Chiang Mai Journal of Science

The aim of this study was to develop and validate a high performance liquid chromatographic (HPLC) system for the analysis of sildenafil citrate in pharmaceutical inhaler preparations. Sildenafil was partially degraded by acid and alkali and was completely degraded by oxidation. Direct exposure to heat and UV in solid state had no effect on the degradation of sildenafil. This method was able to resolve any degradation products from the sildenafil peak. Sildenafil citrate showed UV absorption maximum at 240 and 276 nm. A reversed phase HPLC system for the separation and quantitation of sildenafil citrate assay was successfully developed and validated. The chromatographic conditions employed a C18 column (4.6 x 250 mm) with a mobile phase of 0.2 M ammonium acetate buffer and acetonitrile (40:60 v/v, pH 7.0) at a flow rate of 1.0 mL/min with UV detection at 240 nm. The retention time of sildenafil citrate was about 5 min. The method was specific to the sildenafil at the presence of other common excipients in the inhaler preparation. The method was accurate (99.5% recovery) and precise for both intra-day (0.5-1.0%) and inter-day (1.1%) assays. A linear correlation was obtained over the concentration range of 0.5-500 mg/mL (r²=1.0). The sample solution from metered dose inhalers (MDIs) was stable over 24 h. The LOD and LOQ were 1.30 and 6.10 ng/mL, respectively.