Water with Low Concentration of Surfactant in Dispersed Solvent

Article pubs.acs.org/JAFC

Water with Low Concentration of Surfactant in Dispersed SolventAssisted Emulsion Dispersive Liquid−Liquid Microextraction for the Determination of Fungicides in Wine Wan-Chi Tseng,†,∥ Shang-Ping Chu,†,∥ Po-Hsin Kong,§ Chun-Kai Huang,# Jung-Hsuan Chen,⊥ Pai-Shan Chen,*,§,⊥ and Shang-Da Huang*,† †

Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan Department and Graduate Institute of Forensic Medicine, National Taiwan University, Taipei 10002, Taiwan # Department of Chemistry, National Chung-Hsing University, Taichung 40227, Taiwan ⊥ Forensic and Clinical Toxicology Center, National Taiwan University College of Medicine and National Taiwan University Hospital, Taipei 10051, Taiwan §

ABSTRACT: A sample preparation method, dispersive liquid−liquid microextraction assisted by an emulsion with low concentration of a surfactant in water and dispersed solvent coupled with gas chromatography−mass spectrometry, was developed for the analysis of the fungicides cyprodinil, procymidone, fludioxonil, flusilazole, benalaxyl, and tebuconazole in wine. A microsyringe was used to withdraw and discharge a mixture of extraction solvent and 240 μL of an aqueous solution of Triton X-100 (the dispersed agent) four times within 10 s to form a cloudy emulsion in the syringe. This emulsion was then injected into a 5 mL wine sample spiked with all of the above fungicides. The total extraction time was approximately 0.5 min. Under optimum conditions using 1-octanol (12 μL) as extraction solvent, the linear range of the method in analysis of all six fungicides was 0.05−100 μg L−1, and the limit of detection ranged from 0.013 to 0.155 μg L−1. The absolute recoveries (n = 3) and relative recoveries (n = 3) were 30−83 and 81−108% for white wine at 0.5, 5, and 5 μg L−1, and 30−92 and 81−110% for red wine, respectively. The intraday (n = 7) and interday (n = 6) relative standard deviations ranged from 4.4 to 8.8% and from 4.3 to 11.2% at 0.5 μg L−1, respectively. The method achieved high enrichment factors. It is an alternative sample preparation technique with good performance. KEYWORDS: water with low concentration of surfactant, dispersive liquid−liquid microextraction, fungicides, gas chromatography, improved solvent collection system, wine

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INTRODUCTION Defending against fungal diseases is the main challenge during grape growing for winemaking. To improve the quality and quantity of grapes, a broad spectrum of fungicides is frequently applied during grape cultivation. Although some of them might be human carcinogens investigated by the U.S. Environmental Protection Agency,1 without the use of fungicides in viticulture, large economic losses may be incurred. Under proper use, fungicides have minimal adverse impact on the environment or public health.2,3 However, improper treatment, that is, disregard of reasonable doses and safety periods, leads to fungicide residues in the food chain, soil, and water because of their high mobility and water solubility. This makes them common environmental pollutants.4 In grapes, these residues may be transferred to the must and then to the wine during fermentation, which can be a significant issue for public health.5−13 The maximum residue levels for fungicides in grapes are set at 0.05−0.1 mg kg−1 by the European Union.14 In Taiwan, the maximum residue concentrations of cyprodinil, procymidone, fludioxonil, flusilazole, benalaxyl, and tebuconazole in grapes are 1, 2.0, 1, 0.5, 0.5, and 2.0 mg kg−1, respectively.15 The tolerance for procymidone in wine is set at 5 mg L−1 by the U.S. Food and Drug Administration (FDA).16 Because fungicides in matrices usually occur in trace amounts, sample pretreatment for chromatography is essential to analysis. © 2014 American Chemical Society

