Food Chemistry 159 (2014) 367–373

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Food Chemistry

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Analytical Methods

Determination of ten pyrethroids in various fruit juices:Comparison of dispersive liquid–liquid microextractionsample preparation and QuEChERS method combinedwith dispersive liquid–liquid microextraction

http://dx.doi.org/10.1016/j.foodchem.2014.03.0280308-8146/� 2014 Published by Elsevier Ltd.

⇑ Corresponding author at: Citrus Research Institute, Southwest University,Chongqing 400712, China. Tel./fax: +86 23 68349046.

E-mail address: bljiao@tom.com (B. Jiao).

Yaohai Zhang a, Xuelian Zhang a,b, Bining Jiao a,b,⇑a Citrus Research Institute, Southwest University, Chongqing 400712, Chinab College of Food Science, Southwest University, Chongqing 400716, China

a r t i c l e i n f o

Article history:Received 2 October 2012Received in revised form 6 November 2013Accepted 7 March 2014Available online 17 March 2014

Keywords:PyrethroidsDispersive liquid–liquid microextraction(DLLME)QuEChERSGas chromatography–electron capturedetection (GC–ECD)Fruit juicesGas chromatography–mass spectrometry(GC–MS)

a b s t r a c t

Dispersive liquid–liquid microextraction (DLLME) sample preparation and the quick, easy, cheap, effec-tive, rugged and safe (QuEChERS) method combined with DLLME were developed and compared forthe analysis of ten pyrethroids in various fruit juices using gas chromatography-electron capture detec-tion (GC–ECD). QuEChERS–DLLME method has found its widespread applications to all the fruit juicesincluding those samples with more complex matrices (orange, lemon, kiwi and mango) while DLLMEwas confined to the fruit juices with simpler matrices (apple, pear, grape and peach). The two methodsprovided acceptable recoveries and repeatability. In addition, the applicabilities of two methods weredemonstrated with the real samples and further confirmed by gas chromatography–mass spectrometry(GC–MS).

� 2014 Published by Elsevier Ltd.

1. Introduction

Pyrethroids, a new-type of insecticide, have gained extensiveapplications to prevent and treat insects in modern agriculturedue to their broad-spectrum insecticidal capacity and high effec-tiveness (Ye, Xie, Wu, & Lin, 2006). However, pyrethroid residuesare considered to be one of the most important sources of pollutionin agricultural production, and may be a potential threat to publichealth (Kolaczinski & Curtis, 2004). Therefore, it is necessary to de-velop sensitive and selective methods for the analysis of pyrethroidresidues usually present in trace amounts. Potential analyticalmethods include high performance liquid chromatography (HPLC)(Boonchiangma, Ngeontae, & Srijaranai, 2012), capillary electro-phoresis (CE) (Ye et al., 2006), gas chromatography (GC) (Du,Yan, She, Liu, & Yang, 2010; Matsadiq et al., 2011), gas chromatog-raphy–mass spectrometry (GC–MS) (Cunha, Fernandes, & Oliveira,

2009; Kok, Hiemstra, & Bodegraven, 2005), and gas chromatogra-phy–tandem mass spectrometry (GC–MS/MS) (Payá et al., 2007).

Quick and effective sample preparation coupled with a reliableanalytical method is imperative. Liquid–liquid extraction (LLE) (Re-zaee et al., 2006) and solid-phase extraction (SPE) (Sharif, Man, Ha-mid, & Keat, 2006) are the most common sample preparationmethods widely used for residue analysis. Recently, a growingnumber of studies have focused on two kinds of micro-extractionstermed as liquid-phase microextraction (LPME) and solid-phasemicroextraction (SPME), based on miniaturisation of conventionalLLE and SPE, respectively (Paillakis & Kalogerakis, 2003; Zambonin,Cilenti, & Palmisano, 2002). In 2006, Rezaee et al. developed a no-vel liquid–liquid microextraction method, dispersive liquid–liquidmicroextraction (DLLME) (Rezaee et al., 2006). The new methodhas been widely recognised due to its simplicity, low cost and highenrichment, which made it available to most analytical laborato-ries. Unfortunately, the lack of purification for samples with morecomplex matrices, such as fruit and vegetable, has caused thismethod to be limited to those with simpler matrices, specificallywater and a few fruit juices.

