Abstract
This study describes, for the first, the spectrophotometric investigation for the condensation reaction between varenicline (VRC) and cyclohexa-3,5-diene-1,2-dione (CHDD). The reaction gave a violet-colored product exhibiting maximum absorption peak (lambda(max)) at 540 nm. The variables affecting the reaction were carefully investigated and the optimum conditions were established. The stoichiometry of the reaction was determined, and the reaction pathway was postulated. This color-developing reaction was employed in the development of microwell plate assay for VRC. In this assay, the reaction was carried out in 96-microwell plate and the absorbance of the colored-product was measured by microwell plate absorbance reader. Under the optimized reaction conditions, Beer's law correlating the absorbance with VRC concentration was obeyed in the range of 5 - 100 mu g/mL with good correlation coefficient (0.9986). The limits of detection and quantification were 2.29 and 6.95 mu g/mL, respectively. The assay showed high precision as the values of relative standard deviations (RSD) did not exceed 2%. No interference was observed from the excipients that are present in VRC-containing tablets. The proposed assay was applied successfully for the determination of VRC in its pharmaceutical tablets with good accuracy and precisions; the label claim percentages were 98.80 +/- 1.30%. The results were compared favorably with those of a reference pre-validated method. The proposed assay is practical and valuable in terms of its routine application in determination of VRC in in its bulk and tablets in pharmaceutical quality control laboratories.