Simplified multiresidue method for liquid chromatographic determination of N-methyl carbamate insecticides in fruits and vegetables

A simplified method is described for determining 7 N-methyl carbamates (aldicarb, carbaryl, carbofuran, methiocarb, methomyl, oxamyl, and propoxur) and 3 related metabolites (aldicarb sulfoxide, aldicarb sulfone, and 3-hydroxy carbofuran) in fruits and vegetables. Residues are extracted from crops with methanol; coextractives are then separated by gel permeation chromatography (GPC) or GPC with on-line Nuchar-Celite cleanup for crops with high chlorophyll and/or carotene content (e.g., cabbage and broccoli). Carbamates are separated on a reverse-phase liquid chromatography column, using a methanol-water gradient mobile phase. Separation is followed by postcolumn hydrolysis to yield methylamine, and the formation of a fluorophore with o-phthalaldehyde and 2-mercaptoethanol prior to fluorescence detection. Recovery data were obtained by fortifying 5 different crops (apples, broccoli, cabbages, cauliflower, and potatoes) at 0.05 and 0.5 ppm. Recoveries averaged 93% at both fortification levels except for the very polar aldicarb sulfoxide for which recoveries averaged around 52% at both levels. The coefficient of variation of the method at both levels is less than 5% and the limit of detection, defined at 5 times baseline noise, varies between 5 and 10 ppb, depending on the compound.     

Determination of pesticides in apple-based infant foods using liquid chromatography electrospray ionization tandem mass spectrometry

A liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method was developed and validated to quantify and confirm trace levels of 13 pesticides including aldicarb sulfoxide, aldicarb sulfone, oxamyl, methomyl, formetanate, 3-hydroxycarbofuran, carbendazim, thiabendazole, aldicarb, propoxur, carbofuran, carbaryl, and methiocarb in apple-based infant foods such as apple sauces, apples and strawberries, apples and blueberries, and apples and plums. Data acquisition under MS/MS was achieved by applying multiple reaction monitoring of two fragment ion transitions to provide a high degree of sensitivity and selectivity for both quantification and confirmation. LC/ESI-MS/MS quantitative results were significantly affected by matrices, and thus, the standard addition was employed to compensate for the matrix effects to achieve the best accuracy of the method. Recoveries of 13 pesticides, spiked at 5.0, 25.0, and 45.0 microg/kg, were around 100% using the LC/ESI-MS/MS standard addition. The method detection limits (S/N > or = 3:1) of 13 pesticides were less than 0.2 microg/kg.     

Liquid chromatographic determination of N-methylcarbamate insecticides and metabolites in crops. I. Collaborative study

A liquid chromatographic (LC) multiresidue method for determining residues of N-methylcarbamate insecticides in crops was collaboratively studied in 6 laboratories. Methanol and a mechanical ultrasonic homogenizer are used to extract the carbamates. Water-soluble plant coextractives and nonpolar plant lipid materials are removed from the carbamate residues by liquid-liquid partitioning. Additional crop coextractives (e.g., carotenes, chlorophylls) are removed with a Nuchar SN-silanized Celite column. The carbamate residues are then separated on a reverse phase LC column, using an acetonitrile-water gradient mobile phase. Eluted residues are detected by an in-line post-column fluorometric detection technique. Seven carbamates and 2 carbamate metabolites were included in the collaborative study. Each collaborator determined all the carbamates at 2 levels (approximately 0.05 ppm and United States tolerance) in blind duplicate samples of grapes and potatoes. Fortified and control samples were analyzed. Repeatability coefficients of variation for all the carbamates on the 2 crops averaged 4.7% and ranged from 2.4 to 7.1%. Reproducibility coefficients of variation for all the carbamates on the 2 crops averaged 8.7% and ranged from 5.3 to 12.4%. Accuracy, measured by comparison with fortification values, averaged 95% and ranged from 79 to 103%. The estimated limit of quantitation is 0.01 ppm. The method has been adopted official first action.     

