biuret test A biochemical test to detect proteins in solution, named after the substance biuret (H₂NCONHCONH₂), which is formed when urea is heated. Sodium hydroxide is mixed with the test solution and drops of 1% copper(II) sulphate solution are then added slowly. A positive result is indicated by a violet ring, caused by the reaction of peptide bonds in the proteins or peptides. Such a result will not occur in the presence of free amino acids.

biuret test A chemical test for proteins based on the formation of a violet colour when copper sulphate in alkaline solution reacts with a peptide bond.