Dose of Sulfite  can be controlled by this method :::  Because it readily reacts with oxygen to form sulfate, sulfite is not usually found in natural water systems. In its most common form, sodium sulfite, it is widely used as an oxygen scavenger in feedwater conditioning to prevent pitting in boilers; as a pulping or pulp-bleaching agent by the paper industry; to neutralize residual chlorine in potable water, sewage, industrial effluents, and textile process waters; and as a reducing agent in still other manufacturing processes. 

Sample water over 100°F will cause a false-high reading; therefore, quickly cool to room temperature before testing. To prevent a false-low reading caused by the reaction between sulfite and ambient air or dissolved oxygen, water samples should be capped while cooling and then tested without delay. An iodometric drop test is the most popular field method for determining sodium sulfite concentrations. 

Reagent packs, containing an instruction and chemicals only, may be purchased for use with buret setups. Note: Sulfide and ferrous iron cause positive interference; copper and nitrite cause negative interference.

Limitations of Test :::

This method is rapid and adaptable to field determinations.  It is affected by any oxidizable substances in the water such as organic matter sulfides and nitrites.  The presence of these interfering substances will cause the sulfite content obtained from this titration to by shown as a higher value than actually exists.