368 Y. Zhang et al. / Food Chemistry 159 (2014) 367–373

At present, ‘‘quick, easy, cheap, effective, rugged and safe’’ (QuE-ChERS) sample preparation, is the most common technique formulti-residue pesticides analysis in food, especially fruit and vege-table (Anastassiades, Lehotay, Stajnbaher, & Schenck, 2003). How-ever, the major disadvantage of this technique is the poorenrichment factor, which can lead to higher detection limits, i.e.lower sensitivity, compared with other techniques. Researchersproposed a new method comprised of DLLME pre-concentrationafter QuEChERS extraction (Cunha & Fernandes, 2011; Zhao, Zhao,Han, Jiang, & Zhou, 2007). Coupling these techniques takes advan-tages of the benefits of both methods whilst reducing some of theirdrawback. Moreover, QuEChERS–DLLME sample preparation wid-ens the use of DLLME to those samples with more complex matri-ces. To the best of our knowledge, there are a few reports on theextraction and enrichment of pyrethroid residues in fruit juicesusing QuEChERS–DLLME method, although several studies on theanalysis of pyrethroids in fruit juices using only DLLME have beenreported (Boonchiangma et al., 2012; Cunha et al., 2009; Du et al.,2010; Matsadiq et al., 2011).

In the paper, two sample preparation including DLLME andQuEChERS–DLLME followed by gas chromatography-electron cap-ture detection (GC–ECD) were developed and compared for theanalysis of ten pyrethroids (tetramethrin, bifenthrin, lambda-cyhalothrin, permethrin, cyfluthrin, cypermethrin, flucythrinate,fenvalerate, tau-fluvalinate and deltamethrin) in various fruitjuices. Compared with the existing reports on the analysis of pyre-throid residues in fruit juices, more pyrethroids and fruit juices-types were analysed in this study.

2. Material and methods

2.1. Chemicals and standards

Permethrin was purchased from Sigma–Aldrich Chemie GmbH(Steinheim, Germany). The other nine pyrethroids were obtainedfrom Dr. Ehrenstorfer GmbH (Augsdburg, Germany).

HPLC-grade methanol and acetonitrile were from CNW Tech-nologies GmbH (D}usseldorf, Germany). Acetone, chloroform(CHCl3) and carbon tetrachloride (CCl4) were analytical reagentsfrom Kelong Chemcial Reagent Co. Ltd. (Chengdou, China). Chloro-benzene (C6H5Cl), tetrachloroethylene (C2Cl4), anhydrous MgSO4

and NaCl were analytical reagents from Sinopharm Chemcial Re-agent Co. Ltd. (Shanghai, China). Primary secondary amine (PSA)sorbent (40–63 lm, 6 nm) was obtained from CNW TechnologiesGmbH (D}usseldorf, Germany).

The stock solution of ten pyrethroids was prepared at100 mg L�1 in acetone and stored in glass volumetric flask at�50 �C. Standard working solutions at a series of concentrationswere prepared by the dilution of aliquots of the stock solution intoCHCl3, CCl4, C6H5Cl and C2Cl4, respectively.

2.2. Apparatus

An Agilent 7890A gas chromatograph (Palo Alto, USA) was usedto perform all GC analysis. Ten pyrethroid residues were separatedin a capillary column (DB-1, 30 m � 0.25 mm id � 0.25 lm film).An Agilent 5795C/7890A GC/MS (Palo Alto, USA) was used to per-form the confirmation. A HP-5MS (30 m � 0.25 mm id � 0.25 lmfilm) capillary column was used.

2.3. GC–ECD analysis

All injections were splitless and the volume was 1 lL. The flowrate of the carrier gas (N2, P99.999%) was 1 mL min�1. Thetemperatures of the injector and the l-ECD detector were 200 �C

and 320 �C, respectively. The column temperature programwas from 150 �C (2 min) to 270 �C at 6 �C min�1, then 270 �C for10 min.

2.4. Validation study

A test mixture with standard pyrethroids at a series of concen-trations was prepared and analysed under optimised conditions todetermine linearity. Instrument precision and repeatability (intra-and inter-day variation) were determined using three replicates ofthe standard working solution (0.1 mg L�1). The precision was ex-pressed as relative standard deviation (RSD, %).

