Kinetic-performance and selectivity optimization in supercritical fluid chromatography

Packed-column supercritical fluid chromatography (pSFC) is known for several years to be a cheaper, greener, and/or faster alternative for LC for chiral and preparative separations. However, in the recent years, SFC has gained a renewed interest in the field of achiral analytical separations thanks to the innovations made in instrumental design. nevertheless, the use of the inherently compressible mobile phase in SFC still delivers some difficulties that are not present when performing LC separations. In this PhD research, it was shown that it is possible to deal with these difficulties when SFC performance is measured or in selectivity prediction of SFC separations

Application of the isopycnic kinetic plot method for elucidating the potential of sub-2 micron and core/shell particles in SFC

One of the many advantages that Supercritical fluid chromatography (SFC) is attributed with over high performance liquid chromatography (HPLC) is that it should be possible to use longer columns and/or columns packed with smaller particles at higher velocities. This is due to the higher diffusivity of analytes in supercritical fluids compared to liquids (higher optimum mobile phase velocity) and to the lower viscosity of the mobile phases in SFC compared to HPLC (resulting in lower pressure drops over the column). In this work the isopycnic method to construct kinetic plots for SFC was used to investigate the performance limits of an SFC system when using sub- 2 µm fully porous particles and sub- 3 µm superficially porous particles. This isopycnic kinetic plot method for SFC was developed and tested earlier for SFC separations on bare silica with pure CO2 as mobile phase. In this work, C18 columns were used in combination with more realistic modifier amounts in the mobile phase in order to show the possibilities of measuring the performance of an SFC system as a function of flow rate for realistic chromatographic experimental conditions. Kinetic plot predictions were made for separations on 1 µm and 0.5 µm particles in order to examine the possibilities of working with these very small particles on the used SFC and HPLC systems

Heterogeneous Timed Machines

International audienceWe present an algebra of discrete timed input/output au- tomata that execute in the context of different clock granularities -- timed machines -- as models of systems that can be dynamically inter- connected at run time in a heterogeneous context. We show how timed machines can be refined to a lower granularity of time and how timed machines with different clock granularities can be composed. We propose techniques for checking whether timed machines are consistent or feasi- ble. Finally, we investigate how consistency and feasibility of composition can be proved at run-time without computing products of automata

Implementing stationary-phase optimized selectivity in supercritical fluid chromatography

The performance of stationary-phase optimized selectivity liquid chromatography (SOS-LC) for improved separation of complex mixtures has been demonstrated before. A dedicated kit containing column segments of different lengths and packed with different stationary phases is commercially available together with algorithms capable of predicting and ranking isocratic and gradient separations over vast amounts of possible column combinations. Implementation in chromatographic separations involving compressible fluids, as is the case in supercritical fluid chromatography, had thus far not been attempted. The challenge of this approach is the dependency of solute retention with the mobile-phase density, complicating linear extrapolation of retention over longer or shorter columns segments, as is the case in conventional SOS-LC. In this study, the possibilities of performing stationary-phase optimized selectivity supercritical fluid chromatography (SOS-SFC) are demonstrated with typical low density mobile phases (94% CO2). The procedure is optimized with the commercially available column kit and with the classical isocratic SOS-LC algorithm. SOS-SFC appears possible without any density correction, although optimal correspondence between prediction and experiment is obtained when isopycnic conditions are maintained. As also the influence of the segment order appears significantly less relevant than expected, the use of the approach in SFC appears as promising as is the case in HPLC. Next to the classical use of SOS for faster baseline separation of all solutes in a mixture, the benefits of the approach for predicting as wide as possible separation windows around to-be-purified solutes in semi-preparative SFC are illustrated, leading to significant production rate improvements in (semi-) preparative SFC