Pesticides In Vegetable Samples Research Articles

Advanced QuEChERS Method Using Core-Shell Magnetic Molecularly Imprinted Polymers (Fe3O4@MIP) for the Determination of Pesticides in Chlorophyll-Rich Samples.

Graphitized carbon black (GCB) in the traditional QuEChERS (quick, easy, cheap, effective, rugged, and safe) method was used to remove the interfering substance chlorophyll in vegetable and fruit samples for pesticide residues determination. However, it not only adsorbs pigments, but also adsorbs some planar and aromatic pesticides. In order to solve the shortcoming, a core-shell magnetic molecularly imprinted polymer (Fe3O4@MIP) that can specifically recognize and adsorb chlorophyll was synthesized, and an advanced QuEChERS method with the Fe3O4@MIP as a purification material was developed. This advanced method presents detection that is highly sensitive, specific, and reproducible for planar and aromatic pesticides. The limits of detection (LOD) ranged from 0.001-0.002 mg kg-1, and the limit of quantification (LOQ) was 0.005 mg kg-1. The recovery for the planar and aromatic pesticides was within 70-110% with the associated relative standard deviations < 15% in leek samples by the advanced QuEChERS method. However, in the traditional QuEChERS method with GCB, the recovery of most planar and aromatic pesticides was <60%. It may also be useful for the determination of other pesticides in vegetable samples with quick and easy sample purification.

Exploring a novel silicone surfactant-based deep eutectic solvent functionalized magnetic iron particles for the extraction of organophosphorus pesticides in vegetable samples

The current study discussed the use of silicone surfactant-based deep eutectic solvent as a surface modifier for magnetic iron particles (Fe3O4) to produce a novel adsorbent and its application for the extraction of organophosphorus pesticides (OPPs) in vegetable samples. A deep eutectic solvent (DES) was prepared using low toxic and inexpensive substances such as silicone surfactant (SS) and dodecanoic acid (DoAc). This new eco-friendly SS:DoAc based DES was explored as a substitution to traditional organic reagents for surface modification of Fe3O4 to increase the adsorption capacity and to reduce the matrix interferences, hazardous waste generation and environmental pollution. The newly synthesized SS:DoAc@Fe3O4 adsorbent was successfully characterized and applied in magnetic solid phase extraction (MSPE). Under optimized conditions, the proposed approach exhibited excellent linearity ranging from 0.1 to 200 µg/kg (R2 ≥ 0.9970), low detection limit (0.03–0.1 µg/kg) and acceptable relative recovery (80–119 %) for the studied OPPs.

Distribution of Pesticides in Different Commonly Grown Vegetables of Cameron Highlands, Pahang, Malaysia

Gas chromatography-electron capture detector (GC-ECD) is used to extract and analyse pesticides in vegetable samples collected from Cameron Highlands, Pahang, Malaysia. The limit of detection (LOD) for all pesticides was in the range of 0.03 to 4.5 ng g-1. Recoveries in cabbage, lettuce, and celery ranged from 61.8%-121%, 60-128% and 60%-114%, respectively. The relative standard deviation (RSD) ranged 0.2-15% in cabbage, 0.5-18% in lettuce and 3-19.8% in celery. Organochlorine pesticides (OCPs) concentrations increased down the valley with dichlorodiphenyldichloroethylene (DDE) having the highest concentration at 233 µg kg-1. Organophosphorus pesticides (OPPs) were found to be dispersed throughout the valley, with the highest concentration of parathion ethyl (133 µg kg-1) whereas the pyrethroid pesticides (PYRs) concentrations were comparatively less. The detection frequency in the wet season was highest (5 &lt; - &lt; 100 µg kg-1) for most pesticides. However, in the dry season the pesticides concentrations were higher, at &lt; 5 µg kg-1. PCA analysis indicated that farmers were using a mixture of pesticides.

