Residue analysis of oxytetracycline in water and sediment samples by high-performance liquid chromatography and immunochemical techniques

The performances of an HPLC method and an enzyme-linked immunosorbent assay ( ELISA) have been compared with respect to residue analysis of oxytetracycline in water and sediment samples of fish farms where this antibiotic is used for treating diseases. The ELISA employed in this study was a commercially available kit for determination of tetracycline in food. Due to its cross-reactivity towards oxytetracycline the kit turned out to be suited for water samples down to approximately 1 mu g oxytetracycline L-1 without sample pretreatment. This concentration level could be lowered by a factor of at least 200 using preconcentration by solid-phase extraction (SPE) on Oasis HLB cartridges with elution by 10 mM oxalic acid in methanol. HPLC separation was carried out using a C8 reversed-phase column and a gradient of methanol and water containing 10 mM oxalic acid. The detection limit for water samples after 250-fold preconcentration by SPE was about 0.24 mu g L-1 using UV detection at 360 nm. Recoveries of 98.7% were found at a concentration level of 2 mu g L-1. Satisfactory correlation was observed between the results of HPLC and ELISA. Both methods were also suited for measuring residues of oxytetracycline in sediment samples in the low mu g g(-1) range.