Question

1.) Name the structure required for a positive biuret test.

2.) What functional group is present for a positive Ninhydrin test? Do proteins and amino acids both have the group?

3.) The Xanthoproteic test confirms the presence of which amino acids? Explain why a solution may give a faint, positive test?

Answer 1

1) Biuret test is used to test for the presence of proteins. If the sample contains proteins it will turn to violet colour with the addition of Biuret solution.

2) Ninhydrin is used for the detection of the functional group amino acids

Yes both protein and amino acids contain this group. Proteins are made up of amino acids. So they contain amino acids as well.

3) Xanthoproteic test confirms the presence of amino acids with aromatic groups like tyrosine , tryptophan etc.

Sometimes a solution may give faint yellow colour because all aromatic groups may not undergo nitration easily in this test. So they give a faint colour but still it is considered as a positive test.