Chemical Papers 63 (1) 39–46 (2009)DOI: 10.2478/s11696-008-0090-3

ORIGINAL PAPER

Simultaneous determination of 118 pesticide residues in Chineseteas by gas chromatography-mass spectrometry

aXin Yang*, aDe Chang Xu, aJian Wei Qiu, aHua Zhang, aYing Chun Zhang,aAi Jun Dong, aYing Ma, a,bJing Wang

aSchool of Food Science and Engineering, Harbin Institute of Technology, 150090 Harbin, China

bThe Chinese Academy of Agricultural Sciences, 100081 Beijing, China

Received 10 April 2008; Revised 17 June 2008; Accepted 30 June 2008

An efficient and sensitive method for simultaneous determination of 118 pesticide residues in teashas been established and validated. A multi-residue analysis of pesticides in tea involved extrac-tion with ethyl acetate–hexane, clean-up using gel permeation chromatography (GPC) and solid-phase extraction (SPE), and subsequent identification and quantification of the selected pesticidesby gas chromatography–mass spectrometry (GC–MS). For most of the target analytes, optimizedpretreatment processes led to no significant interference with analysis of sample matrix, and thedetermination of 118 compounds was achieved in about 60 min. In the linear range of each pesticide,the correlation coefficient was R2 ≥ 0.99. At the low, medium and high three fortification levels of0.05–2.5 mg kg−1, 118 pesticides average recoveries range from 61 % to 121 % and relative standarddeviations (RSD) were in the range of 0.6–9.2 % for all analytes. The limits of detection for themethod were 0.00030–0.36 mg kg−1, depending on each pesticide.c© 2008 Institute of Chemistry, Slovak Academy of Sciences

Keywords: pesticides, multi-residue analysis, Chinese tea, GPC, SPE, GC–MS

Introduction

Tea is an old and popular beverage consumedworldwide and valued for its specific aroma and fla-vor as well as health-promoting properties (Yang &Landau, 2000). During recent years, there has beenan increasing public concern and scientific investiga-tion related to the presence and control of pesticideresidues in herbal products and to a more thorough as-sessment of the potential health hazards (Sood et al.,2004; Dejonckheere et al., 1996; Naithani & Kakkar,2004).Trace-level and multi-residue analysis of pesticides

in teas has become more important because of theincreasing challenges of EU regulatory agencies andother tea-importing countries. Generally, analysis ofmost pesticide residues was carried out in a sequenceof several steps, e.g. target extraction from sam-

ple matrix, then clean-up and pre-concentration fol-lowed by chromatographic separation and determina-tion (Tekel & Hatrík, 1996; Cserhati et al., 2004). Forthe sample pretreatment, gel permeation chromatog-raphy (GPC), and solid-phase extraction (SPE) as ef-ficient methods have been widely applied to pesticideresidue analysis. Capillary gas chromatography–massspectrometry (GC–MS) has become very popular inpesticide residue analysis. It could quantify and con-firm the results by selected ion monitoring (SIM) spec-tra. Nowadays, these methods have been widely de-veloped to analyze multi-residues in fresh vegetables,fruit, water and honey. Fillion et al. (2000) adoptedC18 and a carbon cartridge coupled to an aminopropylsolid-phase extraction cartridge (SPE) for cleanup,gas chromatography with mass-selective detection andliquid chromatography with post-column reaction, aswell as fluorescence detection for the determination

