Utility of 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole for development of a highly sensitive stability indicating spectrofluorimetric method for determination of salmeterol xinafoate; application to human plasma

Abstract

A new, simple and rapid spectrofluorimetric method was developed and validated for determination of salmeterol xinafoate in dosage form and spiked plasma. The method is considered as the first attempt for the spectrofluorimetric determination of the investigated drug. The proposed method is based on nucleophilic substitution reaction between salmeterol xinafoate and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) at pH (9) to form a highly fluorescent product that can be measured at 543 nm after excitation at 473 nm. The fluorescence–concentration plot was rectilinear over the concentration range (100–1500 ng mL⁻¹) with a detection limit of 19 ng mL⁻¹. The suggested method was validated according to ICH guidelines and successfully applied for determination of salmeterol xinafoate in its pharmaceutical dosage form and spiked human plasma. The developed method was further extended for a stability study of salmeterol xinafoate under different stress circumstances including alkali, acid, oxidative and photodegradation conditions and the method was proved to be able to determine the intact drug in the presence of its degradation products.