What Is the Principle of the Biuret Test?


Quick Answer

The biuret test detects peptide bonds, and when they are present in an alkaline solution, the coordination complexes associated with a copper ion are violet in color. The protein concentration affects the intensity of the color, and the color will be more intense with more proteins.

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Full Answer

To perform the test, potassium or sodium hydroxide at a 1 percent strong base go onto the sample along with about three to four drops of aqueous copper sulfate. A protein is present if the solution turns purple. Scientists can determine five to 160 milligrams per milliliter. For a measurable color shift, at least three amino acids need to be present in a peptide chain.

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