A new method to determine both sodium chlorite and sodium hypochlorite in mixtures of the two by two-step iodometry is described.
When hypochlorite reacts with potassium iodide in the presence of sodium bicarbonate, iodine is liberated immediately. In the case of chlorite, however, the reaction does not proceed under these conditions. Therefore, at the first step, sodium hypochlorite is analyzed quantitatively by sodium thiosulfate titration in the test solution containing sodium bicarbonate and at the second step, after the addition of sulfuric acid solution, sodium chlorite is titrated.
When determination of sodium chlorite and sodium hypochlorite was carried out by this method, the data were reproducible to less than ±5% on repeated runs.
This method can be adapted for automatic potentiometric titration, and is simple, rapid and accurate. It should be useful for the determination of both food additives.