Enantioselective analysis and degradation of isofenphos-methyl in vegetables by liquid chromatography-tandem mass spectrometry.

The enantioselective degradation of isofenphos-methyl in cowpea, cucumber, and pepper under field conditions was investigated to elucidate the enantioselective environmental behaviors of this pesticide. The concentrations of the enantiomers were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The degradation rates of isofenphos-methyl enantiomers were the fastest in cowpea, followed by cucumber and pepper, with half-lives ranging from 1.48 to 8.06 days. The enantioselective degradation of isofenphos-methyl was characterized by calculating and comparing the values of enantiomer fraction (EF) and enantiomeric selectivity (ES). The degradation rates and enantioselectivities of isofenphos-methyl were different for the three vegetables. (R)-(-)-isofenphos-methyl was degraded faster than (S)-(+)-isofenphos-methyl in cowpea and cucumber, whereas (S)-(+)-isofenphos-methyl underwent preferential degradation in pepper. These results could serve as a reference for the study of enantioselective behavior of isofenphos-methyl in plants and further food safety evaluation, where the enantiomeric differences should be considered in the risk assessment.