Spectrofluorimetric determination of doxepin hydrochloride in commercial dosage forms via ion pair complexation with alizarin red S

A simple and sensitive spectrofluorimetric method has been developed for the determination of doxepin hydrochloride in pharmaceutical preparations. It is based on the formation of ion-pair complex between doxepin and alizarin red S at pH 3.09. The ion pair complex was extracted in dichloromethane and the fluorescence intensity was measured at 560 nm after excitation at 490 nm. The optimum conditions for determination were also investigated. The linear range and detection limit were found to be 2-14 and 0.55 μg/ml, respectively. The method has been successfully applied for the analysis of drug in commercial dosage forms. No interference was observed from common pharmaceutical adjuvant. Statistical comparison of the results obtained by the proposed method with that of the reference method shows excellent agreement and indicates no significant difference in accuracy and precision.