Food Chemistry 128 (2011) 241–253

Contents lists available at ScienceDirect

Food Chemistry

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

Analytical Methods

Simultaneous multiresidue analysis of 41 pesticide residues in cookedfoodstuff using QuEChERS: Comparison with classical method

Ji-Yeon Park a, Jeong-Heui Choi a, A.M. Abd El-Aty b,⇑, Bo Mi Kim a, Jae-Ho Oh c, Jung-Ah Do c

Ki Sung Kwon c, Ki-Hoon Shim d, Ok-Ja Choi d, Sung Chul Shin e, Jae-Han Shim a,⇑a Natural Products Chemistry Laboratory, College of Agriculture and Life Science, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 500-757, Republic of Koreab Department of Pharmacology, Faculty of Veterinary Medicine, Cairo University, 12211-Giza, Egyptc Food Chemical Residues Division, National Institution of Food and Drug Safety Evaluation, 194, Tongil-ro, Eunpyeong-gu, Seoul 122-704, Republic of Koread Department of Food and Cooking Science, Shunchon National University, 413 Jungangno Suncheon, Jeollanam-do 540-742, Republic of Koreae Department of Chemistry and Research Institute of Life Science, Gyeongsang National University, Jinju 660-701, Republic of Korea

a r t i c l e i n f o

Article history:Received 18 October 2010Received in revised form 11 February 2011Accepted 16 February 2011Available online 20 February 2011

Keywords:Multiresidue methodQuEChERSSolvent extractionCooked foodstuff

0308-8146/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.foodchem.2011.02.065

⇑ Corresponding authors. Tel.: +82 62 530 2135; faxtel.: +20 2 27548926; fax: +20 2 35725240 (A.M. Abd

E-mail addresses: abdelaty44@hotmail.com (A.M. Aac.kr (J.-H. Shim).

a b s t r a c t

The principal objective of this study was to develop a simple multiresidue method involving a quick, easy,cheap, effective, rugged, and safe (QuEChERS) extraction method for the identification and quantificationof 41 pesticide residues in cooked foodstuffs including cooked potatoes, radishes, and rice using GC-lECD. The analytes were subsequently confirmed via GC–MS. The results were then compared usingthe classical method established by the KFDA. The quantitation of individual pesticides was based onmatrix-matched calibration curves with a correlation coefficient in excess of 0.993 for the 41 pesticidesselected herein. Using QuEChERS, the mean recoveries ranged between 68.6 and 130.0% for the majorityof the tested pesticides; however, the classical method exhibited low recoveries for dichlofluanid, tetrac-onazole, oxadixyl, fenbuconazloe, and paclobutrazol. After QuEChERS, the LODs and LOQs rangedbetween 0.004 and 0.3 lg/kg and 0.0125 and 1.0 lg/kg, respectively. The proposed method was appliedsuccessfully to determine the residue levels in cooked foodstuffs, and none of the samples containeddetectable amounts of pesticide residues.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

In the modern era, the use of pesticides is both necessary andessential at various stages of cultivation, both to protect agricul-tural crops against pests and to preserve their quality (Klein &Alder, 2003). However, pesticide residues remaining within thefoodstuffs have been implicated in several human health problems,which could range from short-term sickness to chronic diseases.Therefore, pesticide residues in foodstuffs must be monitoredand controlled thoroughly (Saieva et al., 2004; Ngowi, Mbise, Ijani,London, & Ajayi, 2007). In service of this objective, governmentsand international organisations have compiled and published a listof pesticides, which includes their tolerances and maximum resi-due limits (MRLs) (Codex Alimentarius Commission, 2010; KHIDI,2009).

Nowadays, a broad variety of analytical methods have beendeveloped to analyse multiresidues in food products (Fillion,Sauvé, & Selwyn, 2000). A number of techniques have been

ll rights reserved.

: +82 62 530 0219 (J.H. Shim),El-Aty).

bd El-Aty), jhshim@chonnam.

employed for the extraction and purification of pesticides fromfood products; these include liquid–liquid extraction (LLE)(Rissato, Galhiane, Knoll, & Apon, 2004; Torres, Picó, & Mañes,1996), solid-phase extraction (SPE) (Adou, Bontoyan, & Sweeney,2001; Juan-García, Picó, & Font, 2005; Obana, Okihashi, Akutsu,Kitagawa, & Hori, 2003), accelerated solvent extraction (ASE)(Adou et al., 2001), gel permeation chromatography (GPC) (Uenoet al., 2004), microwave-assisted extraction (MAE) (Barriada-Pereira et al., 2007), matrix solid-phase dispersion (MSPD) (Torreset al., 1996) and supercritical fluid extraction (SFE) (Torres et al.,1996; Rissato et al., 2004). However, the majority of the aforemen-tioned methods for the determination of pesticide residues in food-stuff commodities are rather complicated, consume a large volumeof solvent, are labor-intensive and very expensive, owing primarilyto the complexity of analytes and matrices involved. In 2003, Anas-tassiades et al. described the ‘‘Quick, easy, cheap, effective, rugged,and safe’’ (QuEChERS) method for the multiclass, multiresidueanalysis of pesticides from different food matrices with high watercontent (Anastassiades, Lehotay, Stajnbaher, & Schenck, 2003). Thisbasic procedure is predicated on salting-out assisted liquid–liquidextraction with water miscible or partially miscible solvents suchas acetonitrile, followed by a dispersive SPE clean-up with primarysecondary amine (PSA) (Herrero Martín, García Pinto, Pérez Pavón,

242 J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253

& Moreno Cordero, 2010). This method is particularly popular forthe determination of polar, middle polar and non-polar pesticideresidues in various food matrices, due to its simplicity, low cost,amenability to high throughput, and relatively high efficiency re-sults, as well as the minimal number of steps it involves (HerreroMartín et al., 2010). Recently, the QuEChERS method for multiplepesticides in fruits and vegetables has received the distinction ofthe Official Method of AOAC International (Lehotay, 2007).

Residues contained in food products are generally monitored inraw but not cooked samples. Cooking might alter and degrade thechemical structure of analytes. Therefore, in order to evaluate indetail the hazardous effects of pesticides on human health, cookedfoodstuffs appear to be a more reasonable choice of sample. Pota-toes, Korean radishes, and rice are the most frequently consumedfoodstuffs in the Republic of Korea according to a nutrition surveyconducted by the Korea Health Industry Development Institute(KHIDI, 2005), and a number of pesticides are extensively appliedto crops during the cultivation of these foodstuffs.

