DETERMINATION OF RESIDUES OF FLUMEQUINE AND NALIDIXIC, OXOLINIC, AND PIROMIDIC ACIDS IN CATFISH BY LIQUID-CHROMATOGRAPHY WITH FLUORESCENCE AND UV DETECTION

A liquid chromatographic (LC) method is described for determining resi dues of flumequine (FLU) and nalidixic (NAL), oxolinic (OXO), and piro midic (PIR) acids in catfish muscle, The identities of 3 of these resi dues are confirmed by gas chromatography-mass spectrometry (GO-MS), Th e extraction and cleanup procedures are the same for both determinatio n and identification, Analyte isolation involves homogenizing the tiss ue with acetone, defatting the acetone extract with hexane, and extrac ting the compounds into chloroform, The extract is further purified by first partitioning into base and subsequently back-extracting into ch loroform after acidifying the aqueous phase. After the solvent is evap orated, the residue is dissolved in mobile phase, and the analytes are determined by LC with fluorescence detection, excitation at 325 nm an d emission at 365 nm, Catfish muscle was fortified with each quinolone at 5, 10, 20, 40, and 80 ng/g. Overall average recoveries were 83-94% , with relative standard deviations (RSDs) of 5-7%, The method was eva luated also by a second analyst, who determined 4 quinolones added in combination. Average recoveries of quinolones from catfish fortified a t 5, 10, and 20 ng/g were 78-90%, with RSDs of 3-6%, The presence in c atfish muscle of incurred OXO, FLU, and NAL at the 10 ng/g level was c onfirmed by analyzing the decarboxylated quinolones by GO-MS, The rela tive abundances of all 5 major ions for OXO, FLU, and NAL were within 10% of those observed in spectra of standard compounds decarboxylated by the same method.