Ivermectin quantitation with an abamectin internal standard

The potent antiparasitic ivermectin is detected at low concentrations (ng/g) in liver and muscle tissue by liquid chromatography after conversion to a fluorescent derivative with 1-methylimidazole and trifluoroacetic anhydride. This acetylation reaction can be compromised by residual water that leads to decreased yields. Yields of derivatives of ivermectin and abamectin, a related avermectin, are identical under all circumstances tested. Use of abamectin as an internal standard eliminates derivative yield as a source of analytical variation.