foodanalysis. However, the majority of reports on the application ofon-line SPE describe environmental monitoring of aqueoussamples with only a few for food analysis, e.g., mepiquat andchlormequat in pears, tomatoes, and wheat flour [60], and N-methylcarbamates and their metabolites in soil and food [61].Fig. 1 shows a gas chromatogram in SIM mode for a spikedsample of lemon essential oil, previously extracted with aFlorisil cartridge. The temperature ramp is an important step,

because it allowed elimination of residual volatile constituentsof the matrix, remaining after SPE extraction [43].

2.2. Solid-phase micro-extraction

SPME was first developed in 1989 by Pawliszyn and co-

workers and has been marketed by Supelco since 1993. Sub-sequently, the technique has grown enormously [1820]. It canintegrate sampling, extraction, pre-concentration, and sampleintroduction into a single uninterrupted process resulting in highsample throughput. A large number of fiber coatings based onsolid sorbents are now available, in addition to the originalgeneral-purpose poly(dimethylsiloxane) (PDMS) and poly(acri-late) (PA) coated fibers, namely: PDMS/divinylbenzene (DVB),Carbowax/DVB, Carbowax/template resin (TR), Carboxen/PDMS, and DVB/Carboxen/PDMS-coated fibers. Extraction of

Fig. 2. SPME/GC/AED chromatograms obtained from a honey sample, previously fortified with a standard mixture of pesticides: (A) S-181 nm;(B) Cl-479 nm; (C) Br-478 nm. 1 = 100 ng/g chlordimeform, 2 = 150 ng/gdimethoate, 3 = 2 ng/g aldrin, 4 = 20 ng/g parathion-ethyl, 5 = 80 ng/g captan,6 = 20 ng/g chlorfenvinphos, 7 = 3 ng/g dieldrin, 8 = 2 ng/g p,p'-DDE, 9 =0.5 ng/g p,p'-DDD, 10 = 1 ng/g p,p'-DDT, 11 = 10 ng/g bromopropylate, 12 =

3 ng/g tetradifon, 13 = 60 ng/g azinphos-methyl, 14 = 20 ng/g

-cyalothrin, 15 =5 ng/g cumaphos, 16 = 100 ng/g deltamethrin (from Campillo et al. [67]).

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analytes by the new porous polymer SPME fibers with mixedcoating is primarily based on adsorption rather than absorption.Some of these porous polymer SPME fibers with bipolar char-acteristics can be very useful for the simultaneous analysis of

pesticides, enlarging the spectrum of SPMEapplications [6265].Since its introduction, SPME has gained popularity as a simple

solvent-free, reliable, and flexible toolfor the samplingof a varietyof volatile and semi-volatile compounds. SPME has extensively

been used for the direct extraction of pesticides from aqueoussamples [63,6674]. On the other hand, fruit and vegetables,beingmostly in solid or heterogeneous form, do not allow directextraction. However, it is possible to analyze them by SPME aftera previous solvent extraction [62,75,76]. The SPME fiber can also

be suspended in the headspace above the homogenized sample.This option, named headspace-SPME (HS-SPME), eliminatesinterferences, because the fiber is not in contact with the complexmatrices of fruits and vegetables. Several classes of pesticide

residues have been extracted from complex matrices with HS-SPME [7782]. In contrast to the more conventional extractionmethods, SPME does not endeavour to extract all or even most ofthe analytes from a sample. It is this aspect of SPME that can makecalibration problematic. Calibrationin SPME is usuallyperformed

by spiking standards, prepared in pure water. For typical

heterogeneous environmental samples, the assumption is that anSPME fiber would come to equilibrium with only the freelydissolved analytes in the water phase or the analytes in the vapor

phase, depending on the methodology used. However, in such asample the fiber actually directly interacts with each phase in thesample. For example, as an analyte is depleted from the dissolved

phase by sorption on the fiber, the analyte is subsequentlyreplenished via re-equilibration in the other phases in the sample.Although recoveries are usually low (ca. 30%), the goodrepeatability and reproducibility of the methods allows satisfac-tory quantification of the analytes [66,69,70,83].

