Determination of Tetracyclines in water samples using liquid chromatography with fluorimetric detection

A liquid chromatographic method with fluorimetric detection is proposed for the determination of trace levels of oxytetracycline, tetracycline, chlortetracycline and doxycycline in water samples. The analytes are preconcentrated by solid phase extraction using reversed phase polymeric cartridges and acetonitrile as eluent. Preconcentration factors up to 125 can be obtained. The chromatographic separation is performed on a polymeric column with a gradient elution program using mobile phases based on mixtures of acetonitrile and 0.01 mol L-1 oxalic acid aqueous solution at a flow rate of 1.2 mL min(-1). Tetracyclines are post-column derivatized with a reagent solution consisting of 0.1 mol L-1 Mg(II) at pH 9 at a flow rate of 0.6 mL min(-1). The highly fluorescent Mg(II) chelates are detected at lambda(ex) = 374 nm and lambda(em) = 499 nm. The detection limits of the whole process are in the low mu g L-1 level. The proposed method has been applied to the analysis of spiked natural water samples, and recovery rates higher than 80% have been obtained.