*Corresponding author, e-mail: yangxin@hit.edu.cn

40 X. Yang et al./Chemical Papers 63 (1) 39–46 (2009)

of 251 pesticide and degradation product residuesin fruit and vegetable samples. Bordet et al. (2002)adopted SPE cleanup in a column with two succes-sive SPE cartridges (C18 and Florisil) and GC withelectron-capture detector for determination of pesti-cide residues of 21 organochlorines, 6 pyrethroids, and7 PCBs. Cai et al. (2003) applied polyphenylmethyl-siloxane (PPMS) as a coating for solid-phase microex-traction (SPME) combined with microwave-assistedextraction (MAE) to determine the concentrationsof organochlorine pesticides (OCPs) in Chinese teas.The extracts were analyzed by gas chromatography(GC)/electron-capture detection (ECD). Huang etal. (2007) used acetone–ethyl acetate–hexane for theextraction of pesticides, gel permeation chromatog-raphy (GPC) and solid-phase extraction (SPE) forcleanup, and gas chromatography–mass spectrometry(GC–MS) under retention time locked (RTL) condi-tions for the determination of 102 pesticide residuesin teas. Pang et al. (2006) proposed the use of cy-clohexane + ethyl acetate (1 + 1) for the extractionof pesticides from animal tissues, GPC for cleanup,and chromatography–mass spectrometry (GC–MS)and liquid chromatography–tandem mass spectrom-etry (LC–MS–MS) for the determination of 660 pesti-cide residues.After a detailed analysis of the above method-

ologies, a new method for the determination of 118pesticide residues in teas using gas chromatography–mass spectrometry (GC–MS) was developed. Analyti-cal procedures in our methodology were simplified andthe modes of detection were changed so that the accu-racy and reliability of the method could be improved.

Experimental

Apparatus and reagents

An Agilent 6890N gas chromatograph connectedto an Agilent 5973N mass-selective detector equippedwith Agilent 7683 autosampler (Agilent technologies,USA) was used. The column used was a capillary col-umn (DB-1701, 30 m × 0.25 mm i.d. × 0.25 µm, J&WScientific, Inc., USA). For the GPC system (Gilson,France), a Bio-Beads S-X3 (250 mm × 10 mm i.d. × 5µm; Nacalai Tesque, Japan) cleanup column was used.Further, a homogenizer (Qilin, China), rotary evapo-rator (Eyela, Japan), centrifuge (Westfalia SeparatorAG, Germany) and a nitrogen evaporator (Organoma-tion Associates, USA) were used.Acetonitrile (HPLC grade), toluene, toluene–acet-

one, hexane, acetone, and ethyl acetate (PR grade)were purchased from the Sigma company (Poole, UK).Sodium sulfate, anhydrous (analytical-reagent grade),was heated at 650 C for 4 h and kept in a desicca-tor. Pesticide standards were purchased from Supelco(Bellefonte, Pennsylvania, USA) and RDH (Riedel-de-Haen, Seelze, Germany), and were of purity >90

mass %. Stock standard solutions: accurately weighed5–10 mg of individual pesticide standards (accurateto 0.1 mg) were put into a 10 mL volumetric flask,dissolved and diluted to 10 mL with toluene or atoluene–acetone mixture, depending upon each indi-vidual compound’s solubility. Mixed standard solution(mixed standard solution A and B): depending uponproperties and retention time of each pesticide, all 118pesticides were divided into two groups, A and B. Con-centration of the mixed standard solutions was deter-mined depending upon sensitivity of each compoundto the instrument. Depending upon the grouping num-ber, mixed standard solution concentration and stockstandard solution concentration, an adequate amountof individual stock standard solution was pipetted intoa 100 mL volumetric flask; A or B group pesticideswere diluted with toluene. Mixed standard solutionsshould be stored in dark below 4◦C and used withinone month. Working standard mixed solutions in amatrix of A or B group pesticides were prepared bythoroughly mixing an adequate amount of mixed stan-dard solution to 1.0 mL with blank extract.

Methods and analyses

Sample extraction and cleanup: Tea samples werepulverized and homogenized throughout a 150 mesh(0.100 mm) sieve. Then, 2 g of homogenized samplewas accurately weighed into a 100 mL centrifuge tubeand mixed with 5.0 mL of water and 1.0 g of sodiumchloride. The mixture was vortexed for 30 s and al-lowed to stand for 30 min. After a triple extraction,each with 5.0 mL of ethyl acetate–hexane (ϕr = 1:3)for 3 min, followed by centrifugation at 3000 min−1

for 5 min, the organic phase was combined and driedwith 1.0 g of anhydrous sodium sulfate, then filtratedand reduced to about 5 mL with a nitrogen stream at45◦C. The residual extract was diluted to 10 mL withethyl acetate for subsequent purification in GPC.GPC procedure: Diluted extract was reconstituted