2.5. GC–MS confirmation

Helium (P99.999%) was used as the carrier gas at a constantpressure of 117.22 kPa. The injector temperature was 250 �C. Allinjections were pulse splitless and the volume was 1 lL. The col-umn temperature program was from 70 �C to 150 �C at25 �C min�1, from 150 �C to 200 �C at 3 �C min�1, from 200 �C to280 �C at 8 �C min�1, then 280 �C for 10 min. The temperatures ofthe ion source and the MS transfer line were 230 �C and 280 �C,respectively. Data were acquired in the electron impact (EI) modeat a voltage of 70 eV using the selected ion monitoring (SIM) mode.

2.6. Calculations

Enrichment factor (EF), defined as the ratio of the analyte con-centration after DLLME (Csed) to the initial analyte concentration(C0), was calculated as:

EF ¼ Csed

C0ð1Þ

Extraction recovery (ER), used to estimate the preconcentrationefficiency under the optimum conditions, was calculated as:

ER ¼ Csed � Vsed

C0 � Vaq� 100 ð2Þ

where Vsed and Vaq are the volumes of the sedimented phase and thesample, respectively.

2.7. Samples

Eight types of fruit juices were purchased from local supermar-kets. Samples were filtered using Buchner funnel before extractionto remove the sediments. All fruit pulps (2 kg each), excluding lem-on, were prepared from peeled fruit. The whole fruit was used toprepare lemon pulp. A representative portion of these samples(200 g each) was chopped and homogenised in a food chopper.

2.8. DLLME procedure

A filtered sample of 5 g was placed in a sharp-bottom centrifugetube. The mixture of 1 mL of acetone and 60 lL of CCl4 was addedquickly into the tube and the mixture emulsified, forming cloudysolution. The mixture was vortexed for 5 min and centrifuged at4000 rpm for 5 min to sediment the CCl4. Finally, the sedimentedphase was transferred to a trace intubation in a sample vial.

2.9. QuEChERS–DLLME procedure

The QuEChERS procedure was used as the previously reportedwith slight changes (Kok et al., 2005). 1 mL of the extract obtainedby QuEChERS was transferred into a centrifuge tube and 60 lL ofCCl4 was added and the mixture was vortexed for 1 min.

Y. Zhang et al. / Food Chemistry 159 (2014) 367–373 369

The DLLME procedure described below was followed for enrich-ment. 5 g of deionized water was placed in a centrifuge tube. 1 mLof the extract and 60 lL of CCl4 were rapidly injected into 5 g ofdeionized water with a syringe to form cloudy solution. The sam-ples were vortexed for 5 min and then centrifuged at 4000 rpmfor 5 min. Finally, the sedimented phase was transferred to a traceintubation in a sample vial.

3. Results and discussion

3.1. Optimisation of DLLME

Factors likely to impact DLLME and QuEChERS–DLLME such astypes and volumes of extraction solvents and dispersive solvents,ultrasonic time, salt concentration, vortex and centrifugation timewere investigated in detailed.

3.1.1. Selection of extraction solvent and its volumeThe correct solvents are vital for the success of DLLME. In our

study, four common halogenated solvents including CHCl3,C6H5Cl, C2Cl4 and CCl4 were selected for extraction. Extraction effi-ciency was evaluated by comparing the recoveries of the analytes.Fig. 1A showed that carbon tetrachloride was most efficient and itwas therefore used in subsequent experiments.

To investigate the volume effect of CCl4, different quantities ofCCl4 (30–70 lL) were used whilst the dispersant was maintainedat 1 mL. Observably, the extraction efficiency was improved with

Fig. 1. Effects (A) of extraction solvents, (B) of the volumes of extraction solvents, (C) of danalytes in DLLME. 5.00 g of spiked apple juices at 0.01 mg kg�1.

the increase of volume (Fig. 1B). When CCl4 was increased from30 to 60 lL, the recovery of ten pyrethroids was increased from43–68% to 61–103%. However, those peaks of some non-analytesincluding interfering substances appeared more obviously withvolumes greater than 60 lL although the recovery of the pyre-throids continued to increase. Thus, 60 lL of CCl4 was selected asthe optimum volume.

3.1.2. Selection of dispersive solvent and its volumeAcetone, acetonitrile and methanol were chosen as the disper-

sive solvents. Fig. 1C showed that the highest recovery wasachieved with acetone and it was used for all subsequentexperiments.

