Development and validation of a capillary electrophoresis assay for the determination of 3,4-diaminopyridine and 4-aminopyridine including related substances

A capillary electrophoresis (CE) assay has been developed for the quantitation and determination of the impurity profile of the potassium channel blockers 3,4-diaminopyridine and 4-aminopyridine. The compounds were separated from related substances using a capillary of 30 cm effective length, a 50 mM phosphate buffer, pH 2.5 and an applied voltage of 25 kV. The assay was validated with respect to specificity, linearity, range, limits of quantitation and detection, precision and robustness. The method allows the detection and quantitation of impurities at the 0.05% level. The feasibility of the assay was demonstrated by analyzing a commercial sample of 3,4-diaminopyridine. All known related substances could be detected in this sample with the present CE method.