Spectrophotometric microdetermination of nefopam, mebevrine and phenylpropanolamine hydrochloride in pharmaceutical formulations using alizarins

Simple and rapid spectrophotometric procedures have been established for quantitation of nefopam hydrochloride (NF) mebevrine hydrochloride (MB) and phenylpropanolamine hydrochloride (PP). The procedures are based on the reaction between the examined drugs (NF, MB and PP) and alizarin (I), alizarin red S (II), alizarin yellow G (III) and quinalizarin (IV) producing ion-pair complexes which can be measured at the optimum wavelength. The optimization of the reaction conditions is investigated. Beer's law is obeyed in the concentration ranges 0.5-30.0 microg ml(-1). The molar absorptivity, Sandell sensitivity, detection and quantification limits are also calculated. The correlation coefficient was > or =0.9988 (n=6) with a relative standard deviation (R.S.D.) of < or =1.3, for six determinations of 20 microg ml(-1). The methods are successfully applied to the determination of NF, MB and PP in their pharmaceutical formulations.