Residual Determination of Multiple Pesticides in Vegetable Samples by LC-MS/MS Coupled with Modified QuEChERS-dSPE Ionic Liquid-Based DLLME Method

As a matter of fact, the Dietary Guidelines of the United States of America recommended the consumption of more fruits and vegetables to support the healthy condition of the body. Unfortunately, these food materials are being accumulated with pesticidal residues due to the continuous miss-management and excessive application of the chemicals during pre and post-agricultural practices, which compels multiple analysis of pesticidal residues to know their concentration levels for the betterment of food security and safety. For that matter, multi-residues of Thiamethoxam, Propamocarb, Carbaryl, Metalaxyl, Baycarb, Thiobencarb, Diazinon, and Dursban pesticides were determined in the samples of lettuce, garlic, ginger, and bell-pepper using modified QuEChERS-dSPE Ionic Liquid-based dispersive liquid-liquid microextraction (DLLME) method coupled with LC-MS/MS instrument and validated (European Union Guideline). Resultantly, the accuracy (87-127%) and precision (0–22%) were mostly within the acceptable range for the former (70-120%) and latter (≤20%). Meanwhile, the limit of detections (0.01-0.28 µg/kg) and limit of quantitations (0.03-0.93 µg/kg) were satisfactory. The concentration range (5–400 µg/kg) of calibration curves for the evaluated linearity were linear with coefficient of regressions greater than 0.99. The matrix effects for all the analyzed samples were very weak and less effective (≤ -86%). The range (1–25%) for the estimated measurement uncertainties were certifiable and acceptable (≤ 50%). Therefore, the sample preparation method prove effective as validated and useful for the multiple determination of pesticides residues in the analyzed vegetable samples, which are presumably safe for consumption against health issues.

Multiresidue Pesticides Analysis of Vegetables in Vietnam by Ultrahigh-Performance Liquid Chromatography in Combination with High-Resolution Mass Spectrometry (UPLC-Orbitrap MS).

An ultrahigh-performance liquid chromatography in combination with high-resolution mass spectrometry Thermo Q-Extractive Focus Orbitrap MS has been introduced for analysis of multiclass pesticides in vegetable samples collected in Hanoi, Vietnam. Multiclass pesticides were separated on the Thermo Hypersil Gold PFP column utilizing a gradient of the mobile phase consisting of 5 mM ammonium formate, 0.1% formic acid in deionized water, and methanol. The target analytes were detected in the full-scan mode on Thermo Scientific Q-Exactive Focus Orbitrap MS for quantitation at the optimum operating conditions. These conditions included, but not limit to, the resolution of 70000 at the full width at half maximum in both positive and negative mode, mass range from 80 to 1000 m/z, and optimized parameters for the heated electrospray ionization source. The identification of the analytes in real samples was based on retention times, mass to charge ratios, mass accuracies, and MS/MS spectra at the confirmation mode with the inclusion list of target analytes. The mass accuracies of target analytes were from −4.14 ppm (dinotefuran) to 1.42 ppm (cinosulfuron) in the neat solvent and from −3.91 ppm (spinosad D) to 1.29 ppm (cinosulfuron) in the matrix-matched solution. Target analytes in the vegetable-based matrix were extracted by the QuEChERS method. Some critical parameters of the analytical method such as linearity, repeatability, limit of detection, and limit of quantitation have been evaluated and implemented. Excellent LOD and LOQ of the developed method were achieved at the range of 0.04–0.85 and 0.13–2.9 μg·kg−1, respectively. Intraday and interday repeatability of the analytical signal (peak area, n=6) of the developed method were below 3% and 10%, correspondingly. The matrix effect, extraction recovery, and overall recovery were fully investigated by spiking experiments. Experimental results demonstrated that the ionization suppression or enhancement was the main contribution on the overall recoveries of target analytes. Finally, the in-house validated method was applied to pesticides screening in vegetables samples in local villages in Hanoi, Vietnam. The concentrations of all target analytes were below limit of quantitation and lower than US-FDA or EU maximum residue levels.