Assessment of pesticide residues in honey samples from portugal and Spain

Fifty samples of honey collected from local markets of Portugal and Spain during year 2002 were analyzed for 42 organochlorine, carbamate, and organophosphorus pesticide residues. An analytical procedure based on solid-phase extraction with octadecyl sorbent followed by gas chromatography-mass spectrometry (GC-MS), for organochlorines, and by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS), for organophosphorus and carbamates, has been developed. Recoveries of spiked samples ranged from 73 to 98%, except for dimethoate (40%), with relative standard deviations from 3 to16% in terms of repeatability, and from 6 to 19% in terms of reproducibility. Limits of quantification were from 0.003 to 0.1 mg kg(-)(1). Most of the pesticides found in honey were organochlorines. Among them, gamma-HCH was the most frequently detected in 50% of the samples, followed by HCB in 32% of the samples and the other isomers of HCH (alpha-HCH and beta-HCH) in 28 and 26% of the samples, respectively. Residues of DDT and their metabolites were detected in 20% of the samples. Of the studied carbamates, both methiocarb and carbofuran were detected in 10% of the samples, pirimicarb in 4% and carbaryl in 2%. The only organophosphorus pesticides found were heptenophos in 16%, methidathion in 4%, and parathion methyl in 2% of honey samples. Results indicate that Portuguese honeys were more contaminated than Spanish ones. However, honey consumers of both countries should not be concerned about the amounts of pesticide residues found in honeys available on the market.     

Residues of methamidofos, malathion, and methiocarb in greenhouse crops

The diminution of methamidofos, malathion, and methiocarb in different crops grown in greenhouses has been studied, including the presence of metabolites such as malaoxon, methiocarb sulfoxide, and methiocarb sulfone. The analytical method is based on dichloromethane extraction and GC-PFPD analysis. It has been validated establishing performance parameters such as recovery rates, precision, linear ranges, and limits of detection and quantification, which are low enough for ensuring that their corresponding MLRs can be adequately quantified. Samples of treated cucumbers and peppers grown in greenhouses were collected and analyzed during a 15-day period for obtaining the diminution rates of methamidofos and malathion. The behavior of methiocarb in treated green beans and tomatoes has been studied using analysis of variance (ANOVA) as the statistical tool, for establishing the influence of crop, season, application dose, and greenhouse design.     

Direct aqueous injection-liquid chromatography with post-column derivatization for determination of N-methylcarbamoyloximes and N-methylcarbamates in finished drinking water: collaborative study

An interlaboratory method validation study was conducted on EPA Method 531.1, Measurement of N-Methylcarbamoyloximes and N-Methylcarbamates in Water by Direct Aqueous Injection HPLC with Post Column Derivatization, to determine the precision and mean recovery for determination of 10 carbamate pesticide compounds in reagent water and in finished drinking waters. The study design was based on Youden's nonreplicate plan for collaborative tests of analytical methods. The waters were spiked with 10 carbamate pesticides at 6 concentration levels, as 3 Youden pairs. Eight laboratories analyzed the samples by direct aqueous injection, with separation by reverse-phase liquid chromatography and post-column hydrolysis of the carbamates and carbamoyloximes to methylamine, followed by reaction of the methylamine with o-phthalaldehyde and 2-mercaptoethanol using fluorescence detection. Results were analyzed using an EPA computer program, which measured precision and recovery for each of the 10 compounds and compared the performance of the method between water types. The method was acceptable for all analytes tested. After removal of a nonrepresentative data set for aldicarb sulfoxide, no matrix effects were observed; the statistics for the pooled drinking waters were not significantly different from the statistics for the reagent waters. The method has been adopted official first action by AOAC.     

Laboratory studies on the leaching of aldicarb through a tropical soil from Belize,Central America

Studies in temperate regions indicate that the carbamate insecticide aldicarb and its metabolites leach readily through agricultural soils into groundwater. However, little is known about the fate of this nematicide in tropical regions, where its leaching potential may be even greater because of high annual rainfall and the acidic nature and low organic content of many tropical soils. Examination of the leaching behaviour of aldicarb and its metabolites in columns containing soil from Belize, Central America, indicated that total carbamate residues (TCR) could rapidly reach concentrations > 15 mg L^?1 in porewater 1 m below the soil surface within 70 days of application. These values are well in excess of the US EPA Health Advisory level of 0.01 mg L^?1. TCR retention within a given depth interval in the soil columns relative to incoming TCR flux was greatest between 0 and 0.1 m, reflecting high organic matter contents in the upper soil. Retention below 0.1 m was relatively consistent with depth, while differences in relative retention between columns were due to a greater duration of leaching for the second column. Aldicarb was rapidly oxidized to aldicarb sulfoxide and aldicarb sulfone in these soils. The high concentration and mobility of TCR in this acidic soil is attributed to the transformation of the parent compound to the sulfoxide metabolite, which has a lower degradation rate and organic carbon partioning coefficient than aldicarb.     

