196 Chiang Mai J. Sci. 2015; 42(1)

Chiang Mai J. Sci. 2015; 42(1) : 196-207http://epg.science.cmu.ac.th/ejournal/Contributed Paper

A Simple and Sensitive GC-ECD Method for DetectingSynthetic Pyrethroid Insecticide Residues inVegetable and Fruit SamplesNisa Pakvilai [a,b], Tippawan Prapamontol*[b], Prasak Thavornyutikarn [c],Ampica Mangklabruks [d], Somporn Chantara [a,c], Surat Hongsibsong [b] andChoochad Santasup [d][a] Environmental Science Program, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailand.[b] Environment and Health Research Unit, Research Institute for Health Sciences (RIHES), Chiang Mai

University, Chiang Mai, 50200, Thailand.[c] Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailand.[d] Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai,

50200, Thailand.[e] Central Laboratory, Faculty of Agriculture, Chiang Mai University, Chiang Mai, 50200, Thailand.*Author for correspondence; e-mail: tprapamontol@rihes.org; tprapamontol@yahoo.com

Received: 17 May 2013Accepted: 30 July 2013

ABSTRACTA gas chromatographic-electron capture detection (GC-ECD) method was developed

for determinating six synthetic pyrethroids insecticides (i.e. cyhalothrin, permethrin, cyfluthrin,cypermethrin, fenvalerate, and deltamethrin) which have been widely used in fruit orchardsand vegetable growing. The synthetic pyrethroid insecticides were extracted usingdichloromethane and cleaned up by loading onto the graphitized carbon cartridge. Limit ofdetection (LOD) ranged from 1 to 5 ng g-1 and limit of quantitation (LOQ) ranged from 2.5to 10 ng g-1. The relative standard deviation (RSD) of intra-batch and inter-batch ranged from1.8 to 7.4% and 8.9 to 15.7%, respectively. Recoveries at spiked levels (5, 10 and 50 ng g-1.)ranged from 96.8-109.3%, 86.5-96.9% and 83.8-98.4%, respectively. The developed methodwas successfully applied to quantify pyrethroid residues in fruit and vegetable samples fromChiang Mai province, northern Thailand. All samples had detectable levels of at least onesynthetic pyrethoid insecticide residue. This developed method is practical for analysis of sixsynthetic pyrethroid insecticide residues, especially for screening of large quantities of samplesbecause of its short extraction time. Moreover, GC-ECD which is a typical equipment inorganic trace laboratory was successfully employed and provided practical achievement ofsensitivity.

Keywords: GC-ECD, synthetic pyrethroids, simple and sensitive method

Chiang Mai J. Sci. 2015; 42(1) 197

1. INTRODUCTIONSynthetic pyrethroids (Figure 1) are

growing in popularity as product of choiceof insecticides; their structures are similar topyrethrins, natural insecticides extracted fromthe chrysanthemum flower (Chrysanthemum

cineraria folium). Large volumes of syntheticpyrethroid insecticides have been used inagricultural applications on crops and inresidential homes or commercial facilities tocontrol insects[1-4].

Figure 1. Structures of synthetic pyrethroid insecticides analyzed in the present study.

In Thailand, imported amounts ofsynthetic pyrethroids which are mostly usedin agriculture have been increasing everyyear [5]. Farmers prefer using syntheticpyrethroid insecticides because of theirshorter pre-harvest interval of 3-5 days[6-9]. However, synthetic pyrethroidinsecticides were developed to capture theeffective insecticidal activity of botanicalinsecticides, with increased stability in light,yielding longer residence time [10, 11].

Previously published methods fordetermining synthetic pyrethroidinsecticides have used high-pressureliquid chromatography (HPLC) [12-15],gas chromatography with electron capturedetection (GC-ECD) [16-20], and GC withmass spectrometry (MS) [21-23]. GC-ECDis a sensitive detection system for measuringthis group of halogenated synthetic pyrethroid

insecticides. However, other previouslyreported methods required time consumingmultiple extraction steps and inactivationof the GC column to obtain goodchromatographic resolution and peakshapes. In the present study, we report aGC-ECD method that requires a simpleextraction step with good chromatographicresolution of peaks, rendering it rapid andcost effective.

