The Iodometric Determination of Copper and Its Use in Sugar Analysis

In the course of a comparative study of several methods for the determination of sugar in blood, the results of which will be recorded elsewhere, it became desirable to investigate the reaction betsveen copper sulfate and potassium iodide which is concerned in a number of methods for sugar determination (Bang (l), Maclean (2), Scales (3), Lehmann (4), Riegler (4), Peters (4), Kendall (5)). In certain of these methods (Bang, Maclean, Scales) the cuprous oxide formed by the oxidation of the sugar is dissolved in acid1 and reoxidized to cupric salt by a known amount of standard iodine-potassium iodide, the excess of iodine being then titrated with thiosulfate. The oxidation takes place in the presence of considerable excess of cupric salts which under the conditions does not appear to inhibit the oxidation, the latter going apparently to completion. Essentially the same reaction between cupric salts and potassium iodide is the basis of the well known method for the iodometric determination of copper introduced by De Haen in 1854, the details of which have been studied especially by Gooc’h and Heath (6) who give the earlier literature. But in this case cupric salt is reduced to cuprous iodide in the presence of an excess of potassium iodide, with the liberation of free iodine