A new representation for retention time in supercritical fluid chromatography

Chromatography theory: Application to supercritical fluid extraction

“…The above relation also reduces to Eq. 9, the expression developed by Chimowitz and Kelly (1989) for V;p.m equals zero. In the vicinity of the critical point, where large negative partial molar volumes are observed, the contribution of the partial molar volume of the solute in the stationary phase is small.…”

“…This property also plays a major role in the pressure and temperature dependency of the capacity factors in supercritical fluid chromatography and has been used by various investigators for developing a thermodynamic description of solute retention (van Wasen and Schneider, 1980;Yonker et al, 1987;Yonker and Smith, 1988). In chromatography, solute retention is expressed as a dimensionless residence time called the capacity factor: where to is the residence time for an unretained solute, Recently, an expression was developed by Chimowitz and Kelly (1989) that relates the density dependence of the capacity factor in supercritical fluid chromatography to the partial molar volume of the solute at infinite dilution by the expressions:…”

Determination of thermodynamic properties by supercritical fluid chromatography

“…Therefore, the ratiov ∞ 1m /β m,T is relatively insensitive to density [64,65]. Since neitherv ∞ 1s nor (∂µ ∞ 1s /∂w 3s ) T,P,n 2s display the near-critical anomalies, the result is that the ln k 1 versus ln ρ m plots are nearly linear as illustrated in Fig.…”

Analysis of νi/κTx in solvent mixtures at the critical line

“…For this reason, various experimental techniques have been used to circumvent the direct measurement of these properties in the critical region. A convenient method involves the use of SUpercritical fluid chromatography (SFC) to measure solute partial molar volumes close to the critical point in a dilute binary mixture (van Wasan et al, 1980;Erkey and Akgerman, 1990;Shim and Johnston, 1991;Srinivasan and McCoy, 1991;Chimowitz and Kelley, 1989;Recasens et al, 1993;Spicka et al, 1994: Afrane andChimowitz, 1995;Chimowitz and Afrane, 1996). Determination of the required properties from these chromatographic data often depends upon an analysis that appeals to the asymptotic values of specific thermodynamic properties near the critical point.…”

“…In the single solvent case, several studies have used an equation similar to Eq. 1 to measure solute partial molar volume data using chromatographic measurements of capacity factors, quantities related to the adsorption coefficient (van Wasan et al, 1980;Erkey and Akgerman, 1990;Shim and Johnston, 1991;Chimowitz and Kelley, 1989;Recasens et al, 1993;Spicka et al, 1994). Key results in reducing Eq.…”