2. MATERIALS AND METHODS2.1 Chemicals

Ethyl acetate, dichloromethane (analyticalgrade) and graphitized carbon cartridges werepurchased from J.T. Baker (USA). Anhydroussodium sulfate (Na2SO4) was supplied byMerck (Germany). The synthetic pyrethroidinsecticides standards were purchased fromDr. Ehrenstorfer, Augsburg, (Germany).

198 Chiang Mai J. Sci. 2015; 42(1)

2.2 Standard and Sample PreparationSix synthetic pyrethroid insecticides

standards (i.e., lambda cyhalothrin, permethrin,cyfluthrin, cypermethrin, fenvalerate anddeltamethrin) were used for validating themethod; bifenthrin was used as an internalstandard. The standard solutions wereprepared by volumetric measurement inethyl acetate (EA) at a concentration of1 mg mL-1 for the stock solutions. The stocksolutions were diluted with EA to 10, 20,100, 150, 200, 250 and 300 ng mL-1

for intermediate standard solutions.The intermediate standard solutions werethen EA acetate to 1, 5, 10, 20, 50 and 100 ngmL-1 for working standard solutionsand prepared every 4 weeks. All stock,intermediate and working standard solutionswere stored at -20°C.

2.3 InstrumentationA Hewlett-Packard 6890 GC (USA)

equipped with an ECD was used for analyzingsynthetic pyrethroid insecticides. The GCconditions were as follows: injectiontemperature 250°C; detector temperature300°C; carrier gas flow (helium) 1.5 mLmin-1; make-up gas flow (oxygen free nitrogen,OFN) 14.7 mL min-1. Oven temperaturewas programmed as follows: 100°C for1 min, ramped 15°C min-1 to 250°C,ramped 5°C min-1 to 280°C and held for3 min. Injection mode was splitless for1 min and injection volume was 1 L.Synthetic pyrethroid insecticides wereseparated using an HP-5 capillary column(5% phenylmethylpolysiloxane phase with30m × 0.25mm, 0.25mm film thickness).

2.4 Sample PreparationOne kilogram of fresh fruit and

vegetable samples were randomly selectedfrom the markets. To provide samplesrepresentative of typical Chiang Mai diets,fruits and vegetables which were commonlyconsumed and sold in the market everyseason were chosen. Each sample, withoutwashing, was chopped and blended intosmall pieces. Twenty-gram aliquots of eachsample were stored at -20°C prior toanalysis. Pooled samples were preparedfor method validation by using a mixtureof all fruit and vegetable samples. Limits ofdetection (LOD), limits of quantitation(LOQ), recovery, precision, selectivity, andlinearity were studied by using syntheticpyrethroid insecticides spiked pooled samples.The spiked samples were used for qualitycontrol as intra- and inter- batches analyses.

2.5 Sample ExtractionThe sample extraction is shown in

Figure 2. Five grams of homogenized samplewas placed onto a 50-mL PTFE centrifugetube. Four ng g-1 sample of bifenthrin (as aninternal standard) and 5g Na2SO4 were added.The sample was extracted with 10 mLof dichloromethane (DCM) by shakingvigorously for 1 min, following by a 5 minsonication. The extraction was repeatedand the extracts were combined in a 50 mLcentrifuge tube. The combined extract (~15-18 mL) was filtered through a WhatmanNo.1 paper with 5 gNa2SO4 on the paper.The filtered extracts were cleaned up byloading onto a 250 mg graphitized carboncartridge with 8-10 mm Hg pressure (VacElut,Varian, USA). The analytes were elutedwith DCM and the clean filtrate was driedby rotary evaporation on 37°C water bath.The dried residue was redissolved with1 mL in EA and analyzed using GC-ECD.

Chiang Mai J. Sci. 2015; 42(1) 199

Figure 2. Flow diagram of sample preparation for synthetic pyrethroid insecticide residueanalysis using GC-ECD.

2.6 Application of the Method forDetecting Synthetic PyrethroidInsecticides Residues in Vegetable andFruit Samples

Samples were collected in Chiang Maicity, Thailand from February-March 2009.Synthetic pyrethroid insecticide residueswere analyzed in 10 fresh vegetablecommodities (i.e., cabbage, kale, morningglory, cauliflower, broccoli, chinese cabbage,yard long bean, baby corn, cucumber andsweet pea) and 5 fruit commodities (i.e.,strawberry, tangerine, guava, apple and

grape). Vegetables and fruits which werecommonly consumed and sold in themarkets every season were selectedto represent a typical Chiang Mai diet(Table 1). All samples were purchased fromconventional fresh markets and supermarketsin Chiang Mai city and transferred toToxicology Laboratory, Research Institute forHealth Sciences, Chiang Mai Universityaccording to CODEX standard samplingprocedure [24, 25]. Then, the samples wereextracted and analyzed using the developedmethod.

