Biuret test for protein. Test tubes containing negative (left) and positive (right) tests for proteins using biuret reagent. The biuret reagent comprises sodium hydroxide and copper (II) sulphate. In the alkaline conditions provided by the sodium hydroxide, the peptide bonds form a complex with the copper (II) ions, giving the solution a deep violet colour. The more purple the solution, the more protein is present. The solution at left is the normal colour of uncomplexed copper sulphate.
Model release not required. Property release not required.