Chiral method validation and stereoselective degradation of profoxydim isomers in paddy soil

The herbicide profoxydim, which is chiral in nature, is commonly used for weed control in rice. However, traditional achiral analysis treats profoxydim isomers as a single compound, providing only partial and inaccuracy information assuming identical behavior for the four isomers. To address this issue, a sensitive and straightforward chiral analytical method was developed using QuEChERS and chiral HPLC-MS/MS to determine the residues of all four stereoisomers of profoxydim in soil. The method was validated and found to have good accuracy and precision, with recoveries ranging from 88.27 to 104.93% for dry soil and from 98.25 to 106.53% for soaked soil, with RSD values lower than 11.14%. The limit of detection for the profoxydim isomers was 7.6 µg/kg, and the limit of quantification was 25.0 µg/kg. Furthermore, the proposed method was employed for the first time to investigate the individual degradation of novel isolated stereoisomers of profoxydim in soil and the kinetics and evolution of the generated degradation products (DPs). The degradation of the four stereoisomers followed first-order kinetics and was found to be stereoselective, with isomers 1 and 4 preferentially degrading with half-lives of 14.7 and 15.6 h respectively. The profoxydim enantiomers remained configurationally stable without any interconversion throughout the experiment. The findings of this study provide a robust scientific basis for improving profoxydim risk assessment and highlight the need to characterize chiral agrochemical isomers to better understand their environmental distribution and fate.