200 Chiang Mai J. Sci. 2015; 42(1)

Table 1. Common and scientific names of vegetable and fruit samples collected fromChiang Mai city markets between February-March, 2009.

Common name Vegetables1 Cabbage2 Chinese cabbage3 Kale4 Yardlong bean5 Water Convolvulus6 Baby corn7 Cauliflower8 Cucumber9 Broccoli10 Sweet peaFruits1 Strawberry2 Tangerine3 Guava4 Apple5 Grape

Scientific name

Brassica oleracea L. cv. Group CabbageBrassica rapa L. cv. Group Chinese cabbageBrassica alboglabra BaileyVigna unguiculata var. sesquipedalisIpomoea aquatica ForskZea mays L.Brassica oleracea L. var botrytis L.Cucumis sativusBrassica oleracea var.italicaPisum sativum L.

Fragaria ananassaCitrus reticulata BlancoPsidium guajava L.Malus domestica BorkhVitis vinifera L.

3. RESULTS AND DISCUSSIONS3.1 Method Efficiency

The method was optimized to obtaingood recoveries for synthetic pyrethroidinsecticides. The calibration curve for sixsynthetic pyrethroids was constructed at 1,5, 10, 20, 50 and 100 ng mL-1. The multiplepeaks were observed for several synthetic

pyrethroids because the existence ofisomers as shown in Figure 3. Six syntheticpyrethroids, can be separated and detectedunder the conditions described above.

To quantify pyrethroids with multipleisomer, the GC-ECD peak areas of allwere summed [25-27].

Figure 3. A GC-ECD chromatogram of pure standard mixture of 6 synthetic pyrethroids.Peaks are indentified as follows: IS = bifenthrin 20ng mL-1; 1,2,3 = lambda cyhalothrin 10 ngmL-1; 4,8,9,10,11 = cyfluthrin 20ng mL-1; 6,7 = permethrin 5 ng mL-1; 5,12,13,14,15 =cypermethrin 5 ng mL-1; 17,18 = fenvalerate 20ng mL-1 and 16,19,20 = deltamethrin20 ng mL-1.

Chiang Mai J. Sci. 2015; 42(1) 201

A typical chromatogram of unspikedsample is shown in Figure 4 (a). A typicalchromatogram of cabbage spiked with a

mixture of synthetic pyrethroids (10 ng g-1)is shown in Figure 4 (b).

Figure 4. Typical GC-ECD chromatograms of six synthetic pyrethroids: (a) Unspiked sample(b) Extract from 50 ng mL-1 spiked cabbage sample.

3.1.1 LinearityThe linearity was evaluated in

concentration between 80-120% of theexpected concentration range. The calibrationcurves were prepared by spiking syntheticpyrethroid insecticide standard into pooledsamples at final concentrations of 1, 5, 10,20, 50 and 100 ng g-1 samples. Blank orunspiked sample was added bifenthrin as aninternal standard at final concentration 4 ngg-1 sample.

Linearity regression equations andregression coefficients (R2) of extractedsynthetic pyrethroids’ standard mixtureare presented in Table 2. The calibrationcurves (plotted as the spiked concentrationvs area pyrethroid/area internal standard)were linear with correlation coefficients(R2) between 0.9835 and 0.9972. The linearrange was different for each compoundsbut was typically 5-500 ng mL-1

Table 2. Linearity regression equations, regression coefficients (R2), LOD, and LOQ of syntheticpyrethroid insecticides using the present developed method.

