Biuret test is confirmatory test for:
**Core Concept**
The Biuret test is a chemical test used to detect the presence of peptide bonds in proteins. It relies on the reaction between peptides and copper ions to form a purple-colored complex.
**Why the Correct Answer is Right**
The Biuret test is a confirmatory test for the presence of proteins in a sample. This is because the test specifically detects the peptide bonds that link amino acids together in a polypeptide chain. The test works by adding a solution of copper sulfate and sodium hydroxide to the sample, which causes the copper ions to react with the peptide bonds and form a purple-colored complex. This reaction is specific to proteins and is not seen with other biomolecules such as carbohydrates or nucleic acids.
**Why Each Wrong Option is Incorrect**
* **Option A:** The Biuret test is not a confirmatory test for urea, which is detected by other tests such as the urease test or the Berthelot reaction.
* **Option B:** The Biuret test is not a confirmatory test for glucose, which is detected by tests such as the Benedict's test or the Fehling's test.
* **Option C:** The Biuret test is not a confirmatory test for cholesterol, which is detected by tests such as the Liebermann-Burchard test or the Salkowski test.
**Clinical Pearl / High-Yield Fact**
The Biuret test is a useful confirmatory test for detecting the presence of proteins in a sample, and it is commonly used in clinical laboratories to confirm the presence of proteins in urine, serum, or other bodily fluids.
**Correct Answer:** C.