Vortex-Assisted Dispersive Micro-Solid Phase Extraction Using CTAB

Article pubs.acs.org/JAFC

Vortex-Assisted Dispersive Micro-Solid Phase Extraction Using CTABModified Zeolite NaY Sorbent Coupled with HPLC for the Determination of Carbamate Insecticides Pawina Salisaeng,† Prapha Arnnok,† Nopbhasinthu Patdhanagul,‡,§ and Rodjana Burakham*,† †

Materials Chemistry Research Center, Department of Chemistry and Center for Innovation in Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand ‡ Center for Advanced Studies for Industrial Technology, Kasetsart University, Bangkok 10900, Thailand § Department of General Science, Faculty of Science and Engineering, Kasetsart University, Chalermphrakiat Sakon Nakhon Province Campus, Sakon Nakhon 47000, Thailand ABSTRACT: A vortex-assisted dispersive micro-solid phase extraction (VA-D-μ-SPE) based on cetyltrimethylammonium bromide (CTAB)-modified zeolite NaY was developed for preconcentration of carbamate pesticides in fruits, vegetables, and natural surface water prior to analysis by high performance liquid chromatography with photodiode array detection. The small amounts of solid sorbent were dispersed in a sample solution, and extraction occurred by adsorption in a short time, which was accelerated by vortex agitation. Finally, the sorbents were filtered from the solution, and the analytes were subsequently desorbed using an appropriate solvent. Parameters affecting the VA-D-μ-SPE performance including sorbent amount, sample volume, desorption solvent ,and vortex time were optimized. Under the optimum condition, linear dynamic ranges were achieved between 0.004−24.000 mg kg−1 (R2 > 0.9946). The limits of detection (LODs) ranged from 0.004−4.000 mg kg−1. The applicability of the developed procedure was successfully evaluated by the determination of the carbamate residues in fruits (dragon fruit, rambutan, and watermelon), vegetables (cabbage, cauliflower, and cucumber), and natural surface water. KEYWORDS: dispersive micro-solid phase extraction, zeolite, surfactant, carbamate, HPLC

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INTRODUCTION The determination of pesticide residues at trace levels is very significant for environmental protection and food quality control. Carbamate is one of the major classes of pesticides that is widely used in agriculture for protection of crops. Carbamates have high water solubility, which allows them to be taken up by the roots and into the leaves of plants. Therefore, their residues may be widely distributed in fruits, vegetables, agricultural products, as well as in aquatic systems through runoff and leaching from soil into ground and surface waters.1 These compounds are considered hazardous to the environment and human health. Some carbamates are extremely toxic to the central nervous system and are suspected carcinogens and mutagens. Therefore, most nations and organizations, such as the European Commission,2 the Health and Safety Executiv,e3 and the United States Environmental Protection Agency,4 have established standard/regulations for the maximum residue limits (MRLs) of carbamate residues in various products. In Thailand, the MRLs of some carbamate pesticides in agricultural products have been regulated by the National Bureau of Agricultural Commodity and Food Standard (ACFS), that is, carbaryl, 5.0, 3.0, 1.0, and 1.0 mg kg−1 in grape, cucumber, rambutan, and watermelon, respectively; carbofuran, 0.3 and 0.1 mg kg−1 in cucumber and watermelon, respectively; and methomyl, 1.0, 0.2, and 0.2 mg kg−1 in grape, cucumber, and watermelon, respectively.5 Consequently, a simple, sensitive, and reliable method for analyzing the carbamate residues at low concentration levels is required to ensure food quality and to protect a potential hazard for consumers. © XXXX American Chemical Society

Almost all of the analytical techniques for the determination of carbamates in agricultural commodities are based on chromatographic techniques, mainly high performance liquid chromatography (HPLC) with a variety of detection systems, that is, ultraviolet,6−9 photodiode array,10,11 and mass spectrometry (MS).12,13 Generally, carbamates occur in agricultural samples at very low concentrations and in complex matrixes. The matrix effect has been considered as one of the most important sources of analytical uncertainties. Therefore, sample preparation is required for elimination or reduction of matrix concomitants and enhancing the sensitivity by preconcentration of the target analytes. Recently, there is an increasing interest in the development of environmentally friendly sample preparation techniques according to the approach of green analytical chemistry. Attention is being paid to the development of miniaturized and more efficient extraction techniques that could greatly reduce toxic organic solvent consumption. Dispersive solid phase extraction (DSPE), first introduced in 2003 by Anastassiades et al.,14 has been described as a part of the QuEChERS (quick, easy, cheap, effective, rugged, and safe) procedure. Later, DSPE has been widely used as an independent sample preparation procedure.15−19 The method is based on dispersion of the solid sorbent in a sample solution, extraction by sorption, separation of the sorbent from the solution, and Received: December 23, 2015 Revised: February 19, 2016 Accepted: February 25, 2016

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DOI: 10.1021/acs.jafc.5b05437 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry

