[Development of an LC-MS/MS Method for Determining Residual Isoxaflutole and Metabolite B in Livestock Products]

A reliable LC-MS/MS method was developed for determining residual isoxaflutole and its primary metabolite, metabolite B (isoxaflutole diketonitrile), in livestock products. Isoxaflutole is an unstable compound that rapidly degrades to its metabolites. To prevent the conversion of isoxaflutole to its metabolites during sample preparation, a mixture of 4 mol/L HCl and ethanol (1 : 1, v/v) was added to the sample in an amount equivalent to half of the sample weight and mixed. Analytes were extracted with acetonitrile in the presence of n-hexane, followed by partitioning with a mixture of ethyl acetate and n-hexane (3 : 7, v/v) and a sodium chloride solution. The organic layer was cleaned up using an Oasis HLB cartridge and then analyzed by LC-MS/MS. Validation was performed through recovery tests using five livestock products. Samples were spiked with isoxaflutole and metabolite B at 0.01 mg/kg and at the maximum residue limits established for each food. The validation results for the analytes showed excellent recoveries (80-94%) and high precision (<10%).