title: Theoretical evaluation of the advantages and limitations of constant pressure versus constant flow rate gradient elution separation in supercritical fluid chromatography.
abstract: This study reports on the possible advantages of switching from constant flow (cF) based gradient elution separations to constant pressure (cP) based ones in Supercritical fluid chromatography (SFC) by means of mathematical models. All the important parameters (e.g. viscosity) were fitted as a function of pressure and mol% methanol in CO2. It is shown that when switching towards a cP approach in SFC, a time gain of 34% at the end of a 0 to 50% methanol in CO2 gradient is expected. Actual analysis time gains depend on the point at which it is evaluated (e.g. up to 41% after the equilibration step). Due to the dependence of retention on density, cF- and cP-mode do not yield the same selectivity even if the same volumetric-based gradient program is used. Because the components experience a higher average pressure in the cP-mode, the apparent retention factor is slightly lower.
authors.affiliation: Vrije Universiteit Brussel, Department of Chemical Engineering (CHIS-IR), Pleinlaan 2, 1050 Brussels, Belgium.
authors.forename: Ruben
authors.initials: R
authors.lastname: De Pauw
authors.forename: Gert
authors.initials: G
authors.lastname: Desmet
authors.forename: Ken
authors.initials: K
authors.lastname: Broeckhoven
mesh_terms: D025924:Chromatography, Supercritical Fluid / Q000379:methods*; D007700:Kinetics; D008962:Models, Theoretical; D011312:Pressure; D015203:Reproducibility of Results
keywords: Constant pressure; Gradient elution; Kinetic performance; Supercritical fluid chromatography; Variable column length method; Volume based kinetic plot method