Determination of levamisole in animal tissues using liquid chromatography–thermospray mass spectrometry

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Abstract
A method is described for the determination of the anthelmintic levamisole in liver, kidney and muscle using liquid chromatography–thermospray mass spectrometry. Samples are extracted by homogenizing with ethyl acetate, applied to Bakerbond CN solid-phase extraction columns, washed with chloroform–hexane and eluted with methanol. The extracts are evaporated to dryness under nitrogen and the residues are dissolved in mobile phase and injected into the LC–MS system. The positive M + 1 ion at m/z 205 is monitored. The detection limit for the assay is 5 ng g–1. Mean recoveries were about 93% for liver, 85% for kidney and 79% for muscle. The assay has been used for statutory testing purposes and for measuring levamisole concentrations in liver, kidney and muscle from sheep dosed with a commercial drench containing levamisole.