isoprocarb (IPC), methiocarb (MTC), and promecarb (PMC), were obtained from Dr. Ehrenstorfer GmbH (Germany). Stock solutions containing 1000 mg L−1 of each pesticide were prepared in methanol. The working solutions were acquired by diluting the stock solution with water. Deionized water (18.2 MΩ cm) used in all experiments was prepared by a RiOs Type I Simplicity 185 water purification system from Millipore (MA). An aqueous solution of CTAB (Sigma-Aldrich, St. Louis, MO) was prepared by dissolving appropriate reagent in water. HPLC-grade methanol was supplied from Merck KGaA (Darmstadt, Germany). Other reagents used were of analytical reagent grade. Apparatus. Chromatographic separation was performed using a Waters HPLC system (Waters, MA) that consisted of an in-line degasser, a 600E quaternary pump, and a Waters 2996 photodiode array (PDA) detector operated at 220 nm. An Inertsil ODS column (4.6 × 150 mm, 5.0 μm), GL Sciences (Japan), was used as an analytical column. The injection volume was 20 μL. Empower software (Waters, MA) was used for data acquisition. The chromatographic separation of the target carbamate pesticides was carried out on a reversed phase HPLC system with the gradient mobile phase of methanol and water. Gradient elution was performed at a flow rate of 1.0 mL min−1 as follows: started with 45% methanol (0−3 min) and ramped to 60% methanol (3−4 min), decreased to 40% methanol (4−6 min), held for 4 min (6−10 min), increased to 70% methanol (10−12 min), and held for 8 min (12−20 min) before returning to 45% methanol (20−22 min) and holding for 4 min (22−26 min). Preparation of CTAB-Modified Zeolite NaY Sorbent. Zeolite NaY was prepared in the same manner as that conducted by Patdhanagul et al.29 Briefly, two starting solutions were provided, including seed gel and feedstock gel. Seed gel consisted of 10.67Na2O:Al2O3:10SiO2:180H2O (molar ratio). Besides, the composition of feedstock gel was 4.30Na2O:Al2O3:10SiO2:180 H2O (molar ratio). Seed gel was slowly added to feedstock gel, and stirred vigorously. After aging at a room temperature for 24 h, the gel was refluxed at 100 °C for 2 h, then filtered and dried at 110 °C for 3 h. The particle size was measured by scanning electron microscopy (SEM). The average diameter was 9.7 μm. The external surface area and average pore size, which were obtained by the BET method, were 63.4 m2 g−1 and 2.78 nm diameter, respectively. To modify the zeolite NaY surface, our previous procedure was adopted.27 20 mL of 10.0 mmol L−1 CTAB solution was added to a 50 mL Erlenmeyer flask containing 0.5 g of zeolite NaY sorbents. The suspension was shaken mechanically for 24 h at 150 rpm. After the supernatant was decanted, 10 mL of water was added to sorbent. The mixture was then shaken for 10 min at 150 rpm. The supernatant was decanted again. This washing step was repeated twice to ensure that excess or loosely bound CTAB surfactant was removed. The obtained CTAB-modified zeolite NaY sorbents then were air-dried and stored in closed bottles for subsequent uses. VA-D-μ-SPE Procedure. The determination of carbamate pesticides was carried out by VA-D-μ-SPE using CTAB-modified zeolite NaY sorbent followed by HPLC-PDA. For this purpose, an aliquot of 7.00 mL of aqueous carbamate standard or sample solution was added to a 15 mL centrifuge tube containing 40 mg of CTAB-modified zeolite NaY sorbent. A suspension was formed. The mixture was then placed in a vortex mixer for 2 min to enhance the sorption of the target analytes onto the sorbent. After that, the mixture was filtered using a 0.45 μm nylon membrane syringe filter. The carbamate pesticides adsorbed on the solid sorbent were subsequently eluted by 500 μL of methanol. The eluate was evaporated to dryness under the nitrogen stream. The residue was dissolved in 100 μL of methanol before being injected into HPLC for analysis. Preparation of Samples. The natural surface water sample was taken from the lake in Khon Kaen province, Northeastern Thailand, and was sequentially filtered through a 0.45 μm nylon membrane filter before analysis. Fruit (watermelon, dragon fruit, rambutan, and grape) and vegetable (cucumber, cabbage, and cauliflower) samples were purchased from local markets in Khon Kaen province. The samples were cleaned, peeled, and cut into small pieces. They then were homogenized using a commercial food mixer. A representative sample portion of 7.0 g was

subsequent desorption using a suitable solvent. Recently, dispersive micro-solid phase extraction (D-μ-SPE) has been reported as a miniaturized mode of DSPE based on using the micro amounts of solid sorbent. In the D-μ-SPE procedure, the solid sorbent is added directly to a sample solution, and the extraction process relies solely upon shaking and centrifugation.20 Therefore, this procedure requires the use of highly efficient sorbent materials to maintain or even improve the preconcentration of the analytes using only a few milligrams of solid phase. Different sorbent materials have been employed with D-μ-SPE for preconcentration of a variety of analytes, such as single-walled carbon nanohorns (SWNHs) as sorbent for D-μSPE of triazines from waters,21 a polymer cation exchange sorbent for adsorption of morpholine residues in citrus and apple samples,20 and graphene oxide for preconcentration of nicotine from biological and environmental water samples.22 In addition, nanomaterials are also introduced for application as effective sorbent in such process. These include application of zein nanoparticles for extraction of chlorophenols,23 tetraethylenepentamine-functionalized Fe3O4 magnetic polymer nanomaterials for analysis of phenolic environmental estrogens,24,25 and NiZn:S nanoparticles loaded on activated carbon (NiZn:S-AC) for extraction of carbofuran and propoxur in aqueous media.6,26 Concerning the sorbent-based extraction, the choice of sorbent is the main key point because it controls the analytical performance, such as selectivity, affinity, and the capacity of the method. In the past few years, much research contributed to the area of sample preparation has been with respect to the discovery and the application of novel materials as sorbents for analyte extraction. The impact of material chemistry in chemical analysis cannot be overemphasized. Further investigation of new materials with promising structural and chemical reactive properties is increasingly interested for sample preparation technology. Our research group investigated the efficiency of different surfactant-modified sorbents to the preconcentration of carbamate pesticides.27 To date, zeolite NaY modified with cetyltrimethylammonium bromide (CTAB) was investigated as the sorbent for extraction/preconcentration of carbamate pesticides using an online SPE-HPLC system.28 The modified sorbent presented admicelles of CTAB on its surfaces and could be reused for at least five extraction cycles. However, the online system was quite complicated, and the SPE cartridge was necessary for packing the solid sorbent. In addition, a large amount of CTAB-modified zeolite NaY (100 mg) was required. Therefore, further development of the simple extraction procedure using a less amount of the solid sorbent is of great interest. In this work, we proposed, for the first time, the vortex-assisted dispersive micro-solid phase extraction (VA-D-μ-SPE) for sample preparation of carbamate pesticides prior to HPLC determination. The method was based on the application of CTAB-modified zeolite NaY sorbent following its dispersion in sample solution by vortex agitation to enhance the extraction efficiency and facilitate the fast extraction process. Experimental parameters, which effected the extraction efficiency, were evaluated systematically. Applicability of the proposed methodology has been investigated in water, fruit, and vegetable juice samples.

