F324 Unit 4: Chromatography

Chromatography:

• Chromatography is an analytical technique that separates components in a mixture
• During chromatography a mobile phase sweeps a mixture over a stationary phase
  • Stationary phase is fixed in place and does not move
  • Mobile phase moves in a definite direction
• Different components have different affinities for a stationary and mobile phase
  • S.P. interacts with components in the mixture and slows them down.
    • Greater the interaction, the more components are slowed down - so components move over at different speeds + are separated

In Thin Layer Chromatography (TLC): S.P is a solid, M.P is a liquid

In Gas Chromatography (GC): S.P is liquid or solid on solid support, M.P is a gas.

Efficient separaration depends on 2 main factors:

• Adsorption for a solid S.P
  • This is the process by which a solid holds the molecules of a gas solute as a thin film of the surface of a solid.
• Solubility for a liquis S.P

Thin Layer Chromatography:

• S.P is a solid: thin layer of an adsorbent e.g silica gel or alumina
• M.P is a liquid solvent

Producing chromatogram:

• As the solvent rises it meets the spot of sample and the components in mix are swept along with the solvent.
• Separation is acheived by adsorption - some components bind strongly, some weakly and the result is different components are separated and travel different distances up plate.
• Each separated component is seen as a spot on the TLC plate. Use colours or UV radiation to show up by fluorescence.

TLC…