Development Of Analytical Methods For The Determination Of Β-lactam Antibiotic Residues In Meat, Milk And Dairy Products
Authors:   ,   Munster Technological University, Di Rocco Melissa 
Published: August 2024

In this project, analytical methodologies for the determination of β-lactam antibiotic residues in meat and dairy products were developed and validated using ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). The methods included the main penicillins, cephalosporins and carbapenems commonly employed in human or veterinary medicine for the treatment of bacterial infections. A multi-residue method for the analysis of 30 β-lactams was developed and validated in bovine muscle using dispersive-solid phase extraction (d-SPE), reversed-phase chromatography and mass spectrometry detection. A number of sorbent materials were assessed for clean-up, and a simple and straightforward sample preparation protocol developed for the efficient extraction of the antibiotic residues, including the main metabolites of cephapirin and ceftiofur. The stability of the β-lactam compounds during storage and analysis was also investigated, and new knowledge generated. At present, this represents the most comprehensive UHPLC-MS/MS method reported in the literature for the analysis of β-lactams in meat, and also the first UHPLC-MS/MS method available in Ireland for the cephalosporin drugs. Novel chromatographic stationary phases were evaluated to improve the separation of structurally similar β-lactams, and a selective chromatographic separation developed for the determination of 32 analytes in milk using phenyl-column chemistry prior to detection by tandem mass spectrometry. Among the published literature, the proposed methodology for milk analysis included the widest range of β-lactams. The method also reported and investigated for the first time the presence of isobaric interferences between structurally similar compounds. The separation of the 32 analytes was accomplished over a 12 minutes chromatographic run time, while the retention of the polar compounds was also improved. XX The migration of cefquinome residues from naturally contaminated milk collected from treated cows into different dairy products, including skim milk, buttermilk, cream, whey, curd, cheese and butter, was investigated for the first time. The methodologies previously developed were adapted and successfully validated for the analysis of cefquinome residues in all the different matrices. Results showed that cefquinome is excreted in the milk of dairy cows following administration by injection. It was also proved that this drug does not degrade during dairy product manufacture, and it mostly migrates with the high-water containing fractions such as skim milk, buttermilk and whey. This would have food safety implications if residues of the antibiotic were present in the milk. A derivatization procedure based on the stabilisation of ceftiofur and its metabolites to desfuroylceftiofur acetamide was developed and validated in bovine muscle. This was the first time that vibrational shaking was employed for the efficient homogenisation of samples in ceftiofur-related compounds analysis, and also the first method using microwave-assisted extraction to carefully control the deconjugation and stabilisation process of all protein-bound metabolites.