Determination of fenbendazole and oxfendazole in liver and muscle using liquid chromatography-mass spectrometry.

A method has been developed for the determination of the anthelmintics fenbendazole and oxfendazole in liver and muscle samples using liquid chromatography-thermospray mass spectrometry (LC-MS). The samples were homogenized with water, sonicated with methanol and centrifuged. The supernatants were washed with light petroleum and extracted with diethyl ether-ethyl acetate. The extracts were evaporated to dryness, dissolved in mobile phase and injected into the LC-MS system. Fenbendazole and oxfendazole were measured separately using two different mobile phases. Single-ion monitoring of the positive ion at m/z 300 was used for fenbendazole and of m/z 316 for oxfendazole. The detection limits for the assay were 0.05 microgram g-1 for fenbendazole and 0.1 microgram g-1 for oxfendazole. The mean recoveries were 91% for fenbendazole and 86% for oxfendazole. The assay has been used for statutory testing purposes and for measuring the levels of fenbendazole and oxfendazole in liver and muscle from sheep after dosing with a commercial anthelmintic containing fenbendazole.