Synthetic pyrethroid Equation (R2) LOD LOQ insecticides (y=mx+b) (ng g-1) (ng g-1)Lambda cyhalothrin y = 103.3 x + 0.49 0.9961 3.0 5.0Permethrin y = 54.0 x - 0.11 0.9835 1.0 2.5Cyfluthrin y = 97.86 x + 0.59 0.9972 5.0 10Cypermethrin y = 128.33 x + 1.68 0.9872 1.0 2.5Fenvalerate y = 52.1 x + 0.55 0.9899 5.0 10Deltamethrin y = 61.7 x + 0.22 0.9941 5.0 10

202 Chiang Mai J. Sci. 2015; 42(1)

3.1.2 SensitivityThe LOD and LOQ were performed

using the method described by Hornungand Reed [28]. LODs ranged from 1.0 to5.0 ng g-1 and the LOQs ranged from 2.5 to10 ng g-1. In all cases, the obtained LOQswere much lower than maximum residuelimits (MRLs) established by Thailandlegislation for synthetic pyrethroid insecticides.The present study showed comparable orgreater sensitivity method than those fromprevious reported methods using highresolution and expensive equipment,gas chromatography and ion trap massspectrometry, at 1.0-50 ng g-1 [29-32].

3.1.3 Precision and accuracyThe precision was reported by relative

standard deviation (RSD) of intra- andinter-batch of pooled vegetable and fruitsamples spiked with six synthetic pyrethroidsat the concentration 100 ng g-1. Ten tubes ofpooled vegetable and fruit samples wereanalyzed for intra- batch variation. The resultsare shown in Table 3. The RSD of intra- batchvariation obtained was 3.8, 5.5, 1.8, 2.1, 4.3,and 7.4% for lambda- cyhalothrin, permethrin,cyfluthrin, cypermethrin, and fenvalerate,deltamethrin, respectively. Pooled sampleswere processed similarly with every batch ofsample analysis for quality control. The RSDof inter- bath variation obtained was 9.6, 15.7,

11.3, 15.3, 10.3, and 8.9% for lambda-cyhalothrin, permethrin, cyfluthrin,cypermethrin, and fenvalerate, deltamethrin,respectively. Both intra- and inter-batchvariations were acceptable for detectioncriteria at less than 21% [33]. Therefore, thepresent developed method exhibited a goodprecision.

The present study reported accuracy ofthe method by using spiked standard ontothe pooled samples and calculating therecovery values for each synthetic pyrethroidinsecticides. Three level of spiked pool samplewere prepared by mixing vegetable and fruitwith 6 synthetic pyrethroid insecticides atconcentration 5, 10 and 50 ng g-1. The spikedpool samples were extracted with the samemethod with samples extraction. All analyticalsteps were done in triplicate [34]. Percentagerecoveries of the six pyrethroids fromspiked-pool matrices at three concentrationsare presented in Table 4. Recoveries rangedbetween 96.8- 109.3%, 86.5- 96.9% and83.8- 98.4% at low, medium and high spikedlevels, respectively. The relevant recoveryresults of the present study showed that thevalues of recoveries were in range ofacceptable criteria recommended by CODEXranging from 70-110% [35]. Therefore, thepresent developed method was accuratefor quantification of synthetic pyrethroidinsecticides in vegetable and fruit samples.

Table 3. Intra-batch and inter-batch analytical average recovery of six synthetic pyrethroids ina pooled sample (spiked concentrations at 100 ng g-1).

Synthetic pyrethroidinsecticides

Lambda-cyhalothrinBifenthrin (IS)PermethrinCyfluthrinCypermethrinFenvalerateDeltamethrin

Intra- batch (n=10) Inter- batch (n=10)%Recovery±SD

97.9±3.7102.1±1.992.7±5.198.9±1.887.9±1.798.7±4.392.8±6.9

%RSD3.81.95.51.82.14.37.4

%Recovery±SD102.6±9.9107.2±6.281.0±12.891.8±10.394.5±14.4113.9±11.689.7±8.0

%RSD9.65.815.711.315.310.38.9

Chiang Mai J. Sci. 2015; 42(1) 203

Table 4. Recoveries and standard deviation (SD) of individual synthetic pyrethroids at low,medium and high spiked levels in triplicate tests.

