Polyvinyl Alcohol as a Useful Indicator on Iodometry: Volumetric and Spectrophotometric Studies on Iodine-PVA and Iodine-Starch Complexes

摘要

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°C, the PVA indicator gave similar profiles of iodine concentration vs. titration efficiencies (percent recoveries) to those of starch at 0°C. At 0°C, the PVA indicator detected 1.1 mg I2/L (11 µg I2: with 10 mL sample volume) with a high percentage of recovery ( = 95%). Furthermore, at 20°C an iodine concentration of 0.36 mg/L (which corresponds to a residual chlorine concentration of 0.1 mg Cl2/L) could be detected using PVA color indicator assuming an appropriate correction.