Copper-iodometric Reagents for Sugar Determination by Philip A. Shaffer and Michael Somogyi

For the determination of reducing sugars in pure solution or in biological fluids (after suitable pretreatment to remove interfering substances and supplemented where needed by the use of washed yeast), one of the most accurate and convenient methods is the use of copper reagents of the type utilizing iodometric titration of cuprous oxide (Shaffer and Hartmann (l), Somogyi (2)). The delicacy and accuracy attainable in the iodometric titration are such that the error of analysis depends chiefly upon the composition of the copper reagent and the conditions which affect its sensitiveness and reproducibility during the sugar oxidation. With the object of better defining the optimum composition of reagents, the influence of various factors has been studied on the rate of copper reduction and on the maximum reduction equivalent per unit of sugar. For determination of other sugars than glucose or of mixtures of sugars, especially if quite dilute solutions are to be analyzed with maximum accuracy, reagents and directions designed for glucose are usually not suitable, because of wide differences in the rates of copper reduction by different sugars. Instances might be cited in the literature in which neglect of these considerations-the use of reagents and conditions designed for glucose, with other sugars and mixtures-has led to error and confusion. The information here reported, although fragmentary, should permit more intelligent choice of composition of reagents suited for particular purposes. The conditions adopted with the Shaffer-Hartmann microreagent for blood sugar estimation, namely 5 cc. of reagent and 5 cc. of sugar solution in 25 X 200 mm. Pyrex test-tubes, covered