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Chromatography: Adsorption & Partition | chemca

Purification Techniques

Chromatography: Adsorption & Partition

Separation of mixtures based on the differential movement of components through a stationary phase.

By chemca Team • Updated Jan 2026

Chromatography is a modern and versatile technique used for the separation, purification, and testing of the purity of compounds. It relies on the differential distribution of components between two phases: a Stationary Phase (fixed) and a Mobile Phase (moving).

1. Adsorption Chromatography

Principle

Based on the fact that different compounds are adsorbed to different degrees on an adsorbent (Stationary Phase).

Stationary Phase: Solid (e.g., Silica gel, Alumina).
Mobile Phase: Liquid or Gas.
Mechanism: Components that are adsorbed more strongly move slower; components adsorbed weakly move faster.

Types of Adsorption Chromatography:

A. Column Chromatography

The mixture is passed down a glass column packed with the adsorbent. The components separate into distinct bands based on their adsorption affinity.

Example: Separation of plant pigments.

B. Thin Layer Chromatography (TLC)

Separation occurs on a glass plate coated with a thin layer of adsorbent (Silica/Alumina). The solvent moves up by capillary action.

Retardation Factor ($R_f$):

$$ R_f = \frac{\text{Distance moved by the substance from base line (x)}}{\text{Distance moved by the solvent from base line (y)}} $$

Note: $R_f$ value is dimensionless and always ranges between 0 and 1.

2. Partition Chromatography

Principle

Based on the continuous differential partitioning of components between the mobile phase and the stationary phase.

Stationary Phase: Liquid (Water molecules trapped inside the pores of filter paper).
Mobile Phase: Liquid solvent.
Mechanism: Separation depends on the difference in solubility of the components in the two liquid phases.

Main Type: Paper Chromatography

A special quality paper known as Chromatography Paper is used.

The paper acts as a support for the stationary phase (water).
As the mobile phase moves up, components partition themselves between the mobile liquid and the stationary liquid water.
The separated components appear as spots at different heights (Calculated via $R_f$ value).

3. Comparison

Feature	Adsorption Chromatography	Partition Chromatography
Stationary Phase	Solid (Silica/Alumina)	Liquid (Trapped Water)
Basis of Separation	Differential Adsorption	Differential Solubility (Partitioning)
Examples	Column, TLC	Paper Chromatography

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