Determination of ivermectin residues in the tissues of Atlantic salmon (Salmo salar) using HPLC with fluorescence detection.

A sensitive, accurate and reproducible assay for the determination of residual concentrations of ivermectin in the tissues of farmed Atlantic salmon is described. The assay employs the clean-up of an acetonitrile extract of salmon tissue on a Bond-Elut C8 column, followed by derivatization with trifluoroacetic acid anhydride. Following separation using HPLC, 22,23-dihydroavermectin B1a is determined using fluorescence detection. The limit of detection of the assay is 1 ng per g tissue. Liver, taken from fish treated experimentally with ivermectin, was found to contain higher concentrations of 22,23-dihydroavermectin B1a than any other tissue examined. The half-life of 22,23-dihydroavermectin B1a was similar in all tissues studied, ranging from 89 to 98 degree days.