DETERMINATION OF SPECTINOMYCIN RESIDUES IN BOVINE-MILK USING LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

A method capable of quantifying spectinomycin in raw bovine milk was d eveloped and validated for 100-400 ng/mL. In this procedure the milk i s centrifuged at -4 degrees C and the top fat layer removed. The defat ted milk is deproteinated by precipitation with 30% trichloroacetic ac id and centrifugation. The supernatant is washed sequentially with dic hloromethane, hexane, and ethyl acetate. An aliquot of the separated a queous layer is prepared for HPLC analysis by mixing with 1-decanesulf onic acid and filtering. The analyte is separated from the matrix comp onents using an ion-pair mobile phase and a reversed-phase column; the analyte is quantified with an electrochemical detector. Mean recoveri es are 80% for milk fortified at 100 ng/mL, 76% for milk fortified at 200 ng/mL, and 77% for milk fortified at 400 ng/mL. The intralaborator y coefficients of variations are 18%, 6%, and 9%, respectively.