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The Biuret test is a chemical test used for detecting the presence of peptide bonds. indirectly protein as the proteins are made up of amino acids connected together with peptide bonds. In the presence of peptides, a copper(II) ion forms violet-colored coordination complexes in an alkaline solution. 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.