Reversed-phase HPLC determination of sildenafil citrate in the presence of its oxidative-induced degradation products

The determination of sildenafil citrate in the presence of its oxidative-induced degradation products by reversed-phase HPLC is described. The method was validated as stability-indicating by forced decomposition of sildenafil citrate in acid, base, oxidative, thermal, and photochemical media. The chromatographic conditions employed a reversed-phase C-18 column (LiChrospher, 5 mu m, 25 cm x 4.6 mm) isocratic elution with 70 mM potassium phosphate monobasic containing 100 mM triethylamine (pH 3.0)-ACN (70:30, v/v) and ultraviolet (UV) detection at 225 nm. The peak area versus sildenafil citrate concentration proved linear over the 10-160% range of the working analytical concentration of 0.5-mg/mL. Mean absolute recovery of sildenafil citrate using the described method was 100.9 +/- 1.1% (mean +/- SD, n = 9). The precision, expressed as relative standard deviation (RSD), of ten replicate injections of sildenafil citrate reference solution, remained below 0.51%.