and further purified using a Gilson GPC system(Gilson, France) equipped with a cosmosil packed col-umn (250 mm × 10 mm i.d. × 5 µm; Nacalai Tesque,Japan). Reconstituted solution was injected into theGPC column; mobile phase: ethyl acetate–hexane (ϕr= 1:3); flow rate: 3 mL min−1; injection volume: 5mL; detection wavelength: 254 nm. The eluent wascollected between the 5th–16th minute, and concen-trated to about 1 mL for the SPE clean-up.SPE procedure: The SPE columns used in the ex-

periment were Supelco Envi TM-Carb SPE cartridge(3 mL and 250 mg; Supelco, USA) coupled with aNH2-LC SPE cartridge (3 mL and 250 mg; Supelco,USA). Concentrated eluent (1 mL) was introducedinto the SPE column preconditioned with 10.0 mLacetone–toluene (ϕr = 3:1) while the retained pesti-cides on the column were eluted with 10.0 mL acetone–toluene (ϕr = 3:1). The eluents were collected and

X. Yang et al./Chemical Papers 63 (1) 39–46 (2009) 41

Table 1. Retention times, target ions, and qualifying ions of 118 pesticides

Monitored ions (m/z)/%No. Pesticide selected Group Retention time/min

Target ion Qualifying ion 1 Qualifying ion 2

1 EPTC B 8.85 128 189(30) 132(35)2 Allidochlor A 9.25 138 158(10) 173(20)3 Butylate B 9.72 156 146(110) 217(30)4 Promecarb A 9.73 135 150(40) 91(16)5 Dichlobenil B 10.15 171 173(70) 136(15)6 Vernolate B 10.38 128 146(18) 203(10)7 Aminocarb A 10.41 151 186(10) 136(61)8 Etridiazole A 10.58 211 183(85) 140(32)9 Nitrapyrin B 11.10 194 196(98) 198(25)10 Propham A 11.56 179 137(65) 120(50)11 Cycloate A 13.39 154 186(5) 215(15)12 Tecnazene B 13.47 203 261(74) 215(84)13 Heptanophos B 13.77 124 215(18) 250(15)14 Hexachlorobenzene B 14.28 284 286(80) 282(50)15 Diphenylamine A 14.38 169 168(60) 167(30)16 Propachlor B 14.66 120 176(45) 211(10)17 Ethalfluralin A 14.79 276 316(82) 292(41)18 Trifluralin B 15.02 306 264(70) 335(6)19 Benfluralin A 15.10 292 264(21) 276(15)20 Phorate A 15.17 260 121(158) 231(55)21 Sulfotep B 15.30 322 202(44) 238(27)22 Quintozene A 16.21 295 237(160) 249(112)23 Prometon A 16.27 210 225(90) 168(68)24 Terbufos B 16.36 231 153(25) 288(10)25 Clomazone A 16.52 204 138(5) 205(13)26 Terbumeton B 16.63 210 169(65) 225(30)27 Fonofos B 16.76 246 137(140) 174(15)28 Profluralin B 16.86 318 304(48) 347(15)29 Dioxathion A 17.03 270 197(41) 169(20)30 γ-HCH A 17.13 183 219(95) 169(20)31 Propazine B 17.14 214 229(65) 172(50)32 Disulfoton B 17.17 88 274(23) 125(16)33 Etrimfos A 17.20 292 181(40) 277(30)34 Atrazine A 17.22 200 215(52) 183(1)35 Propetamphos A 17.39 138 194(50) 236(31)36 Terbutylazine B 17.47 214 229(33) 173(35)37 Secbumeton B 17.62 196 210(39) 225(40)38 Heptachlor B 17.76 272 237(40) 337(26)39 Diclofenthion A 18.00 223 279(130) 251(43)40 Pronamide A 18.07 173 175(62) 254(20)41 Pirimicarb A 18.13 166 238(32) 138(3)42 Cyanophos B 18.23 243 180(8) 148(4)43 Fluchloralin B 18.41 264 326(210) 306(186)44 Chlorpyrifos-methyl B 18.53 286 288(70) 197(6)45 Aldrin A 18.61 263 265(68) 293(42)46 Desmetryn A 18.77 213 198(60) 171(30)47 Fenchlorophos A 18.84 285 287(70) 125(33)48 Alachlor B 19.17 188 237(35) 269(15)49 Cyprazine A 19.26 212 227(60) 170(30)50 Pirimiphos-methyl B 19.28 290 276(86) 305(75)51 Simetryn B 19.35 213 170(28) 198(16)52 Vinclozolin A 19.41 285 212(110) 198(95)53 Terbutryne A 19.58 241 226(150) 185(109)54 Thiobencarb B 19.59 100 257(25) 259(10)55 Metalaxyl A 19.68 206 249(55) 234(40)56 Aspon B 19.69 210 253(50) 278(12)57 Chlorpyrifos(-ethyl) A 19.82 314 258(60) 286(46)58 Parathion-methyl A 19.94 263 233(65) 246(8)59 Pirimiphos-ethyl B 20.33 333 318(95) 304(70)60 Fenthion A 20.36 278 169(18) 153(10)61 Fenitrothion A 20.60 277 247(60) 260(50)

