The Xanthoproteic test uses a nitration reaction to determine the presence of proteins in a solution. When the sample is treated with a hot, concentrated nitric acid it reacts with aromatic amino acids such as phenylalanine, tyrosine and tryptophan and forms a yellow colored product known as Xantho protein.

What is the principle of Xanthoproteic test?

Xanthoproteic test is used to detect amino acids containing an aromatic nucleus (tyrosine, tryptophan and phenylalanine) in a protein solution which gives yellow color nitro derivatives on heating with conc. HNO3. The aromatic benzene ring undergoes nitration to give yellow colored product.

How does Xanthoproteic test detect phenolic amino acids?

Xanthoproteic Test is used to distinguish amino acids with a phenyl ring, a phenol or an indole group from other amino acids. Xanthoprotein is a yellow acid substance formed by the action of hot nitric acid on albuminous or protein matter and is changed to a deep orange-yellow colour by the addition of ammonia.