what is chromatography and what are its two category? can you send me some videoes of this topic so that i can understand this topic .please send the videoes
Chromatography: The technique of chromatography is based on the difference in the rates at which the components of a mixture move through a porous medium (called stationary phase) under the influence of some solvent or gas (called moving or mobile phase).
Based on the principle involved, chromatography is classified as:
(a) Adsorption chromatography: It is based on the fact that different compounds are adsorbed on an adsorbent to different degrees. When a mobile phase is allowed to move over a stationary phase (adsorbent), the components of the mixture move by varying distances over the stationary phase because of the different adsorption tendencies.
(i) Column chromatography: In this method, a suitable adsorbent such as alumina (Al2O3), silica (SiO2) or Fuller’s earth is packed as a column in a burette-like long tube and acts as a stationary phase. The mixture to be separated is dissolved in a suitable solvent, and the solution is poured on the top of the column of the adsorbent. The component which is adsorbed strongly gets adsorbed at the top. The other components with decreasing orders of their absorbability are held up at different zones down the column in the form of bands.
(ii) Thin layer chromatography: This method involves separation of a mixture of substances over a thin layer of an adsorbent coated on a glass plate. The solution of the mixture to be separated is applied as a small spot. After drying the glass plate is placed in a closed jar containing eluant. As the eluant rises up the plate, the components of the mixture move up along with the eluant to different distances depending on their degree of adsorption and separation takes place.
(b) Partition chromatography: This method is based on differences in tendencies of substances to distribute or partition between the stationary phase and mobile phase. Paper chromatography is a type of partition chromatography in which the mixture to be separated is applied in the form of a drop on the paper. This paper is then suspended in a suitable solvent or mixture of solvents. The solvent rises up by capillary action. Paper selectively retains different components according to their differing partition in two phases.
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