Physicochemical Principles and Applications of Supercritical Fluid Chromatography (SFC). New analytical methods (19)

Abstract

In supercritical fluid chromatography (SFC) compressed gases in the region of their critical temperature are used as mobile phases. SFC has important advantages over gas chromatography (GC) for the separation of low-volatile or thermally unstable substances. Like high pressure liquid chromatography (HPLC) and gel chromatography, it is used for various special applications and preparative separations, e. g. in the petroleum industry and in the separation of oligomers. SFC is of great interest in fundamental research on fluid extraction and for the determination of the physicochemical properties of fluid systems. In this contribution the most important physicochemical, methodological, and instrumental principles of SFC are summarized; characteristic physicochemical applications are the determination of capacity ratios, partition coefficients, partial molar volumes, interaction second virial coefficients, and diffusion coefficients.

Experimental Study of the Critical Behavior of the Isochoric Heat Capacity of Aqueous Ammonia Mixture

“…where T C1 = 647.096 K, P C1 = 22.064 MPa (pure water, IAPWS [70] accepted values), T C2 = 405.4 K, and P C1 = 11.333 MPa (pure ammonia [76,77] and Tillner-Roth [28], (-·-·-·-) crossover model (Kiselev and Rainwater [29]); •-this study, •-Suzuki and Uematsu [42] − 2J /ρ 2 C1 [ρ(l) − ρ C1 ], is also directly related to the Krichevskii function, J = (∂ P/∂ x) ∞ T V , [78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95]. The limiting slope of RT ln K D as a function of the liquidphase density [ρ(l) − ρ C1 ], as the system approaches the critical point, is also given by the Krichevskii parameter as −2 (∂ P/∂ x) ∞ T C V C /ρ 2 C1 , Henry's constant K H near the critical point [95,96], (T ln (K H / f 1 ), and T ln E (where E = y 2 P/P sub 2 is the enhancement factor; P, y 2 , P sub 2 are the pressure, solubility, and sublimation pressure, respectively) are linear in the solvent density, with the slope given by the Krichevskii parameter.…”

Impulse response techniques to measure binary diffusion coefficients under supercritical conditions

“…Determining partial molar volumes (PMV) of a solute at infinite dilution in supercritical fluid mixtures is difficult because accurate PVT data of the mixtures and pure components are required [53]. However, the value can be determined from the retention factor using the CIR method with a polymer-coated capillary or a packed bed composed of polymer-coated porous particles.…”

Experimental study of the one-, two-, and three-phase isochoric heat capacities of n-hexane+water mixtures near the lower critical line. Part II. Krichevskii parameter and thermodynamic and structural properties

“…, which are related to the Krichevskii parameter, are strongly divergent at the pure solvent's critical point [5,6,9,14,[16][17][18]33]. Partial molar properties (…”

“…Thus, thermodynamic behavior of the near-critical dilute solutions is extremely important for understanding the molecular interactions and the microscopic structure of the nearcritical and supercritical solutions where the interaction between solutesolute molecules can be neglected. In the limit of infinite dilution many partial molar properties of the solute ( V ∞ 2 ; H ∞ 2 ; C ∞ P2 ) diverge strongly at the solvent's critical point [5,9,11,[14][15][16][17][18].…”