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Several standard titrametric methods are available for determining residual chlorine.‘-3 These methods are based on the stoichiometric production of iodine by the reaction of residual chlorine with excess iodide ion. In the direct titrametric methods, the liberated iodine is titrated with a standard reducing agent, usually thiosulfate or phenylarsine oxide, at the proper pH until the blue color of the starch-iodine complex develops. Recently, Yang et a14 reported that the accuracy of the starch-iodine end point can be affected by temperature. These investigators pointed out that significant error can result when low concentrations of residual chlorine are determined at temperatures above 2o°C. This paper presents results of a more detailed study of this phenomenon, including a quantitative analysis of the effect of temperature on the starch-iodine end point. |
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