The analysis in this paper shows the relationship between molecular resolution in supercritical fluid chromatography (SFC), and certain divergent thermodynamic properties of solutes dissolved in near-critical fluids. This divergence is most pronounced in the near-critical regime, leading to the hypothesis that this region provides most promise for heightened molecular resolution, which lies at the heart of analytical and separation technologies.A thermodynamic model for representing capacity factor data in SFC is proposed, spanning a wide density range. The model uses a perturbed hard sphere equation for the fluid phase and lattice concepts for the stationary phase. In addition, data are presented for a number of systems and discussed in terms of the analysis provided. For an isomeric system, the data shows that resolution between species increases with the onset of retrograde behavior, resulting in a distinct maximum point.

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This paper presents the experimental technique and data acquired in the evaluation of a separation process in the crossover region of a model supercritical fluid system consisting of benzoic acid, 1-10 decanediol, and carbon dioxide. The results show that by exploiting the crossover effect it is possible to obtain essentially pure benzoic acid (>99.5% purity) with a single temperature cycle. A number of other issues are also discussed including the tradeoff between yield and purity and the manner in which the process variables are specified, which involves the interplay of experiment and model calculations.

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