Application of fabric phase sorptive extraction with gas chromatography and mass spectrometry for the determination of organophosphorus pesticides in selected vegetable samples.

In the present work, a high-efficiency and solvent minimized microextraction technique, fabric phase sorptive extraction followed by gas chromatography and mass spectrometry analysis is proposed for the rapid determination of four organophosphorus pesticides (terbufos, malathion, chlorpyrifos, and triazofos) in vegetable samples including beans, tomato, brinjal, and cabbage. Fabric phase sorptive extraction combines the beneficial features of sol-gel derived microextraction sorbents with the rich surface chemistry of cellulose fabric substrate, which collectively form a highly efficient microextraction system. Fabric phase sorptive extraction membrane, when immersed directly into the sample matrix, may extract target analytes even when high percentage of matrix interferents are present. The technique also greatly simplifies sample preparation workflow. Most important fabric phase sorptive extraction parameters were investigated and optimized. The developed method displayed good linearity over the concentration range 0.5-500ng/g. Under optimum experimental conditions, the limits of detection were found in the range of 0.033 to 0.136ng/g. The relative standard deviations for the extraction of organophosphorus pesticides were<5%. Subsequently, the new method was applied to beans, tomato, brinjal, and cabbage samples. The results from the real sample analysis indicate that the method is green, rapid, and economically feasible for the determination of organophosphorus pesticides in vegetable samples.

Determination of seven pyrethroid pesticide residues in vegetables by gas chromatography using carboxylated multi-walled carbon nanotubes as dispersion solid phase extraction sorbent

ABSTRACTA novel carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) dispersive solid phase extraction (d-SPE) method combined with gas chromatography (GC) with an electron capture detector (ECD) was developed for the determination of seven pyrethroid pesticides in cucumber, spinach, eggplant, tomato and carrot. We optimised d-SPE conditions including the type and volume of the extractant, the type and amount of the sorbent, and shaking time. Under the optimal conditions, the linear range was from 2.0 to 2000 μg kg−1. The recoveries were from 88.5% to 108.2%, with the corresponding RSDs <6%, correlation coefficients 0.9987–0.9998, LOD 0.5–2.9 μg kg−1 and LOQ 1.5–9.7 μg kg−1. The proposed method is simple, fast, and safe, with high recovery and sensitivity, and is applicable to analysis of pyrethroid pesticides in vegetable samples.

Successive monitoring surveys of selected banned and restricted pesticide residues in vegetables from the northwest region of China from 2011 to 2013

BackgroundA wide range of pesticides is applied for crop protection in vegetable cultivation in China. Regulation of pesticide maximum residue limits (MRLs) in vegetables is established but not fully enforced. And pesticide residues in vegetables were not well monitored. This study conducted the monitoring surveys from 2011 to 2013 to investigate the pesticides in vegetables in the northwest region of China.MethodsA multi-residue gas chromatography/mass spectrometry method (GC/MS) was used in determination of pesticides in vegetable samples. The χ2 test was used to compare the concentration of pesticide residues.ResultsA total of 32 pesticide residues were detected in 518 samples from 20 types of vegetables in this study. 7.7% of the detected pesticide residues exceeded the MRLs. The percentages of residues that exceeded the MRLs for leafy, melon and fruit, and root vegetables were 11.2%, 5.1%, and 1.6%, respectively. There was no seasonal difference in the proportion of samples that exceeded the MRLs in different vegetables. A total of 84.3% (27/32) pesticides were detected at concentrations that exceeded MRLs. And of the 27 pesticides that exceeded the MRLs, 11 (40.7%) were banned for use in agriculture. The most frequently detected pesticides were Malathion (9.4%), Dichlorvos (8.7%), and Dimethoate (8.1%).ConclusionThe observed high rate of pesticides detected and high incidence of pesticide detection exceeding their MRLs in the commonly consumed vegetables indicated that the Good Agricultural Practices (GAP) may not be well followed. The management of pesticide use and control should be improved. Well-developed training programs should be initiated to improve pesticide application knowledge for farmers.

