Biuret reaction

Biuret Reaction is a chemical reaction that is used to detect the presence of protein in a sample. The reaction involves the formation of a complex between the protein and a copper ion in an alkaline solution, which results in a color change.

History

The biuret reaction was first described in the early 19th century by the German chemist Justus von Liebig. He discovered that when a solution of biuret (a compound derived from urea) was treated with a solution of copper sulfate in the presence of alkali, a violet color was produced.

Principle

The principle of the biuret reaction is based on the ability of proteins to form a complex with copper ions in an alkaline solution. The copper ions react with the peptide bonds in the protein to form a violet-colored complex. The intensity of the color is directly proportional to the concentration of protein in the sample.

Procedure

The procedure for the biuret reaction involves the addition of a biuret reagent to the protein sample. The biuret reagent is a solution of copper sulfate in a strong alkali, usually sodium hydroxide. The mixture is then incubated for a period of time, typically 20 minutes, to allow the reaction to occur. The resulting color change is then measured using a spectrophotometer.

Applications

The biuret reaction is widely used in biochemistry and clinical chemistry for the quantitative determination of total protein in serum, urine, cerebrospinal fluid, and other biological fluids. It is also used in food analysis to determine the protein content of food products.

Limitations

The biuret reaction has several limitations. It is not specific for proteins, as it can also react with compounds that contain peptide bonds, such as peptides and urea. It also requires a relatively large amount of protein for the reaction to occur, which can be a limitation in samples with low protein concentrations.

See Also

• Protein assay
• Bradford protein assay
• Lowry protein assay