Syntheticpyrethroidinsecticides

Lambda-CyhalothrinPermethrinCyfluthrinCypermethrinFenvalerateDeltamethrin

Low spiked levels Medium spiked levels High spiked levels

Concentration(ng g-1)

10

52052020

Recoveries(mean±SD) 98.4±12.4

106.9±2.7109.3±9.7 96.8±6.9102.7±3.9105.2±2.1

Concentration(ng g-1)

20

1050105050

Recoveries(mean±SD) 92.2±5.7

93.1±4.796.9±5.5

86.5±10.094.1±6.496.5±9.4

Recoveries(mean±SD) 89.0±15

84.8±16.5 98.4±3.3 89.5±9.4 89.6±1.8 83.8±3.0

Concentration(ng g-1)

50

2010020100100

3.2 Synthetic Pyrethroid InsecticidesResidues in Vegetable and Fruit Samplesfrom Chiang Mai, Thailand

Vegetable and fruit samples werecollected from the markets and preparedfor analyzing synthetic pyrethroid residues.The present developed GC-ECD methodwas used for analyzing synthetic pyrethroid

insecticides’ residues, chromatogram ofresidues in vegetable and fruit sampleswere shown in Figure 5. The result showedall samples were contained at least onesynthetic pyrethroid insecticides. The meanconcentration of synthetic pyrethroidresidues detected in vegetable and fruitsamples were reported in Tables 5 and 6.

Figure 5. GC-ECD chromatograms of six synthetic pyrethroids: (a) Extract of a real vegetablesample (b) Extract of a real fruit sample.

Permethrin was detected in all vegetableand fruit samples but at rather lowconcentration. Cypermethrin was detected atthe relatively high concentration in all kindsof samples especially in Chinese cabbage,tangerine, and grape while fenvaleratewas detected at the high concentration in

cauliflower and cucumber samples.In Thailand, the Maximum Residue

Limits (MRLs) in vegetables have been set forfour synthetic pyrethroids including lambdacyhalothrin, cypermethrin, fenvalerate anddeltamethrin. Among fresh fruits, there is onlyMRLs of cypermethrin in tangerine which is

204 Chiang Mai J. Sci. 2015; 42(1)

2,000 ng g-1 which made no samples exceededin the present study. Mean concentration ofcypermethrin residue in vegetable sampleshad exceeded Thailand MRL which set at 50ng g-1. Cypermethrin was detected in all sweetpea samples with the mean concentration of

97.6� 63.5 ng g-1and exceeded Thailand MRLwhich was set at 20 ng g-1. The patterns ofresidues in the present study were comparablewith other report in Japan, China and Ghana[25, 30 and 37] except the cypermethrin wasdetected only in the present study.

Table 6. Concentration of synthetic pyrethroid insecticides in differences kind of fruitfrom Chiang Mai city, Thailand (February, 2009).

Common name of Fruit

Strawberry

Tangerine

Guava

Apple

Grape

Total(n)47

7

10

10

10

10

Mean±SD concentration, ng g-1 (% detection)

Lamda-CyhalothrinND(0)

41.8±34.7(50)ND(0)

5.57±3.6(20)ND(0)

Permethrin8.09±6.1

(100)35.1±17.3

(100)7.75±10.1

(100)7.85±5.1

(100)7.88±6.5

(100)

Cyfluthrin12.5±7.0

(100)21.2±4.4

(100)6.43±2.9

(40)35.0±14.4

(20)7.66±3.8

(20)

Cypermethrin19.8±47.6

(100)320.2±264.2

(100)37.6±20.2

(100)28.2±37.9

(80)1,647±2,574

(90)

Fenvalerate11.6±9.1

(29)12.8±7.3

(40)ND(0)

19.8(100)ND(0)

Deltamethrin10.9±9.6

(100)23.3±10.1

(100)7.80±4.0

(20)12.9±8.7

(30)7.82±4.0

(20)

ND = Not detected

Table 5. Concentration of synthetic pyrethroid insecticides in differences kind of vegetablesfrom Chiang Mai city, Thailand (February, 2009).

ND = Not detected

Common nameof

Vegetables

Cabbage

Chinese cabbage

Kale

Yardlong bean

WaterConvolvulus

Baby corn

Cauliflower

Cucumber

Broccoli

Sweet pea

Total(n) 99

10

10

10

10

10

10

10

10

10

9

Mean±SD concentration, ng g-1 (% detection)Lamda-

Cyhalothrin

6.36±3.3(50)3.00(10)

4.36±2.1(40)8.41(10)ND(0)

13.4±14.7(20)

40.5±59.9(30)ND(0)

7.79±7.0(20)3.00(11)

Permethrin

11.7±8.9(100)

21.4±13.8(100)