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MATERIALS AND METHODS

Chemicals and Reagents. Analytical standard grade carbamate pesticides, including oxamyl (OXM), methomyl (MTM), aldicarb (ADC), propoxur (PPX), bendiocarb (BDC), carbaryl (CBR), B


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Journal of Agricultural and Food Chemistry placed in a 15 mL centrifugation tube and mixed with 10 mL of 1% (v/v) acetic acid in acetonitrile. The mixture then was placed in vortex mixer for 1 min and centrifuged at 4000 rpm for 10 min. After that, anhydrous magnesium sulfate (2.0 g) and sodium acetate (0.4 g) were added. The tube was then centrifuged at 4000 rpm for 10 min. The supernatant was collected and evaporated to dryness at 45 °C. The residue was dissolved in water to the final volume of 7 mL before extraction by the proposed VA-D-μ-SPE procedure. Matrix-match calibration standard was prepared as the above-mentioned procedure, and followed by adding appropriate volumes of the standard solutions of carbamate pesticides before applying D-μ-SPE. Recovery study was also performed by spiking the standard solutions of carbamate pesticides into the homogenized samples.

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RESULTS AND DISCUSSION Separation of the Carbamate Pesticides and Analytical Performance. Under the HPLC condition described above, Figure 3. Effect of desorption solvent volume on the VA-D-μ-SPE of carbamate pesticides.

Figure 1. Effect of sorbent amount on the VA-D-μ-SPE of carbamate pesticides. Figure 4. Effect of vortex time on the VA-D-μ-SPE of carbamate pesticides.

observed in the concentration range of 0.1−70.0 mg L−1 with the coefficients of determination greater than 9907. The limits of detection (LODs) and limits of quantification (LOQs) were considered as the concentrations giving a signal-to-noise ratio of 3 and 10, respectively. The LODs and LOQs ranged from 0.1− 7.0 and 0.3−10.0 mg L−1, respectively. The precision of the method, expressed as the relative standard deviations (RSDs) of the retention time and peak area of the carbamates having the concentrations at LODs, was less than 2.6% and 4.2%, respectively. Optimization of the D-μ-SPE Procedure. Parameters affecting the extraction efficiency of the D-μ-SPE procedure, including sorbent amount, sample volume, vortex time, and desorption solvent volume, were optimized using a univariate method, and the peak area of the nine carbamate pesticides was used as the experimental response. All experiments were performed in triplicate. Effect of the Sorbent Amount. It is a primary consideration to study an appropriate amount of solid sorbent on the extraction efficiency of the VA-D-μ-SPE procedure; therefore, different amounts of CTAB-modified zeolite NaY sorbent in the range of 5−60 mg were investigated, using a sample volume of 1.0 mL, a

Figure 2. Effect of sample volume on the VA-D-μ-SPE of carbamate pesticides.

separation of nine carbamate pesticides was achieved within 22 min, with the following order of elution: OXM (tR = 2.2 min), MTM (tR = 2.9 min), ADC (tR = 8.3 min), PPX (tR = 11.4 min), BDC (tR = 12.7 min), CBR (tR = 16.7 min), IPC (tR = 17.9 min), MTC (tR = 20.8 min), and PMC (tR = 21.2 min). Linearity was C


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Table 1. Analytical Characteristics of the Proposed VA-D-μ-SPE and HPLC Procedures for the Determination of Carbamates intraday precision (%RSD)

interday precision (%RSD)

carbamate

linear range (mg kg−1)

coefficient of determination (R2)

LOD (mg kg−1)

LOQ (mg kg−1)

tR

peak area

tR

peak area

EF

OXM MTM ADC BDC CBR IPC MTC PMC

0.100−20.000 0.100−20.000 4.000−24.000 0.200−20.000 0.004−6.000 0.200−16.000 0.004−6.000 0.050−5.000

