A Photometric Adaptation of the Somogyi Method for the Determination of Glucose

The reliability of the various Somogyi-Shaffer-Hartmann (1, 2) copper reagents for glucose determination in biological material has been established. Adaptation of these reagents to calorimetric use may be accomplished by omission of the iodide and iodate in their preparation, since these interfere with the molybdate color reagents. This omission produces no especial change in the character of the reagents. KI, however, inhibits the autoreduction of the copper and in its absence an unstable reagent results. Nevertheless, if the copper is added to the rest of the reagent on the day of its use, this difficulty is avoided. When the Somogyi micro reagent (2) is used in this way with almost any of the various phosphomolybdate reagents, very satisfactory proportionality is found between color density and glucose taken over a wide range of values. However, all of the phosphomolybdate reagents tried left much to be desired in reproducibility from time to time and lacked the desired stability of color. We therefore tried various color reagents, which led to the development of a new arsenomolybdate reagent. When this reagent was used with Somogyi’s micro reagent, it gave satisfactory stability and reproducibility of color. By this means it has been possible to utilize the copper reagents in a photometric procedure for practically all the uses to which the titrimetric procedures are adapted. These include tissue sugar, glycogen, urine reduction equivalent, maltose, glucuronic acid, etc. However, diastase determinations have not been successful because of the effect of the undigested starch on the clarity of the final colored solution. The reactions involved in the molybdenum blue reaction are uncertain and beyond the scope of this report. Woods and Mellon (3) discuss and give references to the various interpretations of the reaction. Reagents-Analytical reagent grade or the equivalent. 1. Copper Reagent A. Dissolve 25 gm. of N&C03 (anhydrous), 25 gm. of Rochelle salt, 20 gm. of NaHCOs, and 200 gm. of NaiSOa (anhydrous) in about 800 ml. of water and dilute to 1 liter. Filter if necessary.’ This