Effects of pressure drop, particle size and thermal conditions on retention and efficiency in supercritical fluid chromatography

Unexpected retention and efficiency behaviors in supercritical fluid chromatography: A thermodynamic interpretation

“…Secondly, regarding the efficiency of a SFC column and similarly to what has been intensively reported in vHPLC [20][21][22], the experimenter has to make sure that the steepness of the radial density gradients across the column diameter are kept as small as possible. This was clearly revealed by Poe et al [9,10,23] when low-density SFC mobile phases are used (carbon dioxide at elevated temperatures and low pressures). The heat exchanged between the column wall and the external environment should be minimized.…”

“…The efficiency of SFC columns may also be very sensitive to the surrounding thermal environment [9][10][11]. The reproducibility of SFC data depends strongly on the control of the inlet mass flow rate [12], the pressure set by the active back pressure regulator (BPR), the oven temperature, the nature (methanol, acetonitrile, ethanol,...) and concentration (0-40% in volume) of the organic modifier [13][14][15], the nature of the sample solvent [16,17], and the thermal environment in which the SFC column is placed [9][10][11]. SFC instruments, columns, and methods should then be well controlled for the sake of data robustness.…”

Evaluation of stationary phases packed with superficially porous particles for the analysis of pharmaceutical compounds using supercritical fluid chromatography

“…Under isopycnic conditions, the average mobile phase pressure (and thus average density) is kept nearly constant between the different flow rates by adjusting the outlet pressure [40]. This ensures that all experiments are performed in the same average density environment and provide more reliable efficiency results.…”

Maximizing kinetic performance in supercritical fluid chromatography using state-of-the-art instruments

“…Because of these complex behaviours, the approaches used in HPLC to evaluate kinetic efficiency cannot be easily extrapolated to SFC conditions. Currently, three different methodologies are applied for evaluating the kinetic performance of SFC separations: (1) conventional method: changing the flow rate and column inlet pressure with fixed column length at constant outlet pressure, yielding changes in density [26][27][28], (2) isopycnic method: changing the flow rate at a given column length and keeping the average pressure (and thus average density) constant by adjusting the outlet pressure [29] and (3) variable column length method: changing the flow rate and column length by keeping the same inlet and outlet pressure (and thus the average density constant) [24].…”

“…This could be explained by the low mobile phase viscosity consisting in a mixture of CO 2 and small amount of cosolvent. The low viscosity results in enhanced analyte diffusion while the pressure drop remains always low [2,3]. There are several other advantages offered by SFC, including (i) the possibility to perform green separations by reducing the usage of toxic solvents, (ii) the ability to easily scale up from analytical separation to preparative application, (iii) the opportunity to perform both achiral and chiral separations on one unique system, with the same mobile phase and (iv) the capability to achieve very different retention and selectivity compared to RPLC [4][5][6][7][8].…”