A facile, accurate, sensitive and validated spectrophotometric methods for the determination of vardenafil HCl (VARD) and yohimbin HCl (YOHM) in pure and in dosage forms are described. The methods are based on the formation of charge transfer reactions of both drugs as n-electron donor with various π-acceptors: 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6 dicyano-p-benzoquinone (DDQ) and chloranilic acid (p-CLA) to give highly colored complex species. The colored products were quantitated spectrophotometrically at 535, 461 and 840 nm for p-CLA, DDQ and TCNQ, respectively for VARD and at 461 and 841 nm using DDQ and TCNQ reagent, respectively for YOHM. The optimization of the reaction conditions such as the type of solvent, reagent concentration and reaction time were investigated. Beer's law is obeyed in the concentration ranges 5.0-200 μg mL-1 with good correlation coefficient was ≥0.9995 with a relative standard deviation (R.S.D.) of ≤ 0.70%. The molar absorptivity, Sandell sensitivity, detection and quantification limits were also calculated. The proposed methods were successfully applied for determination of VARD and YOHM in tablets with good accuracy and precision and without interferences from common additives by applying the standard addition technique. Developed methods have been validated statistically for their accuracy, precision, sensitivity, selectivity, robustness and ruggedness as per ICH guidelines and the results compared favourably with those obtained using the reported methods.
Vardenafil HCl, Yohimbin HCl, Charge transfer complexes, Spectrophotometry, Pharmaceutical analysis