Determination of sulfonamide residues in the tissues of food animals using automated precolumn derivatization and liquid chromatography with fluorescence detection

A liquid chromatographic method for the determination of sulfachloropyridazine, sulfadiazine, sulfadimethoxine, sulfadoxine, sulfaethoxypyridazine, sulfamethazine, sulfaquinoxaline, and sulfathiazole residues in the muscle, liver, and kidney of food animals using sulfapyridine as internal standard is reported. Tissues are extracted using a modified version of AOAC Official Method 983.31 (Sulfonamide Residues in Animal Tissues). The sample extract is reconstituted in pH 3.0 buffer-acetonitrile (60 + 40) and filtered into an autosampler vial. Using a programmable autosampler of a liquid chromatograph, a portion of the sample is derivatized precolumn with fluorescamine. The sulfonamide derivatives are separated by liquid chromatography using a C18 column with a mobile phase of 0.02M phosphoric acid-acetonitrile (60.5 + 39.5) and detected by fluorescence (excitation, 405 nm; emission, 495 nm). The method was applied to swine and cattle muscle, liver, and kidney; sheep and horse muscle and kidney; and chicken muscle and liver. The mean values for samples fortified with sulfonamides at levels between 0.05 and 0.2 microg/g agreed within 96-99% of spiked levels, with coefficients of variation ranging from 4-10%. The limit of detection (LOD) for all sulfonamides was 0.01 microg/g, with the exception of sulfaquinoxaline, for which the LOD was 0.015 microg/g.