Liquid chromatographic determination of ivermectin in animal plasma with trifluoroacetic anhydride and N-methylimidazole as the derivatization reagent

Ivermectin is a potent anthelmintic agent which was detected at low concentrations in cattle plasma by LC after conversion to a fluorescent derivative. This was accomplished by reaction with acetic anhydride (AA) and pyridine for 24 h at 100 degrees C or with AA and N-methylimidazole (NMIM) for 1 h at 95 degrees C. Substituting trifluoroacetic anhydride (TFAA) for AA reduced the reaction time to less than 30 s at 25 degrees C, yielding an intensely fluorescent derivative with substantially fewer reagent by-products. The need for further sample preparation after derivatization with TFAA-NMIM was thereby eliminated, and detection limits of less than 20 pg ml-1 ivermectin could be achieved with 1 ml of plasma by a considerably simpler analytical procedure.