To achieve low limits of detection (LODs), a variety of techniques such as liquid−liquid extraction,17,18 membraneassisted solvent extraction,19 solid-phase microextraction,20 solid-phase extraction,21−24 and bar adsorptive microextraction25 have been developed to determine fungicides in wine samples. However, the main disadvantage of these methods is that they require considerable time for extracting target analytes into an organic phase or onto sorbents. Therefore, a fast, sensitive, and efficient analytical method is needed. Recently, Rezaee et al. introduced dispersive liquid−liquid microextraction (DLLME).26 This method injects a mixture of a high-density extraction solvent and a water-miscible and polar dispersive solvent into the aqueous sample to form a cloudy mixture, which results in high enrichment. In 2007, Khalili-Zanjani et al. performed liquid−liquid microextraction based on solidification of a floating organic droplet.27 The extraction solvent, which had a melting point near room temperature (10−30 °C), was frozen by transferring the sample to an ice bath after extraction. In 2011, Lee et al. introduced an Received: Revised: Accepted: Published: 9059

April 2, 2014 August 24, 2014 August 25, 2014 August 25, 2014 dx.doi.org/10.1021/jf5036096 | J. Agric. Food Chem. 2014, 62, 9059−9065

Journal of Agricultural and Food Chemistry

Article

The temperature of the GC-MS transfer line was 280 °C, 230 °C for ion source, and 150 °C for quadrupoles. A mass detector in the electron impact mode (70 eV) was used. Spectra were scanned over the m/z range of 50−400 to confirm the retention times of the analytes. Selected ion monitoring mode (SIM) was applied for the determination of fungicides. In the determination of fungicides, two or three ions were selected in Table 1.

automated, dynamic in-syringe liquid-phase microextraction, which was more efficient for extracting pesticides from water samples.28 Several studies have employed low-density solvents as substitutes for toxic halogenated solvents. These developments widened the selection of solvents available for DLLME and extended its application.17,29−34 Ultrasound-assisted emulsification microextraction (USAEME) for DLLME has also been developed to improve the generation of droplets with or without using dispersive solvent.34−38 Another alternative to ultrasound assistance is the use of surfactants. As some surfactants are just soluble in an organic solvent and some are just water-soluble, their presence improves the generation of fine droplets in DLLME.39−41 However, high concentrations of surfactants are generally required to disperse the extraction solvents. Water with a low concentration of surfactant in dispersed solvent-assisted emulsion dispersive liquid−liquid microextraction (WLSSAE-DLLME) was developed recently,42,43 which used in combination with an improved solvent collection system (ISCS) avoids the problems associated with DLLME to analyze water samples.33 In the present study, WLSSAE coupled with gas chromatography−mass spectrometry (GC-MS) was developed to analyze six fungicides in wine samples. The accuracy, precision, linearity, enrichment factor (EF), and LOD of WLSSAE in the analysis of wine samples were evaluated and tested.

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Table 1. Retention Time and m/z Values Selected for SIM Mass Detection compd

retention time (min)

selected ions (m/z)

ANT-d10 CYP PRC FLD FLU BEN TEB

4.96 5.87 6.07 6.61 6.76 7.78 8.22

187, 188, and 189 210, 214, and 225 96, 283, and 285 182 and 248 206, 233, and 234 91, 148, and 206 120, 250, and 252

Extraction Procedure. A diagram of the WLSSAE procedure is shown in our previously published work.42 A 5 mL portion of the blank white wine and DI water (1:1, v/v) spiked with analytes at 5 μg L−1 were transferred to a 10 mL conical-bottom glass centrifuge tube. A mixture of 12 μL of extraction solvent (1-octanol) and 240 μL of water containing 10 mg L−1 Triton X-100 (dispersed solvent) was transferred to an Eppendorf tube. A 500 μL syringe (Reno, NV, USA) was used to pump the mixture back and forth four times within 10 s, and then a cloudy emulsion was formed. This emulsion was then injected into the sample solution. After centrifugation for 5 min at 5000 rpm, an organic droplet formed on the surface of the solution. The phase separation after DLLME of white and red wines is also shown in ref 44. The floating phase, which had a volume of approximately 3.0 ± 0.5 μL, was hard to withdraw into a microsyringe. Therefore, the mixture of the floating phase and aqueous solution was first transferred to a in-house-designed microtube (15 × 3 mm). After centrifugation for 1 min, the organic phase was collected from the upper portion of the microtube by using a 10 μL microsyringe and then injected into the GC-MS system. The ambient temperature was 25 °C.

