Sulfadimethoxine (SDM) residues in chinook salmon muscle were measured by high-performance liquid chromatography (HPLC) and the Charm II test to evaluate the efficacy of the Charm test for the measurement of sulfonamide residues in fish muscle. Both HPLC and Charm analyses were performed in the presence of salmon tissue matrix for the purpose of evaluating the results in field conditions. The sensitivity of the HPLC method was 0.05 μg/g (0.05 ppm) for SDM, while the sensitivity of the Charm II test was at least 0.01 ppm. SDM analysis from salmon fed Romet-30® performed using the Charm assay gave consistently lower values compared to HPLC; however, good agreement was obtained between both methods (r2 = 0.944) over a concentration range of 0.1 to 13.0 ppm in muscle tissue. The large variation in SDM concentrations between fish sampled on common days suggests that a larger number of fish are required for more accurate risk assessment. In the current investigation, the Charm II test was shown to be effective in measuring SDM in salmon muscle tissue for the large sample throughput common with antibiotic-screening strategies.

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