Confirmatory assay for the simultaneous detection of five penicillins in muscle, kidney and milk using liquid chromatography–electrospray mass spectrometry

Abstract

A confirmatory assay using liquid chromatography–electrospray mass spectrometry (LC–EMS) is presented for the simultaneous determination of penicillins V and G along with oxacillin, cloxacillin and dicloxacillin in muscle, kidney and milk. Nafcillin is used as an internal standard. Samples are extracted using acetonitrile and cleaned up using liquid–liquid extraction into dichloromethane. The extracts are injected into a dedicated LC–EMS instrument and any penicillins present are detected using multiple single-ion monitoring. Three or four ions can be detected for each penicillin, meeting one of the recommended EU criteria for confirmatory residue analyses using low-resolution mass spectrometry. The detection limits are below the stipulated EU maximum residue limits for each of the penicillins