12. Separation of species by thin-layer chromatography
Separation of species by thin-layer chromatography
Analysis of the composition of some common medicines.
- ibuprofen tablet
- paracetamol tablet
- caffeine tablet
- aspirin tablet
- Anadin Extra tablet (or equivalent containing aspirin, paracetamol and caffeine)
- pestle and mortar
- TLC plate
- capillary tubes
- developing chamber (or suitable container with lid)
- access to UV lamp.
Preparation of samples
- Use a pestle and mortar to crush the first tablet and transfer to a weighing boat or bottle.
- Dissolve approximately 0.1g of the powdered tablet in 0.5 cm3 of dichloromethane. Two drops of ethanol can be added to help the dissolving process if required.
- Repeat steps 1 and 2 with the Anadin Extra tablet (or similar containing aspirin, paracetamol and caffeine), ibuprofen tablet, aspirin tablet, paracetamol tablet and caffeine tablet.
Thin Layer Chromatography
- Carefully use a pencil to draw a faint line 1 cm above the bottom of a TLC plate and mark five spots, equally spaced along this line.
- Use a capillary tube to apply a tiny drop of each solution to a different origin spot and allow the plate to air dry
- Add approximately 10 cm3 of ethyl acetate to a development chamber (suitable container with a lid)
- Place the TLC plate into the developing chamber, making sure that the level of the solvent is below the spotting line. Replace the lid and make sure it is a tight seal.
- When the level of the solvent reaches about 1 cm from the top of the plate, remove the plate and mark the solvent front with a pencil. Allow the plate to dry in the fume cupboard.
- Place the plate under a UV lamp in order to visualize the spots. Draw around them lightly in pencil.
- Calculate the Rf values of the observed spots.
Practical use of thin-layer chromatography: see BBC News story
RSC Problem based practical activities: problem 5: coursework conundrum (TLC) (click here)
Background reading on chromatography (RSC) (click here)
Thin layer chromatography video (RSC)