Determination of β-lactam residues in foodstuffs of animal origin using supported liquid membrane extraction and liquid chromatography–mass spectrometry

β-Lactams have been used extensively both in human and veterinary medicine practices. In veterinary medicine, they are used mainly as growth promoters as well as chemotherapeutic and prophylactic agents. The occurrence of β-lactam residues in foodstuffs is a serious health hazard. In this work, a sample purification and enrichment technique involving the use of supported liquid membrane have been developed for β-lactams in milk, kidney and liver tissues. The liquid membrane made of n-undecane:di-n-hexyl ether (1:1) was used to enrich a mixture of four β-lactams namely, ampicillin, cloxacillin, penicillin V and penicillin G. Separation and detection of the enriched β-lactam extracts were performed using a high performance liquid chromatography coupled to a mass spectrometer operating under positive ion electrospray mode (LC–PI–ESI–MS). The detection limits (DLs) obtained were found to be 1 ng/kg for penicillin G and penicillin V in kidney and liver tissues and 0.7 μg/L in milk. For ampicillin, the DLs were found to be 1.4 μg/kg in kidney and liver tissues and 1.7 μg/L in milk. Limits of quantification based on a minimal value of the signal-to-noise ratio of 10, were estimated to be 1.1 and 0.01 for penicillin G in kidney and liver tissues, respectively, while for penicillin V it was 0.4 and 0.01 for kidney and liver tissues, respectively. The DL values obtained using this approach were found to be 2–3 order of magnitudes lower than the stipulated tolerance levels as set by the EU and FDA.