Determination of carbamate pesticide residues in vegetables and fruits by liquid chromatography-atmospheric pressure photoionization-mass spectrometry and atmospheric pressure chemical ionization-mass spectrometry

A liquid chromatography-atmospheric pressure photoionization (APPI)-mass spectrometry method was developed for the determination of 22 carbamates including their metabolites in vegetables and fruits. For the optimization of APPI, several APPI ion source parameters were examined. As a result, many carbamates with APPI using the optimized parameter gave simple mass spectra, and a strong signal corresponding to [M + H](+) was observed except for aldicarb. However, some carbamate metabolites gave ammonium adduct ions [M + NH(4)](+) as base peak ions. The mean recovery of each carbamate from grape and onion samples spiked at 5 ng/g was 81.7-105.7%, with relative standard deviations of 3.3-5.9%. Furthermore, matrix constituents did not significantly influence the ionization efficiency. The limit of detection (S/N = 3) in grape and onion was in the range of 0.33-3.33 ng/g. For the robustness of this method, this system has been used to analyze 50 samples, and the intensities for all carbamates were found to be unaffected by the contamination of the APPI source by sample matrix constituents. This result indicates that the method is reliable.     

A simple and rapid assay for analyzing residues of carbamate insecticides in vegetables and fruits: hot water extraction followed by liquid chromatography-mass spectrometry

A simple, specific, and rapid analytical method for determining seven largely used carbamate insecticides in tomato, spinach, lettuce, zucchini, pear, and apple is here presented. This method is based on the matrix solid-phase dispersion technique, with heated water as extractant followed by liquid chromatography (LC)-mass spectrometry (MS) equipped with a single quadrupole and an electrospray ion source. Target compounds were extracted from the vegetal matrixes by water heated at 50 degrees C. After acidification and filtration, 0.25 mL of any aqueous extract was injected in the LC column. MS data acquisition was performed in the selected ion monitoring mode, selecting three ions for each target compound. Heated water appeared to be an excellent extractant because recovery data ranged between 76 (carbaryl in spinach) and 99% (pirimicarb in spinach), with RSDs not larger than 10%. Using trimethacarb (an obsolete carbamate insecticide) as a surrogate internal standard, the accuracy of the analysis varied between 84 and 110%, with RSDs not larger than 9%. On the basis of a signal-to-noise ratio of 10, limits of quantification were estimated to range between 2 (pirimicarb) and 10 ppb (oxamyl) and were not influenced by the type of matrix. When trying to fractionate analytes by using a short chromatographic run time, marked weakening of the ion signals for oxamyl, methomyl, and aldicarb were observed. This effect was traced to polar endogenous co-extractives eluted in the first part of the chromatographic run that interfered with gas-phase ion formation for carbamates. Adopting more selective chromatographic conditions eliminated this effect.     

High pressure liquid chromatographic determination of methomyl and oxamyl on vegetable crops

A reverse phase high pressure liquid chromatographic method is presented for the separation and determination of residues of the carbamates oxamyl and methomyl on vegetables. A liquid-liquid extraction and cleanup procedure is applied to the vegetable extract. Samples are eluted from a muBondapak C18 column and quantitated by ultraviolet absorbance at 240 nm. Recovery data for vegetable samples spiked at 2 ppm are presented.     

Competitive degradation and detoxification of carbamate insecticides by membrane anodic Fenton treatment

The competitive degradation of six carbamate insecticides by membrane anodic Fenton treatment (AFT), a new Fenton treatment technology, was carried out in this study. The carbamates studied were dioxacarb, carbaryl, fenobucarb, promecarb, bendiocarb, and carbofuran. The results indicate that AFT can effectively degrade these insecticides in both single component and multicomponent systems. The carbamates compete for hydroxyl radicals, and their kinetics obey the previously developed AFT kinetic model quite well. Hydroxyl radical reaction rate constants were obtained, and they decrease in the following order: dioxacarb approximately carbaryl > fenobucarb > promecarb > bendiocarb > carbofuran. The AFT is shown to have higher treatment efficiency at higher temperature. Degradation products of the carbamates were determined by gas chromatography/mass spectrometry, and it appears that degradation can be initiated by hydroxyl radical attack at different sites in the molecule, depending on the individual structure of the compound. Substituted phenols are the commonly seen degradation products. The AFT treatment can efficiently remove the chemical oxygen demand of the carbamate mixture, significantly increasing the biodegradability. Earthworm studies show that the AFT is also an effective detoxification process.     