To study the volume effect of acetone, it was varied from 0.4 to1.2 mL in the interval of 0.2 mL while CCl4 was kept at 60 lL. Withthe increase of acetone from 0.4 to 1.0 mL, the extraction efficiencyincreased gradually with recoveries from 21–60% to 61–103%,while the extraction efficiency dropped down slightly above 1 mL(Fig. 1D). Therefore, 1 mL of acetone was selected as the optimumvolume.

3.2. Optimisation of QuEChERS–DLLME

Since the ultimate solution obtained after QuEChERS was usedfor dispersive solvent, the types and volumes of extraction solventswere the only parameters to be optimised. 60 lL of CCl4 was the

ispersive solvents, and (D) of the volumes of dispersive solvents on the recoveries of

Fig. 2. Chromatogram of a standard mixture at 0.1 mg L�1: 1, tetramethrin; 2,bifenthrin; 3, lambda-cyhalothrin; 4, permethrin; 5, cyfluthrin; 6, cypermethrin; 7,flucythrinate; 8, fenvalerate; 9, tau-fluvalinate; 10, deltamethrin.

370 Y. Zhang et al. / Food Chemistry 159 (2014) 367–373

optimum extraction solvent in QuEChERS–DLLME (data notshown), which was the same as the results obtained in DLLME.

3.3. Other conditions of DLLME and QuEChERS–DLLME

To evaluate ultrasonic effect, ultrasound-assisted extractionwas tested (0–5 min). The result showed that recovery of ten

Fig. 3. Chromatograms (A) of a standard mixture at 0.01 mg L�1, (B) of a spiked apple juQuEChERS–DLLME, and (D) a spiked orange juice at 0.01 mg kg�1 after DLLME while thcyhalothrin; 4, permethrin; 5, cyfluthrin; 6, cypermethrin; 7, flucythrinate; 8, fenvalera

pyrethroids was slightly enhanced when ultrasonic treatmentwas increased from 0 to 1 min. However, the recoveries remainedinconstant above 1 min and even decreased. Moreover, the repeat-ability of the recoveries was not satisfactory. So, ultrasound wasnot used for DLLME.

To evaluate salting out effect (commonly sodium chloride), dif-ferent concentrations of NaCl in a range of 0–5% (w/v) at a 1-%interval were investigated. The results revealed that the recoveriesof analytes decreased gradually with the increasing of salt concen-tration. Thus, NaCl was not applied for DLLME.

Centrifugation time has no obvious influence on the extractionefficiency in DLLME (Boonchiangma et al., 2012). Thus, a vortextime of 5 min and centrifugation time of 5 min were used to helpthe cloudy solution form and precipitate at the bottom of the tube.

3.4. Analytical performance

A typical gas chromatogram under the conditions described inSection 2.3 is shown in Fig. 2. Ten pyrethroids were separated in29 min. Although peaks of pyrethroid enantiomers partially over-lapped, they were together integrated without difficulty becausequantification depends on peak area sum for pyrethroidenantiomers.

Fig. 3A displays the chromatogram of ten pyrethroids at0.01 mg L�1 without DLLME, while Fig. 3B shows the chromato-gram from an apple juice spiked at 0.01 mg kg�1 of each of thepyrethroids after DLLME. There was no interference peak in thetypical chromatogram of a blank apple juice after DLLME.Obviously, the signal intensities of all the pyrethroids, namelythe method sensitivity, improved many-fold with application of

ice at 0.01 mg kg�1 after DLLME, (C) of a spiked orange juice at 0.01 mg kg�1 aftere spiked sample is diluted to five times: 1, tetramethrin; 2, bifenthrin; 3, lambda-te; 9, tau-fluvalinate; 10, deltamethrin.

Table 1Analytical performance optimised for the determination of ten pyrethroids.

Pyrethroids Linearrange(lg L�1)

Linear equation Correlationcoefficient (r2)

LOD(lg L�1)

LOQ(lg L�1)

Enrichmentfactor of DLLME

Enrichment factor ofQuEChERS–DDLME

Precision (% RSD)

Intra-day(n = 3)

Inter-day(n = 3 � 3)

