Determination of oxacillin, cloxacillin and dicloxacillin in milk, meat and cheese samples using HPLC and precolumn derivatization

The objective of this work was to develop a confirmatory HPLC method for the determination of oxacillin, cloxacillin and dicloxacillin residues in milk, meat and cheese samples. The assay presented involves the extraction of the compounds to be studied from the sample, with an acidic solution of sodium tungstate, followed by solid-phase extraction and precolumn derivatization. The derivatization of the samples was achieved by the formation of mercury mercaptide derivatives in the presence of imidazole. Chromatographic separations were realized using linear gradient elution and separated compounds were detected at 345 nm. The recoveries of the preparation step were higher than 80% and the limits of detection were lower than the maximal residual limits (MRL) as determined by the Commission of the European Communities.