Indirect spectrophotometric determination of phenylephrine hydrochloride using potassium permanganate and toluidine blue dye

An accurate, sensitive, and indirect spectrophotometric method was developed to determine phenylephrine hydrochloride in its pure form and pharmaceutical preparations. This method is based on the use of potassium permanganate as an oxidizing agent to oxidize the pharmaceutical compound phenylephrine hydrochloride and then the unreacted increase of the oxidizing agent potassium permanganate leads to the discoloration of toluidine blue dye in sulfuric acid medium at (606) nm wavelength. The method followed Beer's law within the concentration range of (1.0-10.0) μg/ml, and the molar absorbance was (1.53×10⁴) L/mol.cm, the LOD value was 1.11 μg/ml and the LOQ value was 3.72 μg/ml, the recovery of the method was 101.19% and the relative standard deviation was 0.73%, and the method was successfully applied to pharmaceutical formulations in drop form.