MATERIALS AND METHODS

Reagents and Samples. All solvents and chemicals used in the study were of analytical grade. Cyprodinil (CYP), procymidone (PRC), fludioxonil (FLD), flusilazole (FLU), benalaxyl (BEN), tebuconazole (TEB), anthracene-d10 (ANT-d10; internal standard), 1-heptanol, 1-octanol, 1-nonanol, Triton X-114, Triton X-100, Tween 80, and Tween 60 were purchased from Sigma-Aldrich (St. Louis, MO, USA). Methanol (liquid chromatography (LC)-MS grade) was obtained from J. T. Baker (Phillipsburg, NJ, USA). Acetone (LC grade) and sodium chloride were purchased from Merck (Darmstadt, Germany). Deionized water (DI water) was obtained by using a Milli-Q reagent water system (Millipore, Milford, MA, USA). Stock solutions of each fungicide and of ANT-d10 were prepared by dissolving each in methanol to obtain a 1000 mg L−1 solution, which was then stored at 4 °C. Standard working solutions and ANT-d10 solution were prepared by diluting each stock solution with methanol to 10 mg L−1. Each sample solution was prepared by spiking pure water with 10 and 5 μg L−1 fungicide and ANT-d10. Two kinds of white wine and one kind of red wine made in California (USA) were purchased from a local supermarket (Hsinchu, Taiwan). All wine samples contained 12% alcohol. The samples were filtered through 0.45 μm membrane filters from Millipore (Bedford, MA, USA) and then stored at 4 °C overnight before analysis. Instrumentation. To separate the aqueous and organic phases, microtubes that were designed in-house (15 × 3 mm; inner diameter, 1.8 mm; total volume, 38 μL; Qing-Fa Co., Hsinchu, Taiwan) were used in the ISCS system. A CN-2200 centrifuge (Hsiantai Machinery Industry, Taipei, Taiwan) and a miVac DUC-12060-C00 centrifuge (Stockholm, Sweden) were used in the study. Analyses were carried out by using a 6850 Agilent Technologies gas chromatograph (Wilmington, DE, USA) with a split/splitless injector operated at 300 °C and a single quadrupole (Agilent Technologies mass detector 5975B). The splitless time was 1 min. The flow rate of helium was 1.0 mL min−1. A 30 m DB-5MS UI-fused silica capillary column (0.25 mm i.d., 0.25 μm film thickness; J&W Scientific, Folsom, CA, USA) was employed in the determination of fungicides. The temperature of the column was initially held at 100 °C, raised to 250 °C at 35 °C min−1, held at 250 °C for 3 min, raised to 300 °C at 10 °C min−1, and then held at 300 °C for 1 min. The carrier gas was helium (purity = 99.9995%), which was further purified by passage through a helium gas purifier (Agilent Technologies model RMSH-2).

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RESULTS AND DISCUSSION Impact of Solvent on Extraction Efficiency. The selection of extraction solvent is important in maximizing the extraction efficiency. The solvents should be immiscible with

Figure 1. Effect of the type of extraction solvent (n = 3). Samples were spiked with 5 μg L−1 of each analyte. Extraction conditions: dispersed solvent volume, 240 μL; surfactant, 1 mg L−1 Triton X-100. 9060

dx.doi.org/10.1021/jf5036096 | J. Agric. Food Chem. 2014, 62, 9059−9065


Article

Type of Surfactant. The selection of surfactant is crucial to the success of the proposed method. As surfactants are soluble in the extraction solvent and in water, they are commonly used to improve the dispersion of extraction solvents. A surfactant with high hydrophilic−lipophilic balance (HLB) has higher hydrophilicity. When the HLB value of a surfactant is between 12 and 16, the surfactant is considered as an oil-in-water emulsifier. Two kinds of well-known polyoxyethylene-type nonionic surfactants, Tween and Triton (Figure 2), were studied. The HLBs of Tween 60, Tween 80, Triton X-100, and Triton X-114 are 14.9, 15.0, 13.4, and 12.3, respectively. Compared with other surfactants, using Triton-X-100 resulted in higher EFs for five of six compounds, especially for BEN and TEB, which had lower extraction efficiency. On the basis of the experimental results, Triton X-100, which had better extraction efficiency and precision for most fungicides, was selected as the dispersed solvent. Volume of Extraction Solvent. Different volumes of the extraction solvent (12, 14, 16, and 18 μL) were tested. When the solvent volume was 50 mg L−1 surfactant, the solution was still an emulsion after centrifugation. The floating phase could not be collected. Therefore, the maximum concentration of surfactant used was 50 mg L−1. When the concentration of