0.9989 0.9991 0.9946 0.9971 0.9996 0.9946 0.9964 0.9984

0.100 0.100 4.000 0.200 0.004 0.020 0.004 0.050

0.200 0.500 5.000 0.400 0.015 0.500 0.015 0.100

0.5 0.5 0.5 1.1 0.2 0.2 0.2 0.3

12.9 18.2 6.3 6.2 10.4 8.4 12.4 20.3

0.7 0.7 0.5 1.1 0.2 0.2 0.2 0.2

13.9 10.2 11.7 6.7 11.2 17.8 11.4 17.9

1 2 11 34 14 16 18 12

sorbent was sufficient for effective extraction and was used in the subsequent studies. Effect of Sample Volume. The sample volume is important in the VA-D-μ-SPE process because it determines the loading capacity of the sorbent. To evaluate this effect, the standard solution of 2.0 mg L−1 OXM and MTM, 5.0 mg L−1 ADC, IPC, MTC, and PMC, 10.0 mg L−1 PPX, 15.0 mg L−1 BDC, and 0.5 mg L−1 CBR was investigated. The sample volume between 1− 10 mL was evaluated using the sorbent amount of 40 mg, vortex agitation for 2 min, and 200 μL of methanol as desorption solvent. The eluate was evaporated to dryness under the nitrogen stream. The residue was dissolved in 100 μL of methanol before being injected into HPLC. The results indicated in Figure 2 demonstrated that the highest peak areas were obtained using the sample volume of 7 mL; above this volume there was a negative deviation. Taking into account these findings, the sample volume of 7.0 mL was selected for further experiments. Effect of Desorption Solvent Volume. According to our previous work, methanol was found to be an appropriate desorption solvent for eluting the carbamate pesticides from the CTAB-modified zeolite NaY sorbent.27 Therefore, in the present work, methanol was adopted as desorption solvent in VA-D-μSPE. Using the mixed standard solution of 2.0 mg L−1 OXM and MTM, 5.0 mg L−1 ADC, IPC, MTC, and PMC, 10.0 mg L−1 PPX, 15.0 mg L−1 BDC, and 0.5 mg L−1 CBR, the volume of methanol needed to obtain quantitative desorption of the target analytes was investigated in the range of 100−2000 μL. Other parameters were kept as follows: sorbent amount, 40 mg; sample volume, 7.0 mL; vortex time, 2 min. The eluate was evaporated to dryness under the nitrogen stream. The residue was dissolved in 200 μL of methanol before being injected into HPLC. As illustrated in Figure 3, the peak area of most studied carbamate pesticides increased with increasing the volume of methanol from 100−500 μL and remained almost constant afterward.

Figure 5. Chromatograms of the carbamate pesticides obtained by direct HPLC and concentrated by VA-D-μ-SPE method. Peak assignment: 1, OXM (2.0 mg L−1); 2, MTM (2.0 mg L−1); 3, ADC (5.0 mg L−1); 4, PPX (7.0 mg L−1); 5, BDC (10.0 mg L−1); 6, CBR (0.5 mg L−1); 7, IPC (5.0 mg L−1); 8, MTC (5.0 mg L−1); 9, PMC (5.0 mg L−1).

vortex time of 2 min, and 200 μL of methanol as desorption solvent. The eluate was evaporated to dryness under the nitrogen stream. The residue was dissolved in 100 μL of methanol before being injected into HPLC for analysis. A mixed standard solution of the target analytes at the concentrations of 5.0 mg L−1 OXM and MTM, 10.0 mg L−1 ADC, IPC, MTC, and PMC, 20.0 mg L−1 PPX, 30.0 mg L−1 BDC, and 3.0 mg L−1 CBR was investigated. As might be expected, the peak areas of the carbamate pesticides increased as the amount of sorbent increased from 5 to 40 mg (see Figure 1). Further increasing the amount of CTAB-modified zeolite NaY did not lead to any further increase in peak areas. Therefore, for the studied concentration ranges, 40 mg of solid Table 2. Determination of Carbamate Residues in Real Samplesa

amount found (mg kg−1) sample waterb cabbage cauliflower cucumber dragon fruit rambutan watermelon grape a

OXM

MTM

0.02

1.93

ADC

BDC

4.48

CBR

IPC

0.01 0.03 0.03

2.46

MTC

PMC

3.39 17.64

0.07 0.04

0.68

Empty cell represents not detected. bConcentration unit: mg L−1. D


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Journal of Agricultural and Food Chemistry Table 3. Recoveries of the Carbamate Pesticides from Real Samples Using the Proposed VA-D-μ-SPE Procedure OXM sample watera

cabbage

cauliflower

cucumber

dragon fruit

rambutan

watermelon

grape

sample watera

cabbage

cauliflower

cucumber

dragon fruit

rambutan

watermelon

grape

a

spiked (mg kg−1) 0.20 3.00 5.00 1.00 3.00 5.00 1.00 3.00 10.00 1.00 3.00 5.00 1.00 3.00 5.00 1.00 3.00 8.00 1.00 3.00 10.00 1.00 3.00 10.00

recovery (%) 105.0 107.2 107.2 91.0 80.7 90.3 91.8 100.0 104.1 95.0 99.0 95.6 96.9 92.4 90.6 106.3 108.4 99.2 83.5 83.1 83.0 113.0 88.0 100.7 CBR

MTM RSD (%)

spiked (mg kg−1)

4.9 3.6 8.4 6.0 2.0 5.8 3.1 14.3 6.7 0.6 0.3 1.0 2.3 15.7 14.9 11.2 10.1 3.2 0.3 2.4 2.8 5.9 4.3 1.5

1.00 5.00 10.00 2.00 4.00 7.00 2.00 4.00 10.00 2.00 4.00 10.00 2.00 5.00 10.00 2.00 5.00 8.00 2.00 5.00 10.00 2.00 5.00 10.00

ADC

recovery (%) 85.3 85.6 90.8 97.8 83.0 94.2 94.7 102.7 97.8 93.7 97.3 103.9 95.5 93.5 95.3 90.6 98.8 83.5 89.0 97.8 88.5 90.0 100.0 110.5 IPC

RSD (%)

spiked (mg kg−1)

8.1 2.8 5.9 8.9 9.5 5.3 5.5 1.0 3.1 6.2 15.5 3.4 1.5 11.0 4.5 6.6 7.9 7.1 5.3 1.9 1.9 10.5 5.6 11.3

6.00 8.00 10.00 5.00 7.00 10.00 5.00 7.00 10.00 5.00 7.00 10.00 5.00 7.00 10.00 5.00 7.00 10.00 5.00 7.00 10.00 5.00 7.00 10.00

recovery (%) 89.7 79.5 85.4 120.6 115.7 117.2 96.4 97.4 108.7 99.7 100.9 94.7 88.6 91.2 109.8 84.3 95.3 89.5 97.0 97.1 90.7 86.4 118.9 102.0 MTC

BDC RSD (%)

spiked (mg kg−1)

