The biuret test would indicate a positive result for proteins in which of the following solutions?
A.
Starch solution
B.
Olive oil
C.
Albumin solution
D.
Distilled water
E.
Glucose solution
The Correct Answer and Explanation is:
The correct answer is C. Albumin solution.
Explanation:
The biuret test is a qualitative assay used to detect the presence of proteins in a solution. This test is based on the ability of proteins to form a complex with copper ions in an alkaline solution, producing a color change.
Biuret Test Principle:
- Biuret Reagent: The biuret reagent contains copper sulfate (CuSO4) dissolved in a strong alkaline solution, typically sodium hydroxide (NaOH).
- Reaction: When proteins are present, the copper ions in the reagent form a complex with the peptide bonds in the proteins. This complex results in a color change, usually from blue to violet or purple, depending on the concentration of protein.
Testing Solutions:
- A. Starch Solution: Starch is a polysaccharide (carbohydrate) and does not contain peptide bonds. Therefore, it does not react with the biuret reagent, and the test will show no color change.
- B. Olive Oil: Olive oil is a lipid (fat) and does not contain proteins or peptide bonds. Hence, it will not react with the biuret reagent and will also show no color change.
- C. Albumin Solution: Albumin is a type of protein found in egg whites and blood plasma. It contains multiple peptide bonds that will interact with the copper ions in the biuret reagent. The biuret test will produce a positive result with a color change from blue to violet or purple, indicating the presence of proteins.
- D. Distilled Water: Distilled water is pure and does not contain proteins. As a result, the biuret test will not show any color change with distilled water.
- E. Glucose Solution: Glucose is a simple sugar (carbohydrate) and lacks peptide bonds. Therefore, it will not react with the biuret reagent, leading to no color change.
In summary, only the albumin solution contains proteins that can form a complex with the copper ions in the biuret reagent, leading to a positive result. The other solutions, being either carbohydrates, lipids, or plain water, do not have the necessary peptide bonds and therefore do not produce a positive result with the biuret test.