Determination of virginiamycin in combination with chlortetracycline in feeds by anion-exchange chromatography

Abstract

Standard additions experiments for chlortetracycline hydrochloride and virginiamycin at a ratio of 16 : 1 showed a positive bias for both the plate and turbidimetric methods. The bias was eliminated by anion-exchange chromatography in both the presence and absence of feed components. When chlortetracycline and virginiamycin pre-mixes were used for fortification of laboratory-prepared feeds at chlortetracycline to virginiamycin ratios of 8 or 16:1, the recovery of virginiamycin, without treatment, was 93–100% using the plate assay and 181–236% with the turbidimetric method. The corresponding values obtained using anion-exchange chromatography were 89–99 and 85–91%, respectively. The anion-exchange technique is necessary if the turbidimetric method is used for the assay.