Hydrophobic coating of polyaniline-poly(propylene oxide) copolymer for direct immersion solid phase microextraction of carbamate pesticides

A nanostructural polyaniline-poly(propylene oxide) (PANI-PPO) composite coating was electrochemically synthesized on a stainless steel wire, by using acidic ionic liquid 1-sulfobutyl-3-methylimidazolium hydrosulfate as supporting electrolyte. The coating showed strong hydrophobicity and allowed for the direct immersion solid-phase microextraction of carbamate pesticides (i.e. 2-(1-methylethoxy) phenyl methylcarbamate, m-tolyl-n-methylcarbamate, 2-(1-methylethyl) phenyl methylcarbamate, 2-(1-methylpropyl) phenol methylcarbamate and 2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) in complex matrices. Moreover, this coating could be used for at least 120 times of extraction. When it was coupled with gas chromatography for the determination of these carbamate pesticides the linear ranges were about 0.1–100μgL−1 and the detection limits were 0.012–0.048μgL−1. It also displayed acceptable repeatability and reproducibility. When a fiber was used for five successive measurements the relative standard deviations (RSDs) were smaller than 8.7%, and the RSDs for fiber-to-fiber were 5.7–12.9% (n=5). The practical feasibility of the proposed method was evaluated by determining carbamate pesticides in vegetable samples and the recoveries for standards added were 79.8–108.8%.

Determination of Carbamate and Organophosphorus Pesticides in Vegetable Samples and the Efficiency of Gamma-Radiation in Their Removal

In the present study, the residual pesticide levels were determined in eggplants (Solanum melongena) (n = 16), purchased from four different markets in Dhaka, Bangladesh. The carbamate and organophosphorus pesticide residual levels were determined by high performance liquid chromatography (HPLC), and the efficiency of gamma radiation on pesticide removal in three different types of vegetables was also studied. Many (50%) of the samples contained pesticides, and three samples had residual levels above the maximum residue levels determined by the World Health Organisation. Three carbamates (carbaryl, carbofuran, and pirimicarb) and six organophosphates (phenthoate, diazinon, parathion, dimethoate, phosphamidon, and pirimiphos-methyl) were detected in eggplant samples; the highest carbofuran level detected was 1.86 mg/kg, while phenthoate was detected at 0.311 mg/kg. Gamma radiation decreased pesticide levels proportionately with increasing radiation doses. Diazinon, chlorpyrifos, and phosphamidon were reduced by 40–48%, 35–43%, and 30–45%, respectively, when a radiation strength of 0.5 kGy was utilized. However, when the radiation dose was increased to 1.0 kGy, the levels of the pesticides were reduced to 85–90%, 80–91%, and 90–95%, respectively. In summary, our study revealed that pesticide residues are present at high amounts in vegetable samples and that gamma radiation at 1.0 kGy can remove 80–95% of some pesticides.

Analysis of 112 pesticide residues in vegetables using dispersive-solid phase extraction and gas chromatography-triple quadrupole mass spectrometry

A method was developed and validated for the simultaneous analysis of 112 pesticide residues in vegetables by gas chromatography coupled with triple quadrupole mass spectrometry (GC-QQQ-MS/MS). It is demonstrated that the optimized conditions could provide a more accurate quantitation and lower limit of quantification of the analysis by dispersive-solid phase extraction (D-SPE) cleanup. The samples were extracted with acetonitrile and toluene (8: 1, v/v), and cleaned up by D-SPE. To every 5 mL extraction solution, 0.8 g MgSO4, 0.05 g graphitized carbon black (GCB), 0.1 g ethylenediamine-N-propyl silyl (PSA) and 0.05 g C18 were added. The extracts were analyzed by GC-QQQ-MS/MS using internal standard method. The recoveries of the 112 pesticides at three spiked levels of 20, 50 and 200 microg/kg were ranged from 53.1% to 138.7%, and among which those of 86 pesticides were from 65.0% to 120.0%. The relative standard deviations (RSD) were less than 12%. The limits of quantifications (LOQs) (signal/noise at 10) were between 1.6 and 13.4 microg/kg. The vegetable samples collected from the market such as garlic chives, cucumber and purple cabbage were analyzed, and the residues of triazophos and fenpropathrin were detected in some of these samples. The method can be applied to the routine analysis for the determination of the 112 pesticides in vegetable samples.

