Separation and determination of nimesulide related substances for quality control purposes by micellar electrokinetic chromatography

A micellar electrokinetic chromatography (MEKC) method has been developed and validated for the determination of nimesulide related compounds in pharmaceutical formulations. Electrophoretic separation of six European Pharmacopoeia (EP) impurities (A–F) was performed using a fused silica capillary (Leff. = 50 cm, Ltot. = 57 cm, 50 μm i.d.) with a background electrolyte (BGE) containing 25 mM borate buffer (pH 9.5), 30 mM sodium dodecyl sulphate and φ = 3% (v/v) acetonitrile. The influence of several factors (surfactant and buffer concentration, pH, organic modifier, applied voltage, capillary temperature and injection time) was studied. The method was suitably validated with respect to linearity, limit of detection and quantification, accuracy, precision and selectivity. The calibration curves obtained for the six compounds were linear over the range 5–12 μg ml−1 (0.05–0.12%). The relative standard deviations (sr) of intra- and inter-day experiments were less than 5.0%. The detection limits ranged between 0.7 and 1.6 μg ml−1 depending on the impurity. The proposed method was applied successfully to the quantification of nimesulide impurities in its pharmaceutical formulation.