Test for Proteins

The biuret test is used to detect the presence of protein in a solution, because it specifically reacts with the peptide bond (-C-N-) that links amino acids together. To perform the test, an equal quantity of sodium hydroxide solution is added to the protein solution and mixed, and then a few drops of dilute (0.5%) copper(II) sulphate solution are added with gentle mixing. If peptide bonds are present, a distinct purple colour develops without any need for heating - the copper ions form a coloured complex with the nitrogen atoms of the peptide bonds. Because the reaction depends directly on the number of peptide bonds available to react, the intensity of the purple colour increases as the concentration of protein in the sample increase …