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Created: 10 April 2010
Leader: Lynnette Heng
Members: Lorelle Ang
Soh Chin Yi
Goh Ai Ting
Li Yuen Ying

Lynnette: KK Hospital- Dietitian
Chin Yi: Gardenia- R&D
Ai Ting: Singapore Sports Council- Nutritionist
Yuen Ying: KH Roberts- lab assistant
Lorelle: OSIP (China)

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THIN LAYER CHROMATOGRAPHY


How does thin layer chromatography work?
Chromatography all have a stationary phase (a solid, or a liquid supported on a solid) and a mobile phase (a liquid or a gas). The mobile phase flows through the stationary phase and carries the components of the mixture with it. Different components travel at different rates.

Thin layer chromatography is done exactly as it says - using a thin, uniform layer of silica gel or alumina coated onto a piece of glass, metal or rigid plastic.
The silica gel (or the alumina) is the stationary phase. The stationary phase for thin layer chromatography also often contains a substance which fluoresces in UV light. The mobile phase is a suitable liquid solvent or mixture of solvents.
The stationary phase - silica gel
Silica gel is a form of silicon dioxide (silica). The silicon atoms are joined via oxygen atoms in a giant covalent structure. However, at the surface of the silica gel, the silicon atoms are attached to -OH groups.
So, at the surface of the silica gel you have Si-O-H bonds instead of Si-O-Si bonds. The diagram shows a small part of the silica surface.




The surface of the silica gel is very polar and, because of the -OH groups, can form hydrogen bonds with suitable compounds around it as well as van der Waals dispersion forces and dipole-dipole attractions.
The other commonly used stationary phase is alumina - aluminium oxide. The aluminium atoms on the surface of this also have -OH groups attached.
What separates the compounds as a chromatogram develops?
As the solvent begins to soak up the plate, it first dissolves the compounds in the spot that you have put on the base line. The compounds present will then tend to get carried up the chromatography plate as the solvent continues to move upwards.
How fast the compounds get carried up the plate depends on two things:
• How soluble the compound is in the solvent. This will depend on how much attraction there is between the molecules of the compound and those of the solvent.
• How much the compound sticks (known as adsorption) to the stationary phase - the silica gel, for example. This will depend on how much attraction there is between the molecules of the compound and the silica gel.

References:
http://www.chemguide.co.uk/analysis/chromatography/thinlayer.html

Johns H.(2008). Current Protocols in Nucleic Acid Chemistry. Thin‐Layer Chromatography. Retrieved from: http://www.currentprotocols.com/protocol/nca03d