Determination of residues of flumequine and nalidixic, oxolinic, and piromidic acids in catfish by liquid chromatography with fluorescence UV detection

A liquid chromatographic (LC) method is described for determining residues of flumequine (FLU) and nalidixic (NAL), oxolinic (OXO), and piromidic (PIR) acids in catfish muscle. The identities of 3 of these residues are confirmed by gas chromatographymass spectrometry (GC-MS). The extraction and cleanup procedures are the same for both determination and identification. Analyte isolation involves homogenizing the tissue with acetone, defatting the acetone extract with hexane, and extracting the compounds into chloroform. The extract is further purified by first partitioning into base and subsequently back-extracting into chloroform after acidifying the aqueous phase. After the solvent is evaporated, the residue is dissolved in mobile phase, and the analytes are determined by LC with fluoresoence detection, excitation at 325 nm and 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 evaluated also by a second analyst, who determined 4 quinolones added in combination. Average recoveries of quinolones from catfish fortified at 5, 10, and 20 ng/g were 78-90%, with RSDs of 3-6%. The presence in catfish muscle of incurred OXO, FLU, and NAL at the 10 ng/g level was confirmed by analyzing the decarboxylated quinolones by GC-MS. The relative 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