Food Chemistry 126 (2011) 646–654

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Food Chemistry

journal homepage: www.elsevier .com/locate / foodchem

Analytical Methods

Analysis of multi-pesticide residues in the foods of animal origin by GC–MS coupledwith accelerated solvent extraction and gel permeation chromatography cleanup

Gang Wu a,b, Xiaoxia Bao b, Shanhong Zhao b, Jianjian Wu b, Ailiang Han a, Qingfu Ye a,⇑a Institute of Nuclear Agricultural Sciences, Key Laboratory of Nuclear Agricultural Sciences of Ministry of Agriculture, Zhejiang University, Hangzhou 310029, Chinab Zhejiang Province Academy of Inspection and Quarantine Science and Technology, Hangzhou 310012, China

a r t i c l e i n f o a b s t r a c t

Article history:Received 21 April 2010Received in revised form 20 October 2010Accepted 31 October 2010

Keywords:Pesticides multi-residuesFood of animal originGC–MSAccelerated solvent extractionGel permeation chromatography

0308-8146/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.foodchem.2010.10.105

⇑ Corresponding author. Address: Institute of NuZhejiang University, 268 Kaixuan Road, Hangzhou 31086971423.

E-mail address: qfye@zju.edu.cn (Q. Ye).

A new analytical method was developed to simultaneously determine residues of 109 pesticides (includ-ing isomers) in the foods of animal origin. Acetonitrile was selected for accelerated solvent extraction(ASE) for effectively extracting the pesticides from the fatty samples. The cleanup was performed withan automated gel permeation chromatography (GPC) cleanup system. The prepared samples were ana-lysed with GC–MS in the selected ion monitoring mode (SIM) using one target and two qualitative ionsfor each analyte. Chlorpyrifos-d10 was used as an internal standard. The lowest limit of detection was0.3 lg kg�1 for some pesticides. The recoveries and relative standard deviations (RSDs) were checkedby spiking untreated samples with pesticides at 0.05, 0.1 and 0.2 mg kg�1. The average recoveries of mostpesticides were from 62.6% to 107.8%. The precision values expressed as RSD were all 620.5% (n = 6).Good linearity (r P 0.99) was observed between 0.05 and 1.5 lg mL�1.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Pesticides play a key role in pest management and preventinghuman being and domestic animals from infectious diseases. How-ever, it is important to remember that any pesticide should beconsidered an active poison (Hogsette, Koehler, & Kaufman,2006). The use of pesticides varies greatly among different partsof the world in types and quantities. Consequently, many interna-tional organisations such as the Codex Alimentarius Commission(CAC), WHO/FAO, and European Union (EU) as well as differentcountries have issued their own pesticide maximum residual limits(MRLs) in the international trade (Lin, 2002). Analysis of pesticideresidues is carried out by using many different methods for extrac-tion and clean-up, followed by a final analysis typically with chro-matographic measurements. Extraction of pesticide residues fromsamples produces complex mixtures that often require samplepurification and preparation steps to isolate the targeted pesticidesfor analysis. In addition, a multi-residue analytical strategy is oftennecessary to facilitate the quantitative determination of individualpesticide residues due to the differences among their chemical andphysical properties and incompatible detection techniques. Thecost of labour and materials, and long turnaround times could be

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significantly reduced if sample preparation and clean-up proce-dures were performed by automated methods.

Many traditional procedures used for extraction of fatty sam-ples are time consuming and solvent intensive. The more widely-used extraction techniques for pesticides are Soxhlet extraction(SOX), shake-flask, liquid–liquid extraction (LLE), solid-phaseextraction (SPE), solid-phase micro-extraction (SPME), matrix so-lid-phase dispersion (MSPD), supercritical fluid extraction (SFE),accelerated solvent extraction (ASE) and microwave-assistedextraction (MAE) (Ahmed, 2001). ASE is an extraction techniquethat speeds up the extraction process and reduces the total amountof solvent used. The system uses conventional solvents at elevatedtemperatures and pressures, which results in improved extractionkinetics to achieve quantitative extraction from solid and semisolidsamples in a short time with a small amount of solvent. This meth-od has been accepted as the standard method for solid sampleextraction by U.S. EPA Method 3545 (U.S. EPA, 2002).

The extraction step is usually followed by a cleanup procedure.The gel permeation chromatography (GPC), first used in 1972 byTindle and Stalling to separate pesticides from fish lipids usingpolystyrene gel, Bio-Beads SX-2, and cyclohexane solvent (Stalling,Tindle, & Johnson, 1972). Another system was further developed in1974, using Bio-Beads SX-3 and toluene–ethyl acetate for quantita-tive recovery of non-ionic chlorinated pesticides and polychlori-nated biphenyl compounds (Hopper, 1982). GPC appears to bethe best suited technique to multi-residue analysis as it affordscleanup of both polar and non-polar pesticides with a single injec-tion on a fully automated system. Therefore, GPC is now consid-

G. Wu et al. / Food Chemistry 126 (2011) 646–654 647

ered a universal cleanup procedure for separating pesticides fromlipids, waxes and other low volatile large non-polar co-extractives.It offers the best protection for GC capillary columns. The volumeof organic eluents used is reduced considerably by miniaturization(Stan, 2000).

A breakthrough in the field of sample preparation is the QuE-ChERS (quick, easy, cheap, effective, rugged, and safe) approachproposed by Lehotay et al. (Anastassiades, Lehotay, Stajnbaher, &Schenck, 2003; Lehotay, de Kok, Hiemstra, & van Bodegraven,2005). Compared with other sample preparation methods, QuE-ChERS is faster and less expensive with more ruggedness and com-patibility for a wide range of pesticide residues in differentcommodities, including baby foods (Kirchner, Húšková, Matisová,& Mocák, 2008). Ueno et al. conducted an extensive study on ana-lytical techniques for pesticide multi-residues in agricultural prod-ucts. Acetonitrile was adopted as the extracting solvent and, aftersalting-out, cleanup was performed by GPC with a graphitised car-bon column, silica gel and Florisil cartridges in series to detect 87pesticides in agricultural products by GC–MS (Ueno, Oshima, Saito,& Matsumoto, 2003, 2004). In 2001, Podhorniak et al. publishedmethods using acetone as extracting solvent and liquid–liquid par-titioning was performed with a miniature Hydromatrix column orwith dichloromethane before cleanup on graphitised carbon blackand primary secondary amine (PSA) cartridges (Podhorniak, Neg-ron, & Griffith, 2001).

