Enantioselective residue analysis of oxathiapiprolin and its metabolite in tea and other crops by ultra high performance liquid chromatography tandem mass spectrometry

Oxathiapiprolin is the first chiral piperidinyl thiazole isoxazoline fungicide developed to control downy mildew and other diseases, and there were no prior reports on its enantiomeric residue. In this study, a modified quick, easy, cheap, effective, rugged and safe extraction and purification method followed by UHPLC-MS/MS determination was firstly developed and validated for the residue analysis of oxathiapiprolin enantiomers and its metabolite IN-E8S72 in green tea and other crops. Oxathiapiprolin enantiomers and IN-E8S72 were separated on a chiral Lux Cellulose-3 column with the use of 0.1% formic acid in acetonitrile and 5 mmol L^-1 ammonium acetate in water as mobile phases. IN-E8S72 was eluted first, followed by (-)-oxathiapiprolin, and then (+)-oxathiapiprolin. The recoveries ranged from 53.3% to 125.3% with relative standard deviations ranging from 1.4% to 16.0%. The limits of quantification for (-)-oxathiapiprolin and (+)-oxathiapiprolin were 0.005 mg kg^-1 in romaine lettuce, head cabbage, potato, grape and garlic, 0.01 mg kg^-1 in soybean and pea, and 0.025 mg kg^-1 in green tea and dry pepper. The limits of quantification of IN-E8S72 were twice those of (-)-oxathiapiprolin. Screening results with real market samples indicated that there was no enantiomeric excess in the oxathiapiprolin residue in romaine lettuce. This article is protected by copyright. All rights reserved.

Keywords: crop; enantioselective residue; oxathiapiprolin; tea; ultra high performance liquid chromatography tandem mass spectrometry.