[Determination of polymyxin E1 and polymyxin E2 in polymyxin E sulfate using micellar electrokinetic capillary chromatography]

A method of micellar electrokinetic chromatography capillary (MECC) has been established for separating polymyxins E1 and E2 in polymyxin E sulfate and determining the contents of E1 and E2. Several factors including the running voltage, the type of surfactant, concentrations of Brij-35 (polyoxyethylene glycol dodecyl ether), NaCl solution and acetonitrile, pH of phosphate were investigated. Under the optimum conditions (10 kV running voltage, phosphate buffer solution (0.01 mol/L, pH 4.1) containing 30 mmol/L Brij-35, 5% (v/v) acetonitrile, 0.167 mol/L NaCl), E1 and E2 were separated with the resolution of 1.94. The contents of E1 and E2 in polymyxin E sulfate were 67% and 32%, respectively. As an example, the relative standard deviations of the intra-assay and inter-assay of polymyxin E1 on the plate number and peak area were less than 5%. The method is simple, rapid, accurate, and reproducible.