To the present time, there have been few studies on automatedmulti-pesticide residues analysis in foods of animal origin (Frenich,Vidal, Sicilia, Rodríguez, & Bolaños, 2006; Hopper, 1999; Pang et al.,2006). A new method was developed in the current study. Themethod included ASE, automated GPC followed by the primary sec-ondary amine (PSA) packing material matrix solid-phase disper-sion, and the qualitative and quantitative detection by GC–MS inSIM mode based on retention times and selected ions and their rel-ative abundances.

2. Experimental

2.1. Chemicals

Acetonitrile, ethyl acetate, acetone, methanol, cyclohexane andn-hexane of HPLC grade were all from Tedia (Fairfield, OH, USA).Sodium sulphate anhydrous (Shanghai, China) was baked at650 �C for 4 h and stored in a desiccator before use. Certified stan-dards of pesticides (Table 1), including organophosphorus, organo-chlorine, carbamate and pyrethroid compounds, with puritiesranging from 95% to 99.9%, were purchased from Dr. Ehrenstorfer(Augsburg, Germany). Chlorpyrifos-d10 with purity of 97% wasfrom Sigma Aldrich (Buchs SG, Switzerland) and used as an internalstandard.

Stock standard solutions were prepared by accurately weighingindividual pesticide standards (5–10 mg, accurate to 0.1 mg) into10-mL volumetric flasks and dissolving and diluting to volume withacetone, ethyl acetate, hexane, or methanol, according to the com-pound’s solubility. Mixed standard solutions were stored in dark at4 �C before use. Chlorpyrifos-d10 was prepared in acetone and usedas the internal standard solution. Deionized water at 18.2 MX wasproduced on a RiOs/ELIX Synergy� water purification system (MIL-LIPORE, Molsheim, France). Working solutions (0.05 to 10 lg mL�1)were prepared by serial dilutions of the stock solutions with ace-tone and stored at �20 �C for a maximum period of 6 months.

2.2. Materials

Extrelut 20 diatomite was purchased from Merck (Darmstadt,Germany). The PSA packing material was purchased from Supelco

(Bellefonte, PA, USA). The polystyrene gel (Bio-Beads S-X3) wasfrom Bio-Rad (Hercules, CA, USA). In total, 50 different samplesof pork, beef, chicken and fish were purchased from local marketsand supermarkets in Hangzhou, China, and were analysed forpesticide residues. Pesticide-free samples monitored by our labo-ratory were used as blank, and to spike aliquots for recoverydetermination.

2.3. Instruments

The GC–MS system consisted of an Agilent 7890A GC (AgilentTechnologies, Shanghai, China), equipped with an Agilent 7683autoinjector (Agilent Technologies, Shanghai, China), coupled toan Agilent 5975C mass-selective detector (Agilent Technologies,Santa Clara, CA, USA). The detector was operated in electron impact(EI) ionisation mode (electron energy 70 eV). The GC was fittedwith a J&W DB-5MS fused silica capillary column (5% phenyl poly-siloxane as non-polar stationary phase, 30 m � 0.25 mm i.d. and0.25 lm film thickness) from Agilent (J&W Scientific, Folson, CA,USA). Helium with a purity of 99.999% from BOC Holdings Co.(Shuzhou, China) was used as the carrier gas. N-EVAP nitrogenblowing instrument was a product of Organomation (Berlin, MA,USA).

Accelerated solvent extraction was performed using a DionexASE 200 system (Dionex, Sunnyvale, CA, USA) equipped with33-mL extraction cells. The cleanup was performed by automatedgel permeation chromatography cleanup system of J2 ScientificAccuPrep MPS™ (J2 Scientific, Columbia, MO, USA). The meat chop-per from Sunzhong (Hangzhou, China) was used to prepare themeat samples. Büchi 205 rotavapor was the product of BüchiLabortechnik AG (Flawil 1, Switzerland). The electronic analyticalscales capable of weighing to 0.1 mg or to 0.01 g were from MettlerToledo (Greifensee, Switzerland).

2.4. Sample extraction and cleanup

The two procedures described below were used for isolation oftarget analytes from the samples of pork, beef, chicken and fishmatrices. The reagent blank samples were prepared under thesame conditions as the other samples, except without the real sam-ple matrix.

2.4.1. ASE extraction procedureTen grams of homogenised pork, beef, chicken or fish meat sam-

ple and 5 g Extrelut 20 were weighed, and mixed in a mortar with apestle till homogeneous and dehydrated. The mixture was loadedinto 33 mL stainless cells and packed tightly. A cellulose micro-fil-ter was placed at one end (bottom) of each cell. Cells were tightlyclosed and extraction was performed under the following condi-tions: extraction temperature, 80 �C; extraction pressure,1500 psi (10.3 MPa); heating time, 5 min; and static extractionperiod, 5 min. The sample was then rinsed with 60% of cell volumeacetonitrile and purged with nitrogen for 100 s with two staticcycles. Under the fixed ASE conditions, extractions were conductedto compare the extraction efficiency of three solvent systems: ace-tonitrile, hexane–acetone (2:1, v/v), and cyclohexane–ethyl acetate(1:1, v/v). The extract was transferred into a flat-bottomed flaskand condensed to a small volume (1–2 mL) on a Büchi rotavaporat 40 �C under vacuum, after which the extract was dried under agentle nitrogen stream. The residue was redissolved in 2 mL ofcyclohexane–ethyl acetate (1:1, v/v) mixture and transferred to a5-mL vial for injection into the GPC system.

2.4.2. Sample cleanupTo remove fat and other matrix interferences, cleanup was done

by using an automated GPC cleanup system J2 Scientific AccuPrep

Table 1The parameters for determination of the 109 pesticides (including isomers) by GC–MS.

No. Pesticides Retention time(min)

Tiona

(m/z)Q1b (m/z) (relativeabundance, %)

Q2c (m/z) (relativeabundance, %)

LOD (S/N = 3)(lg kg�1)

LOQ (S/N = 10)(lg kg�1)

ISTDd d10-Chlorpyrifos 34.990 200 292(39.6) 324(97.9)

1 Propoxur 7.273 110 152(15.4) 81(8.1) 1.0 3.32 Isoprocarb 8.085 121 136(31.8) 103(20.4) 2.0 6.73 Trichlorfon 9.401 109 185(8.2) 220(29) 5.1 17.04 Dichlorvos 9.401 109 185(29) 220(5.6) 6.0 20.05 Trimethacarb 10.491 121 136(88.7) 115(3.8) 1.7 5.76 Fenobcarb 10.592 121 150(18.2) 135(4.6) 1.3 4.37 Carbofuran 11.249 164 149(87.3) 131(35.7) 1.0 3.38 Indoxacarb 14.092 235 203(54.3) 176(34.6) 2.0 6.79 3-Hydroxycarbofuran 17.206 137 147(26) 180(37.1) 3.5 11.7