42 X. Yang et al./Chemical Papers 63 (1) 39–46 (2009)

Table 1. (continued)

Monitored ions (m/z)/%No. Pesticide selected Group Retention time/min

Target ion Qualifying ion 1 Qualifying ion 2

62 Ethofumasate B 20.80 161 286(40) 207(12)63 Butralin B 20.83 266 224(18) 295(12)64 Isopropalin B 20.99 280 238(40) 222(5)65 Triadimefon A 21.06 208 181(70) 210(50)66 Parathion A 21.19 291 235(40) 186(25)67 Pendimethalin A 21.27 252 220(20) 162(10)68 Fenson A 21.49 141 77(105) 268(50)69 Bromophos-ethyl A 21.61 359 303(80) 357(77)70 Isofenphos B 21.66 213 255(44) 185(45)71 Quinalphos A 21.70 146 298(30) 157(70)72 Diphenamid B 21.71 167 239(30) 165(42)73 Chlorbenside A 21.80 268 270(40) 143(11)74 Chlorfenvinphos B 21.83 323 267(140) 269(92)75 Phenthoate A 21.89 274 246(25) 320(5)76 Penconazole B 21.98 248 250(32) 161(92)77 p,p′-DDE B 22.30 318 316(80) 248(70)78 Prothiophos A 22.44 311 267(90) 162(55)79 Flumetralin A 22.71 143 157(25) 404(10)80 Iodofenphos B 22.75 377 379(37) 259(10)81 Dieldrin A 22.79 263 277(80) 380(30)82 Procymidone B 22.91 283 285(70) 255(15)83 Methidathion A 23.00 373 237(40) 272(30)84 Cyanazine A 23.09 225 240(72) 172(75)85 Oxadiazon A 23.37 175 258(65) 302(40)86 Chlorfenson B 23.50 302 177(102) 175(280)87 Aramite A 23.52 185 334(32) 319(38)88 Fenamiphos A 23.62 303 154(56) 288(30)89 o,p′-DDD B 23.68 235 237(64) 165(38)90 Imazalil A 23.77 215 173(75) 175(49)91 Methoprotryne B 23.86 256 213(24) 271(18)92 Tetrasul A 23.89 252 324(65) 254(68)93 Chloropropylate B 24.06 251 141(20) 253(65)94 Flamprop-methyl B 24.19 105 77(25) 276(10)95 Chlorbenzilate A 24.20 251 139(57) 111(23)96 Oxyfluorfen B 24.36 252 361(35) 300(36)97 Chlorthiophos A 24.52 325 297(55) 360(52)98 o,p′-DDT B 24.57 235 237(64) 165(38)99 Ethion A 24.67 231 384(15) 199(10)100 Flamprop-isopropyl B 24.70 105 276(20) 363(3)101 Sulprophos A 24.73 156 322(100) 280(15)102 Etaconazole A 24.80 245 173(85) 247(65)103 Myclobutanil B 25.09 179 288(15) 150(45)104 Benalaxyl B 25.13 148 206(35) 325(16)105 Diclofop-methyl A 25.35 253 340(80) 281(50)106 Propiconazole A 25.44 259 261(65) 173(97)107 Bifenthrin B 25.51 165 166(109) 181(43)108 Mirex A 25.75 272 274(80) 237(50)109 Methoxychlor A 25.93 227 228(18) 212(5)110 Bromopropylate B 25.97 341 183(35) 339(40)111 Benzoylprop-ethyl B 26.03 292 365(35) 260(36)112 Tetramethrin A 26.07 164 135(5) 232(2)113 Fenpropathrin A 26.08 265 181(237) 349(25)114 EPN B 26.45 157 323(15) 169(53)115 Hexazinone B 26.56 171 128(12) 252(3)116 Tetradifon A 26.80 227 354(70) 159(193)117 cis-Permethrin A 27.12 183 184(16) 255(3)118 Fenarimol B 27.48 139 219(70) 330(41)

