High-performance liquid chromatographic determination of virginiamycin in Stafac, premixes and animal feeds

Abstract

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 µg 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.