10 Carbaryl 17.513 144 115(92.9) 89(11.5) 0.61 2.011 Methiocarb 20.774 168 153(66.4) 109(50) 0.55 1.812 Omethoate 22.051 156 110(90.6) 213(6.6) 0.4 1.513 Pyraclofos 22.607 194 138(15) 111(23.9) 0.6 2.014 Tau-fluvalinate 23.03 250 266(18.9) 309(11.1) 1.2 4.015 Pentachloronitrobenzene 25.272 237 249(71) 295(65.9) 1.2 4.016 Sulfotep 25.273 322 202(48.9) 266(29.8) 0.1 0.517 Monocrotophos 25.277 127 192(48.5) 223(17.2) 32.3 107.718 Phorate 25.73 121 231(22.1) 260 (35.5) 0.7 2.519 HCB 25.74 284 249(25.2) 214(14.9) 0.2 0.720 a-BHC 25.761 181 219(81.7) 254(3.4) 0.5 1.621 Dicloran 26.727 206 160(53.3) 176(95) 0.8 2.722 Dimethoate 26.905 125 143(22.4) 229(15.2) 1.5 5.023 Ethoprophos 27.544 158 200(37.7) 242(16.1) 1.8 6.024 b-BHC 28.026 181 219(98.8) 183(10) 0.8 2.725 c-BHC 28.386 181 219(87.6) 254(9.3) 1.7 5.726 Fonofos 28.696 109 137(46.4) 246(41.3) 1.0 3.327 Propetamphos 29.006 138 194(43.9) 236(27.2) 0.3 1.028 Phosphamidon-I 29.245 127 193(10.5) 264(18.3) 3.9 13.029 Disulfoton 29.784 153 186(89.5) 274(66.8) 0.8 2.730 d-BHC 30.353 181 219(92) 254(8.8) 1.3 4.331 Pirimicarb 30.923 166 238(22) 138(7.5) 1.3 4.332 Phosphamidon-II 31.75 127 193(9.5) 264(37.8) 0.8 2.733 Chlorpyrifos-methyl 32.067 286 197(6.9) 212(2.8) 0.3 1.034 Vinclozolin 32.511 212 198(96.8) 212(86.1) 1.0 3.335 Parathion–methyl 32.518 263 246(7.6) 233(10.5) 0.8 2.736 Heptachlor 32.621 272 237(39.3) 372(10.8) 0.4 1.337 Paraoxon 33.567 275 247(81.4) 220(79) 1.1 3.738 Octachlorodipropyl ether 33.575 130 181(18.3) 211(8.6) 0.9 3.039 Fenitrothion 34.234 277 125(81.8) 260(56.6) 0.6 2.040 Pirimiphos–methyl 34.245 290 276(86.1) 305(69.7) 0.2 0.741 Aldrin 34.821 263 293(44.7) 364(2.1) 0.6 2.042 Chlorfenson 34.821 251 139(77.5) 178(6.6) 0.4 1.343 Malathion 35.056 173 158(45.5) 285(5.5) 0.2 0.744 Chlorpyrifos 35.233 197 258(43.9) 314(79.3) 3.2 10.745 Fenthion 35.538 278 169(20.2) 245(5.2) 0.1 0.346 Parathion 35.767 291 235(19.9) 263(13.7) 0.2 0.747 Triadimefon 36.004 208 181(33.9) 293(6.5) 1.1 3.748 Dicofol 36.045 139 215(9.6) 250(29.9) 0.4 1.349 Isofenphos 38.029 213 255(38.4) 345(1.9) 0.9 3.050 Fipronil 38.214 367 213(30.1) 351(7.8) 0.2 0.751 Chlordane-I 38.234 373 237(99.8) 272(61.5) 1.5 5.052 Phenthoate 38.344 274 246(26.7) 320(4.6) 0.4 1.353 Quinalphos 38.357 146 157(74.5) 298(20.4) 0.7 2.354 Procymidone 38.534 283 212(10.6) 255(12.7) 0.4 1.355 Allethrin-I 38.55 123 136(18.6) 168(4.3) 0.42 1.456 Allethrin-II 38.628 123 136(18.9) 168(4.3) 0.55 1.857 Chlordane-II 38.95 373 237(14.9) 272(12.9) 1.5 5.058 Methidathion 39.071 145 125(21.7) 157(18.8) 0.8 2.759 Bromophos–ethyl 39.182 359 303(76) 331(35.6) 0.4 1.360 Hexythiazox 39.437 156 184(54) 227(53.7) 4.0 13.361 a-Endosulfan 39.632 241 265(49.9) 339(34.4) 4.6 15.362 Methothrin-I 40.186 135 123(93.8) 105(22.7) 2.8 9.363 Methothrin-II 40.808 123 135(81) 105(15.8) 0.5 1.764 Pretilachlor 41.163 162 238(88) 262(32) 0.3 1.065 Dieldrin 41.312 263 345(34.1) 380(31) 0.9 3.066 p,p0-DDE 41.415 246 318(81.8) 281(8) 0.9 3.067 o,p0-DDD 41.775 235 165(31.8) 199(12.8) 0.3 1.068 Myclobutanil 41.913 179 206(21.4) 288(12.6) 0.8 2.769 Carboxin 41.956 235 143(59.3) 115(4.8) 0.3 1.070 Buprofezin 42.008 172 249(20.3) 305(28.7) 0.6 2.071 Flusilazole 42.042 233 206(32.8) 315(9.9) 0.3 1.072 Chlorfenapyr 42.515 247 328(54.2) 363(45.5) 2.2 7.373 Endrin 42.521 263 317(17.2) 345(23.4) 1.9 6.374 b-Endosulfan 42.863 237 267(62.6) 339(50.1) 4.4 14.7

648 G. Wu et al. / Food Chemistry 126 (2011) 646–654

Table 1 (continued)

No. Pesticides Retention time(min)

Tiona

(m/z)Q1b (m/z) (relativeabundance, %)

Q2c (m/z) (relativeabundance, %)

LOD (S/N = 3)(lg kg�1)

LOQ (S/N = 10)(lg kg�1)

ISTDd d10-Chlorpyrifos 34.990 200 292(39.6) 324(97.9)