Figure 2. Effect of the type of surfactant for the first extraction solvent (n = 3). Samples were spiked with 5 μg L−1 of each analyte. Extraction conditions: extraction solvent, 1-octanol; volume, 12 μL; dispersed solvent volume, 240 μL; concentration of the surfactant, 1 mg L−1.

water and have low toxicity, and analytes should be highly soluble in such solvents. To apply the above conditions, alcohols 1-heptanol, 1-octanol, and 1-nonanol were tested. To consistently collect 3.0 μL of the floating organic phase, various amounts of extraction solvent (21 μL of 1-heptanol, 12 μL of 1-octanol, and 11 μL of 1-nonanol) had to be combined with 240 μL of Triton X-100 (1 mg L−1) in a microsyringe.43 The mixture was subsequently injected into the sample solution. The results are shown in Figure 1. The experiment revealed that 1-octanol had better EFs than those of the other solvents; it was thus chosen as the extraction solvent for use in subsequent experiments.

Figure 3. Effect of the volume of the surfactant (n = 3). Samples were spiked with 5 μg L−1 of each analyte. Extraction conditions: extraction solvent, 1-octanol; volume, 12 μL; dispersed solvent, Triton X-100; concentration, 10 mg L−1. 9061



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Table 2. Linearity, EFs, LODs, and Precision of Blank White and Red Wines linearitya(n = 3, μg L−1)

EFsb

R2

LODc (μg L−1)

LOQd (μg L−1)

RSDe (%) intraday, n = 7

RSDe (%) interday, n = 6

compd

white

red

white

red

white

red

white

red

white

red

white

red

white

red

CYP PRC FLD FLU BEN TEB

0.05−100 0.05−100 0.1−100 0.05−100 0.1−100 0.05−100

0.05−100 0.10−100 0.05−100 0.05−100 0.05−100 0.50−100

0.9996 0.9999 0.9978 0.9995 0.9998 0.9999

0.9997 0.9998 0.9977 0.9984 0.9999 0.9996

414 430 1313 904 659 1210

349 328 796 505 416 911

0.021 0.018 0.026 0.013 0.020 0.016

0.036 0.092 0.035 0.020 0.051 0.155

0.072 0.061 0.088 0.044 0.066 0.053

0.121 0.306 0.116 0.069 0.173 0.517

7.2 6.1 8.8 4.4 6.6 5.3

2.3 8.9 1.7 0.9 5.4 12.7

11.2 10.1 9.3 4.3 9.7 7.9

3.3 14.1 3.4 5.6 12.6 13.6

Blank white and red wine samples spiked with 0.05, 0.1, 0.5, 1, 5, 10, 50, and 100 μg L−1. bBlank white and red wine samples spiked with 5 μg L−1, n = 3. cLODs were determined as 3 times the standard deviation obtained from seven replicate runs of blank white wine samples spiked with 0.1 μg L−1 of each fungicide. dLOQs were determined as 10 times the standard deviation obtained from seven replicate runs of blank white and red wine samples spiked with 0.1 μg L−1 of each fungicide. eBlank wine samples were spiked with 0.5 μg L−1. a

Figure 4. GC-MS selected ion chromatograms for the analysis of (a) white wine sample and (b) sample spiked with 5 μg L−1 fungicides: IS, ANT-d10; 1, CYP; 2, PRC; 3, FLD; 4, FLU; 5, BEN; 6, TEB.

