Experimental design-based development of a rapid capillary electrophoresis method for determining impurities in the tetrapeptide H-Tyr-(d)Arg-Phe-Phe-NH2

A capillary electrophoresis (CE) method has been developed and validated for separating the tetrapeptide H-Tyr-(d)Arg-Phe-Phe-NH2 and nine related substances. The method was developed using experimental design in a four-step procedure, in which eight variables were investigated in a total of 47 experiments. The preferred background electrolyte (BGE) consisted of 0.1 M malonic acid at pH 2.5 with 7 mM heptakis(2,6-di-O-methyl)-β-cyclodextrin (2,6-DM-β-CD). The separation of H-Tyr-(d)Arg-Phe-Phe-NH2 and the related substances was accomplished within 15 min, with a resolution greater than 1.5 between all peaks. The method was then investigated with respect to its selectivity, linearity, precision, detection limit (LOD) and quantitation limit (LOQ). In addition, a system suitability test was performed and response factors were determined, essentially following International Conference of Harmonization guidelines for the validation of analytical methods. LOD and LOQ for the related substance H-Arg-Phe-NH2 were found to be 0.3 and 0.8 μg/ml, respectively, at a target H-Tyr-(d)Arg-Phe-Phe-NH2 concentration of 1 mg/ml. The method performed well with respect to all of the validation parameters.