Determination of Carbadox and metabolites of Carbadox and Olaquindox in muscle tissue using high performance liquid chromatography–tandem mass spectrometry

A sensitive and robust LC–APCI-MS/MS method has been developed for the unambiguous detection and quantitative determination of the antimicrobial agent Carbadox, its metabolite quinoxaline-2-carboxylic acid and methyl-3-quinoxaline-2-carboxylic acid the major metabolite of Olaquindox. The method was aimed for application in the assaying of muscle tissue so the developed sample preparation scheme subjected samples to enzymatic digestion prior to the application of solid phase extraction clean-up. Subsequently the purified extracts were analyzed by reversed-phase LC–MS/MS in positive APCI and multiple reaction monitoring mode. The method was validated at a level of 1 μg/kg. The decision limits CCα and detection capability CCβ ranged from 0.09 μg/kg to 0.24 μg/kg and from 0.12 μg/kg to 0.41 μg/kg, respectively. The accuracy and precision of the method were satisfactory. The recoveries ranged from 92% to 101% for the metabolites and from 60% to 62% for Carbadox, with coefficient of variances (CVs) less than 12%. The developed method proved efficient and straightforward allowing positive identification and quantitation of the target banned analytes and is thus suitable for application in residue control programmes and metabolism studies.