LIQUID-CHROMATOGRAPHIC DETERMINATION OF FLUMEQUINE, NALIDIXIC-ACID, OXOLINIC ACID, AND PIROMIDIC ACID RESIDUES IN CATFISH (ICTALURUS-PUNCTATUS)

A peer-verified, liquid chromatographic (LC) method for simultaneous d etermination of residues of flumequine (FLU), nalidixic acid (NAL), ox olinic acid (OXO), and piromidic acid (PIR) in catfish muscle is prese nted. Sample workup involves homogenizing tissue with acetone, defatti ng with hexane, and extracting quinolones into chloroform. Sample is p urified further by partitioning into base and then subsequently back-e xtracting into chloroform after acidifying the aqueous phase. After so lvent is evaporated, the residue is diluted with mobile phase, and ana lytes are introduced into an LC system where separations are made with a 5 mu m, reversed-phase polymer column and an isocratic, buffered ac etonitrile-tetrahydrofuran mobile phase. Determinations are made by UV detection at 280 nm for PIR and by fluorescence detection (excitation at 325 excitation and emission at 365 nm) for the other 3 analytes. E ach quinolone was used to fortify catfish muscle at 5, 10, 20, 40, and 80 ng/g. The following recoveries and relative standard deviation (RS D) values represent an average of the 5 levels for each analyte: FLU, 79.7% (RSD = 5.7%); OXO, 80.8% (RSD = 6.3%); PIR, 75.0% (RSD = 5.9%); and NAL, 87.1% (RSD = 10%). Assay of 5 levels (base incurred catfish, plus 4 dilutions with control catfish) of catfish muscle incurred with the 4 quinolones gave the following averages: FLU: base, 198 ng/g (RS D = 2.3%); dilutions, 98.0 ng/g (RSD = 4.2%), 61.6 ng/g (RSD = 4.4%), 21.6 ng/g (RSD = 2.8%), 9.24 ng/g (RSD = 8.7%); OXO, base, 257 ng/g (R SD=6.9%); dilutions, 146 ng/g (RSD = 5.5%), 95.0 ng/g (RSD = 4.1%), 30 .7 ng/g (RSD = 3.8%), 13.7 ng/g (RSD = 4.6%); PIR, base, 22.1 ng/g (RS D = 4.2%); dilutions, 13.7 ng/g (RSD = 6.7%), 6.49 ng/g (RSD = 15%), 2 .65 ng/g (RSD = 15%); and NAL, base, 75.1 ng/g (RSD = 3.8%); dilutions , 42.3 ng/g (RSD = 5.1%), 24.1 ng/g (RSD = 6.3%), 8.59 ng/g (RSD = 4.8 %). A second multiresidue analysis of the 4 quinolones was performed b y an outside analyst. Average recoveries from catfish fortified at 5, 10, 20, and 40 ng/g were FLU, 75.9% (RSD = 4.0%); OXO, 84.0% (RSD = 5. 5%); NAL, 85.6% (RSD = 8.9%); and PIR, 66.2% (RSD = 8.7%).