In this study, we compared the classical method officially sanc-tioned by the Korea Food and Drug Administration (KFDA) with theQuEChERS method (KFDA, 2009), and monitored the presence of 41pesticides in cooked potato, Korean radish, and rice. The foodstuffswere obtained from a large market and boiled, fried, and polished

Table 1Name, retention times (RT), LODs, and LOQs and correlation coefficient (r2), of the tested

No Pesticides RT r2

Group 11 Ethoprophos 9.254 0.9992 Quintozene 10.808 1.0003 Vinclozolin 12.408 0.9944 Fenitrothion 13.346 0.9995 Chlorpyrifos 14.165 0.9986 Tetraconazole 14.588 0.9997 Pendimethalin 15.626 0.9988 Phenthoate 16.308 1.0009 Methidathion 16.953 1.00010 a-Endosulfan 17.380 0.99911 Butachlor 18.041 0.99512 Flutolanil 18.953 0.99813 b-Endosulfan 21.332 0.99914 Cyflufenamid 21.690 0.99815 Diniconazole 22.092 1.00016 Oxadixyl 22.723 0.99917 Endosulfan-sulfate 24.095 1.00018 EPN 27.567 1.00019 Bifenthrin 28.275 0.99820 Tetradifon 29.108 1.00021 Cyhalothrin 31.749, 32.723 1.00022 Pyrazophos 33.419 0.99923 Pyraclofos 33.788 0.99924 Permethrin 36.210, 37.094 0.99825 Fenbuconazole 38.986 0.99926 Cypermethrin 41.496, 41.909, 42.590, 42.929 0.99927 Pyridalyl 44.140 0.99828 Fenvalerate 46.655, 47.888 0.997

Group 229 Diazinon 11.158 0.99630 Tebupirimfos 11.673 0.99331 Chlorpyrifos-methyl 12.419 1.00032 Alachlor 12.666 0.99433 Dichlofluanid 13.615 1.00034 Parathion 14.202 0.99835 Triflumizole 16.908 0.99936 Paclobutrazol 17.219 1.00037 Hexaconazole 18.501 1.00038 Isoprothiolane 19.107 1.00039 Chlorfenapyr 21.700 1.00040 Fenpropathrin 28.546 1.00041 Fenarimol 31.855 1.000

* MRLs were derived from those established by the Korea Food and Drug Administratio

in accordance with the cooking practices established by KHIDI(KHIDI, 2007). The pesticides were analysed via GC-lECD and con-firmed via GC–MS. The data collected using these analytical meth-ods was expected to prove useful in regulating the concentration ofthe residues in foodstuffs, and also in estimating the human healthhazards posed by these residues.

2. Experimental

2.1. Chemicals and reagents

Most of the pesticide reference standards used herein were ofanalytical grade, and were purchased either from Dr. EhrenstorferGmbH (Augsburg, Germany) or Sigma–Aldrich (St Louis, MO, USA).Some pesticide standards were generously provided by the KoreaFood and Drug Administration (Seoul, Republic of Korea), or theNational Agricultural Products Quality Management Service(Gwangju, Republic of Korea). Anhydrous magnesium sulfate andacetic acid were acquired from Junsei Chemical Co. Ltd. (Kyoto,Japan) and Daejung Chemicals & Materials (Siheung, Republic ofKorea) respectively. PSA and C18 EC were purchased from AgilentTechnologies (California, USA). Sodium chloride, sodium acetate,

pesticides.

MRL* LOD (lg/ kg) LOQ (lg/ kg) Main ions, (m/z)

0.005–0.02 0.075 0.25 158, 97, 1390.2 0.004 0.0125 237, 249, 2140.1 0.004 0.0125 198, 212, 2850.05–0.2 0.008 0.025 125, 277, 1090.05–2 0.008 0.025 197, 199, 314– 0.015 0.05 336, 338, 1010.05–0.2 0.015 0.05 252, 162, 281– 0.008 0.025 274, 125, 1210.05–0.2 0.015 0.05 145, 93, 1250.1 0.004 0.0125 237, 195, 1700.1 0.075 0.25 176, 160, 3111.0 0.150 0.5 173, 145, 2810.1 0.004 0.0125 195, 237, 207– 0.015 0.05 91, 118, 188– 0.015 0.05 268, 270, 2320.1–1.0 0.150 0.5 105, 163, 2780.1 0.008 0.025 272, 229, 2370.1 0.008 0.025 157, 169, 1850.05 0.015 0.05 181, 166, 152– 0.004 0.0125 159, 111, 2290.02–0.5 0.030 0.1 181, 197, 208– 0.075 0.25 221, 232, 237– 0.150 0.5 138, 194, 1110.05–2.0 0.030 0.1 183, 163, 1650.05 0.300 1 129, 198, 1250.05–1.0 0.075 0.25 163, 181, 165– 0.015 0.05 204, 109, 1640.05–1.0 0.030 0.1 125, 167, 181

0.1 0.075 0.25 137, 179, 3040.01 0.075 0.25 261, 234, 3180.1 0.008 0.025 286, 288, 1250.2 0.015 0.05 160, 188, 2690.1–15.0 0.008 0.025 123, 167, 2240.05–0.3 0.008 0.025 109, 291, 1391.0 0.015 0.05 278, 206, 179– 0.150 0.5 236, 125, 1670.3 0.015 0.05 214, 175, 2310.5 0.015 0.05 118, 162, 1890.05 0.004 0.0125 247, 137, 249– 0.015 0.05 97, 181, 125– 0.008 0.025 139, 219, 330

n (2009).

Table 2Recovery of pesticides from spiked cooked foodstuffs.

No Pesticide Fortification level (lg/ kg) Mean recovery ± RSDb (%)a

Boiled radish Boiled potato Fried potato Polished rice

Group11 Ethoprophos 0.25 74.2 ± 5.6 82.0 ± 7.3 80.0 ± 5.0 117.3 ± 3.1

2.5 98.1 ± 1.1 88.7 ± 5.5 100.0 ± 1.8 100.7 ± 4.22 Quintozene 0.0125 92.4 ± 1.7 74.3 ± 5.6 85.8 ± 9.0 92.7 ± 4.0

0.125 97.2 ± 3.1 78.9 ± 3.3 99.9 ± 4.0 91.5 ± 6.03 Vinclozolin 0.0125 210.5 ± 9.5 85.4 ± 12.5 83.2 ± 5.1 131.3 ± 8.2

0.125 152.0 ± 6.3 83.4 ± 4.7 95.5 ± 2.0 100.3 ± 4.14 Fenitrothion 0.025 99.0 ± 3.8 83.6 ± 8.7 93.5 ± 6.5 116.2 ± 2.7

0.25 106.6 ± 1.8 86.2 ± 5.3 101.8 ± 1.3 104.1 ± 4.45 Chlorpyrifos 0.025 95.9 ± 4.5 82.6 ± 5.8 75.4 ± 6.3 106.3 ± 3.2

0.25 104.1 ± 1.8 86.5 ± 3.7 97.5 ± 1.9 98.2 ± 4.56 Tetraconazole 0.05 99.5 ± 3.7 85.7 ± 6.9 74.3 ± 4.1 120.3 ± 2.1

