Supercritical phase chromatography

Supercritical Fluid Chromatography, or SFC, uses a mobile phase made up of a fluid or mixture of fluids, generally raised above the critical point by controlling temperature and pressure.

This technique is complementary to liquid chromatography (LC Liquid Chromatography) and gas chromatography (GC Gas Chromatography), as it has its own specific characteristics linked to the properties of supercritical fluids: the density of the supercritical fluid, which is comparable to that of a liquid, combined with lower viscosity and, in the case of carbon dioxide, high compatibility with GC and LC detectors, make it a high-performance technique, mainly with filled LC columns (applications using capillary GC columns having become extremely rare). So :

• high efficiencies per unit time are achieved due to the rapid diffusion of solutes in supercritical fluids due to their low viscosity; separations can therefore be obtained in analysis times around 5 to 10 times shorter than in LC, for an identical stationary phase particle size;

• For the same reason, it is also possible to increase the length of the column and thus achieve very high efficiency, even with filled columns; this is much more difficult to achieve with PLC because of the high pressure drop;

• high selectivities are observed due to the interactions between solutes, stationary phase and mobile phase, which can be varied by adding small amounts of polar modifiers to the supercritical phase; SPC is therefore similar to normal-phase partition chromatography, although most of the stationary phases in LC, including those for reverse phase and chirality, can be used successfully;

• CPS is a "green" technique because it uses non-toxic carbon dioxide instead of organic solvents as the mobile phase. Organic solvent consumption is therefore reduced and, for industrial-scale applications, CO ₂ can be easily recycled and purified ;

• Preparative SPC also has the advantage of enabling solutes to be recovered simply by expanding the mobile phase, with the only traces of residual solvent coming from any polar additives added. This is also important in supercritical phase extraction in the food industry, for example;

• unlike LC, SPC, with a pure carbon dioxide phase, allows coupling with the flame ionization detector (FID) of GPC. It can therefore be advantageously implemented for the separation of a complex mixture of solutes that are little or non-volatile, soluble in supercritical CO ₂ and not easily detectable, such as saturated hydrocarbons, for example....