Use of liquid chromatography- quadrupole time-of-flight mass spectrometry for enantioselective separation and determination of pyrisoxazole in vegetables, strawberry and soil

The present work firstly described the enantio-separation and determination of pyrisoxazole enantiomers in vegetables, strawberry and soil samples by chiral liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-Q-TOF/MS). Pyrisoxazole has two chiral carbon atoms and consists of four stereoisomers. Taking the specific optical rotation measurement and MS analysis data into consideration, the four enantiomers were discriminated as (−)-A, (+)-A, (+)-B and (−)-B corresponding to their elution order under the optimum chromatographic condition. Influences of the mobile phase and column temperature on the enantio-separation selectivity of pyrisoxazole were explored. The perfect baseline separation of pyrisoxazole enantiomers can be achieved within 10 min using methanol- water (70:30, v/v) as mobile phase on chiral Lux Cellulose-3 column. The thermodynamic analysis demonstrated that the enantioseparation of (−)-A and (+)-A, (+)-A and (+)-B were enthalpy driven separation, while the enantioseparation of (+)-B and (−)-B was entropy driven separation. Under the optimum method, method validation including matrix effect, linearity, sensitivity and precision were performed. At the spiked concentration of 10, 50 and 100 μg kg−1, the recoveries of the pyrisoxazole enantiomers in cucumber, tomato, pakchoi, pepper and strawberry samples were 64.2-100% (RSD ≤ 14%); While they were relatively higher in soil samples and all around 120% (RSD ≤10%). The limits of detection are in the range from 0.2 to 1.0 μg kg−1 for cucumber, tomato, pakchoi, pepper, strawberry and soil samples. The developed method was then utilized for monitoring the degradation kinetics of pyrisoxazole enantiomers in strawberry under field trials, which provided the environmental behavior data of chiral pyrisoxazole enantiomers and consequently for further health risk assessment of the chiral pesticides.