evaporated to dryness at 45◦C in a nitrogen stream.Finally, the residue was redissolved in 0.5 mL of ace-

tone for the GC–MS analysis, the solution concentra-tion was 0.004 kg mL−1.

X. Yang et al./Chemical Papers 63 (1) 39–46 (2009) 43

GC–MS analysis: Operating conditions: columntemperature of 40◦C held for 1 min, at 30◦C min−1

to 130◦C, at 6◦C min−1 to 250◦C, at 30◦C min−1

to 300◦C held for 10 min; carrier gas was helium;purity ≥ 99.999 %; flow rate 1.0 mL min−1; in-jection port temperature 290◦C; injection volume1 µL; injection mode was splitless, purge on af-ter 1.5 min; ionization voltage of 70 eV; ion sourcetemperature 230◦C; GC–MS interface temperature280◦C; selected ion monitor mode was set to eachcompound selecting one target ion and two quali-fying ions. Retention times, target ions, and qual-ifying ions of each compound are listed in Ta-ble 1.Qualification and quantification of samples: When

using GC–MS analysis, samples were confirmed tocontain a pesticide if: (i) the observed retentiontimes of the sample solutions peaks were the sameas the peaks for standards in blank matrix ex-tracts; (ii) the selected ions or monitored ions ap-peared (if not sufficient, which should signal thenoise ratio of 3 for LOD and at least 5 for LOQ);and if (iii) the observed abundance ratio of ionswas identical to that of the standard ions. Whenconfirmation by GC–MS SIM failed, samples werere-injected and confirmation was performed usingscan mode (with sufficient sensitivity), such as o,p′-DDT, diphenylamine, etc. External standard quan-tification was adopted for GC–MS; external standardcalibration curve quantification was used for GC–MS.

Results and discussion

Selection of GC–MS conditions

GC conditions were optimized to enable separa-tion of the 118 pesticides in a single GC column. Dif-ferent temperature regimes, flow rates and columnidentities were tested and verified in order to keepthe analytes of the standard mixture in an accept-able run time. Given that the pesticide varieties deter-mined were great in number and their retention timeswere relatively concentrated, ions based on the fol-lowing four criteria were selected: (i) molecular ionsas detecting ions; (ii) fragment ion with high abun-dance, such as base peaks; (iii) characteristic ionswith selectivity minimizing the cross-interferences be-tween different pesticides; (iv) the signal/noise ratioof the selected monitored ions in the matrix shouldbe higher than three, with subtracted background.Based on these criteria, a scanning test of the stan-dard solution of each pesticide to be analyzed wascarried out to describe its scanning mass spectro-gram and retention time. One target ion and twoqualitative ions for each compound were selected (Ta-ble 1).

10 15 20 25 300

2000

4000

6000

8000

10000

Abu

ndan

ce

Retention time / min

Fig. 1. SIM chromatogram of a typical blank tea sample.

10 15 20 25 300

20000

40000

60000

80000

100000

120000

140000

160000

Abu

ndan

ce

Retention time / min

Fig. 2. SIM chromatogram of typical blank green tea spikedwith 0.1 mg kg−1 of target analyte.