0.5 105.9 ± 3.2 82.8 ± 7.1 96.2 ± 1.9 102.7 ± 4.57 Pendimethalin 0.05 97.0 ± 3.9 87.5 ± 4.5 75.9 ± 7.2 106.7 ± 2.8

0.5 103.3 ± 1.7 85.1 ± 3.4 97.9 ± 1.7 98.6 ± 4.58 Phenthoate 0.025 98.5 ± 3.2 77.4 ± 10.7 84.9 ± 5.0 115.8 ± 4.1

0.25 104.1 ± 1.5 82.4 ± 4.3 99.7 ± 1.4 100.8 ± 5.89 Methidathion 0.05 94.2 ± 8.9 83.1 ± 13.3 104.8 ± 6.0 122.0 ± 9.2

0.5 106.5 ± 3.3 87.1 ± 5.5 99.3 ± 1.3 105.5 ± 4.710 a-Endosulfan 0.0125 54.3 ± 7.1 88.3 ± 4.7 102.2 ± 7.0 103.2 ± 3.8

0.125 94.7 ± 2.7 83.8 ± 3.9 96.2 ± 2.2 97.9 ± 4.911 Butachlor 0.25 98.6 ± 5.4 88.3 ± 4.7 77.9 ± 3.9 108.7 ± 3.0

2.5 105.7 ± 3.0 84.8 ± 4.5 94.1 ± 2.2 99.3 ± 4.412 Flutolanil 0.5 99.4 ± 2.4 113.2 ± 7.4 75.0 ± 3.6 108.7 ± 3.0

5 103.2 ± 2.2 86.9 ± 6.2 94.8 ± 1.6 103.5 ± 4.113 b-Endosulfan 0.0125 41.4 ± 4.1 89.3 ± 6.9 108.6 ± 6.5 108.4 ± 3.2

0.125 89.9 ± 2.8 84.6 ± 4.4 96.8 ± 2.5 100.2 ± 4.914 Cyflufenamid 0.05 95.4 ± 3.8 85.9 ± 8.8 71.8 ± 3.5 111.7 ± 4.5

0.5 105.6 ± 3.0 85.5 ± 5.3 99.6 ± 1.0 98.5 ± 4.815 Diniconazole 0.05 94.8 ± 5.6 77.2 ± 11.9 75.1 ± 5.9 114.9 ± 2.8

0.5 103.2 ± 3.8 77.8 ± 7.2 93.8 ± 2.2 100.9 ± 5.516 Oxadixyl 0.5 95.8 ± 4.3 106.1 ± 6.6 71.0 ± 4.8 121.4 ± 1.3

5 101.9 ± 2.7 91.6 ± 6.3 88.1 ± 2.4 105.6 ± 4.517 Endosulfan-sulfate 0.025 73.6 ± 8.7 90.9 ± 7.2 75.0 ± 7.2 110.3 ± 3.6

0.25 103.0 ± 4.9 84.3 ± 5.1 90.9 ± 2.8 100.5 ± 5.318 EPN 0.025 93.3 ± 3.7 84.2 ± 5.8 85.7 ± 7.1 109.9 ± 2.3

0.25 103.9 ± 3.4 84.3 ± 5.1 102.4 ± 1.7 102.0 ± 5.419 Bifenthrin 0.05 99.0 ± 4.0 103.9 ± 2.6 81.6 ± 3.2 102.3 ± 2.6

0.5 107.1 ± 2.4 98.1 ± 4.2 97.5 ± 1.8 104.3 ± 3.920 Tetradifon 0.0125 107.2 ± 5.3 88.7 ± 4.8 79.8 ± 8.1 99.7 ± 4.4

0.125 106.1 ± 2.3 87.0 ± 3.6 97.0 ± 1.7 110.0 ± 18.121 Cyhalothrin 0.1 97.1 ± 5.0 93.9 ± 6.2 97.2 ± 2.0 102.3 ± 2.6

1 104.4 ± 1.6 95.4 ± 5.9 94.2 ± 0.9 103.2 ± 4.722 Pyrazophos 0.25 98.5 ± 4.7 85.3 ± 8.9 82.2 ± 8.1 114.5 ± 2.5

2.5 104.3 ± 3.9 85.8 ± 4.9 95.6 ± 1.4 103.3 ± 4.323 Pyraclofos 0.5 97.4 ± 17.1 70.4 ± 13.3 91.3 ± 7.9 127.6 ± 10.1

5 99.6 ± 11.9 79.1 ± 6.1 82.3 ± 3.1 105.0 ± 5.324 Permethrin 0.1 93.4 ± 5.2 95.5 ± 3.7 85.2 ± 4.0 113.0 ± 1.8

1 104.0 ± 4.0 95.7 ± 3.5 98.3 ± 1.9 101.5 ± 4.025 Fenbuconazole 1 99.8 ± 3.0 88.5 ± 7.5 79.6 ± 5.0 113.0 ± 1.8

10 100.2 ± 2.8 83.7 ± 6.7 96.7 ± 1.5 104.3 ± 4.426 Cypermethrin 0.25 97.3 ± 4.8 81.7 ± 9.7 85.1 ± 4.0 100.7 ± 2.4

2.5 103.4 ± 5.7 94.9 ± 5.7 94.7 ± 1.2 102.4 ± 4.727 Pyridalyl 0.05 95.5 ± 5.3 85.0 ± 8.2 83.3 ± 13.3 99.0 ± 4.0

0.5 101.5 ± 4.6 97.8 ± 4.0 97.8 ± 2.0 104.7 ± 4.728 Fenvalerate 0.1 96.8 ± 4.9 129.5 ± 6.4 73.8 ± 3.8 100.6 ± 2.7

1 130.0 ± 2.2 95.3 ± 6.3 91.9 ± 1.2 102.0 ± 4.6

Group 229 Diazinon 0.25 99.7 ± 4.2 142.1 ± 6.4 71.6 ± 3.2 106.7 ± 1.1

2.5 119.8 ± 5.2 102.5 ± 8.1 102.3 ± 4.1 114.7 ± 2.330 Tebupirimfos 0.25 112.2 ± 10.5 130.5 ± 3.3 78.3 ± 3.6 106.6 ± 1.2

2.5 115.1 ± 7.0 102.7 ± 7.9 103.4 ± 1.7 112.1 ± 2.131 Chlorpyrifos-methyl 0.025 76.1 ± 4.5 94.9 ± 4.0 91.9 ± 2.2 108.1 ± 2.8

0.25 111 ± 6.8 98.3 ± 8.1 110.6 ± 2.5 116.1 ± 2.432 Alachlor 0.05 68.6 ± 6.1 128.9 ± 3.5 85.8 ± 3.1 93.4 ± 2.2

