Comparison of liquid chromatography and capillary electrophoresis methods for quantification of sodium residuals

Liquid chromatography (LC) and capillary electrophoresis (CE) methods were developed to perform the determination of residual sodium in mother liquors and successive washes of an active pharmaceutical ingredient (API). The addition of sodium chloride to the product solution results in rapid and complete crystallization of the API. The LC method was coupled to evaporative light scattering detection (ELSD) while the CE approach was based on indirect UV detection. Both methods were fully validated. Selectivity, response function, trueness, precision, accuracy, linearity and limits of detection (LOD) and quantification (LOQ) were the criteria investigated. The LC–ELSD method was found to be more sensitive than the CE/indirect UV approach. The methods were found to be valid over concentration ranges of 62–500 and 235–1500 ppm for the LC and the CE methods, respectively. Both methods were compared and used for the determination of actual samples coming from different batches of the same API chemical synthesis.