Validation procedure

Tea samples, free of pesticides, were used forthe preparation of a blank matrix. A typical chro-matogram of a blank tea sample is shown in Fig. 1.No matrix interference GC peaks were detected inthe SIM chromatograms for the targeted pesticidesobtained in analyses of blank tea samples fromChina, demonstrating thus the good selectivity of themethod. In the sample pretreatment process, the se-lection of extracting solvent with a proper polarityto match the analyte of interest was beneficial to theprocess efficiency improvement and potential interfer-ences from tea minimization. Small matrix effect onthe MS detection of low level tea samples was foundunder the optimized extraction and chromatographicconditions (Fig. 2).Quantitative analysis was performed using an ex-

ternal standard. Calibration curve was obtained byanalyzing blank tea samples spiked with pesticides atfive different levels. Good linearity of the MS detectorresponse was found for all pesticides at concentrationswithin the test intervals, with the linear regressioncoefficients (R2) higher than 0.990. Signals from thechromatograms of ten blank tea samples were evalu-ated as recommended (European Commission Direc-

44 X. Yang et al./Chemical Papers 63 (1) 39–46 (2009)

Table 2. Linear area (LA), correlation coefficient (R2), limits of detection (LOD), and average recovery (AR) of 118 standardpesticides in tea

No. Pesticide selected LAa/(mg L−1) R2 LOD/(mg kg−1) ARb/% RSD/%

1 EPTC 0.010–1.000 0.9997 0.013 85 5.22 Allidochlor 0.200–2.500 0.9998 0.18 102 1.23 Butylate 0.010–1.000 0.9985 0.010 105 3.54 Promecarb 0.025–0.500 0.9975 0.020 79 5.45 Dichlobenil 0.010–1.000 0.9997 0.0086 106 7.66 Vernolate 0.050–1.000 0.9996 0.051 97 4.47 Aminocarb 0.010–0.500 0.9992 0.0090 85 2.28 Etridiazole 0.200–2.500 0.9976 0.14 114 3.69 Nitrapyrin 0.020–0.500 0.9992 0.021 81 2.910 Propham 0.010–0.500 0.9993 0.0074 95 3.511 Cycloate 0.010–1.000 0.9992 0.0092 104 5.712 Tecnazene 0.010–0.500 0.9992 0.0092 88 2.813 Heptanophos 0.100–2.500 0.9996 0.089 75 1.514 Hexachlorobenzene 0.025–0.500 0.9999 0.025 101 6.815 Diphenylamine 0.050–1.000 0.9990 0.017 79 8.616 Propachlor 0.025–1.000 0.9988 0.039 107 2.817 Ethalfluralin 0.010–1.000 0.9999 0.0089 92 2.918 Trifluralin 0.005–0.100 0.9998 0.0028 103 5.819 Benfluralin 0.025–0.500 0.9998 0.020 87 3.320 Phorate 0.010–0.500 0.9985 0.0085 96 2.721 Sulfotep 0.025–0.500 0.9993 0.022 113 5.822 Quintozene 0.025–0.500 0.9986 0.026 75 2.023 Prometon 0.050–1.000 0.9991 0.030 95 5.224 Terbufos 0.100–1.000 0.9993 0.086 88 4.225 Clomazone 0.025–0.500 0.9998 0.020 76 6.826 Terbumeton 0.010–0.500 0.9990 0.014 83 1.427 Fonofos 0.050–1.000 0.9974 0.052 112 6.928 Profluralin 0.025–0.500 0.9990 0.012 87 3.229 Dioxathion 0.025–0.500 0.9990 0.017 109 1.630 γ-HCH 0.050–1.000 0.9992 0.052 115 5.531 Propazine 0.025–1.000 0.9982 0.020 99 2.332 Disulfoton 0.005–0.100 0.9999 0.0053 119 6.933 Etrimfos 0.025–0.500 0.9998 0.021 77 1.434 Atrazine 0.025–0.500 0.9987 0.017 105 3.535 Propetamphos 0.010–0.500 0.9990 0.0072 81 5.136 Terbutylazine 0.050–1.000 0.9999 0.036 103 4.937 Secbumeton 0.010–0.500 0.9996 0.010 98 2.438 Heptachlor 0.100–2.500 0.9996 0.075 93 1.939 Diclofenthion 0.100–1.000 0.9991 0.17 109 8.240 Pronamide 0.050–1.000 0.9997 0.035 80 1.641 Pirimicarb 0.005–0.100 0.9996 0.0046 100 3.942 Cyanophos 0.010–0.500 0.9993 0.0085 91 0.943 Fluchloralin 0.025–0.500 0.9981 0.020 89 2.244 Chlorpyrifos-methyl 0.025–0.500 0.9996 0.028 110 7.645 Aldrin 0.025–0.500 0.9997 0.024 89 2.546 Desmetryn 0.050–1.000 0.9990 0.032 92 4.547 Fenchlorophos 0.250–2.500 0.9991 0.23 106 0.648 Alachlor 0.025–0.500 0.9990 0.022 119 2.849 Cyprazine 0.010–1.000 0.9995 0.011 79 2.150 Pirimiphos-methyl 0.025–0.500 0.9998 0.020 87 1.651 Simetryn 0.250–2.500 0.9981 0.17 89 6.052 Vinclozolin 0.025–0.500 0.9990 0.030 90 2.853 Terbutryne 0.025–0.500 0.9991 0.016 79 6.554 Thiobencarb 0.010–1.000 0.9992 0.0099 102 2.155 Metalaxyl 0.025–0.500 0.9994 0.022 77 4.356 Aspon 0.025–0.100 0.9991 0.0028 99 0.957 Chlorpyrifos 0.025–0.500 0.9991 0.022 95 1.958 Parathion-methyl 0.010–0.500 0.9990 0.0098 71 2.559 Pirimiphos-ethyl 0.100–1.000 0.9998 0.097 109 3.660 Fenthion 0.025–0.500 0.9991 0.016 103 5.261 Fenitrothion 0.010–0.500 0.9995 0.012 91 2.562 Ethofumasate 0.025–0.500 0.9997 0.015 80 1.6

