HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC DETERMINATION OF VIRGINIAMYCIN IN STAFAC, PREMIXES AND ANIMAL FEEDS

A reversed-phase high-performance liquid chromatographic method with ultraviolet detection is described for the simultaneous determination of the virginiamycin components M1 and S1 in Stafac, premixes and feeds. The concentrations and ratios of the components determine a synergistic activity, which is calculated. Virginiamycin is extracted from Stafac using acetonitrile-water (1 + 1), from feeds using dichloromethane and from premixes using either of the extraction solutions. The acetonitrile extracts are injected directly, the dichloromethane extracts are cleaned by passing them through a silica solid-phase extraction cartridge, followed by two consecutive washings; virginiamycin is desorbed with acetonitrile-water (1 + 1). The peak area response is linear for virginiamycin activities of between 5 and 50-mu-g ml-1. The detection limit in feeds (both pellets and mash) is 5 ppm. The method is specific, accurate and has a good repeatability. It complements well the existing microbiological methods.