(LOQ), precision (as relative standard deviation, RSD), and EF are summarized in Table 2. R2 values of the calibration curves are in the range of 0.9977−0.9999, indicating high linearity within the concentration range used for each analyte. The LODs were calculated as 3 times the standard deviation of seven replicate runs of blank white and red wines spiked with low concentrations of the analytes. LODs for determination of fungicides in the blank wine samples differed substantially and ranged from 0.013 to 0.155 μg L−1. Intra- and interday RSDs for determination of the analytes ranged from 0.9 to 12.7% and from 3.4 to 14.1%, respectively. Application in the Analysis of Wine Samples. To demonstrate the capability of WLSSAE, the procedure was applied to the analysis of fungicides in white wine and red wine samples. The results show that the analyzed samples were free of fungicides (Figure 4). FLU, BEN, and TEB have a broad shoulder (Figure 4b), which might result from the surfactant partially extracted into the 1-octanol phase or from matrix effect of the samples. The wine samples were spiked with the analytes at 0.5, 5, and 50 μg L−1 levels. The absolute recovery (AR) was defined as the percentage of the total analyte (n0) that was extracted into the floating organic phase (norg).

surfactant in the aqueous solution was increased from 0 to 10 mg L−1, the extraction EF was significantly improved. However, EFs declined slightly upon spiking with >10 mg L−1 Triton X-100. Evidently, higher concentrations of Triton X-100 increased the solubility of analytes in the aqueous solutions, resulting in lower EFs. The optimal surfactant concentration in the aqueous solution was therefore 10 mg L−1. Volume of the Surfactant Solution. To investigate the impact of the volume of the aqueous solution, different volumes of aqueous solution (60, 120, 240, and 360 μL) containing 10 mg L−1 Triton X-100 were evaluated (Figure 3). When the volume of aqueous solution was changed from 60 to 240 μL, the EFs were increased. On the other hand, the EFs decreased when the volume of aqueous solution was increased from 240 to 360 μL. Therefore, the volume of aqueous solution was fixed at 240 μL. The surfactant concentration was approximately equivalent to 0.48 mg L−1 in the total volume (5 mL) of the sample solution. Quantitative Aspects. The linearity obtained by using 12 μL of 1-octanol was evaluated under optimum conditions. Calibration curves were constructed by analyzing solutions of white and red wines with DI water (1:1, v/v) at concentrations of 0.05, 0.1, 0.5, 1, 5, 10, 50, and 100 μg L−1. Curves for all fungicides have coefficients of determination (R2) >0.9977. Data on the linear range (LR), R2, LOD, limit of quantification

AR = norg /n0 × 100 9062



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Table 3. Accuracy, Absolute Recoveries (AR), Relative Recoveries (RR), and Precision (RSD) of Fungicides in Spiked White and Red Wines white wine (n = 3)

red wine (n = 3)

WLSSAE

spiked concn (μg L−1)

calcd concn (μg L−1)

AR (%)

RR (%)

RSD (%)

calcd concn (μg L−1)

AR (%)

RR (%)

RSD (%)

CYP

0.5 5 50

0.44 4.7 44.1

52 30 34

88 94 88

4.2 3.6 1.9

0.48 5.1 47.0

56 32 37

96 101 94

4.2 4.3 7.1

PRC

0.5 5 50

0.47 4.3 45.5

43 32 37

93 86 91

6.6 2.2 2.7

0.44 4.1 45.0

40 30 37

88 81 90

1.9 4.2 4.2

FLD

0.5 5 50

0.45 6.2 54.3

76 81 81

90 120 108

5.9 2.4 3.2

0.55 5.5 52.0

92 75 78

109 110 104

2.6 3.0 1.0

FLU

0.5 5 50

0.47 4.3 42.4

78 63 64

94 86 84

2.7 5.8 2.1

0.42 4.2 41.0

69 61 62

84 84 82

7.2 4.6 2.2

BEN

0.5 5 50

0.49 4.1 42.2

54 34 38

97 81 84

1.0 8.9 1.6

0.44 4.2 41.0

49 35 37

87 83 82

6.3 4.3 5.8

TEB

0.5 5 50

0.52 5.1 43.5

83 67 72

104 102 87

4.1 5.4 2.6

0.54 4.9 43.5

85 64 72

107 97 87

2.5 4.9 4.3

Table 4. Comparison of WLSSAE with Other Methods for Analysis of Fungicides in Wine separation/detection methods a

sample

extraction solvent (μL)

