Topics - Langmuir Adsorption Isotherm
Langmuir Adsorption Isotherm
In gas/solid and liquid/solid chromatography the solutes are retained by building up one or more solute layers on the surface of the adsorbent. The original Langmuir adsorption isotherm was for single layer adsorption and gives a curve that describes the fraction of the surface area of the adsorbent covered with solute, as a function of the concentration of the solute in the contacting liquid phase. The Langmuir isotherm is a curve, convex to the solute concentration axis, and flattens out when the total surface is covered with solute. The isotherm for double layer adsorption is similar to single layer adsorption but the initial convex part of the curve is sharper. The adsorption isotherm only tends to linearity at very low concentrations of solute (at very low surface coverage) and so symmetrical peaks will only be achieved with very small samples. As chromatography detectors are very sensitive this does not become a problem as very small samples can be applied.