ABSTRACT
Sulfite is a bivalent polyanion. It occurs in boiler feed water that is treated with sulfite for controlling dissolved oxygen. It also occurs in water subjected to SO2 treatment for the purpose of dechlorination. Sulfite forms sulfurous acid, which gradually oxidizes to sulfuric acid. The excess sulfite in boiler waters can cause corrosion. Sulfite is toxic to aquatic life. Sulfite in water may be analyzed by the following methods: ion chromatography, iodometric method and phenanthroline colorimetric method. The first method is rapid and accurate and can be applied to analyze several anions including sulfite. The minimum detection limit for sulfite by the iodometric method is 2 mg/L, while the detection limit is 0.01 mg/L for the colorimetric method. In the second method, the sample containing sulfite is first acidified and then titrated against a standard solution of potassium iodide–potassium iodate to a blue end point, using starch indicator.
