Biuret reagent is mainly used for the quantitative estimation of protein samples by the Biuret assay method. Biuret reagent consists of Copper sulphate and Sodium potassium tartrate. In Biuret reaction peptides containing three or more amino acid residues form a colored chelate complex with cupric ions (Cu2+) in an alkaline environment containing sodium potassium tartrate. The intensity of the color produced is proportional to the number of peptide bonds participating in the reaction