Volumetric method for sulfate with sulfonazo III

Abstract

Direct volumetric determination of sulfate by barium salt encountered a difficulty in somewhat slow rate of formation of barium sulfate. The authors carried out the titration with an addition of an anionic sufactant to enhance the formation of barium sulfate, and the results were compared with those obtained with an addition of acetone or ethanol. Sulfonazo III was used as the indicator, its color changing from pink to blue at the end point.
The method was applied to the determination of sulfate in several samples including sodium sulfates, solutions of sulfuric acid, and sea water. Nearly satisfactory results were obtained except for the sea water.