12.1±6.9(100)

11.9±9.0(100)

11.8±6.1(100)

11.0±11.2(100)

11.9±4.0(100)

12.8±3.7(100)

10.8±3.1(100)

9.28±5.9(100)

Cyfluthrin

24.7±8.8(100)

16.2±10.3(100)

33.2±16.2(100))

13.6±9.2(100)

9.45±6.8(90)

17.3±8.6(100)

17.8±5.2(70)

16.3±4.1(70)

17.9±9.9(20)

6.65±3.7(56)

Cypermethrin

21.5±16.2(100)

777±1,056(100)

80.6±60.7(100)

23.6±24.6(90)

38.0±34.0(90)

57.1±68.5(90)

96.4±166.2(100)

14. 8±15.9(50)

23.4±13.1(60)

97. 6±63.5(100)

Fenvalerate

12.7±9.3(70)

13.0±9.4(100)

18.4±6.6(70)

11.0±13.2(70)11.0(10)73.7(10)

302±592(40)

50. 4±64.2(10)ND(0)

16.4(11)

Deltamethrin

22.8±11.5(90)

25.1±26.8(90)

30.2±10.9(100)

27.9±11.0(100)

23.3±15.7(80)

16.9±9.6(80)

20.7±7.5(100)

13.0±3.4(100)

11.7±8.8(40)

12.9±7.3(67)

Chiang Mai J. Sci. 2015; 42(1) 205

4. CONCLUSIONSA GC-ECD method has been developed

for detecting 6 synthetic pyrethroid insecticidesin vegetable and fruit samples. The sampleswere extracted in 1 step using DCM andwere further cleaned using graphitizedcarbon black cartridge. The developedmethod showed good recovery (83-106%),precision, and accuracy. Furthermore, thepresent developed method has goodpracticality for the analysis of 6 syntheticpyrethroid insecticides residue in screeningof massive samples and possible to extendthe application for the analysis of syntheticpyrethroid insecticides in a wider rangeof vegetable and fruit crops. Moreover,GC-ECD is a typical equipment in organictrace laboratory was successfully employed,and provided practical achievement ofsensitivity.

ACKNOWLEDGEMENTSThe present study was supported by

the Thailand Research Fund (TRF, ContractDBG5080018) and the Commissions forHigher Education (CHE) through theNational Research University ProgramChiang Mai University, Ministry of Education,Thailand. N.P. thanks the Research Institutefor Health Sciences, Chiang Mai Universityfor laboratory and field work support.

REFERENCES

[1] Cai J., Liu B., Zhu X. and Su Q.,Determination of pyrethroid residues intobacco and cigarette smoke by capillarygas chromatography, J. Chromatogr A.,2002; 964: 205-211. DOI 10.1016/S0021-9673(02)00586-1.

[2] Colume A., Cardenas S., Gallego M.and Valcarcel M., Selective enrichmentof 17 pyrethroids from lyophilisedagricultural samples, J. Chromatogr A.,2001; 912: 83-90. DOI 10.1016/S0021-

9673(01)00546-5.[3] Fischer A.B. and Eikmann T., Improper

use of an insecticide at a kindergarten,Toxicol. Lett., 1996; 88: 359-364. DOI10. 1016/0378-4274(96)82679-8.

[4] Riederer A.M., Hunter R.E.Jr., HaydenS.W. and Ryan P.B., Pyrethroid andorganophosphorus pesticides incomposite diet samples from Atlanta,USA adults, Environ. Sci. Technol., 2009;44: 483-490. DOI 10.1021/es902479h.

[5] Department of Agriculture (DOA).Plant Varieties Protection Division;Available at: http://www.doa.go.th/ard/pdf. Accessed 2 January 2013.

[6] Bouri M., Salghi R., Bazzi L., ZarroukA., Rios A. and Zougagh M., Pesticideresidue levels in green beans cultivatedin Souss Masa valley (Morocco) aftermultiple applications of bifenthrin andlambda-cyhalothrin, Bull. Environ. Contam.Toxicol., 2012; 89: 638-643. DOI 10.1007/s00128-012-0722-8.

[7] Liu W., Qin S. and Gan J., Chiral stabilityof synthetic pyrethroid insecticides,J. Agric. Food Chem., 2005; 53: 3814-3820.DOI 10.1021/jf048425i.

