Development and validation of an HPLC confirmatory method for the determination of seven tetracycline antibiotics residues in milk according to the European Union Decision 2002/657/EC

An HPLC method with diode-array detection, at 355 nm, was developed and validated for the determination of seven tetracyclines (TCs) in milk: minocycline (MNC), TC, oxytetracycline (OTC), methacycline (MTC), demeclocycline (DMC), chlortetracycline (CTC), and doxycycline (DC). Oxalate buffer (pH 4) was used with 20% TCA as a deproteinization agent for the extraction of analytes from milk followed by SPE. The separation was achieved on an Inertsil ODS-3, 5 mu m, 250 x 4 mm(2) analytical column at ambient temperature. The mobile phase, a mixture of A: 0.01 M oxalic acid and B: CH3CN, was delivered using a gradient program. The procedure was validated according to the European Union decision 2002/657/EC determining selectivity, stability, decision limit, detection capability, accuracy, and precision. Mean recoveries of TCs from spiked milk samples (50, 100, and 200 ng/g) were 93.8 - 100.9% for MNC, 96.8-103.7% for OTC, 96.3-101.8% for TC, 99.4-107.2% for DMC, 99.4-102.9% for CTC, 96.-102.7% for MTC, and 94.6-102.1% for DC. All RSD values were lower than 8.5%. The decision limits CC, calculated by spiking 20 blank milk samples at MRL (100 mu g/kg) ranged from 101.25 to 105.84 mu g/kg, while detection capabilitY CCb from 103.94 to 108.88 mu g/kg.