Fig. 3. Chromatogram obtained by using a proposed procedure for the new SPME fiber on the spiked samples of 10 ng ml 1 of each organophosphorus pesticide.

(A) water and (B) apple juice. Peak identification: 1 = dichlorvos, 2 = phorate, 3 = diazinon, 4 = methyl parathion, 5 = fenitrotion, 6 = malathion, 7 = parathion, 8 =ethion (from Linghsuang et al. [62]).



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The most common procedure for desorbing analytes from thefiber in SPME is thermal desorption in the injector of a gaschromatograph, because this desorption method completelyeliminates the use of organic solvents [66,69,79,83]. Theanalytes adsorbed on the fibers can also be desorbed by usinga polar organic solvent, such as MeOH or acetonitrile [84]. This

approach is used to combine this extraction technique with LC orCE. For LC, there is a commercial device that allow desorptionof all analytes accumulated in the fiber directly into the LCinjector. This system provides enhanced sensitivity [85]. Thereare twoways of desorbing analytes from the fiber[83]. When theanalytes are not strongly adsorbed on the fiber, the dynamicmode of desorption by a moving stream of mobile phase issufficient. But when the analytes are more strongly adsorbed onthe fiber, the fiber is dipped in the mobile phase or other strongsolvent for a specified time. Desorption performed in this way isknown as static desorption. Fig. 2 illustrates the elution profilesobtained at different channels from fortified honey, using a non-

polar (100-m) PDMS. As can be observed, the lack ofinterfering peaks provides unequivocal identification [67]. Thesample matrix can affect the SPME extraction efficiency. Fig. 3shows the chromatogram of apple juice compared with that of

pure water containing the same concentration of organophos-phorus pesticides, obtained with a vinyl crown ether polar fiber.The amounts of dichlorvos, malathion, and ethion extractedfrom apple juice were much less than those from pure water[62].

2.3. In-tube solid-phase micro-extraction

In-tube SPME is a relatively new micro-extraction and pre-concentration technique, which can be easily coupled on-line

with LC. An open-tubular capillary column with cross-linkedPDMS coating can be used to trap the analytes. A drying step isnecessary before the enriched compounds can be analyzed bythermodesorption and GC [12,86,87]. When a sample containsnon-volatile high-molecular interfering compounds, such as

proteins, humics acids, and fatty material, analysis by means

of in-tube SPME is difficult. To overcome this difficulty, aporous cellulose filter, protecting the coating, has been usedto determine pesticides [88,89]. On-line in-tube SPMEcontinuous extraction, concentration, desorption, and injec-tion with an autosampler, is commonly used in combinationwith LC and LC/MS.

2.4. Matrix solid-phase dispersion

In 1989, MSPD, a process for the extraction of solid sampleswas introduced by Barker et al. [17]. MSPD performs sampledisruption while dispersing its components into a solid support.

MSPD combines sample homogenization with preliminaryclean-up of the analytes [15]. The method involves the disper-sion of the sample in a solid sorbent, followed by preliminary

purification and the elution of the analytes with a relative smallvolume of solvent. The extracts obtained are generally ready foranalysis, but, if necessary, they can easily be subjected to directextract purification [90].

MSPD has demonstrated its usefulness in several difficultdeterminations [9193]. The most widely used procedure forseparating pesticides from the olive oil matrix has been size-exclusion chromatography (SEC). However, the main pitfallsassociated with this methodology are the use of large amountsof organic solvents and the lack of flexibility to change from

Fig. 4. Comparison of GC/MS full-scan olive oil matrix chromatograms, obtained by size-exclusion chromatography (SEC) and matrix solid-phase dispersion (MSPD)extraction (from Ferrer et al. [92]).



