Why the difference in Adsorption & Partition chromatography principles

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Chromatography is a highly efficient analytical technique which primarily relies on separation of components over a stationary phase.  This happens under the influence of momentum force of mobile phase on the components. But this separation on the stationary phase occurs by two principles viz. adsorption and partition. Hence the term adsorption chromatography and partition chromatography are specifically mentioned under the principle of separation. These two types of chromatography are invariably used based on the nature of component and samples to be analysed. But it seems that higher or well-developed chromatographic techniques used partition principle for component or molecule separation.

Courtesy: kinesis.co.uk

Adsorption chromatography principle:

Adsorption chromatography definition:

Adsorption chromatography is a process of separation of components in a mixture introduced into chromatography system  based on the relative differences in adsorption of components to the stationary phase present in the chromatography column.

Here the molecules or components of the mixture travel with different rates due to differences in their affinity towards stationary phase. Adsorption means a physical attachment between the compound and the particles of stationary phase. Based on the nature, polar compounds adsorb with stronger or greater intensity to the polar stationary phase while non-polar compounds adsorb better  to the non-polar stationary phase than polar components. Hence during separation of components, when we use a polar stationary phase, polar components elute out late due to greater adsorption and non-polar components get out of the column or elute out first. This is exactly reverse on using a non-polar stationary phase.

This adsorption chromatography applies to only solid-liquid or solid-gas chromatographies. Because the adsorbtion phenomenon is inherent property of solids and hence it is used with only solid stationary phase chromtographies.

Partition  (coefficient) chromatography:

Partition coefficient chromatography:

Partition chromatography is process of separation whereby the components of the mixture get distributed into two liquid phases due to differences in partition coefficients during the flow of mobile phase in the chromatography column.

Here the molecules get preferential separation in between two phases. i.e. both stationary phase and mobile phase are liquid in nature. So molecules get dispersed into either phases preferentially. Polar molecules get partitioned into polar phase and vice-verse. This mode of partition chromatography applies to Liquid-liquid, liquid-gas chromatographies and not to solid-gas chromatography. Because partition is the phenomenon in between a liquid and liquid or liquid and gas or gas and gas. But not in solid involvement.

In high performance liquid chromatography (HPLC), Paper chromatography, gas chromatography, high performance thin layer chromatography (HPTLC), partition chromatography is the principle of separation. While in column chromatography, Thin layer chromatography etc. adsorption chromatography is used.

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