This method is about ten times more sensitive than Biuret method. The reagent Folin-Ciocalteu is quite complex and contains phosphomolybdic acid and tungstate. The proteins which contain tyrosine and tryptophan react with these and produce a dark blue colour. A standard protein (BSA) was prepared and used for the assay. This method is based on both the Biuret reaction, where peptide bonds of proteins react with Cu²⁺ under alkaline condition producing Cu⁺, which reacts with Folin’s reagent and reduces phosphomolybdate tungstate to heteropoly-molybdenum blue by the copper catalysed oxidation of aromatic amino acid. A graph is drawn using standard values, and from this, unknown (protein sample) is calculated. This shows how much of protein was present in the isolated protein sample.