A Method for the Determination of Monosac- Charides in the Presence of Disaccharides and Its Application to Blood Analysis*

While attempting to determine the presence of lactase in mammary tissue, it became evident that no satisfactory method for the determination of the hydrolytic products of lactose in the presence of the substrate was available. We, therefore, sought to modify the Barfoed test in order to make it practical for quantitative, as well as qualitative, procedures. Since the publication of Barfoed’s test many other attempts have been made to improve it. Barfoed’s reagent consists of copper acetate and acetic acid. The modifications vary as to the proportions of these two constituents used and as to the time of boiling (1). Too high acidity and prolonged boiling both result in disaccharides giving positive tests (2, 3). The difficulties which arose were due chiefly to the volatilization of the acetic acid. Sieben (4), in order to avoid the loss of the acetic acid, used sealed containers and heated the fluid at 40”. Legrand (5), employing Barfoed’s reagent in volumetric work, collected the CuzO which formed on oxidation of the sugars, on filter paper, treated it with Fe2(S0&, and then titrated with KMn04. This and the int’eresting study of Hinkle and Sherman (6) gave promise of the usefulness of this reagent for the calorimetric determination of monosaccharides in the presence of disaccharides. The principle of the new method is the same as of those devised by Folin and Wu and by Benedict, for the determination of reducing sugars, the only difference being that the solution containing the