Voltammetric method for the determination of sildenafil citrate (Viagra) in pure form and in pharmaceutical formulations

A highly sensitive and simple voltammetric method for the determination of sildenafil citrate (SC) was developed. The method is based on the accumulation by adsorption of SC on a lead film modified glassy carbon electrode (LF/GCE) and then the reduction of SC throughout the stripping step. During the determinations of SC at the lead film electrode three adsorptive stripping voltammetric peaks at -1.2, -1.33 and -1.45 V were observed. The respective response selected for identification and quantification has been evaluated with respect to the composition and pH of the supporting electrolyte, the potential and the time of the lead film formation, the potential and the time of the SC accumulation and other variables. Experimental results indicate an excellent linear correlation between the peak current and concentration in the range of 2 x 10(-9)-1.5 x 10(-7) mol/l (for peaks 1 and 2) and 1 x 10(-8)-1.5 x 10(-7) mol/L (for the peak 3). The detection limits (LOD) for SC following 30 s of accumulation time were equal to 9 x 10(-19) mol/L (for peaks 1 and 2) and 4.5 x 10(-9) mol/L (for the peak 3). The method was successfully applied to the determination of SC in the tablets (Viagra 25 and Viagra 50) and average the contents were in close agreement with those quoted by the manufacturer and with those obtained by the reported spectrophotometric method and voltammetric method using a hanging mercury drop electrode. (C) 2009 Elsevier B.V. All rights reserved.