Utility of certain sigma and pi-acceptors for the spectrophotometric determination of sildenafil citrate (Viagra)

The molecular interaction between sildenafil citrate as electron donor and each of iodine; 7,7,8,8-tetracyanoquinodimethane (TCNQ); 2,3-dichloro-5,6-d icyano-1,4-benzoquinone (DDQ); tetracyanoethylene (TCNE); 2,4,7-trinitro-9- fluorenon (TNF); chloranilic acid (CLA); chloranil (CL) and bromanil (BL) a s acceptors have been investigated spectrophotometrically. Different variab les affecting the reaction were studied and optimized. Beer's law was obeye d in a concentration limit of 10-260 mug/mL for sildenafil citrate. For mor e accurate analysis, Ringbom optimum concentration range was found to be be tween 20-240 mug/mL. The limits of detection and determination were calcula ted and found to be 1.5 and 5.2 mug/mL, respectively. The standard deviatio ns were calculated for different concentrations of sildenafil citrate using various acceptors. A Job's plot of the absorbance versus the molar ratio o f the sildenafil citrate to each of acceptors under consideration indicated (1:1) ratio. The proposed methods were found to be rapid, accurate, precis e and sensitive and could be applied for determination of sildenafil citrat e in pharmaceutical dosage forms (Viagra) without interferences from common additives encountered.