SPE/LC-MS BAμE-LD/GC-MSb

wine water/wine

DLLME-SFO/GCMSc UASEME-SFO/ HPLC-DADd WLSSAEe

wine

methanol (750) + acetonitrile (750) 1-undecanol (50)

water/wine

1-undecanol (30)

wine

1-octanol (12)

linear range (μg L−1)

LOD (μg L−1)

20 255

0.2−2000 0.04−1.6

0.06−0.51 0.004−0.030

24 25

acetone (500)

1

1−300

0.06−0.90

17

Tween 80 (10 mmol L−1, 24 μL) Triton X-100 (10 mg L−1, 240 μL)

1

5−1000

1.2−4.7

38

few seconds

0.05−100

0.013−0.026

this work

dispersive agent (μL)

extraction time (min)

ref

a Solid phase extraction/liquid chromatography quadrupole time-of-flight tandem mass spectrometry. bBar adsorptive microextraction combined with liquid desorption/gas chromatography−mass spectrometry. cDispersive liquid−liquid microextraction based on solidification of floating organic drop/gas chromatography−mass spectrometry. dUltrasound-assisted surfactant-enhanced emulsification microextraction/high-performance liquid chromatography with diode array detection. eWater with low concentration of surfactant in dispersed solvent-assisted emulsion dispersive liquid− liquid microextraction.

fungicides in wine. The results indicate that the proposed method is sensitive and applicable to the analysis of fungicides at trace levels. The method requires a very short extraction time (a few seconds) and 12 μL of extraction solvent only, in contrast to other methods. To extract fungicides from wine samples through the ISCS technique, 0.48 mg L−1 of surfactants was required in using water with low concentration of surfactant as dispersed solvent. The results suggest that high EFs were achieved in a few seconds. The approach afforded high repeatability and high recovery within a short extraction time. WLSSAE employed a few microliters of lowtoxicity, halogen-free organic solvents to extract fungicides in wine samples. The analysis had a wide linear range and low LODs, as well as high precision, EFs, and RRs. The LODs were much lower than the tolerance of procymidone in wine prescribed by the FDA.16 The method is a desirable application for the separation and preconcentration of fungicides at trace levels in wine samples.

ARs were between 30 and 83% for white wine and between 30 and 92% for red wine. The relative recovery (RR) is defined by the following equation: RR = [(Cfound − Creal)/Cadded] × 100

Cfound, Creal, and Cadded are defined as the concentration of analyte after addition of a known amount of standard in the real sample, the concentration of analyte in the real sample, and the concentration of known amount of standard that was spiked to the real sample, respectively. RRs were between 81 and 108% for white wine and between 81 and 110% for red wine. RSDs for the determination of the analytes ranged from 1.0 to 8.9% for white wine and from 1.0 to 7.2% for red wine (Table 3). This shows that after the wine samples were diluted with DI water there was no significant matrix effect using WLSSAE. In Table 4, the performance of WLSSAE is compared with that of other extraction techniques for the determination of 9063



