Determination of the antibiotic zinc bacitracin in animal food by high-performance liquid chromatography with ultraviolet detection

A high-performance liquid chromatographic method with ultraviolet detection has been developed for the analysis of the polypeptide antibiotic zinc bac itracin in adulterated animal feed. Firstly, the process for extraction of the antibiotic from the feed was optimized. This process involved extractio n from the feed at pH 2, centrifugation, liquid-liquid extraction, then sol id-phase extraction. The extract obtained was then dissolved in the mobile phase and injected into the chromatograph. The best analytical results were obtained by use of a C-18 column with a mobile phase comprising a 50:50 % v/v) mixture of 0.3 M phosphate buffer, pH 3, containing 20 mm sodium dodec yl sulfate (SDS) and 19:1 (v/v) acetonitrile-methanol. The analytical signa l (peak area) was monitored at 254 nm. The calibration function was estimat ed between 200 and 1000 mg L-1. The proposed method was applied to the anal ysis of zinc bacitracin present in different fortified animal feed products a[ levels between 5 and 200 mg kg(-1). Recovery rates were between 66 and 85% and the relative standard deviation was below 7%.