Determination of carbaryl, carbofuran and methiocarb in cucumbers and strawberries by monoclonal enzyme immunoassays and high-performance liquid chromatography with fluorescence detection. An analytical comparison.

Carbaryl, carbofuran and methiocarb are three of the most important N-methylcarbamate pesticides. In the present work, the application of laboratory-developed monoclonal antibody-based enzyme-linked immunosorbent assays (ELISAs) to the determination of these compounds in fruits and vegetables is described. Cucumbers and strawberries were spiked with the three carbamates at 10, 50 and 200 ppb. After extraction and clean-up, samples were analyzed by immunoassay and by HPLC with post-column derivatization and fluorescence detection (US Environmental Protection Agency Method 531.1). Results obtained by ELISA correlated well with those obtained by HPLC, both in terms of accuracy and precision. Recoveries were in the 60-90% range by ELISA and in the 50-90% range by HPLC, depending on the particular combination of commodity, pesticide, and fortification level under consideration. ELISAs were also applied to the analysis of non-purified sample extracts with excellent results: recoveries close to 100% were obtained, while maintaining similar precision values. This approach avoids the use of solid-phase extraction columns, saves time, and considerably increases the sample throughput. Results clearly indicate that the developed immunoassays may be suitable for the quantitative and reliable determination of carbaryl, carbofuran and methiocarb in fruits and vegetables even without including clean-up steps. These considerations make these ELISAs very useful analytical tools for monitoring and regulatory programs, without the need of complex and expensive instrumentation.

Monoclonal enzyme immunoassay for the analysis of carbaryl in fruits and vegetables without sample cleanup.

The N-methylcarbamate pesticide carbaryl is one of the most important insecticides used worldwide. In the present work, the validation of a monoclonal antibody-based enzyme immunoassay (ELISA) for the determination of this compound in fruits and vegetables is described. The immunoassay is a competitive heterologous ELISA in the antibody-coated format, with an I(50) value for standards in buffer of 101.0 +/- 26.9 ng/L and with a dynamic range between 31.6 and 364.0 ng/L. For recovery studies, peppers, cucumbers, strawberries, tomatoes, potatoes, oranges, and apples were spiked with carbaryl at 10, 50, and 200 ppb. After liquid extraction, analyses were performed by ELISA on both extracts purified on solid-phase extraction (SPE) columns and crude, nonpurified extracts. Depending on the crop and the fortification level, recoveries in the 59.0--120.0% range were obtained for purified samples and in the 70.0--137.7% range for crude extracts. The carbaryl immunoassay performance was further validated with respect to high-performance liquid chromatography (HPLC) with postcolumn derivatization and fluorescence detection (EPA Method 531.1). Samples were spiked with carbaryl at several concentrations and analyzed as blind samples by ELISA and HPLC after SPE cleanup. The correlation between methods was excellent (y = 1.04x + 0.71, r(2) = 0.992, n = 33), with HPLC being more precise than ELISA (mean coefficients of variation of 5.2 and 12.0%, respectively). The immunoassay was then applied to the analysis of nonpurified extracts of the same samples. Results also compared very well with those obtained by HPLC on purified samples (y = 1.28x - 0.59, r(2) = 0.987, n = 33) while maintaining similar precision. Therefore, the developed immunoassay is a suitable method for the quantitative and reliable determination of carbaryl in fruits and vegetables even without sample cleanup, which saves time and money and considerably increases sample throughput.

Validation of a monoclonal enzyme immunoassay for the determination of carbofuran in fruits and vegetables.

The N-methylcarbamate pesticide carbofuran is a very important insecticide used worldwide. In the present work, the validation of a monoclonal antibody-based enzyme immunoassay (ELISA) to determine this compound in fruits and vegetables is described. The immunoassay is a competitive heterologous ELISA in the antibody-coated format, with an I(50) value for standards in buffer of 740 ng/L and with a dynamic range between 200 and 3100 ng/L. For recovery studies, peppers, cucumbers, strawberries, tomatoes, potatoes, oranges, and apples were spiked with carbofuran at 10, 50, and 200 ppb. After liquid extraction, analyses were performed by ELISA on extracts purified on solid-phase extraction (SPE) columns and crude, nonpurified extracts. Depending on the crop, mean recoveries in the 43.9--90.7% range were obtained for purified samples and in the 90.1--121.6% range for crude extracts. The carbofuran immunoassay performance was further validated with respect to high-performance liquid chromatography (HPLC) with postcolumn derivatization and fluorescence detection (EPA Method 531.1). Samples were spiked with carbofuran at several concentrations and analyzed as blind samples by ELISA and HPLC after SPE cleanup. The correlation between methods was very good (y = 0.90x + 2.66, r(2)() = 0.958, n = 25), with HPLC being more precise than ELISA (mean coefficients of variation of 4.1 and 11.5%, respectively). The immunoassay was then applied to the analysis of nonpurified extracts of the same samples. Results also compared very well with those obtained by HPLC on purified samples (y = 1.02x + 10.44, r(2)() = 0.933, n = 29). Therefore, the developed immunoassay is a suitable method for the quantitative and reliable determination of carbofuran in fruits and vegetables even without sample cleanup, which saves time and money and considerably increases the sample throughput.

Liquid chromatographic determination of five benzoylurea insecticides in fruit and vegetables.

A liquid chromatographic (LC) method was developed to determine 5 benzoylureas--diflubenzuron, hexaflumuron, teflubenzuron, flufenozuron, and lufenuron--in peppers, tomatoes, eggplants, cucumbers, and oranges. Preparation of samples involve extraction with acetone and partitioning into dichloromethane-petroleum ether. A portion of this extract is cleaned up with a solid-phase extraction aminopropyl disposable column. With LC analysis using an RP-8-DB microbore column, acetonitrile-water (70 + 30, v/v) as mobile phase, and photodiode array detection at 254 nm, recovery and repeatability data were collected for the 5 benzoylureas on 4 vegetables and citrus in the range 0.04-2.0 mg/kg. Validated limits of detection and quantitation were 0.01 and 0.04 mg/kg, respectively. The method is reliable for routine analysis of vegetables and fruits.