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.