8.8 4.2 5.2 10.6 12.4 11.9 8.2 3.1 0.1 14.3 6.2 2.3 1.5 3.9 3.8 10.8 3.1 10.4 7.8 2.1 5.8 5.8 0.8 2.4

0.40 5.00 10.00 1.00 3.00 10.00 1.00 3.00 10.00 1.00 3.00 10.00 1.00 3.00 10.00 1.00 3.00 10.00 1.00 3.00 10.00 1.00 3.00 10.00

recovery (%) 82.5 83.0 79.6 110.0 100.0 115.7 87.2 108.1 105.5 113.0 99.7 89.3 101.0 99.2 93.7 92.4 106.5 103.4 91.5 97.3 97.7 107.0 108.0 113.6 PMC

RSD (%) 2.4 3.6 1.9 6.4 12.8 9.4 4.5 2.5 1.2 9.2 2.5 4.8 3.0 10.0 4.8 5.7 6.9 4.4 8.0 4.7 0.5 1.5 4.4 3.4

spiked (mg kg−1)

recovery (%)

RSD (%)

spiked (mg kg−1)

recovery (%)

RSD (%)

spiked (mg kg−1)

recovery (%)

RSD (%)

spiked (mg kg−1)

recovery (%)

RSD (%)

0.07 0.10 1.00 0.05 0.10 0.50 0.05 0.10 1.00 0.05 0.10 1.00 0.05 0.30 1.00 0.20 1.00 2.00 0.10 0.50 1.00 0.10 0.50 2.00

104.3 81.1 109.0 106.0 83.0 97.1 92.5 104.0 113.4 92.6 114.0 93.4 86.0 88.3 117.0 100.4 88.4 81.5 107.0 116.0 83.3 106.0 124.0 100.0

5.1 0.8 6.2 2.1 3.5 1.6 0.9 3.3 0.7 8.3 4.1 1.5 2.2 1.7 2.9 8.9 1.8 3.8 5.5 2.3 7.4 10.4 2.2 1.5

0.30 2.00 5.00 2.00 3.00 5.00 2.00 3.00 10.00 2.00 3.00 5.00 2.00 4.00 10.00 2.00 4.00 10.00 2.00 3.00 7.00 2.00 3.00 7.00

99.6 94.5 79.9 106.7 96.7 97.85 104.1 98.0 103.0 104.8 99.6 117.2 92.0 90.4 94.0 118.2 109.3 119.4 88.0 108.3 82.3 116.0 95.0 104.4

5.3 9.2 2.2 9.2 0.8 5.8 3.9 6.4 8.1 7.2 1.2 4.7 7.2 3.7 3.7 4.1 12.4 3.0 9.1 3.2 4.4 7.7 12.7 3.0

0.50 2.00 5.00 2.00 5.00 15.00 1.00 3.00 7.00 1.00 3.00 5.00 2.00 4.00 7.00 2.00 4.00 7.00 1.00 4.00 7.00 1.50 4.00 7.00

118.0 115.5 104.8 86.0 96.4 81.9 92.3 94.6 110.3 84.5 86.0 108.0 96.3 106.8 99.0 80.5 109.6 114.6 107.0 83.9 82.9 100.7 121.0 96.6

3.4 12.6 8.8 3.6 1.2 2.6 0.9 1.1 6.4 6.7 8.2 1.7 1.7 3.3 4.0 11.2 6.3 4.2 4.6 11.9 1.7 6.4 0.4 1.2

0.50 2.00 5.00 2.00 5.00 15.00 1.00 3.00 7.00 1.00 3.00 7.00 2.00 4.00 7.00 2.00 4.00 7.00 1.00 4.00 7.00 1.00 4.00 7.00

81.4 84.7 80.2 96.5 87.5 92.5 93.1 92.0 100.9 85.0 91.3 95.8 90.0 81.0 99.2 115.9 103.2 89.2 93.9 83.8 87.7 89.0 119.5 116.4

6.6 8.4 1.1 14.3 3.8 2.4 12.3 4.9 6.5 9.4 9.4 1.4 10.7 5.3 10.5 8.7 5.7 13.2 7.6 1.6 0.9 4.3 3.0 1.3

Concentration unit: mg L−1.

Therefore, 500 μL of methanol was selected for further optimization of the next experimental variables. Effect of Vortex Time. In the present work, the vortex was selected for agitation during the extraction step to enhance the extraction efficiency as it provided vigorous stirring of the sample

and the sorbent. The effect of vortex time was evaluated in the range from 0 to 10 min using the sorbent amount of 40 mg, sample volume of 7.0 mL, and 500 μL of methanol as desorption solvent. The eluate was evaporated to dryness under the nitrogen stream. The residue was dissolved in 100 μL of methanol before E


