3,5-Dinitrosalicylic Acid (DNS)

3,5-Dinitrosalicylic acid is an aromatic compound that reacts with reducing sugars and other reducing molecules to form 3-amino-5-nitrosalicylic acid, which absorbs light strongly at 540 nm. It was first introduced as a method to detect reducing substances in urine and has since been widely used, for example, for quantifying carbohydrates levels in blood. It is mainly used in assay of alpha-amylase. However, enzymatic methods are usually preferred due to DNS lack of specificity. An assay for determination of galacturonic acid with 3,5-dinitrosalicylic acid was developed that substantially extends the linear range of detection compared to a previously published method with this reagent. In the improved assay, galacturonic acid was detected with a reagent containing 44 mM 3,5-dinitrosalicylic acid, 4 mM sodium sulfite, and 375 mM sodium hydroxide.