X. Yang et al./Chemical Papers 63 (1) 39–46 (2009) 45

Table 2. (continued)

No. Pesticide selected LAa/(mg L−1) R2 LOD/(mg kg−1) ARb/% RSD/%

63 Butralin 0.010–0.500 0.9980 0.0065 76 4.464 Isopropalin 0.050–1.000 0.9972 0.040 86 3.465 Triadimefon 0.025–0.500 0.9968 0.019 79 2.166 Parathion 0.010–0.500 0.9999 0.0071 95 2.367 Pendimethalin 0.025–0.500 0.9980 0.031 97 5.868 Fenson 0.025–0.500 0.9993 0.020 81 3.669 Bromophos-ethyl 0.100–1.000 0.9986 0.092 105 6.370 Isofenphos 0.050–1.000 0.9992 0.044 85 1.171 Quinalphos 0.025–0.500 0.9997 0.019 113 6.372 Diphenamid 0.010–1.000 0.9985 0.014 71 3.873 Chlorbenside 0.100–1.000 0.9976 0.089 102 2.874 Chlorfenvinphos 0.025–0.500 0.9996 0.015 89 6.375 Phenthoate 0.005–0.100 0.9999 0.0046 82 0.876 Penconazole 0.025–0.500 0.9991 0.015 86 4.377 p,p′-DDE 0.025–0.100 0.9998 0.0016 90 3.878 Prothiophos 0.025–0.500 0.9985 0.027 99 1.579 Flumetralin 0.025–0.500 0.9977 0.029 77 2.680 Iodofenphos 0.025–0.500 0.9998 0.026 93 3.881 Dieldrin 0.025–0.500 0.9991 0.022 121 7.682 Procymidone 0.050–1.000 0.9990 0.00030 87 2.183 Methidathion 0.005–0.100 0.9989 0.0053 94 5.284 Cyanazine 0.025–0.500 0.9996 0.024 89 3.685 Oxadiazon 0.010–0.500 0.9997 0.011 96 6.586 Chlorfenson 0.050–1.000 0.9979 0.049 92 4.187 Aramite 0.010–0.500 0.9998 0.0064 61 2.888 Fenamiphos 0.010–0.500 0.9991 0.0071 93 3.689 o,p′-DDT 0.025–0.500 0.9998 0.020 86 3.490 Imazalil 0.025–0.100 0.9997 0.0021 79 1.691 Methoprotryne 0.025–0.100 0.9994 0.0011 96 4.492 Tetrasul 0.010–0.500 0.9970 0.0091 106 2.793 Chloropropylate 0.025–0.500 0.9993 0.026 109 7.894 Flamprop-methyl 0.010–1.000 0.9988 0.013 88 1.095 Chlorbenzilate 0.025–0.500 0.9989 0.018 97 2.496 Oxyfluorfen 0.250–1.000 0.9990 0.23 113 5.897 Chlorthiophos 0.025–0.500 0.9998 0.026 79 2.998 p,p′-DDD 0.050–1.000 0.9995 0.066 96 6.099 Ethion 0.025–0.500 0.9985 0.016 107 9.2100 Flamprop-isopropyl 0.050–1.000 0.9992 0.037 93 3.9101 Sulprophos 0.050–1.000 0.9969 0.034 110 1.5102 Etaconazole 0.010–0.500 0.9990 0.011 85 4.3103 Myclobutanil 0.005–0.100 0.9997 0.0028 87 0.8104 Benalaxyl 0.010–0.500 0.9976 0.0090 100 7.8105 Diclofop-methyl 0.025–0.500 0.9994 0.022 96 4.2106 Propiconazole 0.250–1.000 0.9996 0.16 89 5.1107 Bifenthrin 0.050–1.000 0.9999 0.043 63 2.5108 Mirex 0.010–0.500 0.9993 0.0086 103 3.9109 Methoxychlor 0.010–0.500 0.9987 0.0099 77 1.5110 Bromopropylate 0.050–1.000 0.9998 0.037 86 8.2111 Benzoylprop-ethyl 0.005–0.100 0.9992 0.0061 96 1.6112 Tetramethrin 0.010–0.500 0.9995 0.011 107 5.9113 Fenpropathrin 0.500–2.500 0.9991 0.36 95 4.6114 EPN 0.010–0.500 0.9997 0.0065 77 8.2115 Hexazinone 0.025–0.500 0.9996 0.015 90 6.8116 Tetradifon 0.025–0.500 0.9991 0.027 97 1.5117 cis-Permethrin 0.010–0.500 0.9997 0.019 93 2.1118 Fenarimol 0.025–0.500 0.9992 0.027 105 0.7

