Chromatographic separation is based on different rates of movement compounds have through a solid adsorbent material filled column.
Differences in the compounds' rates of movement are due to their adsorption to the surface of the solid material: strongly adsorbed compounds spread slowly through the column while weakly adsorbed compounds progress rapidly.
The simplest chromatographic separation is carried out by passing a fluid stream through a separation column, which is fed by a pulse of separable compounds. Continuous process solutions can be complex, including multiple serial connected separation columns and internal recycling streams.
Based on the adsorption of a compound to the surface of a solid
Chromatography is the most selective industrial separation process. It can achieve very difficult separations, such as the separation of optical isomers from each other for medicinal products.
Chromatographic separation is also utilized on a very large scale, for example in the food industry with the separation of glucose and fructose.
As the separation method is based on the adsorption of the compounds to a solid surface, achieving the desired adsorbent material properties is often key to developing a successful separation process.
Adsorption and ion exchange – close relatives in chromatography
Adsorption and ion exchange are closely related separation techniques in chromatography. The aim of these procedures is usually to remove a certain compound or compounds from a liquid stream, while in chromatography the aim is also often to separate two or more compounds from each other.
Adsorption is commonly used to remove harmful compounds from liquids or gases. For example, many organic contaminants, dyes, surfactant detergents, antibiotics, and even heavy metals are adsorbed from water very effectively to polymeric adsorbent or activate carbon surfaces.
Adsorption is also used for cleaning many chemicals during their manufacturing process, as well as in isolating compounds with health benefits from plants.
In ion exchange techniques the ions in a solution (such as N+, Cl etc.) may be selectively replaced by the ions in a solid material.
For example, ion exchange resins for softening water are polymer pellets, whose Na+ ions replace the sensitive Ca2+ and Mg2+ ions in the solution, so that the hardness of the water is reduced. Ion exchange resins are used in water softening, industrial power plants and regular dishwashers. Ion exchange processes are also commonly used for the removal of heavy metals from water.
Professor Tuomo Sainio, D.Sc. (Tech)
Tel. 040 357 8683
LUT School of Engineering Science
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FI-53851 Lappeenranta, Finland
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