Determination of Fructose in the Presence of a Large Excess of Glucose

A modification of the cysteine-sulfuric acid method of Dische and Devi¹¹⁾ is described. The modified procedure is based on the observation that fructose and glucose give different time course of color development. By this modified procedure, fructose in the presence of 100-fold excess of glucose can be determined with an error of about 10%.

Modifications of the anthrone-sulfuric acid method and the phenol-sulfuric acid method are described. By employing the principle of two-point determination of Mokrasch and by modifying the conditions for color development, fructose in the presence of 100-fold excess of glucose can be determined with an error of about 15% by the modified anthrone-sulfuric acid method. The modified phenol-sulfuric acid method also gave the same order of sensitivity and specificity to fructose as the modified anthrone-sulfuric acid method.