The evolution and current state of instrumentation for analytical supercritical fluid chromatography

Supercritical fluid chromatography has contributed significantly to chiral method development and semi-preparative purification in drug discovery, where sensitivity was not an issue. Now, analytical scale SFC's have been validated using a multi-vendor, inter-lab study for quantitation of achiral trace pharmaceutical impurities using sub-2 µm particles, with gradient elution, and UV detection. This should significantly increase the penetration of SFC into both chiral and achiral QA/QC applications. However, there is still work to be done. Extra-column dispersion is no better than previous generations, yet the technique is often superficially called "ultra high performance" SFC (UHPSFC), simply because sub-2 µm packings are used. Dispersion is far too high for use with sub-2 µm particles, requiring extensive hardware modification to use such particles with high efficiency. However, the most common means of reducing system dispersion in ultra high performance liquid chromatography (UHPLC) results in distortion of kinetic performance in SFC. Vendors need to specify or provide standardized plumbing schemes that allow the full use of sub-2 µm fully porous, and sub-3 µm superficially porous particles, with reduced plate height, h ≈ 2 when k' ≈ 2. There is no consensus on how to best perform dynamic compressibility compensation, since each vendor uses different CO₂ pump head temperatures, resulting in subtle differences in flow and composition between vendors.