A catalytic kinetic spectrophotometric determination of organophosphorus pesticides in vegetable samples

A simple selective and sensitive catalytic kinetic spectrophotometric method for the determination of trace amount of organophosphorus pesticides has been proposed. The method is based on the catalytic effect of organophosphorus pesticides (malathion, dimethoate and phorate) on the oxidation of LCV (leuco crystal violet) by potassium iodate in hydrochloric acid medium to give a violet colored dye. The dye shows maximum absorption at 592 nm. The fixed-time method was used for 15 min. The system obeys Beer’s law in the range of 0.02-0.2, 0.032-0.32 and 0.03-0.3 µg mL-1, for malathion, dimethoate, and phorate, respectively. Important analytical parameters such as time, temperature, reagent concentration, acidity etc, have been optimized for complete color reaction. Sandell’s sensitivity and molar absorptivity for the system were found to be 0.0002, 0.0004, 0.0004 µg cm-2 and 1.2 × 10(6), 5.21 × 10(5), 6.3 × 10(5) L mol-1cm-1, respectively. The proposed method was satisfactorily applied to micro-level determination of organophosphorus pesticides in vegetable samples.

Quantification of organophosphate insecticides and herbicides in vegetable samples using the “Quick Easy Cheap Effective Rugged and Safe” (QuEChERS) method and a high-performance liquid chromatography–electrospray ionisation–mass spectrometry (LC–MS/MS) technique

A Quick Easy Cheap Effective Rugged and Safe (QuEchERS) extraction was developed and followed by selective analysis using a liquid chromatography–mass spectrometry method for the quantification of eighteen pesticides in vegetable samples. This method was accurate (⩾99.5%), and it exhibited limits of detection and quantification values in the 0.006–0.091 and 0.020–0.314μgkg−1 ranges, respectively. Furthermore, the coefficients of variations (⩾0.9999) were less than 1% at the low μgkg−1 end of the method. Mean recoveries ranged between 94% and 102%, and relative standard deviations were below 10%. Based on these results, the methodology was proven to be highly efficient, robust, and suitable for monitoring the maximum residue limits (MRL) compliance of a wide range of commodity/pesticide combination. This method was successfully applied to the analysis of vegetable samples that were collected from different government farmers’ markets and street shops in urban areas. The presence of target pesticides was found in the range of 0.016 and 50.85μgkg−1.

Dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography‐diode array detection for the determination of N‐methyl carbamate pesticides in vegetables

This paper described a simple, rapid and efficient method for the determination of N-methyl carbamate pesticides in tomato, cucumber, carrot and lettuce samples by dispersive liquid-liquid microextraction coupled with HPLC-diode array detection. Some experimental parameters that influenced the extraction efficiency, such as types and volumes of extraction and disperser solvents, extraction time and salt effect were examined and optimized. Under optimum conditions, the LOD of the method were 0.5-3.0 μg/kg depending on the compounds and the kind of vegetables. The linearities of the method were obtained in the range of 10.0-300 μg/kg for aldicarb, MTMC, carbofuran and carbaryl, and 20.0-600 μg/kg for isoprocarb, with the correlation coefficients ranging from 0.9921 to 0.9993. The RSD varied from 2.9 to 7.5% (n=5). The recoveries of the method for the five carbamates from vegetable samples at two different spiking levels were ranged from 77.8 to 98.2%. Results showed that the method we proposed can meet the requirements for the determination of N-methyl carbamate in vegetable samples and was finally applied to the analysis of target pesticides in vegetable samples taken from local markets.

