biurettimenetelmä

The Biuret method is a colorimetric chemical assay used to determine the presence of proteins. It relies on the Biuret reaction, which is a chemical reaction that produces a violet color when certain organic compounds, specifically those containing at least two peptide bonds, are treated with a copper(II) sulfate solution in a highly alkaline environment. The Biuret reagent itself is typically a solution of copper(II) sulfate, sodium hydroxide, and potassium sodium tartrate. The sodium hydroxide provides the alkaline conditions necessary for the reaction, while the potassium sodium tartrate acts as a complexing agent to stabilize the copper(II) ions and prevent their precipitation as copper(II) hydroxide.

When proteins are present in a sample, the copper(II) ions in the Biuret reagent form coordination complexes with the nitrogen atoms of the peptide bonds. This complex formation results in a characteristic violet or purple color. The intensity of this color is directly proportional to the concentration of the protein in the sample. By measuring the absorbance of the colored solution at a specific wavelength, typically around 540-560 nanometers, using a spectrophotometer, the protein concentration can be quantified. A calibration curve, generated using known protein concentrations, is usually employed for accurate determination. The Biuret method is a relatively simple and inexpensive assay but is not sensitive to very low protein concentrations and can be affected by the presence of certain other substances that might also react with the reagent.