75 Nitrofen 42.866 283 202(50.5) 253(24.2) 1.2 4.076 p,p0-DDD 44.017 235 165(39.7) 199(13.6) 0.7 2.377 o,p0-DDT 44.017 235 165(39.7) 199(13.6) 0.7 2.378 Iprodione 44.204 187 161(6.4) 244(2.1) 3.7 12.379 Triazophos 45.124 161 257(35.8) 285(25.6) 1.3 4.380 Carbophenothion 45.492 157 199(23.8) 342(38.4) 0.4 1.381 Endosulfan sulphate 45.561 272 387(62.1) 422(19.5) 1.6 5.382 Propiconazole-I 45.745 173 259(85.4) 191(27.7) 1.4 4.783 p,p0-DDT 45.948 235 165(37) 199(12) 1.2 4.084 Propiconazole-II 46.009 173 259(80.1) 191(27.2) 2.6 8.785 Phosmet 47.706 160 192(2.1) 317(4.1) 0.5 1.786 Tetramethrin-I 47.811 164 123(31.6) 135(3.9) 0.8 2.787 EPN 47.861 157 185(28.9) 323(10.8) 1.2 4.088 Bifenthrin 48.016 181 166(28.7) 152(3.2) 0.2 0.789 Tetramethrin-II 48.113 164 123(31.8) 135(4.0) 0.2 0.790 Tebufenpyrad 48.461 318 276(46.1) 333(74) 0.4 1.391 Tetradifon 48.696 159 229(53.5) 356(53.5) 0.8 2.792 Phenothrin-I 48.727 123 183(71.4) 350(5.3) 2.4 8.093 Phosalone 48.903 182 154(19.9) 367925.1) 0.3 1.094 Phenothrin-II 48.925 123 183(61.7) 350(4.7) 0.6 2.095 Azinphos–methyl 48.969 160 132(87.2) 125(21.7) 0.7 2.396 Lambdacyhalothrin-I 49.342 181 197(77.3) 208(52.7) 0.8 2.797 Lambdacyhalothrin-II 49.591 181 197(74.1) 208(65.1) 0.3 1.098 Permethrin-I 50.627 183 163(21.4) 255(2.1) 0.3 1.099 Coumaphos 50.756 362 226(64.7) 334(17.2) 0.1 0.3

100 Permethrin-II 50.817 183 163(30.9) 255(2.0) 0.4 1.3101 Pyridaben 50.823 147 309(6.9) 364(6.1) 0.1 0.3102 Flucythrinate 50.937 197 141(13.6) 157(17.4) 1.8 6.0103 Ethofenprox 52.503 163 183(7.1) 135(15.8) 0.4 1.3104 Esfenvalerate-I 53.594 167 181(59.2) 225(45) 2.5 8.3105 Cyfluthrin-I 53.594 167 225(42.8) 419(25.9) 1.7 5.7106 Cyfluthrin-II 54.034 167 225(42.8) 419(25.9) 4.0 13.3107 Esfenvalerate-II 54.036 167 181(80.5) 225(42.8) 4.0 13.3108 Deltamethrin-I 54.851 181 209(27) 253(79.7) 11.0 33.0109 Deltamethrin-II 55.32 181 209(28.9) 253(89.8) 5.5 18.3

a Target ion, also as quantitative ion, the abundance of Tion as 100%.b Qualitative ion 1.c Qualitative ion 2.d Internal standard.

G. Wu et al. / Food Chemistry 126 (2011) 646–654 649

MPSTM. The GPC organic mobile phase was cyclohexane–ethyl ace-tate (1:1, v/v) in isocratic mode. Bio-Beads S-X3 (40 g) was packedin the column (300 � 10 mm i.d.). The flow rate was 5 mL min�1,detection wavelength was 254 nm, and injection volume was1 mL. The fraction from 8 to 20 min was collected (about 60 mL).The collected GPC fraction was evaporated to a small volume andthen dried under a gentle nitrogen stream. The residue was redis-solved in 5-mL acetonitrile and transferred to a 10-mL centrifugetube, followed by the addition of 0.2 g PSA and mixing on a vortexmetre at 2000 rpm. After centrifugation at 2108g, the organicphase was transferred to another 10-mL centrifuge tube and driedin the N-EVAP nitrogen blowing device. The final solution wasamended with 0.5 mL internal standard solution in acetone andsubjected to analysis by GC–MS.

2.4.3. Qualitative and quantitative analysis by GC–MSThe final samples were analysed on an Agilent 7890A GC,

equipped with an Agilent 7683 autoinjector, coupled to an Agilent5975C mass-selective detector. MS with electron-impact (EI) ioni-sation (electron energy, 70 eV) was performed in the selected ionmonitoring (SIM) mode. The column temperature program wasas below: 60 �C hold for 0 min, ramp at 30 �C min�1 to 100 �C, holdfor 3 min, ramp at 3 �C min�1 to 220 �C, hold for 3 min, ramp at10 �C min�1 to 280 �C, and hold for 10 min. The carrier gas (helium)flow rate was 1.2 mL min�1, injection port temperature was 250 �C,

and injection volume was 2 lL. The injection was made in thesplitless mode with purge on after 1.5 min. The ion source temper-ature was 230 �C, the quadrupole temperature was 150 �C, and theGC–MS auxiliary temperature was 280 �C. In the SIM mode, eachcompound was monitored with one quantitative ion and two qual-itative ions. All of the selected ions were monitored according tothe programmed time and sequence of peaks (Table 2). The reten-tion time, quantitative ions, and the abundance ratios of quantita-tive ions of each compound are given in Table 1. For identificationof pesticides, the retention time and three ions were used with theassistance of the NIST’s pesticide library (Gaithersburg, MD, USA).

3. Results and discussion

3.1. Optimisation of accelerated solvent extraction procedure

The selection of pesticides was based on the MRLs stipulated fora variety of foods by CAC, EU, USA, Japan, and China (Lin, 2002).ASE was selected as the extraction method. In comparison withmethods such as Soxhlet extraction, automated Soxhlet extraction,sonication extraction, supercritical-fluid extraction, or the classicalliquid–liquid partitioning methods, ASE consumes less solvent andtime. It also has marked advantages such as high-level automation,high efficiency of extraction, good selectivity, easy operation,improved safety and good environment-compatibility. The

Fig. 1. (a) The eluting chromatogram of 109 pesticides (including isomers) from the GPC. (b) The eluting chromatogram of pesticides spiked into the beef samples from theGPC.

Table 2The time segmented group of related selected ions monitored for the 109 pesticides (including isomers) in GC–MS analysis.

