Unified Theory of Absorption Chromatography: Gas, Liquid, and Supercritical Fluid Mobile Phases

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Abstract
Based on a simple theoretical model which exploits the isomorphism pervading critical phenomena, a general equation is derived for the solute capacity factor, k′, in a chromatographic system where the stationary phase is an absorbent and the mobile-phase fluid may be an ideal gas, moderately nonideal gas, supercritical fluid or liquid. This comprehensive equation is in the form 2nk′ = 2nk′o + F(TR, ρR), where TR and ρR are the reduced temperature and reduced density of the mobile phase and where 2nk'o, the stationary-phase contribution, corresponds to ideal gas-liquid chromatography (ρR = 0) and F(TR, ρR), the mobile-phase contribution (eqn. 14), is a quadratic function of [sgrave]R and a linear function of TR -1 and solute carbon number (homologous solute series). The limitations and advantages, molecular interpretation, predictions, practical implications and applications, and general utility of this unified theory are discussed, with special emphasis on supercritical fluid chromatography (and extraction).