0.5 116.8 ± 5.6 99.0 ± 7.9 108.3 ± 2.2 115.2 ± 2.733 Dichlofluanid 0.025 75.4 ± 15.8 78.2 ± 10.8 76.2 ± 2.6 82.4 ± 1.7

0.25 17.3 ± 0.6 18.8 ± 11.2 113.8 ± 4.8 103.1 ± 5.234 Parathion 0.025 89.1 ± 3.5 108.1 ± 3.4 90.1 ± 2.9 109.9 ± 1.9

0.25 116.6 ± 5.1 99.1 ± 7.3 111.7 ± 2.6 115.4 ± 2.435 Triflumizole 0.05 69.8 ± 2.9 78.4 ± 9.3 126.6 ± 4.3 105.6 ± 2.7

0.5 79.8 ± 5.6 85.9 ± 14.5 126 ± 4.0 114.6 ± 3.2

(continued on next page)

J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253 243

Table 2 (continued)

No Pesticide Fortification level (lg/ kg) Mean recovery ± RSDb (%)a

Boiled radish Boiled potato Fried potato Polished rice

36 Paclobutrazol 0.5 124.2 ± 4.4 89 ± 10.1 113.7 ± 4.7 88.7 ± 2.25 132.3 ± 4.6 91.9 ± 10.6 103 ± 3.3 113.3 ± 3.1

37 Hexaconazole 0.05 101.6 ± 4.0 91.9 ± 11.4 108.4 ± 4.3 108.6 ± 3.30.5 119.8 ± 6.1 90.5 ± 13.2 114.2 ± 3.3 115.0 ± 3.3

38 Isoprothiolane 0.05 88.2 ± 4.1 87.5 ± 6.7 120 ± 3.0 106.2 ± 2.70.5 110.6 ± 6.7 97.8 ± 9.3 116.1 ± 3.3 113.9 ± 3.2

39 Chlorfenapyr 0.0125 102.6 ± 4.3 92.5 ± 5.2 112.8 ± 4.6 104.9 ± 2.30.125 118.4 ± 5.8 101.1 ± 9.0 115.6 ± 2.9 115.5 ± 3.4

40 Fenpropathrin 0.05 96.0 ± 5.2 108.5 ± 6.7 116.3 ± 4.6 109.4 ± 1.50.5 114.4 ± 5.2 101.8 ± 8.8 117.4 ± 3.1 114.0 ± 3.7

41 Fenarimol 0.025 98.3 ± 3.2 90 ± 12.0 115.4 ± 3.2 104.5 ± 2.30.25 117.1 ± 5.8 89.8 ± 12.8 115.2 ± 3.6 113.6 ± 3.2

a n = 3.b Relative standard deviation.

244 J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253

acetonitrile, acetone and n-hexane were of pesticide grade, andwere purchased from E. Merck (Darmstadt, Germany).

2.2. Standard solution preparation and quantitative analysis

Stock standard solutions (100 lg/mL) of the targeted pesticideswere prepared separately in acetone. All pesticides were dividedinto two groups (Table 1) according to their retention times (RT)in the GC-column, to avoid the overlapping of peaks for some pes-ticides (due to identical or similar retention times in the column).Medium stock solution mixtures were prepared at 100 � the LOQconcentration of each pesticide via serial dilutions in acetone fromthe stock standard solutions. Working solutions were prepared viaserial dilution of the medium stock solutions in matrix to six con-centration levels ranging between the LOQ and 50 � the LOQ. Allstandard solutions were maintained in amber bottles (100 mL)and stored at �24 �C.

2.3. Sample preparation

Foodstuff samples were prepared by boiling, frying, and polish-ing, in accordance with published protocols regarding cookingpractices. Each boiled Korean radish, boiled potato, fried potato,and polished rice sample was smashed and homogenised. Samplesof approximately 10 g were weighed into 50 mL Teflon centrifugetubes, to each of which 2 mL of distilled water, 15 mL of acetoni-trile, and 150 lL of acetic acid were added (pH 5.5–6). 6 g MgSO4

and 1.5 g CH3COONa were then added and immediately shakenfor 1 min, and then the extract was centrifuged for 5 min at3000 rpm at 4 �C. Six milliliters of the upper layer were transferredto a 15 mL Teflon centrifuge tube containing 900 mg MgSO4 and300 mg PSA. Teflon centrifuge tube was shacked for 1 min and cen-trifuged for 5 min at 3000 rpm at 4 �C. Three milliliters from theupper layer of the prepared sample were removed and evaporated.Finally, 1 mL of n-hexane: acetone (8:2, v/v) was added to reconsti-tute the residue and then injected onto the gas chromatographequipped with micro-electron capture detector and mass selectiveion detector.

2.4. Instrumental conditions

2.4.1. GC-lECDAn Agilent Technology 7890 A gas chromatography (California,

USA) equipped with a micro-electron capture detector and an Agi-lent Technology 7683 B auto injector was used for the determinationof the pesticide residues in the cooked foodstuff samples. Separa-tions were conducted on an Ultra-2 column (50 m � 0.32 mm

i.d. � 0.17 lm film thickness, J&W Scientific Products, California,USA) under the following operating conditions: oven temperatureat 100 �C for 1 min, increased to 190 �C at 10 �C/min, hold for10 min, then increased to 220 �C at 5 �C /min, holding for 10 min,then increased to 250 �C/min and a final increase to 290 �C at20 �C/min, followed by holding for 2 min. Nitrogen was employedas a carrier gas, with a flow rate of 2.25 mL/min, and a split ratio of10:1. The detector and injector temperatures were 300 �C and250 �C, respectively. The injection volume was 1 lL.

2.4.2. GC–MSThe 41 pesticides were confirmed via run analysis using an Agi-

lent 6890 gas chromatography with a 5973 N MSD mass selectiveion detector and a HP-5MS capillary column (30 m � 0.25 mmi.d. � 0.25 lm film thickness, J&W Scientific Products, California,USA). GC–MS was operated under the following conditions: oventemperature, 100 �C (5 min), increased at 10 �C/min to 300 �C,and holding for 5 min. Injections were performed in a splitlessmode with an injection temperature of 250 �C. The injection vol-ume was 2 lL; the GC–MS transfer line and mass source tempera-ture were 300 �C and 230 �C, respectively. The carrier gas used wasHe and the column flow rate was 1 mL/min. The electron impactionisation voltage was 70 eV, and the scanned-mass range was50–500 m/z.

2.5. Recovery studies

Cooked foodstuffs in which no pesticides had been previouslydetected were employed for the fortification experiments. Mix-tures at the LOQ and at 10 � the LOQ were spiked in triplicate.The spiked samples were allowed to stand for 2 h to allow forthe adsorption of pesticide onto the samples. They were then pre-pared in accordance with the above-described determinationprocedure.

