The Liquid Chromatography is classified as follows:
- Thin layer chromatography
- Paper chromatography
- Ion exchange
- Column chromatography : Column chromatography is again classified as :
- liquid/ liquid (Partition)
- Liquid/ solid (Adsorption)
- Gel permeation
Introduction to various types of Liquid Chromatography:
Now we will see all above types of Liquid Chromatography in detail as follows:
1) Thin layer chromatography:
[caption id="attachment_1066" align="aligncenter" width="289"]
Thin layer chromatography[/caption]- Separation of black ink on a TLC plate (This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.)
In Thin Layer Chromatography the stationary adsorbents are applied to a planar glass or plastic surface and the mobile phase (sample to be analyzed) is allowed to flow over the stationary phase. For separation of components in the sample anyone of the following techniques is used:
- Adsorption
- Ion exchange
- Partition
- Gel filtration
2) Paper chromatography:
[caption id="" align="alignnone" width="300"]Paper chromatography (This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.)[/caption]
- Paper partition chromatography makes use of strips or hollow cylinders of filter paper to hold the solid and liquid phases. In this system, the drops of the sample solutions are applied to number of parallel strips placed at few inches from the end of each test paper and allowed to dry. These strips of paper are then placed in a chromatographic chamber with a saturating and equilibrating vapor and hung from a solvent downward can be timed and the components can be measured.
3) Column Chromatography:
a) Liquid/ liquid chromatography: In this method, the liquid stationary phase is retained on the surface of packing by physical adsorption and the sample (mobile phase) is allowed to percolates through the column (stationary phase).
b) Liquid/ solid (Adsorption) chromatography: In this method, the stationary phase is formed by a solid adsorbent, generally silica and alumina in powdered form. The sample solution is allowed to percolate through the stationary phase in the column.
c) Gel permeation chromatography: In this method, the separation is based on molecular size and shape. The gel permeation column is packed with a stationary phase in the form of a gel contacting pores of a specific size. The sample solution is allowed to flow over the column bed then the sample penetrates the pores in the packing gel (depending upon the size and shape of the molecules). The large molecules don’t penetrate the gel and leave the column earlier. For more details on Gel permeation click here.
4) Ion Exchange Chromatography:
In ion exchange chromatography, the exchange of ions between solution and solid insoluble in contact with solution takes place. The ion exchange process is reversible. In this process, when a sample is introduced at the top of the ion exchange column, the sample ions are displaced into solution again and then re-exchange on to the resin. This process continuous till the sample ions leave the column. Now the various sample ions corresponding to the different components in the sample are hold on to the resin to different extent. This cause the different time of passage through the column for different ions and separation of the sample components is achieved. For more details on Ion exchange chromatography click here.
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