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for 2 min. Further agitation did not contribute to any improvement of the peak area. Therefore, 2 min vortex was selected for the VA-D-μ-SPE process. Analytical Performance of the Proposed VA-D-μ-SPE Procedure. Under the above-mentioned selected conditions, calibration graphs of the target carbamates have a linear response in the concentration range of 0.004−24.000 mg kg−1 with the coefficient of determination (R2) greater than 0.9946. LODs and LOQs were attained in the range of 0.004−4.000 and 0.015− 5.000 mg kg−1, respectively. The obtained intraday repeatability expressed as the RSDs from six replicate determinations of standard solution (at LOD concentrations) was less than 1.1% and 20.3% for retention time and peak area, respectively. The interday experiments (n = 3 × 3) showed the RSDs of the retention time and peak area of less than 1.1% and 17.9%, respectively. The enrichment factors were calculated as a ratio of slopes of the calibration graphs obtained from the proposed VAD-μ-SPE and direct HPLC analysis, and were found to be up to 34. The analytical characteristics of the proposed method are summarized in Table 1. Chromatograms of carbamate pesticides obtained from direct HPLC and concentrated by the proposed VA-D-μ-SPE procedures are presented in Figure 5. Application to Real Samples. To evaluate the feasibility and applicability, the developed VA-D-μ-SPE procedure was applied for the determination of carbamate residues in real samples, including natural surface water, fruits (dragon fruit, rambutan, grape, and watermelon), and vegetables (cabbage, cauliflower, and cucumber). To compensate the matrix artifacts, the matrix-matched calibration standard curves were performed for real sample determinations. The analytical data are summarized in Table 2. No carbamate pesticide was detected in the water sample. Some carbamate residues including ADC, BDC, and MTC were not found in all studied samples. OXM, MTM, CBR, and IPC were found in the range of 0.01−4.48 mg kg−1 in vegetables. In fruit samples, OXM, MTM, CBR, and PMC were found to be contaminated in the range of 0.04−17.64 mg kg−1. The highest contamination was observed in watermelon sample, which was contaminated by MTM at 17.64 mg kg−1. Unfortunately, PPX could not be determined in all of the studied samples because of low detection property and high matrix effect. The method LOQs for carbamates in the studied fruit and vegetable samples are as follows: OXM, 0.13−8.32 mg kg−1; MTM, 0.21−4.38 mg kg−1; ADC, 0.91−4.63 mg kg−1; BDC, 0.90−0.14 mg kg−1; CBR, 0.02−0.15 mg kg−1; IPC, 0.98−1.87 mg kg−1; MTC, 0.05−1.03 mg kg−1; PMC, 0.63−1.27 mg kg−1. In this work, the method LOQ values were lower than the concentrations found in fruit and vegetable samples. Therefore, the proposed procedure has been successfully utilized in the determination of carbamate residues in fruit and vegetable samples. For application in water sample with trace contamination below the LOQs, an additional sample preconcentration step may be required. To evaluate the accuracy of the method, the relative recovery was tested by spiking carbamate standard solutions at three concentration levels (depending on the analyte) into the samples. The recoveries of the target analytes ranged from 79.5% to 124.0%, with the RSDs between 0.1% and 15.7%. The results are summarized in Table 3. The obtained recoveries were acceptable for analyses of environmental samples and agricultural products. Figures 6 and 7 show the typical chromatograms of water and watermelon extract samples, respectively. Comparison of the VA-D-μ-SPE to Other Methods. The developed VA-D-μ-SPE procedure for analysis of carbamate

Figure 6. Typical chromatograms of blank and spiked natural surface water sample: (a) sample blank; (b) spiked by 0.20 mg L−1 OXM, 1.00 mg L−1 MTM, 6.00 mg L−1 ADC, 0.40 mg L−1 BDC, 0.07 mg L−1 CBR, 0.30 mg L−1 IPC, and 0.50 mg L−1 MTC and PMC; (c) spiked by 3.00 mg L−1 OXM, 5.00 mg L−1 MTM and BDC, 8.00 mg L−1 ADC, 0.10 mg L−1 CBR, and 2.00 mg L−1 IPC, MTC, and PMC; and (d) spiked by 5.00 mg L−1 OXM, 10.00 mg L−1 MTM, ADC, and BDC, 1.00 mg L−1 CBR, and 5.00 mg L−1 IPC, MTC, and PMC. Peak assignment: as described in Figure 5.

Figure 7. Typical chromatograms of blank and spiked watermelon extract sample: (a) sample blank; (b) spiked by 1.00 mg L−1 OXM, 2.00 mg L−1 MTM and IPC, 5.00 mg L−1 ADC, 1.00 mg L−1 BDC, MTC, and PMC, 0.10 mg L−1 CBR; (c) spiked by 3.00 mg L−1 OXM and BDC, 5.00 mg L−1 MTM, 7.00 mg L−1 ADC, 0.50 mg L−1 CBR, and 4.00 mg L−1 MTC and PMC; and (d) spiked by 10.00 mg L−1 OXM, MTM, ADC, and BDC, 1.00 mg L−1 CBR, and 7.00 mg L−1 IPC, MTC, and PMC. Peak assignment: as described in Figure 5.

being injected into HPLC. The mixed standard solution of 2.0 mg L−1 OXM and MTM, 5.0 mg L−1 ADC, IPC, MTC, and PMC, 10.0 mg L−1 PPX, 15.0 mg L−1 BDC, and 0.5 mg L−1 CBR was determined. The obtained results are displayed in Figure 4. It could be seen that a fast achievement of the extraction equilibrium was obtained within 2 min using vortex agitation. This could be due to the large contact area between the dispersed CTAB-modified zeolite NaY sorbents and the aqueous sample solution. As compared to the results obtained from the experiment without vortex process, the extraction efficiency in term of peak area increased significantly in case of using vortex F


Article


Table 4. Comparison of VA-D-μ-SPE to Other Microextraction Procedures for Carbamate Determination in Food Samples methodref VA-D-μ-SPE (this study) carbon nanotubes-reinforced hollow fiber SPME10 magnetic solid-phase extraction using graphene grafted silica-coated Fe3O4 nanocomposite8 sequential injection-bead injection-lab-onvalve using Lichroprep RP-18 beads30 magnetic stirring-assited dispersive liquid− liquid microextraction11 LLME using [C4MIM][PF6] roomtemperature ionic liquid31 ultrasound-assisted mixed anionic−cationic surfactant-enhanced emulsification microextraction32

analytes

samples

0.004−24.000 mg kg−1

0.004−4.000 mg kg−1

1−1000 ng g−1

cucumber, pear

0.5−100 ng g−1

0.09−6.00 ng g−1 0.08−0.2 ng g−1

methomyl, propoxur, carbofuran, carbaryl, isoprocarb, methiocarb, promecarb carbofuran, carbaryl, isocarbophos

