biuret reaction

noun

: a chemical reaction that produces a violet or purple color when biuret or most proteins are exposed to a reagent of copper sulfate in alkaline solution

Note: The biuret reaction is typically used to indicate the presence and concentration of protein in a test sample and occurs when the peptide bonds in a protein react with the copper ions to produce a violet or purple complex. The intensity of color in solution is proportional to the number of peptide bonds.