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

• Published in: Journal of Chromatography A 2015-08, Vol.1406, p.316-323
• Main Authors: Tarafder, Abhijit, Hill, Jason F., Iraneta, Pamela C., Fountain, Kenneth J.
• Format: Article
• Language: English
• Subjects: Chromatography; Isopycnic plots; Pressure dependence; Retention factor; SFC; Supercritical
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2015.05.052

•Pressure strongly affects retention in SFC but the extent of variation is not uniform.•Extent of retention variation with pressure depends on temperature and composition.•Verbal description of the nuances of pressure-effect on retention can become complex.•Pressure-effect in SFC is explained here with a graphical tool i.e. isopycnic plots. This paper aims to demonstrate the effect of pressure variations in modifying analyte retention behavior in SFC. There is a general understanding that in SFC increasing pressure decreases the retention factor (k′), and vice versa. What is not clearly discussed or explained in any recent literature is that these variations can be very different at different operating pressures, temperatures and modifier concentrations. It is important to have a clearer understanding on these variabilities during method development and results analysis. In this paper the nature of k′ variation with pressure, at different temperatures and modifier concentrations, will be explained with the help of isopycnic plots of CO2 and CO2+methanol mixtures.