by Column chromatography is a technique which is used to separate a single chemical compound from a mixture dissolved in a fluid. It separates substances based on differential adsorption of compounds to the adsorbent as the compounds move through the column at different rates which allow them to get separated in fractions. This technique can be used on a small scale as well as large scale to purify materials that can be used in future experiments. This method is a type of adsorption chromatography technique.
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the diffrence of stationary phases employed in liquid chromatography are:
- silica, alumina or porous graphite, used in normal phase chromatography, where in separation is based on the principle of adsorption and or mass distribution,
- Chemically modified silica, polymers or porous graphite, used in reversed-phase chromatography, where in separation is based principal on partition of the molecules between the mobile phase and the stationary phase,
- resins or polymers with acid or basic group, used in ion exchange chromatography, where in separation is based on competition of the ion separated with those in the mobile phase.
- porous silica or polymers, used in size-exclusion chromatography, where in separation is based on differences between the volumes of the molecules to be separated and the corresponding steric exclusion.
- stationary phase like cellulose or amylose derivatives, proteins or peptides, cyclodextrins, etc., chemically modified specially for chiral chromatography for separation of enantiomers.
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Adsorption Chromatography
Adsorption chromatography is a type of LC in which chemicals are retained based on their adsorption and desorption at the surface of the support, which also acts as the stationary phase.
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Adsorption chromatography is a type of LC in which chemicals are retained based on their adsorption and desorption at the surface of the support, which also acts as the stationary phase. This method is also sometimes referred to as liquid-solid chromatography. Retention in this method is based on the competition of the analyte with molecules of the mobile phase as both bind to the surface of the support.
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The degree of a chemical’s retention in adsorption chromatography will depend on the binding strength of this chemical to the support, the surface area of the support, the amount of mobile phase displaced from the support by the chemical, and the binding strength of the mobile phase to the support. Electrostatic interactions, hydrogen bonding, dipole-dipole interactions, and dispersive interactions (ie, van der Waals forces) all may affect retention in this type of chromatography.
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