Tetramethrin 2–10,000 y = 251.85x + 9849.36 0.9998 2 5 110 25 2.9 4.1Bifenthrin 0.5–10,000 y = 358.74x + 29175.27 0.9998 0.5 2 65 18 2.2 4.9Lambda- cyhalothrin 0.2–10,000

y = �1570.54x + 74876.51 0.9996 0.2 1 64 19 3.9 6.3Permethrin 2–10,000 y = 205.10x + 8595.29 0.9996 2 5 104 24 2.1 4.0Cyfluthrin 1–10,000 y = �2201.21x + 67955.49 0.9995 1 4 78 18 2.8 6.4Cypermethrin 2–10,000 y = �1460.15x + 83946.31 0.9995 2 5 86 20 2.5 4.5Flucythrinate 1–10,000 y = �201.19x + 29722.88 0.9990 1 4 104 24 2.3 5.3Fenvalerate 0.5–10,000 y = �564.36x + 33944.35 0.9993 0.5 2 107 16 2.4 5.8Tau-

fluvalinate0.5–10,000 y = �1381.12x + 57236.53 0.9992 0.5 2 93 26 2.8 6.2

Deltamethrin 0.5–10,000 y = �383.27x + 56526.79 0.9990 0.5 2 92 17 3.1 6.0

Y. Zhang et al. / Food Chemistry 159 (2014) 367–373 371

DLLME. The enrichment factors were in a range of 64–110 (Table 1).Thus, DLLME is a very simple and effective method for preconcen-trating pyrethroid residues in apple juices. In addition, recoveriesfrom the other spiked fruit juices including pear, grape, peach, or-ange, lemon, kiwi and mango juices at 0.01 mg kg�1 were exam-ined. Unfortunately, recoveries from orange, lemon, kiwi andmango juices were less than 50% while recoveries from pear, grapeand peach juices were in the range from 64.0% to 108.4%, whichwas caused by different matrices.

Fig. 3C shows the chromatogram from a spiked orange juice at0.01 mg kg�1 after QuEChERS–DLLME. There is no obvious interfer-ence peak in the typical chromatogram of a blank orange juice afterQuEChERS–DLLME. Fig. 3D shows the chromatogram from a spikedorange juice at 0.01 mg kg�1 after DLLME while the spiked sampleis diluted five times in order to compare DLLME with QuEChERS–DLLME. Clearly, better recoveries were obtained by QuEChERS–DLLME than only DLLME alone even if the orange juice has to bediluted. And so it was in lemon, kiwi and mango juices. Thus, QuE-ChERS–DLLME was more suitable for the preconcentration of pyre-throids in orange, lemon, kiwi and mango juices than DLLMEalthough the latter had a higher enrichment factor than the former(Table 1). Interestingly, using both DLLME and QuEChERS–DLLME,achieved acceptable recoveries from fruit juices such as apple,pear, grape and peach in the range 60% to 120%. Considering thepurification capacity of QuEChERS, these results can be explainedin terms of simper matrices in the apple, pear, grape and peachjuices than the orange, lemon, kiwi and mango juices. As a result,QuEChERS–DLLME has found been used widely for extracting andenriching pyrethroid residues in not only rich pulps but also morecomplex matrices than DLLME.

Table 1 provides the linear regression equation and the othercorresponding results. The results reveal a satisfactory linearityfor all analytes with excellent correlation coefficients (r2) higher

Table 2Comparison of the proposed methods and some other methods for the determination of p

Extraction method Instrumentdetector

Analyte Sample

DLLME HPLC–UV 6 Pyrethroids Apple, red grape, orkiwi, passion fruit,pomegranate andguava juices

UA-DLLME GC–FID 2 Pyrethroids Pear juice

DLLME GC–ECD 4 Pyrethroids Peach juice, pulp anDLLME GC–MS 24 Pesticides including 2

pyrethroidsApple juice

DDLME andQuEChERS–DDLME

GC–ECD 10 Pyrethroids Apple, pear, grape,orange, lemon, kiwmango juices

than 0.999 in linear regression equation. The relative standarddeviations (RSDs) of peak areas were below 4% for intra-day preci-sion and less than 7% for inter-day precision. The limits of detec-tion (LODs, S/N = 3) and the limits of quantification (LOQs, S/N = 10) of ten pyrethroids ranged from 0.2 to 2 lg L�1 and 1 to5 lg L�1, respectively. Considering the high enrichment factors ofDLLME and QuEChERS–DLLME, LODs and LOQs of the two methodsare below the MRLs established in China (Chinese pesticide MRLs,Regulation (GB) No. 19648-2006).

