Development of a LC-IT-TOF MS Procedure to Quantify Veterinary Drug Residues in Milk Employing a QuEChERS Approach

A sensitive liquid chromatography coupled to high-resolution tandem mass spectrometry (LC-IT-TOF MS) with electrospray ionization method for the identification and quantification of five antibiotic residues in milk has been developed. For sample preparation, a simple modification of the QuEChERS method was used with further sample cleanup using dispersive solid phase extraction according to AOAC official standards 2007.01. The method yielded acceptable accuracy values for each drug at each level, with mean recoveries (n = 3) ranging from 83 to 92 %. The recovery of antibiotics of the intra-assay ranged from 85 to 95 % (RSD < 9 %) and the inter-assay from 84 to 95 % (RSD < 11 %). A total of 31 milk samples, either pasteurized or fresh whole milk, were analyzed following the method. Amoxicillin and oxytetracycline (two of the pasteurized milk samples), ampicillin and amoxicillin (3 of 25 fresh milk samples), and tetracycline and oxytetracycline (two other fresh milk samples out of 25) were detected at levels below the current Brazilian maximum residue levels.