Development and Validation of a Capillary Zone Electrophoresis Method with Indirect UV Detection for the Simultaneous Determination of Azelaic Acid and Salicylic Acid in Pharmaceutical and Cosmetic Preparations

Azelaic acid (AZA) and salicylic acid (SA) are widely used active ingredients in pharmaceutical and cosmetic formulations for the treatment of acne, rosacea, hyperpigmentation, and other dermatological conditions. Despite their frequent co-administration, analytical methods for their simultaneous determination remain limited. In the present study, a capillary electrophoresis (CE) method with indirect UV detection was developed and validated for the simultaneous determination of AZA and SA in pharmaceutical and cosmetic preparations. Preliminary experiments demonstrated that direct UV detection was unsuitable because of the weak UV absorbance of AZA; therefore, indirect UV detection based on a sodium benzoate background electrolyte (BGE) was used. Following an initial one-factor-at-a-time (OFAT) screening, method optimization was performed using a face-centered central composite design (CCD) to evaluate the effects of BGE concentration, BGE pH, and separation voltage on the separation. The optimum separation was achieved using a 30 mM sodium benzoate BGE at pH 6.5 containing 5% (v/v) methanol, a separation voltage of +18 kV, a capillary temperature of 20 °C, and indirect UV detection at 230 nm. Baseline separation of both analytes was achieved within 5 min. The method was validated according to the ICH Q2(R2) guideline and demonstrated satisfactory accuracy, linearity, precision, selectivity, sensitivity, and robustness. The developed procedure was successfully applied to the analysis of commercial cosmetic formulations containing AZA, SA, or both active ingredients, providing assay results consistent with the declared contents. The proposed CE method provides a simple, rapid, cost-effective, and environmentally friendly alternative for the routine quality control of pharmaceutical and cosmetic formulations containing AZA and SA.