Sensitive spectrophotometric methods for determination of some organophosphorus pesticides in vegetable samples

Three rapid, simple, reproducible and sensitive spectrophotometric methods (A, B and C) are described for the determination of two organophosphorus pesticides, (malathion and dimethoate) in formulations and vegetable samples. The methods A and B involve the addition of an excess of Ce4+ into sulphuric acid medium and the determination of the unreacted oxidant by decreasing the red color of chromotrope 2R (C2R) at a suitable ?max = 528 nm for method A, or a decrease in the orange pink color of rhodamine 6G (Rh6G) at a suitable ?max = 525 nm. The method C is based on the oxidation of malathion or dimethoate with the slight excess of N-bromosuccinimide (NBS) and the determination of unreacted oxidant by reacting it with amaranth dye (AM) in hydrochloric acid medium at a suitable ?max = 520 nm. A regression analysis of Beer-Lambert plots showed a good correlation in the concentration range of 0.1-4.2 ?g mL?1. The apparent molar absorptivity, Sandell sensitivity, the detection and quantification limits were calculated. For more accurate analysis, Ringbom optimum concentration ranges are 0.25-4.0 ?g mL?1. The developed methods were successfully applied to the determination of malathion, and dimethoate in their formulations and environmental vegetable samples.

Sensitive spectrophotometric methods for determination of some organophosphorus pesticides in vegetable samples

Three rapid, simple, reproducible and sensitive spectrophotometric methods (A, B and C) are described for the determination of two organophosphorus pesticides, (malathion and dimethoate) in formulations and vegetable samples. The methods A and B involve the addition of an excess of Ce4+ into sulphuric acid medium and the determination of the unreacted oxidant by decreasing the red color of chromotrope 2R (C2R) at a suitable λmax = 528 nm for method A, or a decrease in the orange pink color of rhodamine 6G (Rh6G) at a suitable λmax = 525 nm. The method C is based on the oxidation of malathion or dimethoate with the slight excess of N-bromosuccinimide (NBS) and the determination of unreacted oxidant by reacting it with amaranth dye (AM) in hydrochloric acid medium at a suitable λmax = 520 nm. A regression analysis of Beer-Lambert plots showed a good correlation in the concentration range of 0.1-4.2 μg mL−1. The apparent molar absorptivity, Sandell sensitivity, the detection and quantification limits were calculated. For more accurate analysis, Ringbom optimum concentration ranges are 0.25-4.0 μg mL−1. The developed methods were successfully applied to the determination of malathion, and dimethoate in their formulations and environmental vegetable samples.

Direct determination of pesticides in vegetable samples using gold nanoelectrode ensembles

Gold nanowires were produced by electrodeposition in polycarbonate membrane, with an average diameter of 200 nm and a height of about 2 μm. The nanowire array prepared by the proposed method can be considered as nanoelectrode ensembles (NEEs). An amperometric pesticides sensor based on gold NEEs has been developed and used for determination of phoxim and dimethoate in vegetable samples. The electrochemical performance of the gold NEEs has also been studied by the amperometric method. The electrode provided a linear response over a concentration range of 5.9 × 10−5 to 1.2 × 10−2 M for phoxim with a detection limit of 4.8 × 10−6 M and 6.3 × 10−5 to 1.1 × 10−2 M for dimethoate. This sensor displayed high sensitivity and selectivity, long-term stability and wide linear range. In addition, the ellipsis of enzyme and the reactivation of enzyme make the operation simple. This sensor has been used to determine pesticides in a real vegetable sample.

