A new colorimetric microestimation of sugar in blood and biological fluids.

Although of the many colorimetric microestimations of sugar the Folin and Wu method (1920) has remained in most widespread use in clinical laboratory practice, the still increasing number of modifications continue to draw attention to several inherent weaknesses of the method which have not yet been eliminated, one of which is the instability of the colour solution. To avoid these drawbacks a more robust and reliable method has been developed, based on the oxidation of the sugar by potassium ferricyanide, and colorimetric determination of the ferrocyanide formed by means of the yellowish-brown solution of its molybdenum compound. Hagedorn and Jensen (1923) had attempted to develop a colorimetric method using the potassium ferricyanide oxidation but met with no success. Folin and Malmros (1929) and later Milton (1942) similarly employed this principle, but their methods failed to gain general recognition, again mainly because of the unsuitable nature of their colour solution for colorimetry. The applicability of the molybdenum ferrocyanide salt to colorimetric measurements was investigated in a series of experiments. It appeared that if the customary concentrated phosphoric acid is replaced by a correspondingly concentrated