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selection of eluting agents & mobile phase in phenomena of adsorption



How eluting agents or mobile phase are selected in the process of adsorption?

In the selection of eluting agent or mobile phase as solvent following two main points should be kept in mind:
First consideration is that either solvent meets the requirement of practical factors such as
Suitable viscosity
Stability
Compatibility with detection
Solubility with respect to the sample
Suitable purity
And ease of removal.
Second is that does the solvent provide maximum resolution for the separation of sample in a given time.
Above given two considerations are also applicable in selection of suitable liquid mobile phase in partition chromatography.

How polarity factor is involved in co relation of selection of eluting agents?

Commonly a polarity related related factor can also be used to co relate the solvents as eluting phases in adsorption chromatography.
Eluotropic series
A group of solvents in order of chromatographic strength is known as eluotropic series.
Commonly used typical solvents
Light petroleum (Pet ether,hexane,heptane)
Cyclo hexane
Carbon tetra chloride
Toluene
Benzene
Chloroform
Ethyl ether
Ethyl acetate
Acetone
n-propanol
Ethanol
Methanol
Water
Pyridine
Organic acids
Inorganic acids and bases
Both eluting and polarity are increasing at the top and less at the bottom.
Relation of polarity of adsorbents and mobile phase
Greater will be the polarity of the adsorbed solute. Larger will be the polarity of mobile phase and this case happens at that time when it goes to the suitable eluting agent.due to this reason adsorption is not generally used for the separation of polar compounds,because binding is too much strong which is not compatible with the polarity of eluting agent to overcome this binding.
Use of mix solvents
Mix solvents can also be used by providing that they are miscible.
Example
Ethanol and chloroform can also be used by a gradual change in the ratio which is incorporated into the eluting mixture.

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