Accurate measurements of experimental parameters in supercritical fluid chromatography. I. Extent of variations of the mass and volumetric flow rates

Previous reports have highlighted the influence of the properties of the mobile phase flow rate on the column performance achieved in supercritical fluid chromatography (SFC). In SFC both the mass and the volumetric flow rates have unique influences on the chromatographic performance and the determination of their exact values is critical. It is well understood that the mass flow rate stays constant along an SFC system whereas the volumetric flow rate may vary considerably, but the extent of these variations and the role of the individual operating parameters in influencing these variations have not been clearly reported yet. The factors that control the mass and the volumetric flow rates in an SFC system are discussed and the possible extent of variations of these flow rates under different operating pressures and temperatures are demonstrate quantitatively.

► Only the mass flow rate along the column is constant along an SFC column under most conditions.
► The volumetric flow rate varies widely, depending on the local temperatures and pressures.
► Precise reference should be given to the conditions under which flow rate measurement is made.
► The lack of such a reference prevents the reproducibility of the results.
► Accurate measurements of mass flow rate are required to permit reproducibility of results.