3. Results and discussion

3.1. Gas Chromatographic Determination

Pesticide analysis and confirmation were conducted in SIMmode based on the use of the target and two qualifier ions. Pesti-cides were identified according to their retention times, target,and qualifier ions. Table 1 shows the pesticides with their qualifierions in SIM.

Fig. 1. Typical chromatograms of blank, standard, and recovery of tested pesticides in various foodstuffs. Please refer to Table 1 for pesticide names. Group 1A: standardmixture in acetone at LOQ concentration; Group 1B: boiled radish blank; Group 1C: standard mixture in boiled radish matrix at LOQ concentration; Group 1D: boiled potatoblank; Group 1E: standard mixture in boiled potato matrix at LOQ concentration; Group 1F: fried potato blank; Group 1G: standard mixture in fried potato matrix at LOQconcentration; Group 1H: polished rice blank; Group 2a: standard mixture in acetone at LOQ concentration; Group 2b: boiled radish blank; Group 2c: standard mixture inboiled radish matrix at LOQ concentration; Group 2d: boiled potato blank; Group 2e: boiled potato blank by classical method; Group 2f: standard mixture in boiled potatomatrix at LOQ concentration; Group 2 g: fried potato blank; Group 2 h: standard mixture in fried potato matrix at LOQ concentration; Group 2i: polished rice matrix blank;Group 2j: standard mixture in polished rice matrix at LOQ concentration.

J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253 245

Fig. 1 (continued)

246 J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253

Fig. 1 (continued)

J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253 247

3.2. Methods Validation

3.2.1. LinearityChromatographic responses to certain pesticides have been

shown to be influenced by the effects of matrices, which are them-selves simultaneously influenced by other factors such as pesticidecharacteristics, matrix type, and matrix/analyte concentration(Hajs�lova et al., 1998). Matrix effects can enhance the transfer ofchromatographic responses of some pesticides (Wong et al., 2003;Sánchez-Brunete, Albero, & Tadeo, 2004). Because the alternativesare either less practical or have no detectable effect, the mostcommon method used to prevent matrix effects involves the useof matrix-matched calibration standards (Lehotay, Mastovska,Lightfield, & Gates, 2010). In this study, calibration curves wereprepared in matrices extracted from blank foodstuffs and the linear-ities, limits of detection (LODs), and limits of quantification (LOQs)were calculated. All linearity values, which were calculated asdetermination coefficients (r2), were above 0.993 (Table 1).

3.2.2. Limits of detection and quantificationThe limit of detection is the smallest concentration from which

it is possible to deduce the presence of an analyte, and the limit of

quantification is the smallest quantity required to quantify theanalyte with a reasonable degree of statistical certainty (Shimet al., 2007). The LODs were calculated considering a value 3 timesthe background noise level obtained for blank samples, whereasthe LOQs were determined considering a value 10 times the back-ground noise. Most of the LOQs were lower than the MRLs estab-lished by the Korea Food and Drug Administration (KHIDI, 2009).The relevant values are listed in Table 1.

3.2.3. RecoveryPercent recoveries were between 68.6 and 130.0% for most of

the pesticides, with the notable exception of dichlofluanid, in bothboiled foodstuffs tested (Table 2). In boiled Korean radish, vincloz-olin evidenced very high recovery rates (210.5 and 152.0%) andpaclobutrazol exhibited slightly higher recovery (132.3%) at a con-centration of 10 � the LOQ. The high recovery rates of these pesti-cides could be explained by the interfering peaks from the blanksample (Fig. 1). The RSDs were below 20%, which suggests thatthe extraction procedure could be appropriate for use in the rou-tine analysis of the targeted pesticide residues in cooked food-stuffs. The findings of this study were consistent with the official

Fig. 1 (continued)

248 J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253

Fig. 1 (continued)

J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253 249

Fig. 1 (continued)

250 J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253

Fig. 1 (continued)

Table 3Comparison of recovery using the QuEChERS and classical method.

No Pesticides Fortified level(lg/kg)