No. Segment time(min)

Monitored ions (m/z) Dwell timea

(ms)

1 3 81,103, 110, 121, 136, 152 502 8.47 94, 126, 141 503 9.04 109, 145, 185, 220 504 9.96 115, 121, 131,135, 136, 149, 150, 164 305 12.05 176, 203, 235 506 15.18 137, 147, 180 507 18.15 89, 115, 144 508 20 109,110,136,142, 153, 156, 168,183,213, 250,266, 309 259 24 121, 127, 181, 192, 202, 214, 219, 223, 231, 237, 249, 254,260, 266, 284, 295, 322 20

10 26.05 125, 143, 160, 176, 206, 229 2511 27.04 158, 179, 181, 200, 219, 227, 242, 254, 304 2512 28 109, 127, 137, 138, 193, 194, 229, 236, 246, 264, 266 2513 29.33 138, 153, 166, 181, 186, 219, 238, 254, 274 2514 31.2 111, 127, 130, 138, 181, 193, 194, 197, 198, 211, 212, 220, 233, 237,246, 247, 263, 264, 272, 275, 285, 286, 372 2015 33.73 125, 260, 276, 277, 290, 305 2516 34.4 107, 117, 139, 158, 169, 173, 178, 181, 182, 197, 200,215, 235, 245, 250, 251, 258, 263, 264, 278, 285, 291,292, 293, 314, 324,

36420

17 36.96 123, 125, 136, 145, 146, 156, 157, 168, 184, 212, 213, 227,237, 241, 246, 255, 265, 272, 274, 283, 298, 303, 320, 331,339, 345,351, 359, 367, 373

20

18 39.9 105, 123, 135 5019 40.6 105, 115, 123, 135, 143, 162, 165, 172, 179, 199, 206, 233,235, 238, 246, 249, 262, 263, 281, 288, 305, 315, 318, 345,380 2020 42.3 202, 237, 247, 253, 263, 267, 283, 317, 328, 339,345, 363 2521 43.1 161, 165, 187, 199, 235, 244, 257, 285 2522 45.24 157, 165, 173, 191, 199, 235, 259, 272, 342, 387, 422 2523 46.86 123, 125, 132, 135, 152, 154, 157, 159, 160, 164, 166, 181, 182,183, 185, 192, 229, 276, 317, 318, 323, 333, 350, 356, 367 2024 49.2 181, 197, 208 5025 50 135, 141, 147, 157, 163, 183, 197, 226, 255, 309, 334, 362, 364 2526 53.02 167, 181, 209, 225, 253, 419 25

a Dwell time per ion (ms).

650 G. Wu et al. / Food Chemistry 126 (2011) 646–654

conditions used in the ASE extraction were developed from the U.S.EPA standard SW-846 method and Richter et al. (Richter, Jones,

Ezzell, & Porter, 1996; US EPA, 2002). To increase extraction effi-ciency, Extrelut 20 was chosen as a desiccant and disperser during

Table 3Recoveries and the relative standard deviations (RSD) obtained at three fortification levels for 109 pesticides (including isomers) in beef samples (n = 6).

No. Pesticide Spiked 0.05 mg kg�1 Spiked 0.1 mg kg�1 Spiked 0.2 mg kg�1

Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%)

1 Propoxur 65.4 ± 3.2 4.9 73.9 ± 11.5 15.6 73.8 ± 5.2 7.02 Isoprocarb 64.3 ± 1.7 2.7 71.1 ± 4.3 6.1 68.1 ± 4.7 6.93 Trichlorfon 65.6 ± 4.6 6.3 70.2 ± 2.6 3.7 72.3 ± 7.7 10.74 Dichlorvos 65.8 ± 4.5 6.0 70.2 ± 2.6 3.7 72.3 ± 7.7 10.75 Trimethacarb 66.2 ± 5.0 7.5 80.5 ± 7.5 9.3 82.1 ± 8.1 9.96 Fenobcarb 69.6 ± 5.4 7.7 81.4 ± 11.1 13.7 81.9 ± 10.0 12.37 Carbofuran 69.2 ± 7.4 10.7 77.4 ± 10.7 13.8 80.6 ± 7.9 9.88 Indoxacarb 73.3 ± 11.1 15.2 79.3 ± 5.0 6.3 85.6 ± 4.9 5.79 3-Hydroxycarbofuran 74.4 ± 4.8 6.5 76.8 ± 8.8 11.4 80.1 ± 6.4 8.0

