Highly sensitive spectrofluorimetric method for determination of doxazosin through derivatization with fluorescamine; Application to content uniformity testing.

A highly sensitive, simple and selective spectrofluorimetric method has been developed and validated for determination of doxazosin mesylate in pure form, pharmaceutical formulations and human plasma. The method is based on the reaction between doxazosin mesylate and fluorescamine in Teorell buffer solution (pH 3) to give highly fluorescent derivative that can be measured at 489 nm using excitation wavelength of 385 nm. Different experimental parameters affecting the reaction were carefully studied and optimized. The calibration plot was constructed over the concentration range of 16-400 ng mL(-1) with quantitation limit of 14.3 ng mL(-1). The developed procedure was validated according to ICH guidelines and the results were satisfactory. The proposed method has been successfully applied to the analysis of the cited drug in its pharmaceutical preparations as well as for content uniformity testing. The results showed excellent agreement with the reported method with respect to precision and accuracy. In addition, the drug concentration was determined in the spiked human plasma by the suggested method with % recovery in the range of 96.2-98.3% (SD; 0.76-0.93, n=5).