Aim of Biuret Test The Biuret Test is done to show the presence of peptide bonds which are the basis for the formation of proteins These bonds will make the blue Biuret reagent turn ID: 931884
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Slide1
Biuret Test
For protein detection and quantitative analysis
Slide2Aim of Biuret TestThe Biuret Test is done to show the presence of
peptide bonds
, which are the basis for the formation of
proteins
. These bonds will make the
blue
Biuret reagent turn
purple
.
Slide3Structure of Biuret Solution
Biuret reagent
, made of sodium hydroxide and copper (II) sulfate, is used for determining the presence of protein in a sample. The
test
relies on the reaction between copper ions and peptide bonds in an alkaline solution. A violet color
indicates
the presence of proteins.
Slide4Peptides contain three or more amino acid residues form a colored chelate complex with cupric ions (Cu2+) in an alkaline enviroment contain sodium potassium tartrate.
Single
amino acids and dipeptide do not react with biuret solution but tripeptides and larger polypeptides or proteins will react to produce the blue to violet complex that absorbs the light at 540nm
.
One
cupric ion forms a colored coordination complex with four to six nearby peptides bonds. Color intensity produced is proportional to th number of peptide bonds present in the
reaction.
Slide5Principle
The
biuret reagent (copper sulfate in a strong base) reacts with peptide bonds in proteins to form a blue to violet complex known as the “biuret complex”.
N.B. Two peptide bonds at least are required for the formation of this complex.
Slide6Procedure
Sample Preparation
Measure different amount of
Egg Albumin
(0.250,0.500,0.750,1.000)g individually .
Use distilled water for preparing clear solution of
egg albumin
(50ml) of each .
Stir it well with glass rod .
Measure 0.500 g of
Glycine
on Sensitive balance .
Use distilled water for preparing clear solution of
Glycine solution
(100 ml) .
Stir it well with glass rod
.
Biuret Reagent Preparation
Measure 8 g of
NaOH
on sensitive balance .
Use distilled water for preparing clear solution
of
NaOH
Solution (100 ml) .
Stir
it well with glass rod .
Measure 1 g of CuSO
4
on
Sensitive balance
.
Use distilled water for preparing clear solution
of CuSO
4
Solution (100 ml) .
Stir it well with glass rod .
Slide7Observations
No change ( solution remains
blue)
The solution turns from blue to violet
The solution turns from blue to
pink
Interpretation
Proteins are not present
Proteins are present
Peptides or peptones
are
short chains of
amino
acid residues