Topics - Isotherms
The term isotherm has changed its meaning somewhat over the years. The ‘classical adsorption isotherm’ was the original name given to a graph relating the volume of gas adsorbed on an adsorbent surface to the partial pressure of the gas in contact with it at a constant temperature. The variables used in the adsorption isotherm have changed and, with the introduction of chromatography, has been used to describe relationships involving adsorption from liquid-solid systems as well as gas-solid systems. In chromatography, the adsorption isotherm usually refers to the graph relating the mass of solute adsorbed on the surface against the concentration of the solute in the fluid in contact with the surface. The two most common adsorption isotherms met in chromatography are the Langmuir adsorption isotherm and the Freundlich adsorption isotherm.