Food and Drug Administration pesticide residue monitoring of foods: 1978-1982

Pesticide residues in foods are reported for the 5-year period 1978-1982 [fiscal years (FY) 78-82]. Results were compiled from the 2 complementary elements that comprise the Food and Drug Administration's (FDA) program for monitoring pesticide residues in foods. Under regulatory monitoring, which focuses on residues in raw agricultural commodities, a total of 49,877 samples (30,361 domestic and 19,516 import) that included fresh fruits and vegetables, grains, milk and dairy products, seafoods, and a variety of processed foods were analyzed. No residues were found in about 55 and 44% of the domestic and import samples, respectively. About 3% of the domestic and 7% of the import samples were classed as violative. Data from the Total Diet Study, which is conducted to determine dietary intakes of a variety of chemicals, showed that residues of 42 pesticides were found in 1044 composites of table-ready foods. Results of FDA's monitoring for FY78-82 demonstrate that pesticide residue levels in the U.S. food supply were generally well below regulatory limits, and dietary intakes were manyfold lower than the Acceptable Daily Intakes established by international agencies.     

Use of SMS as a Compost Matrix to Degrade Pesticide Residuals

Pesticide rinsates have been found to be one source of surface water and groundwater contamination. Practical waste treatment methods that achieve environmental protection standards applicable to pesticide rinsates are limited (Kuo, 1993). The research to be presented was conducted to investigate the feasibility of using SMS as an adsorption medium and as a microorganism source to remediate synthetic technical grade rinsate solutions containing up to 30 mg/L of three carbamate insecticides, namely, carbaryl, carbofuran and aldicarb. All experiments were conducted in the laboratory using bench scale complete mixing batch reactors (CMBR) at 25°C.

The results indicated that the SMS was able to adsorb the candidate pesticide from aqueous solution. The process was found to exhibit nonlinear “favorable” adsorption behavior which was characterized by the Freundlich isotherm model. Rates were enhanced by the increase of organic contents in the SMS.

The SMS microorganisms were found to be more adapted to detoxifying the carbamate solutions than seed derived from domestic wastewater activated sludge. Inhibition of the SMS cultures by the insecticides was not indicated. The degradation rates were described by the Monod model, with carbaryl and carbofuran rated “readily” biodegradable, while aldicarb rated “hardly” biodegradable.

Future research needs to address other classes of pesticides, including organophosphates; pilot-scale studies using commercial grade formulations; and fundamental research dealing with identifying the unique microbial consortium found in SMS.     

Ion-pairing liquid chromatographic determination of benzimidazole fungicides in foods

A method is described for determining residues in foods of thiabendazole, thiophanate methyl, the di-oxygen analogue metabolite [dimethyl 4,4'-O-phenylene bis (allophanate)] that is the metabolite name of the latter, and methyl-2-benzimidazole carbamate, which is the major metabolite and fungitoxic principle common to both thiophanate methyl and benomyl. The residues are extracted from the product using methanol and are partitioned into dichloromethane after initial acidification and again after subsequent alkalinization of the extract. Residues are separated and quantified by reverse-phase liquid chromatography using an ion-pairing mobile phase with UV and fluorescence detectors in tandem. Recoveries from 7 different food crops fortified at 0.2-35 ppm levels ranged from 64 to 105%.     

Determination of sulfur amino acids and tryptophan in foods and food and feed ingredients: collaborative study

Samples of 4 foods, 1 animal feed, isolated soy protein, and beta-lactoglobulin were analyzed by 9 laboratories to determine concentrations of cysteine as cysteic acid, methionine as methionine sulfone, and tryptophan. Sulfur amino acids were determined by AOAC method 43.A08-43.A13 for food and feed ingredients, in which samples are oxidized with performic acid before protein hydrolysis with 6N HCl. Tryptophan was determined after protein hydrolysis with 4.2N NaOH. In both methods, free amino acids were separated by ion-exchange or reverse-phase chromatography. Each laboratory was provided with detailed methods and with sealed vials containing solutions of standards. Samples were analyzed in duplicate, and variation between laboratories was determined. Coefficients of variation between laboratories for the 6 samples ranged from 5.50 to 11.8% for methionine as methionine sulfoxide, 8.59 to 17.3% for cysteine as cysteic acid, and 3.87 to 16.1% for tryptophan. Amino acid recoveries were determined by analysis of beta-lactoglobulin and were based on expected levels of each amino acid obtained from amino acid sequence data. The mean recovery of cysteine was 97% with a range of 88-119%. For methionine, mean recovery was 98% (range 89-115%) and for tryptophan, 85% (range 59-102%). Method 43.A08-43.A13 for food and feed ingredients has been adopted official first action for determination of cysteine and methionine in processed foods. The alkaline hydrolysis method has been adopted official first action for determination of tryptophan in foods and food and feed ingredients.     