watermelon, guava, cowpea, cabbage, water

5−12 000 μg L−1

1−20 μg L−1

tea drinks

1−1000 μg L−1

methomyl, propoxur, carbofuran, carbaryl, isoprocarb, methiocarb, promecarb carbofuran, carbaryl, isoprocarb, methiocarb, promecarb

watermelon, cantaloupe, strawberry, orange, apple, water fruit juices, water

0.1−15.0 μg mL−1

0.13−0.61 μg L−1 2−40 μg mL−1

2−5000 μg L−1

0.1−5.0 μg L−1

http://www.acfs.go.th/standard/download/MAXIMUM_RESIDUE_ LIMITS_new.pdf (accessed November 7, 2015). (6) Khodadoust, S.; Talebianpoor, M. S.; Ghaedi, M. Application of an optimized dispersive nanomaterial ultrasound-assisted microextraction method for preconcentration of carbofuran and propoxur and their determination by high-performance liquid chromatography with UV detection. J. Sep. Sci. 2014, 37, 3117−3124. (7) Basheer, C.; Alnedhary, A. A.; Rao, B. S. M.; Lee, H. K. Determination of carbamate pesticides using micro-solid-phase extraction combined with high-performance liquid chromatography. J. Chromatogr. A 2009, 1216, 211−216. (8) Sun, M.; Ma, X.; Wang, J.; Wang, W.; Wu, Q.; Wang, C.; Wang, Z. Graphene grafted silica-coated Fe3O4 nanocomposite as absorbent for enrichment of carbamates from cucumbers and pears prior to HPLC. J. Sep. Sci. 2013, 36, 1478−1485. (9) Vera-Avila, L. E.; Márquez-Lira, B. P.; Villanueva, M.; Covarrubias, R.; Zelada, G.; Thibert, V. Determination of carbofuran in surface water and biological tissue by sol-gel immunoaffinity extraction and on-line preconcentration/HPLC/UV analysis. Talanta 2012, 88, 553−560. (10) Song, X.-Y.; Shi, Y.-P.; Chen, J. Carbon nanotubes-reinforced hollow fibre solid-phase microextraction coupled with high performance liquid chromatography for the determination of carbamate pesticides in apples. Food Chem. 2013, 139, 246−252. (11) Wang, X.; Cheng, J.; Zhou, H.; Wang, X.; Cheng, M. Development of a simple combining apparatus to perform a magnetic stirring-assisted dispersive liquid-liquid microextraction and its application for the analysis of carbamate and organophosphorus pesticides in tea drinks. Anal. Chim. Acta 2013, 787, 71−77. (12) El Atrache, L. L.; Sghaier, R. B.; Kefi, B. B.; Haldys, V.; Dachraoui, M.; Tortajada, J. Factorial design optimization of experimental variables in preconcentration of carbamates pesticides in water samples using solid phase extraction and liquid chromatography-electrospray-mass spectrometry determination. Talanta 2013, 117, 392−398. (13) Moreno-González, D.; Huertas-Pérez, J. F.; Garcia-Campana, A. M.; Bosque-Sendra, J. M.; Gamiz-Gracia, L. Ultrasound-assisted surfactant-enhanced emulsification microextraction for the determination of carbamates in wines by ultra-high performance liquid chromatography−tandem mass spectrometry. J. Chromatogr. A 2013, 1315, 1−7. (14) Anastassiades, M.; Lehotay, S. J.; Štajnbaher, D.; Schenck, F. J. Fast and easy multiresidue method employing acetonitrile extraction/ partitioning and “dispersive solid-phase extraction” for the determination of pesticide residues in produce. J. AOAC Int. 2003, 86, 412−431. (15) Fu, M.; Xing, H.; Chen, X.; Chen, F.; Wu, C.-M. L.; Zhao, R.; Cheng, C. Ultrathin-shell boron nitride hollow spheres as sorbent for dispersive solid-phase extraction of polychlorinated biphenyls from environmental water samples. J. Chromatogr. A 2014, 1369, 181−185. (16) Tang, S.; Lee, H. K. Application of dissolvable layered double hydroxides as sorbent in dispersive solid-phase extraction and extraction

AUTHOR INFORMATION

Corresponding Author

*Tel.: +66 4300 9700, ext 42174. Fax: +66 4320 2373. E-mail: [email protected]. Funding

The Thailand Research Fund and Khon Kaen University are acknowledged for supporting the TRF Research Scholar to R. Burakham (Grant no. RSA5580004). We gratefully acknowledge the partial support for this research from the Center for Innovation in Chemistry (PERCH-CIC), Commission on Higher Education, Ministry of Education, and Materials Chemistry Research Center, Khon Kaen University. R.B. and P.A. also gratefully acknowledge financial support from the Royal Golden Jubilee (RGJ) Ph.D. program (Grant no. PHD/0082/ 2554). Notes

The authors declare no competing financial interest.

■

LODs

fruits (dragon fruit, rambutan, watermelon), vegetables (cabbage, cauliflower, cucumber), water apple

residues was compared to different microextraction methods, as summarized in Table 4. The sensitivity of the proposed method in term of LODs is almost comparable to that obtained from other microextraction methods. The presented method achieves low LODs, which are below the MRLs of the carbamate residues in agricultural products.5 The better linear range for the determination of a variety of carbamate residues was obtained using the VA-D-μ-SPE. The developed microextraction technique exhibits good extraction efficiency for the studied analytes under the simple operation process without the need of additional centrifugation, and offers advantages in terms of the number of carbamates analyzed.