[8] Qin S., Budd R., Bondarenko S., Liu W.and Gan J., Enantioselective degradationand chiral stability of pyrethroids insoil and sediment, J. Agric. Food Chem.,2006; 54: 5040-5045. DOI 10.1021/jf060329p.

[9] Zhang Z.Y., Zhang C.Z., Liu X.J. andHong X.Y., Dynamics of pesticideresidues in the autumn Chinesecabbage (Brassica chinensis L.) grownin open fields, Pest Manag. Sci., 2006;62: 350-35. DOI 10.1002/ps.1174.

[10] Jenkins D.W., Hensens A., Lloyd J.,Payne M., Cizmarik P. and Hamel S.,Development and validation of a‘universal’ HPLC method for pyrethroidquantification in long-lasting insecticidalmosquito nets for malaria control and

206 Chiang Mai J. Sci. 2015; 42(1)

prevention, Trop. Med. Int. Health, 2012;18: 2-11. DOI 10.1111/tmi.12011.

[11] Miyamoto J., Kaneko H., Tsuji R. andOkuno Y., Pyrethroids, nerve poisons:How their risks to human health shouldbe assessed, Toxicol. Lett., 1995; 82-83:933-940. DOI 10.1016/0378-4274(95)03604-0.

[12] Arayne M.S., Sultana N. and Hussain F.,Validated RP-HPLC method fordetermination of permethrin in bulk andtopical preparations using UV-visdetector, J. Chromatogr. Sci., 2011; 49:287-291. DOI 10.1093/chrsci/49.4.287.

[13] Boonchiangma S., Ngeontae W. andSrijaranai S., Determination of sixpyrethroid insecticides in fruit juicesamples using dispersive liquid-liquidmicroextraction combined with highperformance liquid chromatography,Talanta, 2012; 88: 209-215. DOI 10.1016/j.talanta.2011.10.033.

[14] Das M., Roy L., Picado A., Kroeger A.,Rijal S. and Boelaert M., Deltamethrinand permethrin residue on long-lastinginsecticidal nets after 18 months ofuse in a visceral leishmaniasis-endemicarea in Nepal, Trans R. Soc. Trop. Med.Hyg., 2012; 106: 230-234. DOI10.1016/j. trstmh.2012.01.007.

[15] Dong H., Bi P. and Xi Y., Determinationof pyrethroid pesticide residues invegetables by solvent sublationfollowed by high-performance liquidchromatography, J. Chromatogr. Sci., 2008;46: 622-626. DOI 10.1093/chromsci/46.7.622.

[16] Barbini D.A., Vanni F., Girolimetti S. andDommarco R., Development of ananalytical method for the determinationof the residues of four pyrethroids inmeat by GC-ECD and confirmation byGC-MS, Anal. Bioanal. Chem., 2007;389: 1791-1798. DOI 10.1007/s00216-007-1440-7.

[17] Chauhan R., Monga S. and KumariB., Effect of processing on reductionof lambda-cyhalothrin residues intomato fruits, Bull. Environ. Contam.Toxicol., 2011; 88: 352-357. DOI10.1007/s00128-011-0483-9.

[18] Huang Y., Zhou Q. and Xiao J.,Establishment of trace determinationmethod of pyrethroid pesticides withTiO2 nanotube array micro-solidphase equilibrium extraction combinedwith GC-ECD, Analyst, 2011; 136:2741-2746. DOI 10.1039/C0AN01029D.

[19] Hunter R.E.Jr., Riederer A.M. andRyan P.B., Method for the determinationof organophosphorus and pyrethroidpesticides in food via gas chromatographywith electron-capture detection, J. Agric.Food Chem., 2010; 58: 1396-1402. DOI10.1021/jf9028859.

[20] Liu D. and Min S., Rapid analysis oforganochlorine and pyrethroid pesticidesin tea samples by directly suspendeddroplet microextraction using agas chromatography-electron capturedetector, J. Chromatogr. A, 2012; 1235:166-173. DOI 10.1016/j.chroma.2012.02.070.

[21] Fialkov A.B., Moragn M. and Amirav A.,A low thermal mass fast gaschromatograph and its implementationin fast gas chromatography massspectrometry with supersonic molecularbeams, J. Chromatogr. A, 2011; 1218:9375-9383. DOI 10.1016/j.chroma.2011.10.053.

