Monitoring of benzylpenicillin in ovine milk by HPLC

A method for ‘in vivo’ determination of the oxytetracyclin residues in ovine milk at low levels is described. Two groups of Sardinian breed sheep were treated with a dose of oxytetracycline by intramammary infusion and intramuscular administration, respectively. Oxytetracycline residues in extracts obtained from a preliminary cleanup procedure, were detected by an isocratic high-performance liquid chromatography (HPLC) method. Linear calibration plots were obtained over a large concentration range of 1 mg ml−1–10 ng ml−1, with correlation coefficients higher than 0.996. Recoveries between 85.8 and 98.9% were obtained. Limit of detection (LOD) and limit of determination (LOQ) were 5.2 and 17.5 ng ml−1, respectively. This method would be useful for routine monitoring of oxytetracycline residues in ovine dairy milk