Determination of Reducing Sugars by FIA —Automation of Somogyi-Nelson Method

To measure reducing sugars, a spectrophotometric method called the Somogyi-Nelson method, which was developed in the 1940s, is still in use today. This method measures the amount of reducing sugar by spectrophotometrically measuring the molybdenum blue produced by reacting cuprous oxide, which is produced when copper(II) is reduced with reducing sugar under alkaline heating, with arsenic molybdic acid. Its operation requires skill and is time consuming. We investigated how to automate this method using FIA. Since the manual method involves heating in a boiling water bath, it is necessary to pay attention to the uniformity of heating and to prevent air oxidation. In the flow analysis method, there is no need to worry about air oxidation, and the heating reaction is carried out in a coil enclosed in an aluminum block bath, precisely temperature controlled at over 100°C. By using an autosampler, we have completed a practical automatic analysis method that is quick and has good reproducibility. The results of measuring oligosaccharides with reducing power compared with manual methods showed good agreement, confirming the practicality of the method.