Simultaneous determination of nalidixic acid, oxolinic acid and piromidic acid in fish by high-performance liquid chromatography with fluorescence and UV detection.

A simple and rapid method for the simultaneous determination of nalidixic acid (NA), oxolinic acid (OXA) and piromidic acid (PMA) in cultured fish has been developed by high-performance liquid chromatography (HPLC). The drugs were extracted with 0.1% metaphosphoric acid-methanol (6:4), followed by a Sep-Pak C18 clean-up procedure. The HPLC separation was carried out on a Kaseisorb LC ODS 300-5 column (25 cm x 4.6 mm I.D.) using 5 mM phosphate buffer-acetonitrile (6:4) as a mobile phase. A fluorescence detector was used for NA and OXA at the excitation wavelength of 325 nm and the emission wavelength of 365 nm and an ultraviolet detector at 280 nm for PMA. The calibration graphs were rectilinear from 1 to 10 ng for OXA, from 2 to 20 ng for NA and PMA. The recoveries of NA, OXA and PMA added to fish were 81.5-85.3, 83.7-88.7 and 80.9-84.9%, respectively, with high accuracy. The limits of detection were 0.01 micrograms/g for each drug.