Authors: Z. Şermin GÖNENÇ, Uğur AKMAN, Aydın K. SUNOL
Abstract: The effects of temperature, pressure and supercritical fluid density on the solubility-retention relationship of solutes in supercritical fluid chromatography are investigated. New retention data for naphthalene, phenanthrene, benzoic acid and 2-methoxy-naphthalene is obtained as a function of pressure at different temperatures. The bulk of the data is taken near the critical region of the mobile gas where the anomalities are expected. This data is used to compare two approaches for thermodynamic modeling of pressure dependence of solute retention. In these approaches, mobile-phase partial molar volumes of the solutes are determined either from bulk solubility data or from infinite-dilution fugacity coefficients. In both approaches, an integrated from of retention pressure relation is utilized to explicitly reveal the nature of interactions between the stationary phase and the solute. The approach that utilizes infinite-dilution fugacity coefficient better predicts the pressure dependence of retention, especially for solutes that are substantially soluble near the critical point of the mobile phase. Relationships between pressure and temperature dependence of solubility and retention of solutes are also investigated.
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