HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ANALYSIS OF ROMET-30 IN CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA) - WASH-OUT TIME, TISSUE DISTRIBUTION IN MUSCLE, LIVER AND SKIN, AND METABOLISM OF SULFADIMETHOXINE

A high-performance liquid chromatographic (HPLC) assay was developed for the determination of Romet-30 residue levels in Chinook salmon muscle and liver tissues. The extraction recoveries averaged 66, 78 and 83% for ormetoprim (OMP), sulfadimethoxine (SDM) and N-4-acetyl-SDM (N-4-Ac-SDM), respectively, in muscle tissue; 61 and 72% for SDM and N-4-Ac-SDM, respectively, in liver tissue. The HPLC assay had a lower detection limit of 0.05 mu g/g for OMP, SDM and N-4-Ac-SDM in muscle tissue, and a lower detection limit of 0.20 mu g/g for SDM and N-4-Ac-SDM in liver tissue. OMP could not be quantified in liver due to the presence of substantial amounts of co-extracted endogenous substances. The HPLC assay was applied to the analysis of Romet-30 residues in Chinook salmon after gastric intubation with Romet-30 at water temperatures between 8.0 and 9.0 degrees C. Different disposition characteristics were found in muscle and liver tissues. The presence of N-4-Ac-SDM in liver tissue was confirmed by MS and MS-MS analyses. An estimation of SDM and N-4-Ac-SDM residue levels in skin tissue was obtained and the disposition of these two compounds was similar to the disposition in muscle tissue.