RP 12 - 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

RF value = distance travelled by component / distance travelled by solvent

Question 3

How do you carry out TLC?

Answer 3

1) Add solvent to a jar and seal to create a saturated environment.
2) Draw a pencil line on the TLC plate and spot samples along this line using a capillary tube.
3) Add the TLC plate to the jar making sure solvent is below the pencil line.
4) The solvent rises up the TLC plate bringing components of the sample with it.
5) Draw a pencil line where the solvent finishes and allowed to dry.

Question 4

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

Answer 4

Because if drawn in ink, this will dissolve in 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 in 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 base line?

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 UV lamp/light
• Sometimes the plate is sprayed with a chemical/locating agent to show invisible spots for example ninhydrin