Adsorption chromatography

The adsorption chromatography , in the default language and adsorption chromatography , is a special chromatography method, in which the stationary phase adsorbent is. The separation takes place through repeated adsorption and desorption .

During the adsorption process, a substance carried by the mobile phase is deposited on the surface of the solid, stationary phase. Relatively weak physical forces ( Van der Waals forces ) or stronger chemical forces of attraction can be responsible for the adsorption .

The van der Waals forces of physical adsorption are around 8–40 kJ / mol. The mathematical description of the adsorption isotherm was carried out by Herbert Freundlich and, strictly speaking, is only valid for the linear initial range. Due to the more intensive interactions of the smaller particles, their speed is lower than that of the larger particles, since smaller particles also offer a larger surface.

Chemical adsorption is based on hydrogen bonds or ionic relationships (80–600 kJ / mol). The mathematical description of the adsorption isotherm was made here by Irving Langmuir and, strictly speaking, is only valid for a monomolecular coverage of the stationary phase.

It is important for the chromatographic separation that the forces in these interface reactions are not too strong and that the processes are reversible (“reversible”) until equilibrium is established.

Adsorption equilibria are dependent on the concentration of the adsorbable substances in the mobile phase, on the temperature, the pressure and on the ratio of the amount of adsorbent to the amount of adsorbable substance. Adsorbents have different selectivities towards different molecules.

Therefore the sample must not be too concentrated (interference effects).