Residues of b-lactam antibiotics in bovine milk: HPLC-MS/MS confirmatory analysis after microbial assay screening

The analysis to detect antimicrobial residues in milk are usually performed in two steps: first, a microbiological method, based on the inibition of microbial growth, is used as a screening tool. Second the samples found positive are confirmed by a chernical method. A confirmatory method has to be able to detect which molecule is present in the sample and to quantitate it. HPLC-UV is the technique usually adopted as a confirmatory method. The use of this technique has some limitations. We developed a very fast chernical method based on HPLC-MS/MS. This method is able to process a great number of samples per day, giving an error-proof confirmation and with a very high sensitivity. The method has been validated and tested on 27 bovine milk samples found positive by a microbioiogical method at the IZSLER of Brescia.