10 Carbaryl 70.3 ± 4.7 6.7 82.1 ± 9.0 11.0 83.8 ± 4.6 5.511 Methiocarb 74.5 ± 6.4 8.6 79.1 ± 11.0 13.9 84.7 ± 9.1 10.812 Omethoate 67.2 ± 4.4 6.5 72.6 ± 5.7 7.9 81.8 ± 10.4 12.813 Pyraclofos 78.7 ± 9.0 11.5 97.0 ± 8.0 8.2 92.6 ± 14.0 15.114 Tau-fluvalinate 73.2 ± 6.9 9.5 77.5 ± 2.9 3.7 80.2 ± 11.0 13.715 Pentachloronitrobenzene 74.3 ± 13.2 17.8 69.1 ± 5.3 7.7 86.9 ± 12.0 13.816 Sulfotep 74.0 ± 8.8 11.9 77.3 ± 5.2 6.7 74.7 ± 6.1 8.217 Monocrotophos 69.7 ± 4.5 6.4 78.9 ± 9.9 12.5 79.8 ± 6.3 7.818 Phorate 71.2 ± 1.8 2.5 74.9 ± 1.4 1.9 72.5 ± 4.1 5.619 HCB 67.1 ± 4.6 6.9 85.2 ± 11.2 13.1 94.8 ± 8.4 8.820 a-BHC 74.7 ± 3.8 5.1 81.3 ± 6.0 7.4 88.8 ± 12.7 14.321 Dicloran 68.6 ± 4.2 5.9 79.8 ± 7.0 8.7 84.3 ± 7.3 8.722 Dimethoate 66.6 ± 5.0 7.5 78.4 ± 6.2 7.9 77.5 ± 9.4 12.123 Ethoprophos 71.8 ± 11.2 15.6 78.6 ± 5.3 6.7 81.3 ± 8.3 10.224 b-BHC 72.8 ± 6.9 9.6 78.6 ± 7.2 9.2 75.3 ± 4.9 6.525 c-BHC 72.9 ± 6.9 9.6 77.8 ± 6.9 8.8 74.8 ± 5.1 6.826 Fonofos 74.6 ± 6.0 8.0 83.2 ± 10.1 12.2 84.0 ± 11.0 13.127 Propetamphos 78.1 ± 10.1 13.0 79.9 ± 10.5 13.2 88.6 ± 9.6 10.928 Phosphamidon-I 80.3 ± 7.6 9.5 77.8 ± 5.6 7.2 86.5 ± 7.4 8.529 Disulfoton 74.8 ± 14.0 18.7 82.2 ± 12.4 15.2 80.6 ± 10.9 13.530 d-BHC 70.4 ± 8.0 11.4 84.6 ± 4.7 5.6 88.4 ± 12.5 14.131 Pirimicarb 73.8 ± 8.9 12.2 77.9 ± 10.3 13.3 83.4 ± 13.1 15.732 Phosphamidon-II 81.4 ± 8.6 10.5 77.7 ± 5.6 7.2 87.9 ± 7.1 8.133 Chlorpyrifos–methyl 73.9 ± 5.7 7.7 82.3 ± 7.6 9.2 86.5 ± 8.1 9.434 Vinclozolin 73.3 ± 7.8 10.7 81.2 ± 8.3 10.3 86.4 ± 15.6 18.135 Parathion–methyl 74.4 ± 10.6 14.2 77.4 ± 5.4 7.0 94.6 ± 14.9 15.736 Heptachlor 69.7 ± 9.6 13.8 82.4 ± 14.9 18.0 92.2 ± 15.9 17.337 Paraoxon 77.5 ± 6.9 9.0 82.8 ± 4.4 5.3 83.1 ± 6.1 7.338 Octachlorodipropyl ether 71.9 ± 6.8 9.5 89.3 ± 10.3 11.6 89.2 ± 18.3 20.539 Fenitrothion 73.1 ± 13.3 18.2 82.0 ± 4.2 5.1 88.4 ± 14.4 16.340 Pirimiphos–methyl 70.2 ± 6.0 8.6 72.2 ± 6.2 8.5 84.6 ± 10.4 12.341 Aldrin 70.4 ± 8.2 11.7 75.5 ± 7.4 9.9 91.8 ± 13.6 14.842 Chlorfenson 78.0 ± 10.3 13.2 80.1 ± 3.3 4.1 88.3 ± 7.4 8.443 Malathion 68.7 ± 4.3 6.2 75.8 ± 7.8 10.3 88.8 ± 14.1 15.944 Chlorpyrifos 74.7 ± 7.6 10.1 76.6 ± 11.4 14.9 83.5 ± 4.8 5.845 Fenthion 69.9 ± 6.7 9.5 74.2 ± 6.8 9.1 81.6 ± 7.9 9.746 Parathion 75.7 ± 9.3 12.3 83.9 ± 10.1 12.0 87.1 ± 16.6 19.047 Triadimefon 74.3 ± 6.4 8.6 80.5 ± 8.1 10.0 90.3 ± 7.7 8.648 Dicofol 91.7 ± 16.1 17.6 81.0 ± 1.9 2.3 84.1 ± 6.6 7.849 Isofenphos 84.1 ± 2.8 3.3 84.6 ± 3.0 3.5 88.7 ± 12.7 14.350 Fipronil 74.6 ± 12.2 16.4 75.9 ± 4.9 6.5 81.6 ± 9.1 11.151 Chlordane-I 75.4 ± 8.1 10.8 76.6 ± 7.9 10.3 83.8 ± 9.2 11.052 Phenthoate 72.4 ± 9.4 13.0 85.3 ± 8.6 10.1 87.6 ± 10.3 11.753 Quinalphos 82.2 ± 16.3 19.8 79.4 ± 8.0 10.1 95.1 ± 11.3 11.954 Procymidone 70.4 ± 8.1 11.6 80.2 ± 13.6 16.9 87.1 ± 13.5 15.555 Allethrin-I 74.5 ± 7.2 9.7 78.5 ± 7.3 9.3 89.7 ± 15.4 17.156 Allethrin-II 76.3 ± 5.1 6.5 80.5 ± 8.2 8.4 90.2 ± 13.1 15.257 Chlordane-II 76.0 ± 8.8 11.6 77.1 ± 8.8 11.4 83.8 ± 9.2 11.058 Methidathion 73.8 ± 1.8 2.4 78.7 ± 4.9 6.3 83.7 ± 12.0 14.359 Bromophos–ethyl 71.0 ± 10.9 15.3 79.9 ± 10.9 13.6 81.2 ± 8.9 11.060 Hexythiazox 75.3 ± 7.7 10.2 83.4 ± 12.8 15.3 86.3 ± 15.4 17.961 a-Endosulfan 68.7 ± 9.9 14.5 78.6 ± 10.9 13.8 80.6 ± 11.9 14.762 Methothrin-I 78.2 ± 10.6 13.6 84.9 ± 3.8 4.5 91.4 ± 8.1 8.963 Methothrin-II 77.9 ± 10.8 13.8 85.6 ± 3.7 4.4 91.8 ± 9.0 9.864 Pretilachlor 78.8 ± 7.0 8.9 80.4 ± 8.9 11.1 93.2 ± 12.5 13.465 Dieldrin 82.6 ± 7.4 9.0 93.8 ± 5.7 6.0 82.3 ± 6.8 8.266 p,p0-DDE 78.5 ± 9.8 12.5 80.3 ± 7.9 9.9 85.8 ± 5.7 6.767 o,p0-DDD 75.9 ± 11.2 14.7 84.8 ± 11.6 13.6 87.8 ± 8.6 9.968 Myclobutanil 80.2 ± 8.8 11.0 81.8 ± 9.6 11.7 86.7 ± 15.4 17.869 Carboxin 80.7 ± 3.5 4.4 80.9 ± 3.7 4.6 91.7 ± 9.3 10.170 Buprofezin 81.9 ± 3.4 4.2 93.1 ± 4.0 4.3 91.4 ± 12.1 13.271 Flusilazole 82.2 ± 7.7 9.4 80.5 ± 12.6 15.7 93.7 ± 12.8 13.772 Chlorfenapyr 75.9 ± 9.7 12.8 81.2 ± 10.9 13.5 86.9 ± 11.9 13.773 Endrin 88.3 ± 4.4 5.0 90.1 ± 13.9 15.4 89.1 ± 8.4 9.3

(continued on next page)

G. Wu et al. / Food Chemistry 126 (2011) 646–654 651

Table 3 (continued)

No. Pesticide Spiked 0.05 mg kg�1 Spiked 0.1 mg kg�1 Spiked 0.2 mg kg�1

Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%)