Mean recovery ± RSDb (%)a

Boiled radish Boiled potato Fried potato Polished rice

Classical QuEChERS Classical QuEChERS Classical QuEChERS Classical QuEChERS

Group11 Ethoprophos 1.25 82.9 ± 2.1 95.2 ± 4.7 89.6 ± 3.5 100.6 ± 12.1 75.5 ± 1.6 96.3 ± 2.1 14.6 ± 13.6 105.3 ± 5.32 Quintozene 0.0625 70.0 ± 5.7 95.6 ± 4.8 80.0 ± 0.1 85.1 ± 12.0 69.3 ± 4.6 91.1 ± 4.4 12.0 ± 47.1 95.3 ± 7.13 Vinclozolin 0.0625 2826.0 ± 9.0 185.0 ± 11.4 72.0 ± 0.1 93.1 ± 16.0 72.0 ± 0.1 69.8 ± 3.7 16.4 ± 0.1 113.5 ± 3.44 Fenitrothion 0.125 78.0 ± 3.0 102.7 ± 2.6 87.0 ± 2.0 95.4 ± 14.7 81.3 ± 2.3 93.9 ± 2.9 20.2 ± 1.4 110.3 ± 3.25 Chlorpyrifos 0.125 81.0 ± 2.5 101 ± 2.7 81.0 ± 2.0 94.5 ± 11.6 80.0 ± 0.1 89.0 ± 3.1 20.2 ± 1.4 100.3 ± 3.96 Tetraconazole 0.25 40.5 ± 8.4 106.1 ± 4.2 53.0 ± 16.4 97.2 ± 12.5 38.7 ± 1.2 89.1 ± 3.0 14.1 ± 1.0 111.8 ± 3.27 Pendimethalin 0.25 76.0 ± 2.1 101.5 ± 2.9 78.5 ± 1.0 93.9 ± 12.0 72.0 ± 10.4 90.1 ± 1.9 19.0 ± 7.4 104.3 ± 4.18 Phenthoate 0.125 75.0 ± 2.7 103.3 ± 5.1 85.0 ± 2.0 90.9 ± 12.9 82.7 ± 2.3 93.0 ± 1.3 20.2 ± 1.4 105.5 ± 7.39 Methidathion 0.25 73.5 ± 2.6 105.9 ± 3.2 88.0 ± 1.6 98.2 ± 13.1 84.0 ± 3.5 89.8 ± 1.8 27.0 ± 5.2 111.6 ± 3.410 a-Endosulfan 0.0625 72.0 ± 0.1 85.3 ± 3.2 72.0 ± 0.1 93.9 ± 13.6 72.0 ± 0.1 87.9 ± 3.2 24.4 ± 2.3 103.4 ± 4.311 Butachlor 1.25 60.6 ± 10.0 104.5 ± 3.8 84.6 ± 1.0 95.3 ± 12.0 82.9 ± 0.1 87.2 ± 3.5 14.8 ± 7.6 105.8 ± 3.612 Flutolanil 2.5 91.2 ± 4.7 105.5 ± 5.4 78.8 ± 1.4 103.5 ± 10.9 80.0 ± 1.2 90.2 ± 2.6 7.4 ± 26.8 103.5 ± 4.313 b-Endosulfan 0.0625 72.0 ± 0.0 78.8 ± 3.6 72.0 ± 0.1 95.8 ± 11.4 72.0 ± 0.1 88.8 ± 3.4 24.4 ± 2.3 124 ± 3.714 Cyflufenamid 0.25 75.0 ± 1.5 104.2 ± 5.1 84.5 ± 1.0 97.9 ± 11.9 82.0 ± 0.1 90.5 ± 2.2 23.0 ± 6.1 106.6 ± 3.415 Diniconazole 0.25 83.5 ± 3.0 102.3 ± 3.6 84.0 ± 1.6 89.8 ± 12.3 82.7 ± 2.3 86.4 ± 2.6 25.0 ± 5.7 107.2 ± 4.216 Oxadixyl 2.5 ND 102.1 ± 6.6 ND 109.7 ± 11.6 ND 80.9 ± 1.6 0.0 ± 0.1 106.6 ± 4.117 Endosulfan-sulfate 0.125 75.0 ± 2.7 98.1 ± 2.8 76.0 ± 0.1 94.5 ± 11.7 77.3 ± 2.3 83.4 ± 4.8 22.0 ± 12.9 107.5 ± 3.418 EPN 0.125 69.0 ± 2.9 103.6 ± 3.3 73.0 ± 2.0 105.4 ± 12.8 76.0 ± 0.1 96.5 ± 2.6 26.0 ± 10.9 108.6 ± 3.119 Bifenthrin 0.25 78.5 ± 1.3 108.3 ± 4.8 69.0 ± 1.2 113.2 ± 10.6 81.3 ± 1.2 91.8 ± 3.0 61.0 ± 2.3 106.4 ± 5.620 Tetradifon 0.0625 72.0 ± 0.0 105.4 ± 3.4 74.0 ± 4.0 316.7 ± 10.6 80.0 ± 0.1 91.3 ± 3.1 24.4 ± 2.3 105.5 ± 2.421 Cyhalothrin 0.5 70.3 ± 1.4 99.6 ± 8.0 75.0 ± 1.4 103.2 ± 11.4 77.7 ± 0.6 85.9 ± 3.1 58.5 ± 6.0 107.2 ± 4.522 Pyrazophos 1.25 81.3 ± 2.0 104.3 ± 3.8 86.3 ± 1.4 94.8 ± 9.9 88.0 ± 0.1 88.6 ± 2.7 12.2 ± 16.2 110 ± 2.623 Pyraclofos 2.5 87.4 ± 4.5 101.5 ± 2.7 107.6 ± 2.6 85.3 ± 9.9 101.1 ± 0.7 66.9 ± 7.5 22.6 ± 8.8 111.1 ± 7.024 Permethrin 0.5 84.0 ± 7.7 100.5 ± 4.2 76.5 ± 1.0 108 ± 10.3 86.0 ± 1.0 92.7 ± 2.8 46.5 ± 7.6 103.3 ± 4.725 Fenbuconazole 5 2.2 ± 0.0 101.4 ± 4.3 11.2 ± 13.2 95.9 ± 9.6 ND 90.3 ± 2.3 ND 109.4 ± 2.426 Cypermethrin 1.25 71.4 ± 1.7 100.4 ± 7.9 74.8 ± 1.1 101 ± 9.2 78.8 ± 0.7 86.5 ± 3.6 51.2 ± 11.0 105.4 ± 3.827 Pyridalyl 0.25 73.0 ± 1.6 100.8 ± 5.2 69.5 ± 1.0 112.2 ± 11.7 77.3 ± 1.2 90.2 ± 3.3 58.0 ± 4.9 105.8 ± 5.928 Fenvalerate 0.5 72.0 ± 1.6 101.6 ± 8.0 74.8 ± 1.0 100 ± 8.8 78.7 ± 0.6 74.8 ± 19.8 51.5 ± 4.1 104.6 ± 4.0

Group 229 Diazinon 1.25 85.5 ± 3.5 119.1 ± 10.4 100.7 ± 9.7 110.6 ± 3.1 94 ± 11.1 87.2 ± 4.3 75.6 ± 5.7 115.4 ± 2.830 Tebupirimfos 1.25 91.5 ± 5.2 117.3 ± 10.7 111.3 ± 9.6 110.6 ± 4.8 103.1 ± 12.8 85.8 ± 3.9 77.5 ± 7.5 113.6 ± 2.731 Chlorpyrifos-methyl 0.125 83.0 ± 4.6 102.8 ± 9.7 97.0 ± 9.1 103.4 ± 4.8 92 ± 9.8 101.2 ± 4.6 72.0 ± 5.6 115.2 ± 2.532 Alachlor 0.25 74.5 ± 4.6 109.1 ± 9.1 80.0 ± 12.1 95.4 ± 3.5 80 ± 9.1 96.1 ± 4.0 63.3 ± 9.1 116.4 ± 1.733 Dichlofluanid 0.125 ND 21.7 ± 16.5 86.0 ± 17.6 43.4 ± 4.5 52 ± 34.7 109.6 ± 4.5 76.0 ± 9.1 95.7 ± 9.634 Parathion 0.125 81.0 ± 4.7 111.0 ± 10.7 98.0 ± 10.3 103.7 ± 4.1 99 ± 12.8 100.4 ± 4.1 70.7 ± 11.8 116.1 ± 2.235 Triflumizole 0.25 93.0 ± 4.2 75.2 ± 11.4 139.5 ± 9.5 89.4 ± 7.0 143 ± 16.0 118.4 ± 5.5 96.7 ± 8.4 110.5 ± 2.236 Paclobutrazol 2.5 ND 132.7 ± 10.5 100.5 ± 12.8 98.6 ± 3.2 99.9 ± 12.2 95.7 ± 3.4 76.5 ± 9.7 111.9 ± 3.937 Hexaconazole 0.25 69.0 ± 8.7 115.0 ± 12.3 86.5 ± 11.5 94.9 ± 4.6 95.5 ± 3.0 108.7 ± 4.9 67.3 ± 7.5 117.6 ± 2.138 Isoprothiolane 0.25 90.0 ± 1.9 102.9 ± 11.4 112.0 ± 8.6 100.3 ± 5.4 102.5 ± 24.6 111.6 ± 4.7 87.0 ± 8.1 116.0 ± 1.439 Chlorfenapyr 0.0625 82.2 ± 3.1 115.0 ± 12.6 94.0 ± 10.7 106.1 ± 3.3 101.3 ± 5.7 110.5 ± 4.9 76.0 ± 7.4 117.4 ± 2.440 Fenpropathrin 0.25 86.9 ± 3.1 111.8 ± 13.8 104.0 ± 8.3 105.4 ± 3.9 105.5 ± 9.1 112.1 ± 5.0 88.0 ± 7.9 117.0 ± 2.641 Fenarimol 0.125 79.4 ± 1.5 112.2 ± 12.6 91.0 ± 11.6 95.3 ± 4.3 95 ± 10.5 110.0 ± 4.6 72.0 ± 9.6 115.1 ± 2.2

a n = 3.b Relative standard deviation.

