Confirmatory assay for the determination of tetracycline, oxytetracycline, chlortetracycline and its isomers in muscle and kidney using liquid chromatography-mass spectrometry.

A confirmatory method is described for the determination of tetracycline, oxytetracycline and chlortetracycline in muscle and kidney using liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry. The tetracyclines were extracted from tissue using glycine-HCl buffer and concentrated using solid-phase extraction. HPLC separation was carried out using a gradient and the tetracyclines were detected using a bench-top LC-MS system. Several ions could be monitored for each tetracycline, allowing ion ratio measurements to be made. The detection limits for the assay were in the region of 10 ng/g in muscle and 20 ng/g in kidney. Validation was carried out at half the maximum residue limit, the maximum residue limit and two times the maximum residue limit. The formation of epimers and tautomers of the tetracyclines, their presence in incurred tissues and difficulties in their accurate quantitation is discussed.