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one method to another. Moreover, the separation of thepesticide fraction (which has a low molecular weight) from thewhole fatty matrix (mainly triglycerides) is very difficult toaccomplish by SEC, because those two fractions are partiallyoverlapping. Normally, a compromise between purity of theextract (minimizing the amount of fat in the pesticide fraction)

and acceptable pesticide recoveries must be made. Thisusually involves the lost of some of the pesticides [92], thusyielding lower mean percentage recoveries. These drawbackscan be partially circumvented with the use of the MSPD,which involves less reagent consumption and waste generationand provides more flexibility. In addition, the resultantextracts are cleaner than those obtained by SEC, as can beseen in Fig. 4, where the full-scan GC/MS olive oil matrixchromatogram obtained by means of SEC is compared withthat obtained with MSPD. The chromatogram obtained byextraction with the MSPD method was much cleaner than thatobtained with SEC at two different collection times of the

pesticide fraction. This illustrates the capabilities of MSPD to provide clean extracts of such complex matrices with a highfat content.

2.5. Stir-bar sorptive extraction

In 1999, a new extraction technique was developed byBaltusen et al. [94]. In this extraction technique, known as stir-

bar sorptive extraction (SBSE), a magnetic stir bar, coatedwith 50300 l of polydimethylsiloxane (PDMS), is used. Theextraction mechanisms and advantages are similar to those ofSPME, but the enrichment factor, which is determined by theamount of extractive phase is up to 100 times higher. InSBSE, analytes are adsorbed on a magnetic rod, coated withPDMS, by stirring with it for a given time. After that, the stir

bar is either thermally desorbed on-line with capillary GC/MSor by organic solvents to be subsequently injected into an LCsystem [95].

Fig. 5. GC/TSD chromatograms of organophosphorus pesticides, obtained by an optimized SBSE method from: (A) water solution (800 ng/l); (B) spiked cucumber

sample (0.5 ng/g) and (C) a potato incurred sample. 1 = monocrotophos, 2 = phorate, 3 = dimethoate, 4 = parathion-methyl, 5 = malathion, 6 = fenitrothion, 7 =fenthion, 8 = chlorpyrifos, 9 = parathion, 10 = methidathion, 11 = triazophos, 12 = ethion (from Liu et al. [96]).



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Table 3In-tube SPME methods for pesticides

Analytes Matrices Pre-treatment Characteristics Elution Recovery (%) Detec

Phenylurea (6)and carbamate(6) pesticides

Water andwine

Samples extracted with 15 draw/ejectcycles 60-cm-long capillary,no buffer solutions or salts were used

PPY coated on inner surface of afused-silica capillary (60 cm,0.25 mm i.d.). Capillary cleanedwith acetone and MeOH, driedwith N2, and coupled to LC

SPME, coupledautomated in-tube toLC desorption withmobile phases

95104 (water)8997 (wine)

LC/U

Phenylurea (6)and carbamate(6) pesticides

Water andwine

Samples extracted with 15 draw/ejectcycles 60-cm-long capillary,no buffer solutions or salts were used.

PPY coated on inner surface of afused-silica capillary (60 cm, 0.25 mmi.d.). Capillary cleaned with acetone

and MeOH, dried with N2, andcoupled to LC

SPME, coupledautomated in-tube toLC desorption with

mobile phases

95104 (water)8997 (wine)

L C / EMS

Carbamates (6) Water Extraction by moving the samplein and out of the extraction capillary(25 aspirate/dispense steps at aflow-rate of 63 l/min)

Coated GC capillary (SPB-1, SPB-5,PTE-5, Supelcowax, Omegawax 250)and retention gap capillary(fused-silica without coating) wereused in the in-tube SPME

Desorption in-tubeSPME procedurewith MeOH

97100 LC/U

Organochlorinepesticides(15 OCP)

Water 1.2 cm of fiber, coated with 1 g/l ofPH-PPP in toluene. Extraction at 23 Cfor 30 min. in 30% NaCl and at pH 10.

PC-HFME Polymer-coatedhollow fiber. 600 m of i.d.,200 m wall; 0.2 m pore size

Sonication withhexane for 10 min.

