Enantioselective determination of the chiral pesticide isofenphos-methyl in vegetables, fruits, and soil and its enantioselective degradation in pakchoi using HPLC with UV detection.

Abstract

An enantioselective method for the simultaneous determination of the chiral pesticide isofenphos-methyl in vegetables, fruits, and soil has been established using high-performance liquid chromatography with UV detection. The complete enantioseparation was conducted by reversed-phase liquid chromatography with a cellulose-tris-(4-methylbenzoate) chiral stationary phase (CSP) (Lux Cellulose-3). The effects of different mobile phase compositions, temperatures, and flow rates on enantioseparation were also investigated. The experimental and calculated electronic circular dichroism spectra indicate that the first peak is (S)-(+)-isofenphos-methyl and the second peak is (R)-(-)-isofenphos-methyl. Alumina-A and Florisil solid-phase extraction (SPE) columns were used to cleanup for vegetable, fruit, and soil samples. The mean recoveries of the two enantiomers ranged from 83.2 to 110.9% with intra-day relative standard deviations (RSDs) from 3.2 to 10.8% and inter-day RSDs from 3.6 to 10%. Good linearity (≥0.9992) was obtained for the two enantiomers in all matrix-matched calibration curves in the range of 0.25 to 20mgL(-1). The limit of detection for two enantiomers in six matrices was in the range of 0.008 to 0.011mgkg(-1), and the limit of quantification was estimated to range from 0.027 to 0.037mgkg(-1). The results indicated that this method was a convenient and dependable approach for the simultaneous determination of isofenphos-methyl enantiomers in food and environmental samples. The stereoselective degradation of isofenphos-methyl in pakchoi has shown that the (R)-(-)-isofenphos-methyl isomer (half-life t 1/2 = 2.2days) degraded faster than the (S)-(+)-isomer (t 1/2 = 1.9days). Graphical Abstract The enantioselective determination and enantioselective degradation of the chiral pesticide isofenphos-methyl.