Potentiometric Titrations of L-Ascorbic Acid, p-(Methy!amino)phenoI Sulfate and Hydroquinone with an Iodide-Selective Electrode

Abstract

A rapid method has been established for the determination of P-aseorbic acid, -(methylamino)phenol sulfate and hydroquinone by potentiometric argentimetric titration using an iodide-selective electrode. The reactions involved were (1), (2) and (3), and the iodide ion produced by the reactions with iodine in methanol was determined. In a typical example, a sample containing 5∼44 mg L-ascorbic acid, 2∼35 mg p-(methylamino) phenol sulfate or 1— 23 mg hydroquinone was taken into a 200 ml amber-glass titration cell and treated with excess of an 0. 05 moll I iodine-methanol solution. The volume was adjusted with distilled water to make a 100 m/ solution which was then titrated potentiometrically with a 0.001∼0.1 mol// standard silver nitrate solution at room temperature. The whole procedure required only 5∼lOmin. L-Ascorbic acid (0. 2∼44 mg), p-(methylamino)phenol sulfate (0. 2∼35 mg) and hydroquinone (0.1∼23 mg) were determined with a relative error and relative standard deviation of less than 1.7%. The best results with a relative error and relative standard deviation of less than 0. 3% were obtained using 44 mg of L-ascorbic acid, 35 mg of p-(methylamino)phenol sulfate and 23 mg of hydroquinone. L-Ascorbic acid in drugs and the commercial sample of hydroquinone were determined by this method. © 1980, The Chemical Society of Japan. All rights reserved.