[22] Koch D.A., Clark K. and Tessier D.M.,Quantification of pyrethroids inenvironmental samples using NCI-GC-MS with stable isotope analoguestandards, J. Agric. Food Chem., 2013; 60:2330-1339. DOI 10.1021/jf3048912.

[23] Mao X., Wan Y., Yan A., Shen M. andWei Y., Simultaneous determination of

Chiang Mai J. Sci. 2015; 42(1) 207

organophosphorus, organochlorine,pyrethriod and carbamate pesticides inRadix astragali by microwave-assistedextraction/dispersive-solid phaseextraction coupled with GC-MS,Talanta, 2012; 97: 131-141. DOI 10.1016/j.talanta.2012.04.007.

[24] Food and Agriculture Organization/World Health Organization (FAO/WHO). 2003. Guidelines on GoodLaboratory Practice in Residue Analysis.CAC/GL 40-1993.

[25] Nakamura Y., Tonogai Y., Tsumura Y.and Ito Y., Determination of pyrethroidresidues in vegetables, fruits, grains, beans,and green tea leaves: Applications topyrethroid residue monitoring studies,J. AOAC Int., 1993; 76: 1348-1361.

[26] Lopez-Lopez T., Gil-Garcia M.D.,Martinez-Vidal J.L. and Martinez-GaleraM., Determination of pyrethroids invegetables by HPLC using continuouson-line post-elution photo irradiationwith fluorescence detection, Anal. Chim.Acta, 2001; 447: 101-111. DOI 10.1016/S0003-2670(01)01305-8.

[27] California Department of Foodand Agriculture. Determination ofPyrethroids in Sediment Water UsingTriple Quadrupole GC/MS/MS. 2011;Available at: http://www.cdpr.ca.gov/docs/emon/pubs/anl_methds/emon-sm-05-022.pdf. Accessed 2 January 2013.

[28] Hornung R.W. and Reed L.D.,Estimation of average concentration inthe presence of nondetectable value,Appl. Occup. Environ. Hyg. 1990; 5(1):46-51. DOI 10.1080/1047322X.1990.10389587

[29] Banerjee K., Savant R.H., Dasgupta S.,Patil S.H., Oulkar D.P. and Adsule P.G.,Multiresidue analysis of syntheticpyrethroid pesticides in grapes by gaschromatography with programmedtemperature vaporizing-large volume

injection coupled with ion trap massspectrometry, J. AOAC Int., 2010; 93:368-379.

[30] Kuang H., Miao H., Hou X., ZhaoY., Wu Y. and Xu C., Simultaneousdetermination of 16 pyrethroid residuesin tea samples using gas chromatographyand ion trap mass spectrometry,J. Chromatogr. Sci., 2010; 48: 771-776.DOI 10.1093/chromsci/48.9.771.

[31] Sahoo S.K., Chahil G.S., Mandal K.,Battu R.S. and Singh B., Estimation ofbeta-cyfluthrin and imidacloprid inokra fruits and soil by chromatographytechniques, J. Environ. Sci. Health B,2011; 47: 42-50. DOI 10.1080/03601234.2012.607765.

[32] You J., Wang D. and Lydy M.J.,Determination of pyrethroid insecticidesin sediment by gas chromatography-iontrap tandem mass spectrometry, Talanta,2010; 81: 136-141. DOI 10.1016/j.talanta.2009.11.050.

[33] Center for Drug Evaluation and Research(CDER) Reviewer Guidance- Validationof Chromatographic Methods (Nov1994); Available at: www.FDA.GOV/CDER. Accessed 2 January 2013.

[34] Zan K.L. and Chantara S., Optimizationmethod for determination of carbofuranand carboxin residues in cabbages bySPE and HPLC-UV, Chiang Mai J.Sci., 2007; 34(2): 227-234.

[35] Codex Alimentarius., Food StandardsProgramme. 2000. Pesticide Residues inFood. Method of analysis andsampling, Volume 2A Part I, WorldHealth Organization.

[36] Crentsil, K.B., Archibold, B.-K., Dzifa,D., Jacob, A. and Anita, O.T. Monitoringof pesticide residues in fruits andvegetables and related health riskassessment in Kumasi metropolis, Ghana,Res. J. Environ. Earth Sci., 2011; 3(6): 761-771.