Biuret Test
Objective
The biuret test is a chemical test used for detecting the presence of peptide bonds.
Base Theory
In the presence of peptides, a copper(II) ion forms a violet-colored complex in an alkaline solution.Several variants on the test have been developed.
The Biuret reaction can be used to assay the concentration of proteins because peptide bonds occur with the same frequency per amino acid in the peptide. The intensity of the color, and hence the absorption at 540 nm, is directly proportional to the protein concentration, according to the Beer-Lambert law. In spite of its name, the reagent does not in fact contain biuret ((H2N-CO-)2NH). The test is so named because it also gives a positive reaction to the peptide bonds in the biuret molecule.
Procedure
An aqueous sample is treated with an equal volume of 1% strong base (sodium or potassium hydroxide most often) followed by a few drops of aqueous copper(II) sulfate. If the solution turns purple, protein is present. 5–160 mg/mL can be determined.
The biuret test is a chemical test used for detecting the presence of peptide bonds.
Base Theory
In the presence of peptides, a copper(II) ion forms a violet-colored complex in an alkaline solution.Several variants on the test have been developed.
The Biuret reaction can be used to assay the concentration of proteins because peptide bonds occur with the same frequency per amino acid in the peptide. The intensity of the color, and hence the absorption at 540 nm, is directly proportional to the protein concentration, according to the Beer-Lambert law. In spite of its name, the reagent does not in fact contain biuret ((H2N-CO-)2NH). The test is so named because it also gives a positive reaction to the peptide bonds in the biuret molecule.
Procedure
An aqueous sample is treated with an equal volume of 1% strong base (sodium or potassium hydroxide most often) followed by a few drops of aqueous copper(II) sulfate. If the solution turns purple, protein is present. 5–160 mg/mL can be determined.
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