The Biuret Test
Shows positive test for:
How to perform the test:
Prepare a solution or suspension of the sample by placing ~0.2 g in 10 ml of water. Ten drops of 1.5 M NaOH (a colorless solution) and 2 drops of 0.1 M CuSO4 (a light blue solution) are added.
A positive test is indicated by:
a deep blue/purple color due to the copper ion complex with the amide group of the protein.
a negative test (left) and a positive test (right)