Voltammetric behavior of sildenafil citrate (Viagra) using square wave and adsorptive stripping square wave techniques -: Determination in pharmaceutical products

The behavior of sildenafil citrate (SC) was studied by square wave technique, leading to two methods for its determination in aqueous samples (pH 2.0) and pharmaceutical formulations. The application of the square wave (SW) without the adsorptive accumulation shows the maximum response at -1.03 V. Besides, SC gave two adsorptive stripping voltammetric (AdSV) peaks at -1.03 and -1.15 V using an accumulation potential of -0.80 V. The effect of experimental parameters that affect this determination are discussed. For the stripping technique, SC proved to be more sensitive, yielding signals three or four times larger than those obtained by applying a square wave scan without the previous accumulation. The calibration graph to determine SC was linear in the range 5 x 10(-9) to 9 x 10(-7) M by stripping mode with a time of accumulation t(acc) of 10 s. The relative standard deviations obtained for concentration levels of SC as low as 1.0 x 10(-7) M with square wave was 2.5% (n=10) and for 1.0x10(-7) M with stripping square wave was 3.1% (n=10) in the same day. The two proposed methods (SW and SWAdSV) were applied to the determination of SC in three pharmaceutical products (Viagra 25, Viagra 50 and Viagra 100) with very good recoveries with respect to the labelled values. (C) 2000 Elsevier Science B.V. All rights reserved.