Biuret & Emulsion Tests
(Protein & Lipids)
Biuret Test
• Biuret test is used to test for the presence of proteins
by:
• Detecting the presence of peptide bonds
Biuret Test
Procedure
1. Add the sample to be tested to a clean test tube.
Biuret Test
Procedure
2. Add Biuret A (sodium hydroxide) to the test tube.
• This is to make the solution alkaline.
Biuret Test
Procedure
3. Add Biuret B [copper (II) sulphate] to the test tube.
3.1. Mix the solution gently.
Biuret Test
Procedure
4. Record results
• If proteins are present: colour change from blue 
purple
• If proteins are absent: no
colour change.
Emulsion Test
• Used to detect the presence of lipids.
A fine dispersion of
minute droplets of one
liquid in another in which
it is not soluble.
What is an
emulsion?
Emulsion Test
• Lipids are nonpolar molecules that do not dissolve in
water
• BUT, will dissolve in organic solvent such as ethanol.
• This is a qualitative test: does not give a quantitative
value of how much lipid may be present.
Emulsion Test
Procedure
1. Add the sample to be tested to a clean test tube.
Emulsion Test
Procedure
2. Add ethanol to the test tube.
• Mix solution thoroughly to dissolve any lipids.
Emulsion Test
Procedure
3. Add water to the test tube.
• Mix solution gently.
Emulsion Test
Procedure
4. Record results.
• If lipids are present: cloudy white
• If lipids are absent: no change
Emulsion Test
Reasoning
• Reason for cloudy white substance:
• Lipids dissolve in ethanol.
• When water is added, lipids separate to form lipid
globules.
• Lipids are hydrophobic.
Learning Check
Question 1
• Explain why the Biuret test is a
qualitative test.
Learning Check
Question 1
• Name the bond that is found
between adjacent amino acids.
Learning Check
Question 1
• Name the bond that is found
between adjacent amino acids.