DETERMINATION OF IVERMECTIN IN SALMON MUSCLE-TISSUE BY LIQUID-CHROMATOGRAPHY WITH FLUORESCENCE DETECTION

A liquid chromatographic method was developed for determination of ive rmectin B-1a (IVR) extracted from raw fortified and incurred Atlantic salmon muscle tissues. The method was also used to determine fortified doramectin (DOR) in Atlantic salmon. Tissue extract was applied to a C-8 solid-phase extraction (SPE) column, followed by a silica SPE colu mn. Residues in the eluate were treated with trifluoroacetic anhydride and methylimidazole to dehydrate the IVR molecule and form an aromati c fluorescent moiety with a trifluoroacetic ester, This product was su bsequently treated with ammonium acetate in methanol to cleave the est er and convert the functional group back to a stable alcohol form. The analytes were determined by fluorescence with excitation at 272 nm an d emission at 465 nm. A C-18 Hypersil column was used for analysis wit h a mobile phase of acetonitrile-water (90 + 10, v/v) and an oven temp erature of 65 degrees C, IVR and DOR were determined at 5 fortificatio n levels (1, 5, 10, 20, and 40 ppb). Intra-assay absolute recoveries r anged from 75 to 89% for IVR and from 73 to 85% for DOR, Relative stan dard deviations (RSDs) were <7% in all cases. The limit of detection ( 3 x baseline noise) was 0.25 ppb extracted from tissue. Incurred tissu es had an average concentration of 32 ppb, with an RSD of 3%.