Abstract
This study represents the first report on the development and validation of a highly sensitive fluorimetric method for determination of varenicline (VRC) in tablets and plasma. The method was based on nucleophilic substitution reaction of VRC with 7-chloro-4-nitrobenzoxadiazole (NBD-Cl) in an alkaline buffered medium (pH 9) to form a highly fluorescent derivative that exhibited maximum fluorescence intensity at 550 nm after excitation at 470 nm. The factors affecting the reaction were carefully optimized. The stoichiometry of the reaction was determined, and the mechanism was postulated. Under the optimum reaction conditions, a linear relationship with good correlation coefficient (r = 0.9993) was found between the fluorescence intensity and VRC concentrations in the range of 5-250 ng ml(-1). The limits of detection and quantitation were 2.5 and 8.3 ng ml(-1), respectively. The method was reproducible as the relative standard deviations of the results did not exceed 2%. The proposed method was successfully applied to the determination of VRC in its bulk and tablets with good accuracy; the label claim percentage was 99.17 +/- 1.06%. The proposed method is valuable for routine application in quality control laboratories for determination of VRC.