Analysis of polymyxin B sulfate by capillary zone electrophoresis with cyclodextrin as additive: Method development and validation

A capillary zone electrophoresis method for analysis of polymyxin B sulfate is described. In this method, triethanolamine (TEA)–phosphate buffer at pH 2.5 was employed to reduce the adsorption of analyte onto the capillary wall. Methyl-β-cyclodextrin (M-β-CD) and 2-propanol (IPA) were found to be necessary for selectivity enhancement. In order to optimize the method and to control its robustness, a central composite design was performed with four parameters, i.e. concentration of M-β-CD, TEA, IPA and buffer pH. The optimal separation conditions were as follows: capillary, 55 cm (50 μm I.D., 47 cm effective length); 130 mM TEA–phosphate buffer (pH 2.5) containing 5 mM M-β-CD and 5% IPA; 24 kV (51 μA) applied voltage; column temperature, 20°C. Further, linearity and limits of detection quantification were examined. Three commercial samples were analyzed quantitatively.