12. Separation of species by thin-layer chromatography

Separation of species by thin-layer chromatography

Analysis of the composition of some common medicines.

Method

  • dichloromethane
  • 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

  1. Use a pestle and mortar to crush the first tablet and transfer to a weighing boat or bottle.
  2. 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.
  3. 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

  1. 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.
  2. Use a capillary tube to apply a tiny drop of each solution to a different origin spot and allow the plate to air dry
  3. Add approximately 10 cm3 of ethyl acetate to a development chamber (suitable container with a lid)
  4. 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.
  5. 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.
  6. Place the plate under a UV lamp in order to visualize the spots. Draw around them lightly in pencil.
  7. 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)