Biuret Test: Definition, Procedure & Reagent

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  • 0:04 Gummy Bears
  • 0:53 What Is Biuret Reagent?
  • 1:40 Biuret Test Procedure
  • 2:40 Lesson Summary
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Lesson Transcript
Instructor: Sarah Pierce

Sarah has a doctorate in chemistry, and 12 years of experience teaching high school chemistry & biology, as well as college level chemistry.

This lesson describes a common test for proteins called the biuret test. A description of the reagent used in the biuret test as well as the procedure for measuring protein concentration will be covered.

Gummy Bears

Imagine that you are eating gummy bears with your friend Sharon. You decide to look at the nutritional information and notice that in a serving of gummy bears, which is about 17 of the little fellows, there are 2 grams of protein!

You and Sharon are absolutely shocked. Who knew that such a small serving of candy would have so much protein? Sharon claims that there must be a mistake. There is no way the candy can contain protein! You read the label and notice that the gummy bears contain gelatin, which you vaguely remember is a source of protein. You and Sharon decide to design an experiment to test if gelatin is the source of protein in the gummy bears. After a little research, you decide you want to use a biuret test, which tests for the presence of proteins. What exactly is this test and how does it work? Let's find out!

What Is Biuret Reagent?

A biuret reagent is used to determine the presence of an analyte, or a chemical substance, in solution. Specifically, it tests for protein in a sample. If the sample turns purple when the biuret reagent is added, then there is protein in the sample. If the sample remains blue, then there is no protein. The biuret reagent can be made in a few different ways, but all the methods contain copper sulfate mixed in a basic solution. Biuret reagents can also be purchased from a variety of chemical supply companies.

The biuret reagent contains copper ions, or charged atoms of copper. The charge on the ions of copper are +2. When the copper ions come in contact with peptide bonds, the charge changes to +1 and the color changes from blue to purple.

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