■

linear range

oxamyl, methomyl, aldicarb, propoxur, bendiocarb, carbaryl, isoprocarb, methiocarb, promecarb carbofuran, carbaryl, isoprocarb, diethofencarb, methiocarb metolcarb, carbaryl, pirimicarb, diethofencarb

REFERENCES

(1) Santaladchaiyakit, Y.; Srijaranai, S.; Burakham, R. Methodologies aspects of sample preparation for the determination of carbamate residues: A review. J. Sep. Sci. 2012, 35, 2373−2389. (2) European Commission. Pesticide EU-MRLs Database Regulation (EC) No. 396/2005. http://www.ec.europa.eu/sanco_pesticides/ public/index.cfm (accessed November 7, 2015). (3) Health and Safety Executive. Maximum Residue Level (MRL) Database. https://secure.pesticides.gov.uk/MRLs/main.asp (accessed November 7, 2015). (4) United States Environmental Protection Agency. Regulation of Pesticide Residues on Food. http://www2.epa.gov/pesticide-tolerances (accessed November 7, 2015). (5) National Bureau of Agricultural Commodity and Food Standard. Thai Agricultural Standard. Pesticide residues: Maximum residue limits. G


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Journal of Agricultural and Food Chemistry by co-precipitation for the determination of aromatic acid anions. Anal. Chem. 2013, 85, 7426−7433. (17) Wen, Y.; Niu, Z.; Ma, Y.; Ma, J.; Chen, L. Graphene oxide-based microspheres for the dispersive solid-phase extraction of non-steroidal estrogens from water samples. J. Chromatogr. A 2014, 1368, 18−25. (18) Meng, L.; Chen, C.; Yang, Y. Suspension dispersive solid phase extraction for preconcentration and determination of cobalt, copper, and nickel in environmental water by flame atomic absorption spectrometry. Anal. Lett. 2015, 48, 453−463. (19) Tang, S.; Lin, X. H.; Li, S. F. Y.; Lee, H. K. In-syringe dispersive solid-phase extraction using dissolvable layered double oxide hollow spheres as sorbent followed by high-performance liquid chromatography for determination of 11 phenols in water. J. Chromatogr. A 2014, 1373, 31−39. (20) Chen, D.; Miao, H.; Zou, J.; Cao, P.; Ma, N.; Zhao, Y.; Wu, Y. Novel dispersive micro-solid-phase extraction combined with ultrahighperformance liquid chromatography-high-resolution mass spectrometry to determine morpholine residues in citrus and apples. J. Agric. Food Chem. 2015, 63, 485−492. (21) Jiménez-Soto, J. M.; Cárdenas, S.; Valcárcel, M. Dispersive micro solid-phase extraction of triazines from waters using oxidized singlewalled carbon nanohorns as sorbent. J. Chromatogr. A 2012, 1245, 17− 23. (22) Mahpishanian, S.; Sereshti, H. Graphene oxide-based dispersive micro-solid phase extraction for separation and preconcentration of nicotine from biological and environmental water samples followed by gas chromatography-flame ionization detection. Talanta 2014, 130, 71− 77. (23) Farhadi, K.; Matin, A. A.; Amanzadeh, H.; Biparva, P.; Tajik, H.; Farshid, A. A.; Pirkharrati, H. A novel dispersive micro solid phase extraction using zein nanoparticles as the sorbent combined with headspace solid phase micro-extraction to determine chlorophenols in water and honey samples by GC-ECD. Talanta 2014, 128, 493−499. (24) Zhao, Y.-G.; Chen, Z.-H.; Pan, S.-D.; Zhu, H.; Shen, H.-Y.; Jin, M.C. Simultaneous analysis of eight phenolic environmental estrogens in blood using dispersive micro-solid-phase extraction combined with ultra fast liquid chromatography-tandem mass spectrometry. Talanta 2013, 115, 787−797. (25) Asgharinezhad, A. A.; Mollazadeh, N.; Ebrahimzadeh, H.; Mirbabaei, F.; Shekari, N. Magnetic nanoparticles based dispersive micro-solid-phase extraction as a novel technique for coextraction of acidic and basic drugs from biological fluids and waste water. J. Chromatogr. A 2014, 1338, 1−8. (26) Li, N.; Zhang, L.; Nian, L.; Cao, B.; Wang, Z.; Lei, L.; Yang, X.; Sui, J.; Zhang, H.; Yu, A. Dispersive micro-solid-phase extraction of herbicides in vegetable oil with metal-organic framework MIL-101. J. Agric. Food Chem. 2015, 63, 2154−2161. (27) Arnnok, P.; Burakham, R. Retention of carbamate pesticides by different surfactant-modified sorbents: A comparative study. J. Braz. Chem. Soc. 2014, 25, 1720−1729. (28) Arnnok, P.; Patdhanagul, N.; Burakham, R. An on-line admicellar SPE-HPLC system using CTAB-modified zeolite NaY as sorbent for determination of carbamate pesticides in water. Chromatographia 2015, 21−22, 1327−1337. (29) Patdhanagul, N.; Srithanratana, T.; Rangsriwatananon, K.; Hengrasamee, S. Ethylene adsorption on cationic surfactant modified zeolite NaY. Microporous Mesoporous Mater. 2010, 131, 97−102. (30) Vichapong, J.; Burakham, R.; Srijaranai, S.; Grudpan, K. Sequential injection-bead injection-lab-on-valve coupled to highperformance liquid chromatography for online renewable micro-solidphase extraction of carbamate residues in food and environmental samples. J. Sep. Sci. 2011, 34, 1574−1581. (31) Vichapong, J.; Burakham, R.; Srijaranai, S.; Grudpan, K. Room temperature imidazolium ionic liquid: A solvent for extraction of carbamates prior to liquid chromatographic analysis. Talanta 2011, 84, 1253−1258. (32) Vichapong, J.; Burakham, R. Novel ultrasound-assisted mixed anionic-cationic surfactant-enhanced emulsification microextraction

combined with HPLC for the determination of carbamate pesticides. Anal. Methods 2012, 4, 2101−2108.

H


Vortex-Assisted Dispersive Micro-Solid Phase Extraction Using CTAB

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