J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253 251

Fig. 2. Monitoring sample chromatography from boiled potato.

252 J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253

methods requirements established by the KFDA (70–130%) (NIFDS,2009).

3.3. Comparison of sample preparation methods

Triplicate recovery experiments with 41 pesticides were con-ducted at a concentration level of 5 � the LOQ, exactly in accor-dance with the extraction procedure for the multi-classpesticide multiresidue method established by the KFDA and QuE-ChERS. Each homogenised foodstuff sample (50 g) was placed intoa 200 mL Erlenmeyer flask with 100 mL of acetonitrile andshacked for 30 min. The samples were filtered and transferredinto separation funnels, followed by the addition of 15 g of so-dium chloride, and the filtrate was subsequently shaken vigor-ously for 3 min. 20 mL of sample was obtained and evaporated.The samples were then cleaned up with an SPE cartridge and ana-lysed via GC-lECD. Table 3 shows the recovery results, which wascompared with those of the QuEChERS method. Most of the pes-ticides evidenced similar recoveries via both methods; however,some of the pesticides exhibited different values. In QuEChERS,the recovery rates were between 68.6 and 130%, with the excep-tions of dichlofluanid and vinclozolin. On the contrary, the KFDAmethod yielded low recoveries for dichlofluanid, tetraconazole,oxadixyl, fenbuconazole, and paclobutrazol. Additionally, the pol-ished rice samples analysed via the classical methods establishedby the KFDA generally evidenced low recovery rates. Because theQuEChERS method uses acetate buffering, it frequently yieldedhigher and more consistent recoveries for the problematic, pH-dependent pesticides than the unbuffered method (Lehotay,Mastovská, & Yun, 2005). In the boiled potato sample, dichloflua-nid yielded an 86.0% recovery using the KFDA method; however,this may be attributable to the interfering peaks from the blanksample (Fig. 1). Traditionally, SPE cleanup involves the use ofplastic cartridges containing 250–1000 mg of sorbent material,vacuum manifolds, column preconditioning, solvent waste frac-tions, collection fractions, solvent evaporation steps, manualoperation, and multiple solvents. Proper performance of SPE re-quires knowledge of the practice and theory of the technique,and also requires training and careful attention on the part ofthe analyst. Common factors that affect reproducibility in SPE in-clude difficulties with the adjustment of the vacuum (and thusthe flow rate), channeling, and the column going dry. SPE doesnot lend itself readily to automation, and automated SPE devicesare quite expensive, require maintenance, and lack versatility fornon-routine applications. Certainly, the column-based SPEmethod has some advantages over alternative approaches, but it

remains far from ideal in practice (Anastassiades et al., 2003).The pesticide recovery rates were slightly lower when using theSPE clean-up column due to an attenuation of the matrixenhancement effect (Schenck & Howard-King, 1999) or the inter-action of the compound with the matrix (Barriada-Pereira et al.,2004). The pesticides could have been retained in the clean-upcolumn if a polar solvent was used (Sharif, Man, Hamid, & Keat,2006). Triflumizole evidenced high recoveries (more than 130%)in both potato samples in accordance with the KFDA method. Thiseffect appears to be the result of peak interference and/ or salt-ing-out effects resulting from the use of sodium chloride (Serôdio& Nogueira, 2004; Cho et al., 2008).

All RSDs were less than 20%. This suggested that the methoddeveloped herein could be considered appropriate, comparativelyeconomical, and time-efficient for the analysis of a number of pes-ticides simultaneously in foodstuff samples, relative to the KFDAmethod.

3.4. Method application

Radish, potato, and rice samples were collected from eight mar-kets in Gwangju, Republic of Korea, and each of the 8 samples werecooked according to the appropriate cooking practices. The sampleswere then analysed using the QuEChERS method. It was noted thatthe boiled potato samples evidenced a peak with a retention timesimilar to that of b-endosulfan (Fig. 2). However, when the samplewas confirmed via GC–MS, it did not match the b-endosulfan. Thismight be the result of an interfering peak generated as the conse-quence of mechanical error.

4. Conclusion

The principal objective of this study was to compare the estab-lished classical method with the QuEChERS method in cookedfoodstuff samples. The majority of the pesticides exhibited similarrecovery rates in tests of both methods; however, the classicalmethod evidenced low recoveries for dichlofluanid, tetraconazole,oxadixyl, fenbuconazole, and paclobutrazol. In particular, polishedrice samples that were analysed via the classical method almost allevidenced low recovery rates. The QuEChERS method was appliedfor the analysis of foodstuffs, and none of the compounds were de-tected in the cooked samples. These results showed that the QuE-ChERS method developed herein is simple and exhibits acceptablelevels of sensitivity and accuracy to fulfill the requirements of mul-tiple pesticide residue analysis applied to cooked foodstuffs.

J.-Y. Park et al. / Food Chemistry 128 (2011) 241–253 253

Acknowledgments

This work was supported by grants (09072 KFDA 947) from TheKorea Food and Drug Administration (KFDA).

References

Adou, K., Bontoyan, W. R., & Sweeney, P. J. (2001). Multiresidue method for theanalysis of pesticide residues in fruits and vegetables by accelerated solventextraction and capillary gas chromatography. Journal of Agricultural and FoodChemistry, 49, 4153–4160.

Anastassiades, M., Lehotay, S. J., Stajnbaher, D., & Schenck, F. J. (2003). Fast and easymultiresidue method employing acetonitrile extraction/partitioning and‘‘dispersive solid-phase extraction’’ for the determination of pesticide residuesin produce. Journal of AOAC International, 86, 412–431.

Barriada-Pereira, M., González-Castro, M. J., Muniategui-Lorenzo, S., López-Mahía,P., Prada-Rodríguez, D., & Fernández-Fernández, E. (2004). Determination of 21organochlorine pesticides in tree leaves using solid-phase extraction clean-upcartridges. Journal of Chromatography A, 1061, 133–139.

Barriada-Pereira, M., González-Castro, M. J., Muniategui-Lorenzo, S., López-Mahía, P.,Prada-Rodríguez, D., & Fernández-Fernández, E. (2007). Comparison of pressurizedliquid extraction and microwave assisted extraction for the determination oforganochlorine pesticides in vegetables. Talanta, 71, 1345–1351.

