Polyvinyl alcohol as a useful indicator on iodometry: Volumetric and spectrophotometric studies on iodine-PVA and iodine-starch complexes

Iodometry is one of the easiest, most rapid and accurate methods for the determination of a relatively small amount of oxidizing agent, such as residual chlorine. Starch has long been used as a useful color indicator in iodometry. However, we found that PVA (polyvinyl alcohol with partially saponificated; e.g., saponification degree of 88%) is a more useful color indicator than starch. For example, at 20 degreesC, the PVA indicator gave similar profiles of iodine concentration vs. titration efficiencies (percent recoveries) to those of starch at 0 degreesC. At 0 degreesC, the PVA indicator detected 1.1 mg I-2/L (11 mug It: with 10 mt sample volume) with a high percentage of recovery (= 95%). Furthermore, at 20 degreesC an iodine concentration of 0.36 mg/L (which corresponds to a residual chlorine concentration of 0.1 mg CI2/L) could be detected using PVA color indicator assuming an appropriate correction.