Residues of the herbicide fenoxaprop-P-ethyl, its agronomic safener isoxadifen-ethyl and their metabolites in rice after field application.

Fenoxaprop-P-ethyl is a herbicide used on cereals and in particular on rice, the degradation of which leads to several relevant metabolites. The herbicide is used together with an agronomic safener such as isoxadifen-ethyl, which also generates some metabolites. The present work was aimed at developing and validating an analytical method for the determination of the above parent compounds and their main metabolites in the edible fractions of rice. Parent compounds were extracted in acetonitrile and determined by gas chromatography with a mass spectrometer detector, while metabolites were extracted in acetonitrile and analysed by liquid chromatography tandem mass spectrometry. The method was validated through recovery tests in rice straw, grain and plant: accuracy was in the range 76-86% and 90-103% for parent compounds and metabolites respectively. Precision, as relative standard deviation, was in the range 3-11% and 6-17% for parent compounds and metabolites respectively. The limit of detection was 0.01 mg kg(-1) for each analyte, while the limit of quantification was set at 0.05 mg kg(-1). The analytical method is suitable for quantitative determination of each analyte considered in rice commodities.