Experiment 68

Objective

To identify the presence of proteins in a solution using the Biuret test.

Introduction

The Biuret test is used to detect proteins by observing the color change in an alkaline medium when a protein solution is heated with copper sulfate (CuSO₄). The test produces a red or violet color complex due to the formation of a copper-protein coordinate complex in a sodium salt medium.

Reaction:

NH2 ​- CRH-COOH + CuSO4 ​+ NaOH → [Cu(NH2 ​- CRH-COONa)]2

Materials

Chemicals

●      Protein solution

●      Sodium hydroxide (NaOH)

●      Copper sulfate (CuSO₄)

Apparatus

●      Two test tubes

●      Two test tube holders

●      Dropper

●      Bunsen burner

Reagents

●      3–4 ml of protein solution in a test tube

●      1 ml of NaOH

●      A few drops of CuSO₄

Procedure

1.    Place the protein solution in a test tube and secure it in a test tube holder.

2.    Add 1 ml of NaOH to the solution.

3.    Add a few drops of CuSO₄ to the mixture.

4.    Heat the mixture for 5–6 minutes using a Bunsen burner.

5.    Stop heating once a color change is observed.

Observation

The solution develops a red or violet color complex, indicating the presence of protein.

Questions

1.    What color forms during the Biuret test?

2.    What is a protein?

3.    How is protein identified in this test?

4.    What complex forms in the Biuret test?