<P> The biuret test (Piotrowski's test) is a chemical test used for detecting the presence of peptide bonds . In the presence of peptides, a copper (II) ion forms violet - colored coordination complexes in an alkaline solution . Several variants on the test have been developed, such as the BCA test and the Modified Lowry test . </P> <P> The biuret reaction can be used to assess the concentration of proteins because peptide bonds occur with the same frequency per amino acid in the peptide . The intensity of the color, and hence the absorption at 540 nm, is directly proportional to the protein concentration, according to the Beer - Lambert law . </P>

What is the biuret test used to test for in the medical field