Recoveries achieved from the spiked fruit juices (apple, pear,grape and peach) at two concentrations (0.01 and 0.1 mg kg�1)using DLLME ranged from 61.5% to 108.4% (RSDs, 1.3–5.6%) and64.3% to 98.9% (RSDs, 2.0–6.3%), respectively. The recovery of somepyrethroids was less than 70% (bifenthrin, lambda-cyhalothrin,cyfluthrin, cypermethrin, flucythrinate, tau-fluvalinate and delta-methrin). On the other hand, the recovery achieved from thespiked samples (orange, lemon, kiwi and mango) at the same con-centrations using QuEChERS–DLLME ranged from 65.5% to 137.5%(RSDs, 2.8–8.6%) and 62.6% to 126.7% (RSDs, 2.4–7.2%), respec-tively. The recoveries of bifenthrin in spiked mango juices wereless than 70%, and those of some pyrethroids were higher than130% (tetramethrin, permethrin and tau-fluvalinate). Hence wecan conclude that DLLME and QuEChERS–DLLME provide accept-able accuracy and precision.

Table 2 summarises the details of the proposed method and theother methods which have been applied for pyrethroids determi-nation. Clearly, the proposed method has higher sensitivity thanmost of the recently published methods.

3.5. Matrix effects

Matrix components have an observable effect on the detectionof target analytes by either enhancing or weakening their signal

yrethroids residues in fruit juices.

LOD Recovery (%) EF Ref.

ange, 2–5 lg L�1 84–94 62–84 Boonchiangma, Ngeontae,and Srijaranai (2012)

2–3 lg kg�1 92–107 344–351 Du, Yan, She, Liu, and Yang(2010)

d peel 3–18 ng L�1 73–106 409–1089 Matsadiq et al. (2011)0.4–2 lg L�1 60–105 42–58 Cunha, Fernandes, and

Oliveira (2009)peach,i and

0.2–2 lg L�1 62–108 and63–138

64–110 and16–26

Proposed method

Fig. 4. Chromatograms (A) of apple juice by GC–ECD after DLLME, (B) by of apple juice GC–MS after DLLME, (C) of orange pulp by GC–ECD after QuEChERS–DLLME, and (D) oforange pulp by GC–MS after QuEChERS–DLLME: (1) lambda-cyhalothrin standard at 0.2 mg L�1; (2) sample contaminated with lambda-cyhalothrin; (3) tau-fluvalinatestandard at 0.2 mg L�1; (4) sample contaminated with tau-fluvalinate.

372 Y. Zhang et al. / Food Chemistry 159 (2014) 367–373

intensities, so different matrix-matched calibrations were put intouse (Boonchiangma et al., 2012). The matrix effects in organic sol-vent and in blank samples were estimated by comparing the slopesof the calibration curves. The test revealed that there was no signif-icant difference between the organic solvent and the real samples(data not shown).

3.6. Analysis of real samples

The proposed analytical methods were used for the determina-tion of ten pyrethroid residues in marketed fruit juices. In addition,pyrethroid residues in fruit pulps and peels were tested using QuE-ChERS–DLLME. One of ten pyrethroids, namely lambda-cyhaloth-rin, was found in fresh apple juice at about 2 lg kg�1. Tau-fluvalinate was found in the orange pulp at about 3 lg kg�1

(Fig. 4A and C). To confirm these results, the same samples wereanalysed using GC–MS (Gianni et al., 2008), a technique recom-mended for pesticides. About 2 lg kg�1 of lambda-cyhalothrinwas found in the apple juice and about 3 lg kg�1 of tau-fluvalinatewas found in the orange pulp, which were in accordance with theresults by GC analysis (Fig. 4B and D).

4. Conclusions

In this paper, two rapid and simple sample preparation meth-ods DLLME and QuEChERS–DLLME followed by GC–ECD weredeveloped and compared for ten pyrethroid residues in variousfruit juices. These methods offered acceptable recoveries and lim-ited variation from day-to-day. DLLME was suitable for those fruitjuices with simper matrices and QuEChERS–DLLME for all the fruitjuices. The proposed methods demonstrated pyrethroid residues insome fruit juices in the Chinese market.

Acknowledgements

This work was supported by the National Key Technology R&DProgram (Nos. 2007BAD47B07 and 2009BADB7B04), ChinaAgriculture Research System (No. CARS-27), Natural ScienceFoundation of Chongqing (Nos. cstc2013jcyjA0435 andcstc2013jjB80009) and Fundamental Research Fund for the CentralUniversities (No. XDJK2012C059).

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