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(17) Rodriguez-Cabo, T.; Rodriguez, I.; Ramil, M.; Cela, R. Dispersive liquid-liquid microextraction using non-chlorinated, lighter than water solvents for gas chromatography mass spectrometry determination of fungicides in wine. J. Chromatogr., A 2011, 1218, 6603−6611. (18) Vaquero-Fernandez, L.; Sanz-Asensio, J.; Fernandez-Zurbano, P.; Sainz-Ramirez, M.; Lopez-Alonso, M.; Epifanio-Fernandez, S. I.; Martinez-Soria, M. T. Development of a liquid-liquid extraction method for the determination of pyrimethanil, metalaxyl, dichlofluanid and penconazol during the fermentative process of must by GC-NPD. J. Sci. Food Agric. 2009, 89, 750−757. (19) Moeder, M.; Bauer, C.; Popp, P.; van Pinxteren, M.; Reemtsma, T. Determination of pesticide residues in wine by membrane-assisted solvent extraction and high-performance liquid chromatographytandem mass spectrometry. Anal. Bioanal. Chem. 2012, 403, 1731− 1741. (20) Martins, J.; Esteves, C.; Limpo-Faria, A.; Barros, P.; Ribeiro, N.; Simoes, T.; Correia, M.; Delerue-Matos, C. Analysis of six fungicides and one acaricide in still and fortified wines using solid-phase microextraction-gas chromatography/tandem mass spectrometry. Food Chem. 2012, 132, 630−636. (21) López-Fernández, O.; Rial-Otero, R.; González-Barreiro, C.; Simal-Gándara, J. Surveillance of fungicidal dithiocarbamate residues in fruits and vegetables. Food Chem. 2012, 134, 366−374. (22) Montes, R.; Rodriguez, I.; Ramil, M.; Rubi, E.; Cela, R. Solidphase extraction followed by dispersive liquid-liquid microextraction for the sensitive determination of selected fungicides in wine. J. Chromatogr., A 2009, 1216, 5459−5466. (23) Lagunas-Allue, L.; Sanz-Asensio, J.; Martinez-Soria, M. T. Optimization and validation of a simple and fast method for the determination of fungicides in must and wine samples by SPE and GC/MS. J. AOAC Int. 2012, 95, 1511−1519. (24) Fontana, A. R.; Rodriguez, I.; Ramil, M.; Altamirano, J. C.; Cela, R. Solid-phase extraction followed by liquid chromatography quadrupole time-of-flight tandem mass spectrometry for the selective determination of fungicides in wine samples. J. Chromatogr., A 2011, 1218, 2165−2175. (25) Almeida, C.; Nogueira, J. M. F. Comparison of the selectivity of different sorbent phases for bar adsorptive microextraction − application to trace level analysis of fungicides in real matrices. J. Chromatogr., A 2012, 1265, 7−16. (26) Rezaee, M.; Assadi, Y.; Milani Hosseini, M. R.; Aghaee, E.; Ahmadi, F.; Berijani, S. Determination of organic compounds in water using dispersive liquid-liquid microextraction. J. Chromatogr., A 2006, 1116, 1−9. (27) Khalili Zanjani, M. R.; Yamini, Y.; Shariati, S.; Jönsson, J. A. A new liquid-phase microextraction method based on solidification of floating organic drop. Anal. Chim. Acta 2007, 585, 286−293. (28) Lee, J.; Lee, H. K. Fully automated dynamic in-syringe liquidphase microextraction and on-column derivatization of carbamate pesticides with gas chromatography/mass spectrometric analysis. Anal. Chem. 2011, 83, 6856−6861. (29) Zacharis, C. K.; Tzanavaras, P. D.; Roubos, K.; Dhima, K. Solvent-based de-emulsification dispersive liquid-liquid microextraction combined with gas chromatography-mass spectrometry for determination of trace organochlorine pesticides in environmental water samples. J. Chromatogr., A 2010, 1217, 5896−5900. (30) Shi, Z. G.; Lee, H. K. Dispersive liquid-liquid microextraction coupled with dispersive μ-solid-phase extraction for the fast determination of polycyclic aromatic hydrocarbons in environmental water samples. Anal. Chem. 2010, 82, 1540−1545. (31) Farajzadeh, M. A.; Seyedi, S. E.; Shalamzari, M. S.; Bamorowat, M. Dispersive liquid-liquid microextraction using extraction solvent lighter than water. J. Sep. Sci. 2009, 32, 3191−3200. (32) Chen, H.; Chen, R. W.; Li, S. Q. Low-density extraction solventbased solvent terminated dispersive liquid-liquid microextraction combined with gas chromatography-tandem mass spectrometry for the determination of carbamate pesticides in water samples. J. Chromatogr., A 2010, 1217, 1244−1248.

AUTHOR INFORMATION

Corresponding Authors

*(P.-S.C.) Phone: +886-2-2312-3456, ext. 65495. E-mail: [email protected]. *(S.-D.H.) Phone:+886-937997973. E-mail: sdhuang@mx. nthu.edu.tw. Author Contributions ∥

W.-C.T and S.-P.C. contributed equally to this work.

Funding

This study was supported by the Ministry of Science and Technology of Taiwan (NSC 99-2113-M-007-004-MY3). Notes

The authors declare no competing financial interest.

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REFERENCES

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