Application of ion-exchange cartridge clean-up in food analysis IV. Confirmatory assay of benzylpenicillin, phenoxymethylpenicillin, oxacillin, cloxacillin, nafcillin and dicloxacillin in bovine tissues by liquid chromatography-electrospray ionization tandem mass spectrometry

A multiresidue analytical method was developed for the confirmation of benz ylpenicillin (PCG), phenoxymethylpenicillin (PCV), oxacillin (MPIPC), cloxa cillin (MCIPC), nafcillin (NFPC) and dicloxacillin (MDIPC) in bovine tissue s using electrospray ionization liquid chromatography-tandem mass spectrome try (LC-ESI-MS-MS) with a product ion scan mode. All penicillins gave [M-H] (-), [M-K-CO2](-) and [M-H-141](-) as the product ion, when [M-H](-) was se lected as the precursor ion. Combination of an ion-exchange cartridge clean -up and the LC-ESI-MS-MS method can reliably identify all of these penicill ins fortified at a concentration of 0.05 mg/kg in bovine tissues, including liver, kidney and muscle. The limits of confirmation satisfy the maximum r esidue limits for each of the penicillins established by the World Health O rganization, US Food and Drug Administration, European Union and Japan. (C) 2001 Elsevier Science B.V. All rights reserved.