Determination of tetracycline residues in animal tissues by liquid chromatography

A simple liquid chromatographic (LC) method was developed for the determination of tetracyclines (oxy-tetracycline, tetracycline and chlortetracycline) in animal tissues. Isolation of tetracyclines from biological matrices was performed with oxalic buffer followed by dechelation and deproteinization with oxalic acid-acetonitrile solution. For clean-up solid phase extraction with a SDBI (styrene-divinylbenzene) cartridge was used. LC analysis was performed on a polymeric analytical column (PLRP-S 5 microns, 150 x 4.6 mm) and using an oxalic acid mobile phase (0.01 M oxalic acid - acetonitrile 75:25, v/v). The whole procedure was validated for intra- and inter-assay reproducibility determination by assaying muscle, liver and kidney samples supplemented with tetracyclines at the level of 50, 100 and 200 ng/g, respectively. The statistical evaluation demonstrates high absolute recovery (> 80%) and low coefficient of variation (< 10%) for all analysed samples. The detection limits for tetracyclines were 10-15 ng/g in muscle, and 20-25 ng/g in liver and kidney samples, depending on the analyte.