Principles of Adsorption at Solid Surfaces and their Significance in Gas/Solid and Liquid/Solid Chromatography

Abstract

The basic principles of gas adsorption and adsorption from liquid mixtures onto solid surfaces are outlined, and the analogies and differences between the two phenomena are explained. In both cases there exists a gradual transition from the low-temperature regime in which the adsorbate forms a well-defined adsorbed layer, to the situation at high temperatures and high bulk densities (or high bulk concentrations) when the adsorbed amount can be expressed only as a surface excess. Monolayer models for single and mixed gas adsorption (based on the Scaled-Particle theory) and for the adsorption from binary liquid mixtures (Parallel-Layer model) are presented. The significance of such models for gas/solid and liquid/solid adsorption chromatography is discussed. In particular, the retention of a small pulse of a given component at finite concentrations of this or other adsorbable components in the eluent (elution on a plateau) and the elution of solutes by a binary liquid eluent is considered in some detail.