Instructions for preparation and use
Version 1.0 | July 2016
Post-16 Biology specifications in England require students to be familiar with Benedict’s reagent for the detection of reducing sugars. This is in the context of ‘qualitative tests for the identification of biological molecules’, as specified by the subject criteria for biology (DfE, 2014). The same DfE criteria also require students to use ‘appropriate instrumentation to record quantitative measurements, such as a colorimeter …’. Most biology specifications also suggest that students carry out practical investigations of enzyme activity. It is in this latter context that we suggest that the DNSA (3,5-dinitrosalicylic acid) test, a quantitative measure of reducing sugars, is used. DNSA is more sensitive and easier to use than Benedict’s reagent. Used with a colorimeter, it is ideal for measuring the action of enzymes such as invertase, cellulase and amylase where
reducing sugars are produced. Thus it helps to meet two of the important practical requirements of the current (English) biology specifications.
How it works
On heating with reducing sugars, the 3-nitro (NO2 ) group of DNSA is reduced to an amino (NH2 ) group.