Matrix-effects of vegetable commodities in electron-capture detection applied to pesticide multiresidue analysis.

The influence of the sample matrix in the analysis of pesticides in vegetable samples has been studied in order to determine if the matrix content introduces a systematic or proportional (or both) bias in the measurements. Experiments have been carried out during a 4-month period, in which calibration curves, prepared in solvent and in vegetable matrix, were prepared and analysed. A statistical treatment has been applied in order to: (i) check the stability of such calibrations during the period studied; (ii) compare both solvent and matrix-matched calibrations; and (iii) obtain a correction function. Applying the correction function to the results obtained with a solvent calibration it is possible to make a prediction of the values obtained applying a matrix-matched calibration. The performance of the correction function has been validated with recovery data. Finally the uncertainty derived from the use of each calibration plot and the correction function has been calculated.

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.

Evaluation of endosulfan residues in vegetables grown in greenhouses.

The reduction in residue levels of endosulfan with time after treatment of tomatoes, green beans, peppers and cucumbers grown in different types of commercial greenhouses (flat- and asymmetric-roof greenhouses) in Almería (Spain) was investigated. A study of the major and minor degradation products of endosulfan in peppers and cucumbers (endosulfan-sulfate, -ether and -lactone) was carried out using gas chromatography-tandem mass spectrometry (GC-MS/MS). To establish the influence of environmental conditions on the degradation of endosulfan, several field trials have been carried out in which crops were sprayed at different rates (full, half- and quarter- of those rates recommended) during two seasons (spring and winter). For statistical purposes, the disappearance of endosulfan with time was considered to follow a pseudo-first-order reaction. Analysis of variance (ANOVA) has been applied to the results obtained. Half-lives of residue disappearance were 4.03-4.68 days in green beans, 4.03-4.20 days in tomatoes, 8.22 days in peppers and 7.97 days in cucumbers. Half-lives in spring were shorter than in the winter season. The application rate and the type of greenhouse did not influence the half-lives.