Spectrophotometric determination of quinine hydrochloride in pharmaceutical preparations

Abstract

Quinine hydrochloride (I) reacts with Bromophenol Blue in an acid medium (pH 6.2) to give a red color. This chromogen can be extracted into benzene-chloroform (1:1) and shows an absorption maximum at 585 mμ. The recommended analytical procedure is as follows. Take a sample containing 40 mg of (I) in a stoppered flask. Add 5 ml of dil. HCl and 50 ml of water and warm on a water bath at 60°C. Cool to room temperature. Transfer the solution to a 100 ml volumetric flask and add water to make up to 100 ml. Centrifuge this solution and pipet 50 ml of the supernatant into a 100 ml beaker. Add 10 ml of 0.5M KH2PO4 solution and adjust pH to 6.2 with 0.1N NaOH. Transfer the solution to a 100 ml of volumetric flask and add water to make up exactly to 100 ml. Transfer a 2 ml aliquot into a 50 ml glass-stoppered centrifuge tube and add 2 ml of buffer (pH 6.2) 1 ml of 0.06% Bromophenol Blue solution and 20 ml of benzene-chloroform (1: 1). Shake for about 5 min centrifuge and allow to settle the benzene-chloroform layer. Measure the absorbance at 585 mμ (ET) against benzene-chloroform. At the same time measure the absorbance of the standard solution (Es) and determined the amount of (I) by ET/Es× 1.100. Quinine sulfate was analysed by the same method the value being caluculated by ET/Es× 1.048. © 1970, The Japan Society for Analytical Chemistry. All rights reserved.