The Mechanism of Chromatographic Retention - Solvent/Solute Interactions with Adsorbent Surfaces > Mono-layer Adsorption > Page 41

Mono-layer Adsorption

A solvent can be adsorbed from a solvent mixture on the surface of silica gel according to the Langmuir adsorption isotherm. Consider the situation depicted in figure 17.


Figure 17. The Distribution of Solvents A and B as a Mono-layer on a Silica Gel Surface

Let the surface be in contact with a solution of solvent (B) at a concentration (c) g/ml in solvent (A) and let the fraction of the area covered by solute (B) molecules be (a) and consequently, the area fraction occupied by solute (A) will be (1-a).

Under equilibrium conditions, if the number of molecules of solute (B) striking the surface covered with solvent (A) and adhering is (n') and the number of molecules of solvent (B) leaving the surface covered with solvent (B) is (n''),

Then n' = n''