Spectrophotometric determination of phenylephrine hydrochloride in pharmaceutical preparations

Studies on analysis of mixed pharmaceutical preparations. VII

Abstract

Phenylephrine hydrochloride (I) reacts with dimethyl-p-phenylenediamine and K₃Fe (CN) ₆ in an alkaline medium (borate buffer : pH 9.0) to give a green color (indophenol dye). The latter can be extracted into chloroform, which shows an absorption maximum at 610 mμ.
A new spectrophotometric method for (I) based on this color reaction was established, and was applied to the determination of (I) in pharmaceutical preparations. The influences of 48 compounds on the determination were investigated, among which those by acetaminophene, salicylamide, sulpyrine, ascorbic acid etc. were eliminated by chloroform extraction from an acidic medium.
The analytical procedure was as follows. Take the sample containing 6 mg of (I) in a separatory funnel. Add 20 ml of water and 10 ml of 10% HCl, and extract 3 times with 30 ml portions of chloroform. Transfer the aqueous layer to a 100 ml volumetric flask, and add water to make up to exactly 100 ml. Take 50 ml of this solution into another 100 ml volumetric flask, and add water to make up to 100 ml.
Transfer a 2 ml aliquot into a 25 ml glass-stoppered test tube, and add 5 ml of 0.2M borate buffer, 3 ml of 0.05% dimethyl-p-phenylenediamine solution, 10 ml of chloroform and 1 ml of 1% K₃Fe (CN) ₆ solution.
Shake for about 5 min., and allow to separate the chloroform layer.
Add Na₂SO₄ to dehydrate the chloroform layer. Filter, and measure the absorbance at 610 mμ (E_T) against chloroform. At the same time, the absorbance of the standard solution (E_S) is determined and the amount of (I) is calculated by E_T/E_S.