Extractive spectrophotometric determination of nimodipine through ion-pair complex formation with bromothymol blue

Abstract

A new spectrophotometric method was established for the determination of nimodipine (NMD) in pharmaceutical formulations. This method is based on the formation of a yellow ion-pair complex between the reduced nimodipine and bromothymol blue (BTB) in an acidic medium. Chloroform was used as an optimal solvent for the extraction of ion-pair complex and measured the absorbance of this complex at wavelengths of 414.5 nm. The effect of optimum condition via extracting solvent, volume of dye, shaking time, reaction ratio was studied. Beer’s law is obeyed in the concentration ranges of 4.0-50.0 μg/mL with a molar absorptivity of 1.50x104 L.mol-1.cm-1 and limit of detection (LOD) of 1.87 μg/mL. The accuracy and precision of the method were evaluated on an intra-day and inter-day basis. The relative error (%RE) and the relative standard deviation (%RSD) were < 5.0% while the recovery (%) was 99.05-103.25. The proposed method was applied successfully to determine nimodipine in pharmaceutical preparation (Nomitop, Bayer).