The application of high-performance liquid chromatography to the determination of vitamin A in animal feeding stuffs has been investigated. Particular emphasis has been given to some of those aspects that would be of importance to official control methods. Vitamin A exists as six geometric isomers, some or all of which may be present in feed extracts. The effect of this on both ultraviolet and fluorescence quantitation is described, using all-trans retinol and 13-cis retinol as examples of the different isomers. The isomers were eluted coincidentally from a reversed-phase column; information on the isomeric composition of the feed extracts was obtained by means of the maleic anhydride reaction. These results were confirmed by a normal phase chromatographic procedure which resolved all-trans and 13-cis retinol.
A high-performance liquid chromatographic (HPLC) method for the determination of methyl benzoquate in poultry feedingstuffs is described. Methyl benzoquate is extracted from the feedingstuff with 2% methanesulphonic acid in methanol and the extract partially purified by partition into dichloromethane from hydrochloric acid solution. Major feed interferences are removed by ion-exchange chromatography followed by a second partition into dichloromethane. The methyl benzoquate content of the sample extract is determined by HPLC on an octadecylsilane column. Using this procedure, a mean recovery of greater than 95% was obtained for a range of poultry feeds medicated at 5 and 10 mg kg-1. For a feed medicated at 1 mg kg-1 the mean recovery was 93%.
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