Determination of vardenafil in pharmaceutical formulation by HPLC using conventional C18 and monolithic silica columns

A simple HPLC analysis for the identification and quantification of vardenafil in a pharmaceutical tablet formulation was performed on a conventional C₁₈ and Chromolith Performance RP-18e monolithic columns with acetonitrile-phosphate buffer mixtures as mobile phases. The effects of the proportion of organic solvent (from 20% to 90%), phosphate buffer pH (from 2 to 7.5) and flow rate (from 1 to 5 mL/min) were studied. The best chromatographic conditions were 20:80 (v/v) acetonitrile-10 mM phosphate buffer, pH 3.0, as mobile phase at 1 mL/min flow rate for the C₁₈ column, whereas 30:70 (v/v) acetonitrile-10 mM phosphate buffer, pH 3.0, as mobile phase at 2 mL/min flow rate was best for the monolithic column. Methanol was found to be a suitable solvent for extraction of the active substance from tablets. For the C₁₈ and monolithic column, the calibration plots were linear (R² = 0.9996 and 0.9997, respectively) in the concentration range 10-1000 μg/mL. Limit of detection (LOD) and limit of quantification (LOQ) values were 0.10 and 0.31 μg/mL for the C₁₈ and 0.11 mL and 0.32 μg/mL for the monolithic column. Intra-assay and inter-assay precision studies reflected a high level of reliability and reproducibility of the method. The proposed method is selective, precise (RSD = 0.45%), and accurate (recovery = 103-107%) in both columns used.