Pressure and density dependence of capacity ratios in supercritical fluid chromatography (SFC) with carbon dioxide as mobile phase

Determination of thermodynamic properties by supercritical fluid chromatography

“…The partial molar volume of the solute at infinite-dilution in the stationary phase,v ∞ 1s , is often substituted by the molar volume of the pure solute that can be estimated using group-contribution methods (Sectio 4.1.1). At the temperatures and pressures near the critical point of the mobile phase fluid,v ∞ 1s is often negligible compared tov ∞ 1m that acquires large negative values [56,67]. If the effects of dissolution of the mobile phase fluid in the stationary phase are to be taken into account, a thermodynamic model is needed to calculate (∂µ ∞ 1s /∂w 3s ) T,P,n 2s and to correlate V s /V m , β s,T,σ , and (∂w 3s /∂P) T,σ (Section 4.1.4).…”

“…Under the conditions mentioned in the introduction to section 2, the isothermal change of the solute retention factor with pressure in a (1 + 2 + 3) system (without a cosolvent) is given by [21,22,[56][57][58][59][60]:…”

“…(6) and (7) were used extensively to determine the partial molar volumes of diverse solutes at infinite-dilution in scCO 2 . The selection of solutes included aromatic hydrocarbons [21,22,[56][57][58][68][69][70][71][72][73], C 6 -C 16 n-alkanes and alkylated cyclohexanes [68], benzoic acid and 2-methoxynaphthalene [69,71], C 3 -C 9 aliphatic and C 10 terpenic alcohols [74], coenzyme Q 10 [75], polyunsaturated long-chain carboxylic acids [76,77] and their ethyl esters [78], C 21 -C 40 n-alkanes [79], and β-carotene and vitamin E [80]. The effect of the correction for uptake of scCO 2 by the stationary phase could only be tested in naphthalene [73] where sufficient amount of independentv ∞ 1m data were available [81].…”

Fluid Phase Equilibria of Mixtures at High Pressure

“…Thus, k can be calculated from t and t , and from k the partition coefficient K. In Fig. 12 experimental log k values are plotted against p and p of supercritical carbon dioxide as a mobile phase at 40°C for sfc experiments with alkanes having from 10 to 30 carbon atoms [37]; for details see the legend of …”

Use of isopycnic plots to understand the role of density in SFC – I. Effect of pressure variation on retention factors

“…Some of the most important work on this topic had been reported in the early literature of SFC [13][14][15][16]. Assuming thermodynamic equilibrium between the two phases of a solute at infinite dilution, van Wasen and Schneider [13] derived the following dependencies of retention factor on pressure (ref Eq. (1)) and density (ref.…”