Microbiological and chemical analysis of polymyxin B and polymyxin E (colistin) sulphates

Samples of the sulphates of polymyxin B and polymyxin E (colistin) have been assayed microbiologically. The content of phenylalanine was determined in the samples of polymyxin B. The compositions of the samples obtained by using thin-layer chromatography, gas-liquid chromatography and high-performance liquid chromatography were compared. The relative merits of each method are discussed.