Simultaneous determination of quinolone and β-lactam residues in raw cow milk samples using ultrasound-assisted extraction and dispersive-SPE prior to UHPLC−MS/MS analysis

A new sensitive, selective and accurate method to determine 17 quinolone and 14 β-lactam antibiotic residues in raw cow milk samples has been validated. The method is based on the extraction of the antibiotics by ultrasound-assisted extraction (UAE) followed by a clean-up step using a dispersive solid-phase extraction (d-SPE) sorbent. Experimental designs have been used for extraction and clean-up optimization. The extraction solvent selected was a mixture of acetonitrile/methanol/McIlvaine buffer solution (60:25:15; v/v/v) at pH 6. A volume of 15 mL of this extraction solvent was added to freeze-dried milk samples and the mixtures were sonicated during 20 min at 70% amplitude. The extracts were further cleaned-up with PSA (primary-secondary amine) sorbent and analysed by UHPLC-ESI(+)-MS/MS. Cincophen and piperacillin were used as surrogates for quinolones and β-lactams, respectively. The method was validated according to European Directive 2002/657/EC and FDA guideline. Recovery rates ranged from 96.0% to 104.5%. The limits of quantification of the method ranged from 0.3 to 2.0 ng g−1, while inter- and intra-day variability was under 7.1% in all cases. The method was applied to the determination of selected antibiotics in 28 raw cow milk samples. A percentage of 28% of the samples were positive in any of the studied antibiotics, however, only 11% were considered non-compliant with the current European Union legislation (Commission Regulation 37/2010).