Enantio- and Chemo-Selective HPLC Analysis of Silodosin on an Amylose-Based Chiral Stationary Phase

A direct enantio- and chemo-selective high-performance liquid chromatographic method was developed for determining the enantiomeric impurity of the chiral active pharmaceutical ingredient silodosin. The simultaneous separation of enantiomers of silodosin and its main organic related substances listed in the Japanese Pharmacopoeia (JP) monograph for drug substance was achieved on Chiralpak AD-3 (250 mm × 4.6 mm, 3 μm) column under normal-phase isocratic conditions. The optimized conditions employed the mixture <i>n</i>-heptane-ethanol-diethylamine (70:30:0.1) (<i>v</i>/<i>v</i>/<i>v</i>) as a mobile phase and a temperature of 35 °C. The complete separation of the enantiomers of silodosin and its main impurities was obtained within 12 min. The chromatographic method has been validated according to the International Conference on Harmonization (ICH) guidelines and compared with the method reported in the JP monograph. The standard curve for silodosin exhibited linearity (R² > 0.999) within the concentration range of 1.13-2500 µg mL^-1. The Chiralpak AD-3 has demonstrated a remarkable level of efficiency, enabling the attainment of limits of quantitation for silodosin of 1.13 µg mL^-1 (equivalent to 0.057% of a sample solution of 2 mg mL^-1) and ranging from 0.48 µg mL^-1 to 1.94 µg mL^-1 for other impurities.