RESUMEN
A multi-residue method was developed for monitoring antibiotic residues in milk using liquid chromatography coupled to a tandem quadrupole mass spectrometer (LC/MS-MS). Two very short extractions followed by two LC/MS-MS acquisitions allowed the screening of 58 antibiotics belonging to eight different families (penicillins, cephalosporins, sulfonamides, macrolides, lincosamides, aminoglycosides, tetracyclines, and quinolones). This method is currently implemented in the laboratory in a qualitative way, i.e. monitoring the presence or absence of residue in a sample and identification of the analyte before the confirmation step. In order to assess the performance of this method, a validation strategy described in an internal guideline for the validation of screening methods was applied. The aim of the validation was to prove sufficient sensitivity of the method to detect all the targeted antibiotics at the level of interest (maximum residue limit, MRL) at least. According to European Commission Decision 2002/657/EC, the suitable sensitivity of a screening method can be demonstrated when the CCbeta is below or equal to the MRL and so the false-compliant rate below or equal to 5% at the MRL level. The validation scheme was established in order to take into account various variability factors: the apparatus response, the interday repeatability, the matrix effect, etc. The results of the validation clearly demonstrate the suitability of this method for the detection and identification of more than 50 antibiotics and they are in agreement with the results obtained in routine analysis.