PP-2- Identifying Amino Acids Through The Use Of Paper Chromatography

Question 1

Outline the stages of paper chromatography

Answer 1

Preparing the chromatogram
Running the chromatogram
Developing the chromatogram
Calculating Rf values

Question 2

Describe how you would prepare a chromatogram

Answer 2

The chromatogram is cut so that the bottom can extend into the solvent and a vessel can be used to hold it in place
The origin is drawn a few cm from the bottom in pencil
The solutions are spotted on the origin in pre-determined positions.
Let the spots dry then repeat step 3

Place lid on top of the tank to allow the air to become saturated

Question 3

Why is the origin not drawn in pen?

Answer 3

It could affect the results

Question 4

Why is the chromatogram only handled at the corners/edges

Answer 4

To avoid contamination from amino acids on the hand

Question 5

Describe how you would run the chromatogram

Answer 5

Carefully suspend the chromatogram into the solvent it’s important to ensure:
The line does not make contact with the solvent
It is securely attached
It is not suspended at an angle
The chromatogram should be taken out before the solvent has reached the top

Question 6

Describe how you would develop the chromatogram

Answer 6

Spray the dry chromatogram with ninhydrin in a fume cupboard to mark the solvent front
The chromatogram should then be re-dried then the amino acids will appear as purple spots

Question 7

Why is the ninhydrin sprayed in a fume cupboard?

Answer 7

It can be harmful to breathe in

Question 8

Describe how you would calculate Rf values

Answer 8

Measure the distance from the origin to the solvent front
Measure the distance from the origin to the centre of the amino acid being investigated
The Rf value is calculated by distance moved by solvent/ distance moved by solute