Sulfite ions (SO32−) may occur in boilers and boiler feedwaters treated with sulfite for dissolved oxygen control, in natural waters or wastewaters as a result of industrial pollution, and in treatment plant effluents dechlorinated with sulfur dioxide (SO2). Excess sulfite ion in boiler waters is deleterious because it lowers the pH and promotes corrosion. Control of sulfiteion in wastewater treatment and discharge may be important environmentally, principally because of its toxicity to fish and other aquatic life and its rapid oxygen demand.
- Selection of Method
The iodometric titration method is suitable for relatively clean waters with concentrations above 2 mg SO32−/L. The phenanthroline colorimetric determination, following evolution of sulfite from the sample matrix as SO2, is preferred for low levels of sulfite.