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Using high-performance liquid chromatography with diode-array detection (HPLC-DAD) technique, a confirmatory method for the determination of trace levels of tetracyclines (oxytetracycline, tetracycline, chlortetracycline and doxycycline) and their 4-epimers (4-epioxytetracycline, 4-epitetracycline and 4-epichlortetracycline) in animal tissues (muscle) was developed.

The samples are extracted with a mixture of succinic acid 0.1 M (pH 4) and methanol after the addition of metacycline as internal standard. The clean-up is carried out by metal chelate affinity chromatography with a following concentration step on an OASIS HLB polymeric reversed phase column. The chromatographic separation of the seven analytes is achieved in 10 min on a short monolithic column (50 mm x 4.6 mm i.d.) using a gradient elution.

The method was validated in bovine muscle following the Commission Decision 2002/657/EC criteria: samples spiked at four concentration levels (0.25, 0.5, 1 and 1.5 times the maximum residue limit) were analysed. Method trueness and precision (repeatability and intra-laboratory reproducibility) as well as decision limits (CC alpha) and detection capabilities (CC beta) are reported. (c) 2008 Elsevier B.V. All rights reserved.