Cho, S. K., Abd El-Aty, A. M., Jeon, H. R., Choi, J. H., Shin, H. C., & Shim, J. H. (2008).Comparison of different extraction methods for the simultaneousdetermination of pesticide residues in kiwi fruit using gas chromatography-mass spectrometry. Biomedical Chromatography, 22, 727–735.

Codex Alimentarius Commission. (2010). Pesticide residues in food. Rome: FAO/WHO Food Standard. Available from: http://www.codexalimentarius.net/mrls/pestdes/jsp/pest_q-e.jsp.

DI, K. H. I. (2005). National health and nutrition survey. Seoul: Ministry of Health andWelfare.

DI, K. H. I. (2007). Dietary intake and risk assessment of contaminants in Korean foods.Seoul: KFDA.

DI, K. H. I. (2009). MRLs for pesticides in foods. Seoul: KHIDI.Fillion, J., Sauvé, F., & Selwyn, J. (2000). Multiresidue method for the determination

of residues of 251 pesticides in fruits and vegetables by gas chromatography/mass spectrometry and liquid chromatography with fluorescence detection.Journal of AOAC International, 83, 698–713.

Hajs�lova, J., Holadova, K., Kocourek, V., Poustka, J., Godula, M., Cuhra, Petr, Kempn,Milan, et al. (1998). Matrix-induced effects: A critical point in the gaschromatographic analysis of pesticide residues. Journal of Chromatography A,800, 283–295.

Herrero Martín, S., García Pinto, C., Pérez Pavón, J. L., & Moreno Cordero, B. (2010).Determination of trihalomethanes in soil matrices by simplified quick, easy,cheap, effective, rugged and safe extraction and fast gas chromatography withelectron capture detection. Journal of Chromatography A, 1217, 4883–4889.

Juan-García, A., Picó, Y., & Font, G. (2005). Capillary electrophoresis for analyzingpesticides in fruits and vegetables using solid-phase extraction and stir-barsorptive extraction. Journal of Chromatography A, 1073, 229–236.

KFDA (2009). 4.1.2 Multi class pesticide multiresidue method. In Food Code Vol. II(pp. 194-209). Seoul: KFDA. Available from: http://www.foodnara.go.kr/portal/site/kfdaportal/infotelegram/.

Klein, J., & Alder, L. (2003). Applicability of gradient liquid chromatography withtandem mass spectrometry to the simultaneous screening for about 100pesticides in crops. Journal of AOAC International, 86, 1015–1037.

Lehotay, S. J. (2007). Determination of pesticide residues in foods by acetonitrileextraction and partitioning with magnesium sulfate: Collaborative study.Journal of AOAC International, 90, 485–520.

Lehotay, S. J., Mastovska, K., Lightfield, A. R., & Gates, R. A. (2010). Multi-Analyst,Multi-Matrix Performance of the QuEChERS Approach for Pesticide Residues inFoods and Feeds Using HPLC/MS/MS Analysis with Different CalibrationTechniques. Journal of AOAC International, 93, 355–367.

Lehotay, S. J., Mastovská, K., & Yun, S. J. (2005). Evaluation of two fast and easymethods for pesticide residue analysis in fatty food matrixes. Journal of AOACInternational, 88, 630–638.

Ngowi, A. V., Mbise, T. J., Ijani, A. S., London, L., & Ajayi, O. C. (2007). Pesticides use bysmallholder farmers in vegetable production in Northern Tanzania. CropProtection, 26, 1617–1624.

NIFDS (2009). Explanation of analytical method in the food code. In Manual ofpesticide residue analytical method in the Food Code (pp. 92-104). Seoul: NIFDS.

Obana, H., Okihashi, M., Akutsu, K., Kitagawa, Y., & Hori, S. (2003). Determination ofneonicotinoid pesticide residues in vegetables and fruits with solid phaseextraction and liquid chromatography mass spectrometry. Journal ofAgricultural and Food Chemistry, 51, 2501–2505.

Rissato, S. R., Galhiane, M. S., Knoll, F. R., & Apon, B. M. (2004). Supercritical fluidextraction for pesticide multiresidue analysis in honey: Determination by gaschromatography with electron-capture and mass spectrometry detection.Journal of Chromatography A, 1048, 153–159.

Saieva, C., Aprea, C., Tumino, R., Masala, G., Salvini, S., Frasca, G., et al. (2004).Twenty-four-hour urinary excretion of ten pesticide metabolites in healthyadults in two different areas of Italy (Florence and Ragusa). Science of TotalEnvironment, 332, 71–80.

Sánchez-Brunete, C., Albero, B., & Tadeo, J. L. (2004). Multiresidue determination ofpesticides in soil by gas chromatography-mass spectrometry detection. Journalof Agricultural and Food Chemistry, 52, 1445–1451.

Schenck, F. J., & Howard-King, V. (1999). Rapid solid phase extraction cleanup forpesticide residues in fresh fruits and vegetables. Bulletin of EnvironmentalContamination and Toxicology, 63, 277–281.

Serôdio, P., & Nogueira, J. M. F. (2004). Multi-residue screening of endocrinedisrupters chemicals in water samples by stir bar sorptive extraction-liquiddesorption-capillary gas chromatography–mass spectrometry detection.Analytica Chimica Acta, 157, 21–32.

Sharif, Z., Man, Y. B., Hamid, N. S., & Keat, C. C. (2006). Determination oforganochlorine and pyrethroid pesticides in fruit and vegetables using solidphase extraction clean-up cartridges. Journal of Chromatography A, 1127,254–261.

Shim, J. H., Abd El-Aty, A. M., Choi, J. H., & Choi, Y. S. (2007). Post-harvest HPLCdetermination of chlorfluazuron residues in pears treated with differentprograms. Biomedical Chromatography, 21, 695–700.

Torres, C. M., Picó, Y., & Mañes, J. (1996). Determination of pesticide residues in fruitand vegetables. Journal of Chromatography A, 754, 301–331.

Ueno, E., Oshima, H., Saito, I., Matsumoto, H., Yoshimura, Y., & Nakazawa, H. (2004).Multiresidue analysis of pesticides in vegetables and fruits by gaschromatography/mass spectrometry after gel permeation chromatographyand graphitized carbon column cleanup. Journal of AOAC International, 87,1003–1015.

Wong, J. W., Webster, M. G., Halverson, C. A., Hengel, M. J., Ngim, K. K., & Ebeler, S. E.(2003). Multiresidue pesticide analysis in wines by solid-phase extraction andcapillary gas chromatography-mass spectrometric detection with selective ionmonitoring. Journal of Agricultural and Food Chemistry, 51, 1148–1461.