LP-62 HPLC-MS/MS-Based Determination of Metalaxyl Residues and Their Enantiomeric Distribution in Food Matrices

The widespread use of chiral pesticides in agriculture, combined with their potential for enantioselective degradation in the environment, poses serious concerns for food safety and public health. Approximately 25% of agrochemical active ingredients are chiral, and their environmental behavior often depends on the stereoselective fate of individual enantiomers. Metalaxyl, a systemic fungicide commonly applied to fruits and vegetables, is marketed both as a racemate and as the single (R)-(+)-enantiomer (Metalaxyl-M). Given the distinct biological activities and environmental behaviors of its enantiomers, it is essential to monitor both total residue levels and enantiomeric distributions in food matrices 1 , 2 . In this study, we developed and applied a high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) method for the determination of metalaxyl residues in fruit and vegetable samples obtained from local supermarkets. Chromatographic separation of total metalaxyl was achieved using an achiral Zorbax Eclipse Plus C18 column (250×4.6 mm, 5 µm), while enantiomeric resolution was performed on a chiral Lux Cellulose-4 column (250×4.6 mm, 5 µm). The mobile phase consisted of acetonitrile and water with 0.1% formic acid (50:50, v/v), operated under isocratic conditions at 1.0 mL/min. Both UV-VIS and MS/MS detectors were employed in series. The influence of chiral selector chemistry and mobile phase composition on peak shape and separation efficiency was evaluated during the analysis. Method validation demonstrated satisfactory sensitivity, with a limit of quantification (LOQ) of 0.4 µg/g. All tested food samples contained detectable levels of metalaxyl, yet all were found to be below established regulatory thresholds. Moreover, enantioselective analysis revealed varying enantiomeric distributions, suggesting possible stereoselective degradation or accumulation mechanisms in different matrices. These findings emphasize the importance of incorporating chiral analytical approaches in routine pesticide residue monitoring programs, particularly for compounds like metalaxyl that are marketed and behave enantioselectively.