Visual Colorimetric Determination of Sulfate Ion in Water Using Coprecipitation Phenomenon of Potassium Permanganate and Barium Sulfate

Abstract

An on-site analytical technique for the colorimetric determination of sulfate ion in a water sample was developed based on the formation of purple precipitates as mixed crystals composed of barium sulfate with permanganate. Potassium permanganate solution and acidic barium chloride solution with hydrochloric acid were added in sequence into 1.5 mL of the sample, then the mixed crystals precipitated and suspended. The residual excess of permanganate ion remaining in the mother solution was reduced with ascorbic acid to turn it colorless. At that time, colors of the suspended precipitates became observable. The intensity of purple color tone of the suspension varied depending on the concentration of sulfate ion. The concentration was determined semi-quantitatively by visual comparison of the intensity with standard color charts. The proposed colorimetry permitted us to determine sulfate ion at the range of 50 to 2000 mg L−1. The time required for the on-site analysis was less than one minute. We applied the colorimetry to the real drainage samples taken from biological desulfurization systems and obtained good results useful for maintenance of them.