a) Range covering tea samples with 5 different spiked levels (n = 5); b) covering tea samples with 0.1 mg kg−1 spiked level (n = 5).

tive 2002/657/EC) to estimate the lower limits of de-tection (LOD) (Table 2).Analytical results were validated by establishing

the precision and recovery test. Precision was repre-

sented by an estimate of the variability of measure-ments and the reproducibility of the test method. Re-covery of each pesticide was tested at different concen-trations to assess the accuracy of the method. Every

46 X. Yang et al./Chemical Papers 63 (1) 39–46 (2009)

spiking level was assessed in five repetitions. Precisionof the method was described as the value of relativestandard deviation (RSD), recovery of the assay wascalculated from the percentage of the mean calculatedconcentration to the nominal spiking value. Concen-tration of the different spiking levels, average recoverydata and RSD values obtained are shown in Table 2.Recoveries (n = 5) were calculated as follows: % Re-covery = [(cF − cU)/cS] × 100, where cF = concen-tration of pesticides measured in the fortified sample,cU = concentration of pesticides measured in the un-fortified sample (set to zero), and cS = concentrationof pesticides added to the fortified sample. Recoveriesof the analytes ranged from 61 % to 121 %. Repeata-bility of the peak areas for all pesticides expressed asRSD was in the range of 0.6–9.2 %.

Conclusions

The multi-residue analysis method proposed andvalidated in this work used SPE-GC–MS for sensitiveidentification and determination of 118 pesticides intea samples. The liquid–liquid extraction using a mix-ture of ethyl acetate–hexane proved to be the optimalmethod for extracting multi-class pesticides from teasamples. With a further clean-up by GPC and SPEpretreatment provided high extraction efficiency andlow matrix effects thus enabling adaptation of this sen-sitive and selective method for routine multi-residueanalysis of pesticides in tea matrices. The method de-scribed here was found practicable for routine residueanalysis of pesticides in tea matrices.

Acknowledgements. This work was financially supported bythe Chun Hui project of the Chinese Ministry of Education(Z2005-1-23001) in the state scientific and technological devel-opment of the 11th Five-Year-Plan Period.

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