RP12 - Thin-layer chromatography (TLC)

Question 1

What are the uses of thin layer or paper

chromatography?

Answer 1

To separate a mixture into its constituent components for analysis.
This allows identification by the calculation and
comparison of Rf values.

Question 2

How do you calculate an Rf value?

Answer 2

Distance travelled by

component ÷ Distance travelled by solvent

Question 3

How do you carry out TLC?

Answer 3

1. Add solvent to a jar. Seal to create saturated environment.
2. Draw a pencil line on TLC plate. Spot samples along this line
   using a capillary tube.
3. Add TLC plate to jar. Make sure solvent is below pencil line.
4. The solvent rises up the TLC plate, bringing components of
   the samples with it.
5. Draw a pencil line where the solvent finishes (don’t allow it to
   travel to the top of the plate). Allow to dry.

Question 4

Why must any lines drawn on the TLC plate be in pencil?

Answer 4

Because if drawn in ink, this will dissolve in the solvent and run up the plate with the other components, contaminating the plate.

Question 5

Why should the solvent be below the pencil line?

Answer 5

If above the pencil line, the solvent will
dissolve all samples and they will not run
up the plate.

Question 6

What happens if your sample is too concentrated?

Answer 6

If your sample is too concentrated then

the spots overlap.

Question 7

What happens if you use less solvent and have a high baseline?

Answer 7

If you use less solvent and have a high

baseline you will get large spots.

Question 8

How do you view the spots on a TLC plate?

Answer 8

Some spots may be visible, others may only be visible under a UV lamp/light.
Sometimes the plate is sprayed with chemical /locating agent to show ‘invisible’ spots.