74 b-Endosulfan 69.6 ± 6.2 8.8 79.4 ± 7.9 9.9 88.2 ± 8.2 9.375 Nitrofen 82.1 ± 10.3 12.5 78.9 ± 9.0 11.4 81.7 ± 14.1 17.376 p,p0-DDD 73.8 ± 7.6 10.3 79.9 ± 5.0 6.3 86.8 ± 11.9 13.777 o,p0-DDT 73.8 ± 7.6 10.3 79.9 ± 5.0 6.3 86.8 ± 11.9 13.778 Iprodione 74.9 ± 13.8 18.4 73.3 ± 2.4 3.3 81.0 ± 10.8 13.479 Triazophos 79.3 ± 5.2 6.6 90.9 ± 5.5 6.1 89.9 ± 15.3 17.180 Carbophenothion 82.2 ± 11.9 14.5 80.7 ± 4.3 5.3 86.9 ± 10.8 12.581 Endosulfan sulphate 74.8 ± 10.1 13.5 85.2 ± 3.1 3.7 90.2 ± 3.7 4.182 Propiconazole-I 86.6 ± 8.9 10.3 79.8 ± 5.3 6.7 89.9 ± 11.7 13.083 p,p0-DDT 73.2 ± 12.6 17.2 81.6 ± 9.7 11.9 80.7 ± 4.8 5.984 Propiconazole-II 86.8 ± 8.9 10.3 79.3 ± 6.7 8.4 85.4 ± 4.5 5.285 Phosmet 77.7 ± 4.4 5.6 78.9 ± 5.4 6.8 83.6 ± 1.7 2.186 Tetramethrin-I 78.0 ± 10.1 12.9 85.1 ± 5.8 6.8 77.2 ± 7.8 10.187 EPN 74.0 ± 3.9 5.4 80.7 ± 3.0 3.7 80.7 ± 5.8 7.288 Bifenthrin 71.4 ± 14.6 20.4 84.5 ± 6.3 7.5 89.7 ± 5.0 5.589 Tetramethrin-II 78.0 ± 10.1 12.9 85.1 ± 5.8 6.8 77.2 ± 7.8 10.190 Tebufenpyrad 74.1 ± 9.2 12.5 76.7 ± 8.1 10.6 81.8 ± 10.3 12.691 Tetradifon 78.6 ± 16.6 21.1 79.0 ± 11.0 13.9 84.2 ± 7.2 8.692 Phenothrin-I 76.9 ± 8.9 11.6 78.5 ± 2.7 3.4 82.6 ± 7.4 8.993 Phosalone 87.9 ± 10.6 12.0 81.2 ± 5.9 7.2 88.8 ± 6.7 7.594 Phenothrin-II 76.9 ± 8.9 11.6 79.3 ± 3.2 4.1 82.6 ± 7.4 8.995 Azinphos-methyl 71.4 ± 11.4 16.0 85.6 ± 5.8 6.7 91.2 ± 8.4 9.296 Lambdacyhalothrin-I 75.8 ± 5.6 7.4 81.6 ± 6.3 7.7 71.4 ± 3.6 5.197 Lambdacyhalothrin-II 75.8 ± 5.6 7.4 82.3 ± 6.1 7.4 71.4 ± 3.6 5.198 Permethrin-I 77.1 ± 10.6 13.7 84.5 ± 9.1 10.8 86.2 ± 8.1 9.499 Coumaphos 72.6 ± 5.9 8.1 87.3 ± 2.8 3.2 95.1 ± 11.3 11.9

100 Permethrin-II 76.6 ± 9.8 12.7 89.6 ± 7.0 7.8 84.2 ± 6.4 7.5101 Pyridaben 74.8 ± 8.1 10.9 83.1 ± 6.6 7.9 86.9 ± 7.4 8.5102 Flucythrinate 79.1 ± 4.2 5.3 78.2 ± 3.9 4.9 84.8 ± 9.2 10.8103 Ethofenprox 79.2 ± 6.8 8.6 90.9 ± 11.6 12.8 97.4 ± 9.5 9.7104 Esfenvalerate-I 70.5 ± 8.6 12.2 79.5 ± 8.9 11.2 81.1 ± 3.1 3.8105 Cyfluthrin-I 74.6 ± 10.0 13.5 76.6 ± 5.7 7.5 90.2 ± 8.1 9.0106 Cyfluthrin-II 74.5 ± 10.1 13.6 77.8 ± 5.3 6.8 90.3 ± 8.0 8.9107 Esfenvalerate-II 73.5 ± 9.5 12.9 80.0 ± 8.5 10.6 80.8 ± 3.3 4.1108 Deltamethrin-I 77.6 ± 7.2 9.2 78.0 ± 7.2 9.2 81.3 ± 11.0 13.5109 Deltamethrin-II 77.6 ± 7.2 9.2 78.4 ± 7.8 9.9 84.6 ± 11.0 13.0

652 G. Wu et al. / Food Chemistry 126 (2011) 646–654

sample packing to reduce moisture and increase permeation of sol-vents into the sample matrix. The same ASE conditions were usedthroughout the analysis of all samples.

According to Frenich et al. (2006) and Pang et al. (2006), threeextracting solvents of acetonitrile, hexane + acetone (2 + 1) andcyclohexane + ethyl acetate (1 + 1) were initially tested. We deter-mined the extraction efficiencies using beef at a fortification levelof 0.2 mg kg�1 (n = 3). The efficiencies of extraction by acetonitrile,hexane–acetone (2:1, v/v), and cyclohexane–ethyl acetate (1:1, v/v) were similar for most of the pesticides. For hexane + acetone(2 + 1), the recoveries were from 64.3 ± 5.3% to 90.4 ± 6.1%; forcyclohexane + ethyl acetate (1 + 1), the recoveries were from68.1 ± 6.3% to 92.4 ± 4.4%; and for acetonitrile, the recoveries werefrom 69.0 ± 5.7% to 95.4 ± 7.5%. However, less fat was found in theextract with acetonitrile than the other two solvent systems. Ace-tonitrile was therefore chosen as the extraction solvent for furthermethod optimisation and evaluation.

3.2. Optimisation of cleanup procedure

GPC was previously used for cleanup prior to analysis of over400 pesticides in food stuff using GC–AED, GC–ECD, GC–NPD, andGC–MS (Stan, 2000). In this study, to assure that all pesticides werecollected from the GPC step, the eluting chromatogram of pesticidestandard solution and the sample fortified with the same pesti-cides were recorded by the GPC UV detector (Fig. 1). These figuresshowed that the fatty compounds and the analytes were separatedeffectively by the GPC elution.

GPC was applied as a nondestructive and semiautomatic clean-up method in this study, using 300 mm � 10 mm i.d glass columns

packed with Bio-Beads S-X3. According to Fig. 1, when the flowrate was 5 mL min�1, the first fraction from 0 to 8 min of the eluant(about 40 mL) contained the lipids and was discarded. The repre-sentative fraction from 8 to 20 min (about 60 mL) was collected.In Pang et al. (2006), the GPC cleanup column was 400 � 25 mmi.d (Gilson, France) also packed with Bio-Beads S-X3, and the elutedfraction of 22–40 min was collected. Frenich et al. used a cleanupcolumn from Waters (Milford, MA, USA) that was packed with sty-renedivinilbenzene co-polymer in 19 � 150 mm and 19 � 300 mm,respectively, and subsequently collected the elution fraction from15 to 22 min (Frenich et al., 2006). The GPC collection time was dif-ferent in this study due to the use of different column packingmaterials or different column dimensions than previous studies.

