Determination of residues of oxolinic acid and flumequine in freeze-dried salmon muscle and skin by HPLC with fluorescence detection

A procedure for the determination of residues of oxolinic acid (OA) and flumequine (FLU) in freeze-dried salmon muscle with attached skin, using reversed-phase high-performance liquid chromatography, is described. OA and FLU were extracted by a solid-liquid extraction procedure: after addition of hydrochloric acid, extraction used successively ethyl acetate, sodium hydroxide and chloroform. Liquid chromatography was performed on a 5 mum PuroSpher RP-18E(R) cartridge using acetonitrile and 0.02 M aqueous orthophosphoric acid solution as mobile phase, with fluorescence detection. The performance of the method was established by spiking tissues with OA and FLU before the freeze-drying step. The method was linear over the concentration range 50-2000 ng/g freeze-dried tissue. Limits of detection and quantitation were 3.2 and 16 ng/g wet weight tissue respectively both for OA and FLU. Mean extraction recoveries of OA and FLU from freeze-dried tissue were 85.5 and 85.2% respectively. The method is suitable as a regulatory one for determination of residues of OA and FLU in freeze- dried salmon tissue.