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Effect of Ethyl Alcohol on the Dinitrosalicylic Acid Assay for Reducing Sugars

Nyla Z. Numan and John C. Ford

The determination of reducing sugars, especially glucose, is of considerable interest. An assay attributed to Miller using 3,5-dinitrosalicyclic acid (DNS) is widely used but suffers from some limitations. It is, nonetheless, convenient and recommended by the IUPAC Commission on Biotechnology for measuring cellulase activity. We found that 5-10% concentrations of methanol, ethanol, 1- and 2-propanol interfered with the DNS assay and gave a positive error (an apparent increase in glucose) when aqueous standards were used for calibrating the assay. For ethanol concentrations beyond about 15%, the assay gave a negative error. In the case of ethanol, this was due to an effect of ethanol on the color-forming reaction as well as a slight effect on the spectral absorbance of the product.