Multi-residue determination of veterinary drugs in milk by ultra-high-pressure liquid chromatography-tandem mass spectrometry.

A simple, selective and fast multi-residue method was developed to determine 18 veterinary drugs in milk by ultra-high-pressure liquid chromatography coupled to tandem quadrupole mass spectrometry. The selected antibiotics include quinolones, sulphonamides, macrolides, anthelmintics and one tetracycline. An extraction procedure based on QuEChERS methodology (quick, easy, cheap, effective, rugged and safe), consisting of a liquid extraction of the milk samples with acetonitrile without sample clean up was performed. The extract was centrifuged and the supernatant was filtered prior to chromatographic analysis. Several chromatographic conditions were optimized in order to obtain a fast separation (less than 10 min). The antibiotics were detected by electrospray ionization in positive ion mode with multiple reaction monitoring (MRM) and mass spectrometric conditions were optimized in order to increase selectivity and sensitivity. The developed method was validated in terms of linearity, trueness, precision, limits of detection (LODs) and quantification. Mean recoveries ranged from 70% to 110% and interday precision was lower than 21%. LODs ranged from 1 to 4 microg/kg. Finally, the method was applied to real samples and only traces of tylosin and fenbendezol were detected in two samples.