Determination and confirmation of tulathromycin residues in bovine liver and porcine kidney via their common hydrolytic fragment using high-performance liquid chromatography/tandem mass spectrometry

An accurate, reliable, and reproducible analytical method using HPLC/MS/MS for the determination of tulathromycin residues in bovine liver and porcine kidney via their common hydrolytic fragment (CP-60,300) was developed and validated. Briefly, the method involved an initial acid treatment of intact tissues, which yielded the common fragment (CP-60,300). A portion of the acid hydrolyzate was purified by SPE using a strong cation exchange cartridge. Evaporation of the purified extract was followed by reconstitution in aqueous buffer and analysis by HPLC/MS/MS under isocratic conditions. The developed method provided acceptable sensitivity for determinative surveillance of tulathromycin in porcine kidney and bovine liver with an LOQ of 7.50 and 2.75 microg/g, respectively. The overall recovery and precision of 45 determinations of each tissue were 97.8% (5.3%) for porcine kidney and 96.9% (7.9%) for bovine liver. Accuracy, precision, linearity, specificity, and ruggedness were demonstrated. An HPLC/MS/MS method was also developed for use in these tissues as a confirmatory assay following modifications to the MS detection parameters. The confirmatory method demonstrated acceptable sensitivity for confirmatory evaluation of tulathromycin in porcine kidney and bovine liver at tolerances of 15 and 5.5 microg/g, respectively.