Rapid Determination of Sulfanilamide Derivatives by Amperometric Titration with Potassium Iodate Utilizing the Bromination Reaction

Abstract

Six sulfanilamide derivatives were precisely determined by the amperometric titration with potassium iodate. The reduction current of iodate ion at a rotating platinum electrode (2000rpm) was measured at a potential of +0.6 V vs. SCE. The method is based on the bromination of sulfanilamide derivatives with potassium iodate in the presence of potassium bromide and the hydrochloric acid (or sulfuric acid). Sulfanilamide (2×10^-5∼10^-3 mol/l), N¹- (6-methoxy3-pyridazinyl) sulfanilamide (2×10^-5∼2×10^-3 mol/l), N'-(2, 6-dimethyl-4-pyrimidinyl) sulfanilamide (2×10^-5∼2×10^-3 mol/l) and 4-amino-N- (5-methyl-3-isoxazolyl) benzenesulfonamide (2×10^-5∼10^-3 mol/l) were determined with the relative error and the coef ficient of variation both less than O.3 %. N1-(2-Pyrimidinyl) sulfanilamide (2×10^-4∼10^-3 mol/l) and N-[4-(2-thiazolylsulfanoyl)phenyl]phthalamic acid (2×10^-5∼2×10^-4 mol/l) were determined with the relative error less than 2% and the coefficient of variation less than 0.2%. The presence of tablet diluents (starch, lactose, magnesium stearate, calcium phosphate and sodium hydrogencarbonate)did not disturb the determination. The recommended procedure proceeded as follows. After 5 ml of 2×10^-3 moli/ sulfanilamide, was introduced into the titration cell, 7.5 ml of 4 moli/potassium bromide, 3 ml of 10 mol/l hydrochloric acid and water were added to make total volume up to 50 ml. The resultant solution was titrated at room temperature with 0.05 ml portions of potassium iodate standard solution at intervals of 10 s. The experimental conditions for other sulfanilamide derivatives are shown in Table 1. Titration time was about 7 min.