Paper 3: Required practical 12 - Thin layer chromatography (TLC)

Question 1

What are the uses of thin layer or paper chromatography?

Answer 1

• To separate a mixutre into its constituent components for analysis
• Allows identification by the calculation and comparison of Rf values

Question 2

How do you carry out TLC?

Answer 2

1. Add solvent to a jar, seal to create a saturated environment
2. Draw a pencil line on the TLC plate, spot samples along this line with a capillery 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 (not the top of the plate), allow to dry

Question 3

Why must any lines be drawn in pencil?

Answer 3

If in ink, it would dissolve in the solvent and run up the plate with the other components, contaminating the plates

Question 4

Why should the solvent be below the pencil line?

Answer 4

If above, the solvent will dissolve all samples and they won’t run up the plate

Question 5

What happens if you sample is too concentrated?

Answer 5

The spots will overlap

Question 6

What happens if you use less solvent and have a higher base line?

Answer 6

You get large spots

Question 7

How do you view the spots on a TLC plate?

Answer 7

• Under UV light
• Spray ninhydrin - turn purple