Mixed liquids for single-drop microextraction of organochlorine pesticides in vegetables

A new approach for the extraction of nine kinds of organochlorine pesticides (OCPs) from vegetable samples coupling single-drop microextraction with gas chromatography–mass spectrometry was presented. Experimental parameters, such as organic solvent, exposure time, agitation and organic drop volume were controlled and optimized. An effective extraction was achieved by suspending a 1.00 μL mixed drop of p-xylene and acetone (8:2, v/v) to the tip of a microsyringe immersed in a 2 mL donor aqueous solution and stirred at 400 rpm. The approach was applied to the determination of OCPs in vegetable samples with a linearity range of 0.05–20 ng mL −1 for α-, β-, γ-, δ-hexachlorobenzene (BHC) and dicofol, 0.5–20 ng mL −1 for dieldrin and 2,2-bis(4-chlorophenyl)-1,1-dichloroethane (DDD) or 0.5–50 ng mL −1 for 2,2-bis(4-chlorophenyl)-1,1-dichloroethylene (DDE) and 2-(2-chlorophenyl)-2 (4-chlorophenyl)-1,1,1-trichloroethane ( p, p′-DDT). Correspondingly, the determination limit at an S/N of 3 ranged from 0.05 ng mL −1 for α-, β-, γ-, δ-BHC to 0.2 ng mL −1 for dicofol, dieldrin or p, p′-DDT. The relative recoveries were from 63.3 to 100%, with repeatability ranging from 8.74 to 18.9% (relative standard deviation, R.S.D.). The single-drop microextraction was proved to be a fast and simple approach for the pre-concentration of organochlorine pesticides in vegetable samples.

Application of hollow fiber supported liquid membrane extraction to the simultaneous determination of pesticide residues in vegetables by liquid chromatography/mass spectrometry

A new analytical procedure using a hollow fiber supported liquid membrane (HFSLM) has been developed for the simultaneous determination of pesticide residues in vegetables by liquid chromatography (LC) coupled with electrospray mass spectrometry (MS). The extraction technique requires minimal sample preparation and solvent consumption. Optimum extraction conditions have been evaluated with respect to sample pH, ionic strength, liquid membrane composition, extraction time, stirring rate and acceptor composition. The extraction method has been validated for matrices such as cucumber, tomato and pepper, indicating that cucumber can be selected as representative matrix for routine analysis of these food commodities. Linear ranges of pesticides in vegetable samples were 10 to 200 microg/kg, and the repeatability of the method was less than 20% for the lowest calibration point. The limits of detection ranged from 0.06 to 2.7 microg/kg and the limits of quantification from 0.2 to 9.0 microg/kg, which were low enough to determine the pesticide residues at concentrations below or equal to the maximum residue levels (MRLs) specified by European Union. The method was finally applied to the determination of more than 20 pesticides in market vegetable samples and the concentrations found in these samples were always lower than the MRLs. This new approach can be considered as a powerful alternative to the traditional extraction techniques.

Determination of pesticides in vegetable samples using an acetylcholinesterase biosensor based on nanoparticles ZrO2/chitosan composite film

An amperometric pesticides inhibition biosensor has been developed and used for determination of pesticides in vegetable samples. To eliminate the interference of ascorbic acid, multilayer films of polyelectrolyte (chitosan/polystyrensulfonate) were coated on the glass carbon electrode. Then, acetylcholinesterase was immobilized on the electrode based on surface-treated nanoporous ZrO2/chitosan composite film as immobilization matrix. As a modified substrate, acetylthiocholine was hydrolysed by acetylcholinesterase and produced thiocholine which can be oxidized at +700 mV vs. SCE. Pesticides inhibit the activity of enzyme with an effect of decreasing of oxidation current. The experimental conditions were optimized. The electrode has a linear response to acetylthiocholine within 9.90 × 10−6 to 2.03 × 10−3 M. The electrode provided a linear response over a concentration range of 6.6 × 10−6 to 4.4 × 10−4 M for phoxim with a detection limit of 1.3 × 10−6 M, over a range of 1.0 × 10−8 to 5.9 × 10−7 M for malathion, and over a range of 8.6 × 10−6 to 5.2 × 10−4 M for dimethoate. This biosensor has been used to determine pesticides in a real vegetable sample.