Qualitative test for Protein
Biuret Test
The biuret test, also known as Piotrowski's test, is a chemical test used for detecting the presence of peptide bonds. Biuret is a compound formed by heating urea to 180° C. When biuret is treated with dilute copper sulfate in alkaline condition, a purple colored compound is formed.
In the presence of peptides, a copper(II) ion forms mauvecolored (pale purple color) coordination complexes in an alkaline solution. This is the basis of biuret test widely used for identification of proteins.