Simultaneous Determination of Four Antibiotics in Raw Milk by UPLC-MS/MS Using Protein Precipitation as Sample Preparation: Development, Validation, and Application in Real Samples

In this study, a rapid and simple analytical method was proposed, based on protein precipitation as sample preparation for simultaneous determination of tetracycline, oxytetracycline, penicillin G and ceftiofur in raw milk by ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). The method was applied to raw milk samples from dairy cows medicated with tetracycline for subclinical mastitis. Samples were collected from the adjacent teat to the teat treated with tetracycline of eight different cows at 24, 48, 72 and 96 h after treatment. The limits of quantification of the proposed method ranged between 1 and 5 ng g-1 and limits of detection ranged between 0.1 and 0.5 ng g-1. The recoveries ranged from 61 to 111% and the linear range was 1 to 2064 ng g-1 for tetracycline and oxytetracycline, and 5 to 2064 ng g-1 for penicillin G and ceftiofur. Approximately 75 and 63% of the treated animals revealed more tetracycline than legally recommended at 72 and 96 h since last treatment, respectively.