Oxycarboxin(5,6-dihydro-2-methyl-N-phenyl-1,4-oxathiin-3-carboxamide-4,4-dioxide) as oxanthiin fungicide is a systemic fungicide commonly used as a seed treatment to control various fungi that cause seed and seeding diseases in agronomic and horticultural crops. An analytical method was developed using HPLC-UVD/MS to precisely determine the residue of oxycarboxin. The oxycarboxin residue was extracted with acetone from representative samples of five raw products which comprised hulled rice, soybean, Kimchi cabbage, green pepper, and apple. The extract was diluted with saline water, and dichloromethane partition was followed to recover oxycarboxin from the aqueous phase. Florisil column chromatography was additionally employed for final purification of the extract. Oxycarboxin was separated and quantitated by HPLC with UVD using a Zorbax SB-AQ C18 column. Accuracy of the proposed method was validated by the recovery from crop samples fortified with oxycarboxin at 3 levels per crop in each triplication. Mean recoveries ranged from 78.3% to 96.1% in five representative agricultural commodities. The coefficients of variation were less than 10%. Limit of quantitation of oxycarboxin was 0.04 mg/kg as verified by the recovery experiment. A confirmatory technique using LC/MS with selected-ion monitoring was also provided to clearly identify the suspected residue. Therefore, this analytical method was reproducible and sensitive enough to determine the residue of oxycarboxin in agricultural commodities.
