Analytical procedure for the determination of chlortetracycline and 4-epi-chlortetracycline in pig kidneys

A liquid chromatography-diode array detection (LC-DAD) procedure has been developed for assaying chlortetracycline (CTC) and its 4-epimer (4-epi-CTC) residues in pig kidneys. The procedure involved extraction with 0.1 M oxalic buffer followed by protein precipitation with trichloroacetic acid. Further solid-phase extraction (SPE) clean-up on a Strata X polymeric cartridge was allowed to obtain an extract suitable for LC analysis. Chromatographic separation was carried out on a C8 analytical column, using isocratic elution with methanol-acetonitrile-0.01 M oxalic acid (15:15:70, v/v/v) at ambient temperature. The flow-rate was 1.2 ml/min and the eluate was analysed at 365 nm. The whole procedure was evaluated according to the requirements of the European Union regulation 2002/657/EC determining specificity, decision limit (CCα), detection capacity (CCβ), trueness, precision and robustness during validation process. The decision limit (CCα) was 674.8 μg/kg for CTC and 683.6 μg/kg for 4-epi-CTC. The detection capacity (CCβ) was 683.6 and 696.3 μg/kg for CTC and 4-epi-CTC, respectively. The recoveries of CTC and 4-epi-CTC from spiked samples at the levels of 300, 600 and 900 μg/kg (0.5 × MRL, 1 × MRL and 1.5 × MRL) were higher than 70%. This method has higher throughput than reported previously extraction method with oxalic acid and acetonitrile used for dechelation and deproteinization.