Effect of some pesticides on plant growth,root nodulation and chlorophyll content of chickpea

Different concentrations, viz. 5, 10 and 25 ppm of aldicarb, carbofuran, phorate fensulfothion and fenamiphos were observed for their pesticidal effects on chickpea plant in terms of various plant growth parameters such as plant length as well as weight, pod numbers, root-nodulations and chlorophyl content. Significant improvement in plant growth was noted in lower concentrations such as 5 and 10 ppm of different pesticides but 5 ppm concentration proved highly effective and non-phytotoxic. The phytotoxic effect was noted in those plants treated with 25 ppm concentration of all the pesticides. Carbofuran was found to be most effective for improvement of over all plant growth and fensulfothion the least.     

Determination of coumaphos and its oxygen analog in eggs and milk by using a multiresidue method with liquid chromatographic quantitation and capillary gas chromatographic/mass spectrometric confirmation

A multiresidue method for carbamate insecticides was adapted for the determination of coumaphos and its oxygen analog in eggs and milk. Eggs were extracted with acetonitrile and milk was extracted with acetone. Co-extractives were removed using liquid partitioning and charcoal column procedures described in the carbamate method. Coumaphos and its oxygen analog were determined by using a high performance liquid chromatograph equipped with a fluorescence detector. Recovery studies were performed for the 2 compounds at levels of 0.01 and 0.10 ppm in eggs and 0.01 and 0.02 ppm in milk. Overall average recovery was 100% (range 95-109%). In a trial of the method by another laboratory, the recovery of coumaphos and its oxygen analog from milk averaged 87 and 96%, respectively. Data are presented on the capillary gas chromatographic/mass spectrometric confirmation of coumaphos residues.     

Evaluation of capillary gas chromatography for pesticide and industrial chemical residue analysis. II. Comparison of quantitative results obtained on capillary and packed columns

Results of pesticide and industrial chemical residue determinations, using both capillary and packed column gas chromatography (GC), in 3 Food and Drug Administration (FDA) laboratories have been compiled and compared. Samples consisted of food products collected for routine residue screening by the respective laboratories. Extracts were prepared by conventional multiresidue methodology. Capillary column systems and operating conditions were selected at the discretion of each laboratory and were therefore variable, although split/splitless injectors in the split mode were used with prescribed precautions in all cases. Packed column systems were operated as specified in the FDA Pesticide Analytical Manual (PAM). Overall correlation between the 2 systems, expressed as the average ratio of packed column result to capillary column result, was 0.99 for 120 determinations in 41 samples. The higher resolving power of the capillary systems allowed quantitation of several residues that were incompletely separated and therefore unquantifiable using the packed columns. Capillary column GC with the split injection technique, used with appropriate precautions, was found to be both reliable and advantageous for regulatory determination of pesticide and industrial chemical residues in foods and feeds.     

On-line trace enrichment for determination of aldicarb species in water, using liquid chromatography with post-column derivatization

Liquid chromatography combining on-line trace enrichment together with a very selective detection technique is used for the determination of aldicarb, aldicarb sulfoxide, and aldicarb sulfone. Sensitivity is increased by loading a 10 mL volume of ground water on a concentrator column installed in the loop position of a 6-port injection valve. Switching the valves allows the concentrated material to be backflushed onto the analytical column by a methanol-water gradient mobile phase. Separation is followed by post-column hydrolysis to yield methylamine, and formation of a fluorophore with o-phthalaldehyde and 2-mercaptoethanol prior to fluorescence detection. The process requires virtually no sample cleanup and provides good precision on recoveries from different matrixes. Minimum detection limit, defined as 5 times baseline noise, is less than 70 ng/L for the 3 compounds.     

Oxidation and hydrolysis determination of sulfur amino acids in food and feed ingredients: collaborative study

Samples of 6 food and feed ingredients and a purified protein, beta-lactoglobulin, were analyzed by 7 laboratories to determine the concentrations of cysteine as cysteic acid and methionine as methionine sulfone. Samples were oxidized by reaction with performic acid before hydrolysis with 6N HCl. The free amino acids were then separated and measured by ion-exchange chromatography on dedicated amino acid analyzers. Each laboratory was provided with a detailed method as well as sealed vials containing solutions of standards. For the determination of cysteine as cysteic acid, the coefficients of variation between laboratories for duplicate samples ranged from 7.13 to 10.8% for the 6 ingredients. For the determination of methionine as methionine sulfone, the coefficients of variation between laboratories for duplicate samples ranged from 1.18 to 12.8% for the 6 ingredients. Cysteine and methionine recoveries were determined by analysis of beta-lactoglobulin and were based on expected levels of each amino acid from amino acid sequence data. The mean recovery of cysteine was 95% with a range of 91-101%. The mean recovery of methionine was 101% with a range of 98-106%. This method has been adopted official first action.