Residual analysis and selective degradation of profenofos enantiomers in citrus

An analytical method of the chiral stationary phase/high performance liquid chromatography-tandem mass spectrometry technique coupled with QuEChERS for determination of the enantiomers of profenofos in citrus was developed, and the selective degradation behavior of profenofos enantiomers in citrus was studied through field experiments. The sample preparation involved quick extraction with acetonitrile and cleaning-up with multi-walled carbon nanotube sorbent. The enantiomers of profenofos were separated by a ND (2)-RH chiral column, detected by tandem mass spectrometry in multi-reaction monitoring (MRM) mode, and quantified using matrix-matched calibration curves. The results showed good linear relationships for the analytes in the concentration range of 2.5-250 μg/L with their correlation coefficients (r) >0.999 6. The limits of quantitation (LOQs) were 5 μg/kg. The average recoveries of the two enantiomers of profenofos in citrus ranged from 76% to 83% at three spiked levels(5, 100, 500 μg/kg) and the relative standard deviations (RSD) were between 2.6% and 6.0%. Field experiments were conducted to study the differences in the degradation of profenofos enantiomers in citrus. The results of dynamic experiments showed that degradation of the enantiomers of profenofos in citrus conformed to the first-order reaction kinetic equation, and the half-lives of (+)-profenofos and (−)-profenofos were 12.53 d and 14.14 d, respectively. The enantiomer fraction (EF) value of the profenofos enantiomers in the field experiments reached 0.43 after 30 d of application, indicating that there were significant enantio-selectivity in the degradation of profenofos enantiomers in citrus.