Abstract
Abstract Gas-liquid chromatographic methods are described for the determination of melengestrol acetate (MGA) in cattle feed supplements containing 0.000011–0.000220% MGA (0.05–1.0 mg/lb). A sample is extracted with hexane in a continuous liquid-liquid extractor and, if necessary, the extract is purified by treatment with activated carbon, solvent partition from hexane into aqueous methanol and then into methylene chloride, followed by column chromatography with alumina and silica columns. MGA in liquid feed and a few dry feed supplements may be determined directly in the initial extract by GLC. MGA in most dry feed supplements may be determined using only the solvent parition cleanup step; a few samples containing a low level of MGA and a large amount of co-extracted material may require all of the cleanup steps. MGA is measured by GLC, using a 1% OV-17 column, a 63Ni electron affinity detector, and cholesteryl chloroacetate as an internal standard. Recovery of MGA averages better than 90% with a coefficient of variation on the order of 7% for the feed supplements studied.
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