Method validation and application of a selective multiresidue analysis of highly polar pesticides in food matrices using hydrophilic interaction liquid chromatography and mass spectrometry.

The effectiveness of highly polar pesticides in agriculture is well known, while their low costs contribute to the frequent use. On the other hand, their physicochemical properties make their analytical determination a challenging task. The aim of this study is the evaluation of a methanol-based extraction method with a simple clean-up step using a selective multiresidue LC-MS/MS method for 14 highly polar pesticides and their metabolites. For the clean-up step, several sorbents from different brands, with diverse mechanisms of action, were tested. Different dilution factors for the final extract were also evaluated in order to check the impact on the matrix effects. The optimised method was validated for matrices from different commodity groups. Recovery studies performed with grapes, lettuce, orange, oat and soya beans showed absolute average recoveries in the range 70-120% with relative standard deviation values below 20% for almost all the pesticides tested. The matrix effects observed were very different in each matrix and for each individual pesticide evaluated. Therefore, isotopically labeled procedural internal standards were used for all compounds in order to correct for recovery and matrix effects. Method Limits of Quantification for most analyte-matrix combinations were 0.02 or 0.05 mg kg-1. The final optimised method appeared to be reproducible and robust in routine analysis of a wide variety of fruits, vegetables and cereals. Monitoring results are presented to show the occurrence of the compounds studied in real samples. The residue concentrations ranged from 0.023 to 30 mg kg-1 for the analytes detected.

Miniaturisation and optimisation of the Dutch mini-Luke extraction method for implementation in the routine multi-residue analysis of pesticides in fruits and vegetables.

This paper presents the validation and further miniaturisation of the well-known Dutch mini-Luke method for high water and acid content matrices for 175 pesticides amenable to liquid- and gas chromatography-mass spectrometry. For optimisation of the method, recovery tests with different sample/extraction solvent ratios, varying amounts of dichloromethane and salts were performed with fifty representative pesticides. Solvent consumption could be reduced considerably, especially for the dichloromethane (by a factor of 3). Recovery studies performed with lettuce and orange matrix spiked at 0.005, 0.01 and 0.02 mg/kg yielded average recoveries in the range 70-120% with relative standard deviation values below 20% for almost all the pesticides tested. The linearity over three orders of magnitude was demonstrated (r(2) > 0.99). The matrix effect could be considered as not significant. The limit of quantification was 0.005 mg/kg for 96% of the compounds. The optimised New Dutch mini-Luke ("NL"-) method was applied successfully in routine analysis and the EUPT FV-16 sample.