Contents
What is Biuret reagent?
Proteins are detected using Biuret reagent . This turns a mauve or purple colour when mixed with protein.
What is Biuret reagent formula?
A formula for biuret reagent is (per liter final volume) 9 gm Sodium potassium tartrate (f.w. 282.22), 3 gm Copper sulfate x 5 H2O (f.w. 249.68), 5 gm Potassium iodide (166.0), all dissolved in order in 400 ml 0.2 M NaOH (f.w. 40.0) before bringing to final volume. The volume can be scaled up or scaled down of course.
What are the reagents used to test proteins?
Reagents and food testing
| Food sample | Reagent | Colour of positive result |
|---|---|---|
| Reducing sugar | Benedict’s | Brick red precipitate |
| Starch | Iodine | Blue-black |
| Protein/amino acids | Biuret (a mixture of sodium hydroxide and copper sulfate). | Lilac/purple |
| Fat | Ethanol | White emulsion |
Why is it called biuret reagent?
The biuret reaction can be used to assess the concentration of proteins because peptide bonds occur with the same frequency per amino acid in the peptide. The test is named so because it also gives a positive reaction to the peptide-like bonds in the biuret molecule.
Why would you use biuret reagent?
A Biuret test is a chemical test used to determine the presence of a peptide bond in a substance. In presence of an alkaline solution, blue-colored copper II ion can form a complex with the peptide bonds since the peptide has unshared electron pairs in nitrogen and oxygen of water.
Why is biuret test used?
The biuret test is a chemical test that can be used to check for the presence of peptide bonds in a given analyte. In this test, the presence of peptides results in the formation of pale purple coloured (or mauve coloured) coordination compounds of the copper(II) ion (when the solution is sufficiently alkaline).
What is the biuret test used for?
Biuret test is used for detecting compounds with peptide bonds. A biuret reagent may be used to test the aqueous sample. This blue reagent is made by combining sodium hydroxide and copper sulfate solutions.
Why is CuSO4 used in biuret test?
Alkaline CuSO4 reacts with compounds containing two or more peptide bonds to give a violet colored product which is due to formation of co-ordination complex of cupric ions with un-shared electron pairs of peptide nitrogen and O2 of water.
What colour is biuret?
We used Biuret’s reagent to detect the presence of proteins in solution. The reagent is pale blue when pure, but when mixed with proteins, the resulting reaction produces a pale purple color.
What makes up the Biuret reagent in a peptide test?
The biuret reagent is made up of hydrated copper sulfate, sodium hydroxide, and Rochelle salt (sodium-potassium tartrate). Here, the Rochelle salt acts as a chelating agent and stabilizes the copper (II) ions. The copper (II) present in the biuret reagent binds itself to the nitrogen atoms that are present in the protein peptides.
What can be used as an alternative for Biuret reagent?
The peptide bond is the chemical bond that holds amino acids together. There are other alternatives for biuret reagent and these are copper sulphate and sodium hydroxide. Fehling’s solutions A and B can be used too. The hydrated copper sulphate is the one responsible for the formation of Cu (II) ions forming the chelate complex.
What is the charge of a Biuret reagent?
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. just create an account. No obligation, cancel anytime. Want to learn more?
What makes a positive biuret test a positive test?
The peptide bonds in Biuret give a positive result for the test hence the reagent is named so. It is considered as a general test for compounds (proteins and peptides) having two or more peptide (CO-NH) bonds.