Chiral Separation and Determination of Multiple Organophosphorus Pesticide Enantiomers in Soil Based on Cellulose-Based Chiral Column by LC–MS/MS

Abstract

The widespread use of organophosphorus pesticides (OPs) has raised significant environmental and health concerns due to their residues in soil and potential entry into the food chain. This study introduced chiral analysis methods for four OPs—methamidophos (METHP), dipterex (DIP), malathion (MALA), and isothiophos-methyl (ISOME)—using liquid chromatography–tandem mass spectrometry (LC–MS/MS) with cellulose-based chiral columns. Three distinct methods were established: one for METHP, another for DIP, and a third for MALA and ISOME. Key chromatographic variables, including organic mobile phases and column temperatures, were systematically optimized, achieving maximum resolutions (Rs) of 1.61 for METHP, 2.40 for DIP, 1.70 for MALA, and 2.02 for ISOME. The QuEChERS method was employed for sample pretreatment, ensuring high recoveries. All three methods demonstrated excellent linearity (R > 0.998), accuracy with recoveries ranging from 79% to 121%, precision with RSD% < 11%, and sensitivity with low limits of enantiomer detection (LODs) as low as 0.17 µg/kg for METHP, 0.087 µg/kg for DIP, 0.062 µg/kg for MALA, and 0.054 µg/kg for ISOME, representing a sensitivity improvement of 16–172 times compared to existing methods. Field soil samples from Yangzizhou District, Nanchang, China, revealed significant contamination by ISOME, with concentrations of a single enantiomer reaching up to 8343 µg/kg, while MALA exhibited varying enantiomeric ratios with depth. This study provides robust analytical tools for monitoring chiral OP residues in soil, contributing to food safety and environmental protection.