A submicrodetermination of glucose.

The reduction of ferricyanide ions in alkaline solution followed by formation of Prussian blue (ferric ferrocyanide), which is measured quantitatively, has been the basis of a method for the estimation of blood sugar (1). This method has been modified several times (2-6). Though the reduction reaction suffers from lack of specificity, the convenience and sensitivity of the procedure often make it the method of choice, especially when the reducing materials in the system are known. The calorimetric method of Folin and Malmros (3), as modified by Horvath and Knehr (5), is perhaps the most convenient modification. The Prussian blue is held in suspension by Duponolr and is measured with the aid of a photoelectric calorimeter. The range of the method is 20 to 140 y of glucose. Occasionally a more sensitive method is preferable. In this paper, a modification of the ferricyanide reduction method, which has a range of 1 to 9 y of glucose, is described.