<P> In the BCA test, Cu forms a deep purple complex with bicinchoninic acid (BCA), which absorbs around 562 nm, producing the signature violet color . The water - soluble BCA / copper complex absorbs much more strongly than the peptide / copper complex, increasing the sensitivity of the biuret test by a factor of around 100: the BCA assay allows to detect proteins in the range of 0.0005 to 2 mg / mL). Additionally, the BCA protein assay gives the important benefit of compatibility with substances such as up to 5% surfactants in protein samples . </P> <P> In the Lowry protein assay Cu is oxidized back to Cu by Mo in Folin - Ciocalteu's reagent, which forms molybdenum blue (Mo). Tyrosine residues in the protein also form molybdenum blue under these circumstances . In this way, proteins can be detected in concentrations between 0.005 and 2 mg / mL . Molybdenum blue in turn can bind certain organic dyes such as malachite green and Auramine O, resulting in further amplification of the signal . </P> <P> In Poland, the Biuret Test is more commonly called as the Piotrowski Test, in honor of the Polish toxological chemist, Jerzy Kazimierz Piotrowski (b . 1926) of Lodz . </P>

Would you expect free amino acids to react with biurets solution