Analytical Sciences

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

Tetsutaro YOSHlNAGA,*  Tomoharu SHIRAKATA,* Hideo DOHTSU,* Hiroshi HIRATSUKA,** Miki HASEGAWA,*** Michio KOBAYASHI,*** and Toshihiko HOSHI***

*Department of Applied Chemistry, Faculty of Engineering, Kyushu Institute of Technology, Sensuicho, Tobata, Kitakyushu 804-8550, Japan
**Department of Chemistry, Faculty of Engineering, Gunma University, Tenjincho, Kiryu, Gunma 376-8515, Japan
***Department of Chemistry, Faculty of Science and Engineering, Aoyamagakuin University, Chitosedai, Setagaya, Tokyo 157-8572, Japan

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 ug 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.

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