Usually, additional clean-up steps should be used to furtherdecrease the matrix effect. The elution was treated by the PSA asmatrix solid phase disperse treatment. In this study the purifica-tion obtained was considered as sufficient for obtaining a cleanextract with minimal damage to the GC column and no furthercleanup by SPE seemed necessary.

3.3. Method validation

To confirm that the optimised method was suitable for applica-tion, a validation process was carried out by establishing the basicanalytical parameters. Precision, recovery, linear range and bothdetection (LOD) and quantification (LOQ) limits were evaluatedfor the analytical approach developed using samples of pork, beef,chicken and fish.

Selection of conditions in GC–MS analysis including the choiceof quantitative and qualitative ions for each target compound is

G. Wu et al. / Food Chemistry 126 (2011) 646–654 653

of great importance. A quantitative ion and two qualitative ionswere selected for each compound. On the basis of the retentiontime of the 109 pesticides (including isomers), and to ensure sen-sitivity for each pesticide, all of the ions to be determined for eachgroup were monitored at the programmed time based on the se-quence of the compounds’ eluted peaks. The number of ions withinany programmed time was fixed and attention was paid to thepeaks eluting near the end of one programmed period and thoseeluting near the beginning of the next programmed period (Table2). The dwell time for each ion was adjusted to ensure that eachpeak was of a cycled scan in the constant cycling scan time andthat the number of data acquisition points was sufficient for allthe compounds monitored. Changing the dwell time did not affectthe results of integration. Under the GC–MS conditions selected,analysis was performed to determine the linear range for the 109pesticides (including isomers). The fortification concentration giv-ing a signal-to-noise ratio (S/N) P 3 for each pesticide was definedas the limit of detection (LOD) for the developed method, and thefortification concentration giving an S/N P 10 was considered asthe limit of quantification (LOQ). The LODs and LOQs of the 109pesticides (including isomers) are also given in Table 1. Pesticide-free samples monitored by our laboratory were used as the blankmatrix for spiking to determine recoveries. Beef samples free ofpesticide residues were used for the fortification precision test atthe concentrations of 0.05, 0.1 and 0.2 mg kg�1. The samples wereequilibrated for 2 h after fortification with the pesticides, so thatthe pesticides were thoroughly absorbed, before they wereextracted. Recoveries and precisions obtained for the three fortifi-cation levels are listed in Table 3. The average recoveries of thepesticides by the method ranged from 62.6% to 107.8%. The relativestandard deviation (RSD) values for all pesticides were below 20.5%(n = 6).

In Pang et al. (2006), the average recoveries for 437 pesticidesfell within 40–120%, among which 417 analytes, 95% of the ana-lytes, showed recoveries between 60% and 120%, while the remain-ing 20 analytes (5%) had recoveries between 40% and 60%. InFrenich et al. (2006), recoveries were between 70.0% and 104.4%for chicken samples, 68.5–102.9% in pork and 69.9–105.8% in lambsamples. The RSD values as determined in the current study, at

Table 4Pesticide residues found in the pork, beef, chicken and fish samples from localmarkets.

Sample ID Sample Pesticides found Concentration(mg kg�1)

Class

1# Fish Carbofuran 0.084 Carbamatep,p0-DDE 0.103 OCPsa

5# Fish Carbofuran 0.016 Carbamatea-Endosulfan 0.024 OCPsb-Endosulfan 0.036 OCPsc-BHC 0.017 OCPs

13# Beef Coumaphos 0.081 OPPsb

p,p0-DDE 0.063 OCPsChropyrifos 0.114 OPPs

14# Beef Chropyrifos 0.025 OPPsp,p0-DDE 0.067 OCPsc-BHC 0.104 OPPs

25# Pork p,p0-DDE 0.022 OCPsc-BHC 0.026 OCPsChropyrifos 0.089 OPPs

36# Pork Coumaphos 0.012 OPPsc-BHC 0.025 OCPsp,p0-DDE 0.034 OCPs

47# Chicken c-BHC 0.031 OCPs48# Chicken c-BHC 0.027 OCPs

p,p0-DDE 0.040 OCPs

a Organochlorine pesticides.b Organophosphorus pesticides.

<20.5%, are therefore to be considered acceptable for residueanalysis.

3.4. Application for analysis of meat, poultry and fish samples

Samples of pork, beef, chicken and fish from local marketswere prepared and analysed using the developed sample prepara-tion, cleanup and analysis methods. Pesticide residues weredetected in 16% of the total samples (or 8 out of 50 samples).The residues were found in the pork, beef, chicken and fish sam-ples (Table 4). p,p0-DDE was detected in six samples at concentra-tions ranging from 0.022 to 0.103 mg kg�1, while c-BHC,carbofuran, a-endosulfan, and b-endosulfan were each found inone fish sample. The most common pesticide residues found werep,p0-DDE and c-BHC. Chlorpyrifos or coumaphos was found in thebeef and pork samples. These findings coincided with the factthat chlorpyrifos and coumaphos are the most used pesticidesin the livestock production. The diversity of pesticide classes,including organochlorine (a-endosulfan, b-endosulfan, p,p0-DDE,c-BHC), organophosphorus (chlorpyrifos, coumaphos) and carba-mate (carbofuran), showed that the proposed method was versa-tile and sensitive for the determination of multi-residues ofpesticides in samples of animal origin.

4. Conclusions

The method developed in this study was reliable, simple, andrapid (only about 2 h for the entire sample preparation and analy-sis). It consumed only small amounts of solvents, and was there-fore more environment-friendly than the conventional methods.The method was sensitive (LOQs at the low lg kg�1 level, such as0.3 lg kg�1 for fenthion) for the determination of multiple pesti-cide residues in foods of animal origin. Compared with the tradi-tional sample preparation methods, results from this studyshowed that this new method can be considered a fast and easyalternative technique with great ruggedness, high degree of auto-mation and good suitability for screening multiple pesticides inthe foods of animal origin. The proposed method provided a goodimprovement in the analysis of multi-residues of pesticides, andmay be used for the implementation of regulations of CAC, EU,USA, the positive list system of Japan, and GB 2763-2005 of ChinaMRLs.

Acknowledgements

The authors acknowledge the support from the Office of Scienceand Technology of Zhejiang Province for key scientific and socialdevelopment projects (Foundation item No. 2005C23068) andMinistry of Agriculture of China (Project No. 200803034).

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