85106 GC/M

Triazine herbicides(6 triazines)

Bovine milkand sewagesludge samples

65 m PDMS/DVB fiber. Extractionat 80 C for 40 min. in 30% NaCland at pH 10

HFM-SPME Polypropylenehollow fiber. 600 m (i.d.),200 m wall; 0.2 m pore size

Desorptions insplitless mode

88107 (milk)93113 (sludge)

GC/M

i.d.: inner diameter; HF: hollow fiber; HFM: hollow-fiber membrane; PC-HFME: polymer-coated hollow-fiber micro-extraction; HFM-SPME: hollow-fiber membran

flame-thermoionic detector; PH-PPP: polyhydroxylated polyparaphenylene; PDMS/DVB: polydimethylsiloxane/divinylbenzene; PPY: polypyrrole; PMPY: poly-N-met


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Typical chromatograms of organophosphorus pesticides instandard solution and a spiked cucumber sample, obtained bySBSE/GC/TSD, are shown in Fig. 5.

3. Applications

Selecting a suitable method of residue analysis will depend

on the problem at hand as well as on the final goal. To quote twowidely different situations, when large sample series have to bemonitored for a group of pesticides, such as organophosphorus

pesticides, sample throughput will be an important criterionsince speed is of the essence. In this situation, a screeningmethod is selected, because high sample throughput and speedare the characteristics of such a method. When, on the otherhand, samples are suspected to contain a prohibited pesticide,such as, e.g., methylparathion in oranges, method selectivitywill no doubt be the main criterion, because avoiding false non-compliant results is now of overriding importance. In thissituation, a confirmatory method is of interest, because it

provides full or complementary information, enabling confir-mation of the identity of the substance. Here our discussion will

be limited to method selection and a few comments on SPE thatcan be considered relevant in light of recent trends in pesticideresidue analysis.

The applications of the different SPE methods since 2003 for pesticide residues in food and environmental analysis arecompiled in Table 1 (SPE methods), Table 2 (SPME methods),Table 3 (in-tube SPME methods), Table 4 (MSPD methods), and

Table 5 (SBSE methods). An evaluation of the scientific literatureof the years 20032006 shows that some 100 papers on pesticide/drug residue analysis have been published. With regard to sampletreatment, SPE and SPME were found to be very popular, beingused in, respectively, 17 and 25% of all studies. The application ofMSPD, in-tube SPME,and SBSE is reported in only a fewpapers.In several instances, SPE and SPME were used in combination:after analyte isolation by means of SPE, the pesticides wereenriched by using a suitable SPME procedure. Fig. 6 displays theLC/MS chromatogramof an orange sample, extracted by different

procedures: solvent extraction (ethyl acetate), MSPD, and SBSE.This figure shows differences in sensitivity between the threeextraction methods as well as the absence of a carbendazim signalwhen SBSE was used [96].

Fig. 6. LC/MS chromatograms of an orange sample containing 0.02 mg/kg carbendazim, 0.07 mg/kg hexythiazox, 0.1 mg/kg methidathion, and 0.07 mg/kgpyriproxyfen after (A) ethyl acetate extraction (B) SBSE, and (C) MSPD. Peak identification: 3 = carbendazim, 5 = methidathion, 9 = pyriproxyfen, 10 = hexythiazox(from Blasco et al. [91]).



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4. Conclusions

Comparison of the above procedures applied to the SPE of pesticide residues indicates:

Conventional off- and on-line SPE is already a well-

established and routine technique. SPME and SBSE in combination with GC/MS or LC are

solvent-free or almost solvent-free procedures, obviating theneed for further preparation steps.

One advantage of SPME is the possibility of full automation;SBSE cannot yet be completely automated.

SPME is now a widely accepted and reliable technique forthe determination of several organic compounds. In theheadspace mode, it allows attainment of satisfactory LODsand cleaner chromatograms for volatile analytes.

SPME has been widely used in recent years, as demonstratedthe large number of applications reported in the literature in

comparison with other SPE procedures.

Acknowledgments

This work was financially supported by the Spanish Ministryof Science and Technology and the European RegionalDevelopment Funds (ERDF) (Project AGL2003-01407) and

by the Conselleria dEmpresa, Universitat i Ciencia (Project GV2005-109).

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Determination of Pesticides in Food and Environment

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