doi:10.1016/j.chroma.2007.01.115 
Copyright © 2007 Elsevier B.V. All rights reserved.
Enantioseparation of 1-phenyl-1-propanol on cellulose-derived chiral stationary phase by supercritical fluid chromatography II. Non-linear isotherm
Stefan Ottigera, Johannes Klugea, Arvind Rajendranb and Marco Mazzottia, 
, 
aETH Zurich, Institute of Process Engineering, Sonneggstrasse 3, 8092 Zurich, Switzerland
bSchool of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore, Singapore
Available online 5 February 2007.
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Abstract
The separation of the enantiomers of 1-phenyl-1-propanol by supercritical fluid chromatography on a chiral stationary phase, which consists of cellulose tris (3,5-dimethylphenylcarbamate) coated on a silica support (Chiralcel-OD), is studied under overloaded, non-linear chromatographic conditions. Pulse experiments are performed at a temperature of 30 °C using supercritical CO2 modified with methanol as a mobile phase. The parameters of the binary Langmuir adsorption isotherm are determined by the inverse method, comparing experimental and simulated peak responses. Isotherm parameters are derived for modifier concentrations between 1 and 5% (w/w) and operating pressures between 125 and 185 bar, and the dependency of the isotherm parameters, namely the Henry constant and the saturation capacity, on operating conditions is investigated.
Keywords: Enantioseparation; Supercritical fluid chromatography; Adsorption isotherm; 1-Phenyl-1-propanol
Fig. 1. Schematic of the SFC setup used in this study.
Fig. 2. Experimental (dotted) and simulated (solid) pulse responses of 1-phenyl-1-propanol on Chiralcel-OD of different injected concentration. (a) 500, 250, 100 and 50 g/L of racemic mixture and (b) 200 g/L of pure enantiomers R and S. Operating conditions: pressure, 170 bar; modifier concentration, 4.9%.
Fig. 3. Dependence of Henry constant on pressure at different modifier concentrations cm, in % (w/w). The points are the experimental data, whereas the lines represent the correlation in Eq. (9). Symbols: closed, R enantiomer; open, S enantiomer. Lines: solid, R enantiomer; dotted, S enantiomer.
Fig. 4. Dependence of Henry constant on mobile phase (CO2 + modifier) density at different modifier concentrations cm, in % (w/w). The points are the experimental data, whereas the lines represent the correlation in Eq. (9). Symbols: closed, R enantiomer; open, S enantiomer. Lines: solid, R enantiomer; dotted, S enantiomer.
Fig. 5. Dependence of Henry constant on modifier concentration at different pressures. The points are the experimental data, whereas the lines represent the correlation in Eq. (9). Symbols: closed, R enantiomer; open, S enantiomer. Lines: solid, R enantiomer; dotted, S enantiomer.
Fig. 6. Measured non-linear isotherms for the more retained enantiomer S at different pressures (P) and modifier concentrations cm, in % (w/w).
Fig. 7. Dependence of saturation capacity on pressure at different modifier concentrations cm, in % (w/w). The points are the experimental data, whereas the lines represent the correlation in Eq. (10). Symbols: closed, R enantiomer; open, S enantiomer. Lines: solid, R enantiomer; dotted, S enantiomer.
Fig. 8. Dependence of saturation capacity on mobile phase (CO2 + modifier) density at different modifier concentrations cm, in % (w/w). The points are the experimental data, whereas the lines represent the correlation in Eq. (10). Symbols: closed, R enantiomer; open, S enantiomer. Lines: solid, R enantiomer; dotted, S enantiomer.
Fig. 9. Dependence of saturation capacity on modifier concentration at different pressures. The points are the experimental data, whereas the lines represent the correlation in Eq. (10). Symbols: closed, R enantiomer; open, S enantiomer. Lines: solid, R enantiomer; dotted, S enantiomer.
Table 1.
Mass transfer coefficient of 1-phenyl-1-propanol on Chiralcel-OD at different pressure and modifier concentration levels
Table 2.
Langmuir adsorption isotherm parameters of 1-phenyl-1-propanol on Chiralcel-OD at different pressure and modifier concentration levels
Table 3.
Set of parameters for Henry constant correlation on density and modifier concentration, corresponding to Eq. (9).
Table 4.
Set of parameters for saturation capacity correlation on density and modifier concentration, corresponding to Eq. (10)
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