IMPROVEMENT OF CHEMICAL-ANALYSIS OF ANTIBIOTICS .18. IDENTIFICATION OF RESIDUAL TETRACYCLINES IN BOVINE-TISSUES BY TLC FABMS WITH A SAMPLE CONDENSATION TECHNIQUE

To reliably identify residual tetracycline antibiotics (TCs) oxytetracycline, tetracycline, chlortetracycline, and doxycycline in bovine tissues, a confirmation method using thin-layer chromatography/fast atom bombardment mass spectrometry (TLC/FABMS) has been established. This method consists of the following four steps: (1) extraction of TCs from bovine tissues with McIlvaine buffer (pH 4.0) containing 0.1 M ethylenediaminetetraacetate (Na2EDTA); (2) elution of the TCs from prepacked C18 cartridges, pretreated with Na2EDTA, with ethyl acetate followed by methanol-ethyl acetate (5:95 v/v) as eluents; (3) separation of the TCs on a reversed-phase C-8 TLC plate with methanol-acetonitrile-0.5 M oxalic acid solution (pH 2.0) (1:1:4 v/v) as a solvent system; and (4) TLC/FABMS with a condensation technique employing thioglycerol as a matrix. The method can reliably identify TCs fortified at concentrations of 0.1 ppm in bovine tissues, including muscle, liver, and kidney, and has been successfully applied to the identification of residual TCs in bovine incurred samples.