There are many reasons to monitor sulfite concentration in water. In industrial applications, a sulfite concentration of approximately 20 mg/L must be maintained to prevent pitting and oxidation of metal components as in boiler feed and effluent waters. A high level of sulfite results in a lowered pH, thus promoting corrosion. The monitoring of sulfite is important in environmental control. Sulfite ions are toxic to aquatic life forms and their ability to remove dissolved oxygen in water will destroy the delicate ecological balance of lakes, rivers, and ponds.
Hanna Instruments offers an iodometric titration method to determine sulfite. With this method iodide ions react with iodate ions in the presence of sulfuric acid to form iodine. The sulfite present in the water sample then reduces the iodine back to iodide. When the sample has an excess of iodate added then iodine is generated. The iodine present forms a blue complex with a starch indicator. This color change determines the end point of the titration.
The sulfite Chemical Test Kit (CTK) follows 1987 Annual Book of ASTM Standard, Volume 11.01 Water (1) and Standard Methods for the Examination of Water and Waste-water, 20th Edition, 1998 methods.