Development and Validation of LC Method for Determination of the Enantiomeric Purity of Silodosin in Bulk Drug Substances

A simple, rapid, novel and normal phase chiral HPLC method has been developed for the separation of S-Silodosin from R-Silodosin and quantitative determination of S-Silodosin enantiomer in Silodosin bulk drugs. The proposed method was based on normal phase chromatographic separation on Polysaccharide-Based Chiral Stationary Phase, Chiral pak AS-H column (250mm ×4.6mm i.d.; particle size,5µ) at a temperature of 28°C using a mobile phase consisting of n-Hexane, Ethanol and Diethyl amine (600 : 400 : 0.1 v/v/v) at a flow rate of 1mL.min-1 with an injection volume of 10μL. Quantitation was achieved with UV detection at 270 nm based on peak area with linear calibration curves. The elution times of S-Silodosin and R-Silodosin were 5.0 min and 6.0 min respectively. In this proposed chiral HPLC method, the resolution between S-Silodosin and R-Silodosin was found to be greater than 1.5. The developed method was validated with respect to linearity, accuracy, precision, solution stability, ruggedness, robustness, limit of detection and limit of quantification. The recovery obtained for S-isomer was in between 102.2 % and 104.4%. The detection limit obtained for S-isomer was 0.04µg.mL-1 and the quantification limit was 0.13µg.mL-1 respectively. Linearity was performed for the S-isomer from LOQ to 150%. The correlation coefficient obtained for S-isomer was more than 0.999. The solution stability of Silodosin bulk drug was determined and the compound was found to be stable up to 48 hrs. As the method has less run time (10 min), it can be useful in quality control laboratories for routine analysis. Key words: R-Silodosin, S-Silodosin, Polysaccharide-based chiral stationary phase, High performance liquid chromatography and Method validation.