Recent Developments and Future Challenges in Supercritical Fluid Chromatography

Supercritical fluid chromatography (SFC) in its various forms has been around for over 30 years during which, it has been applied in numerous fields, including the analysis of fats and oils, pesticides, pharmaceuticals, hydrocarbons and fine chemicals. Even so, despite early promise, it initially failed to make significant inroads into the HPLC market and has only relatively recently started to develop beyond a niche technique.

The major attraction of SFC lies in its ability to bridge the gap between more widely used separation techniques, gas and liquid chromatography, by combining the advantages of both and very few of the disadvantages of

either. This supercritical fluid (usually carbon dioxide) has a very low viscosity and therefore analytes tend to have a very high diffusivity, which in turn facilitates greater interactions with the stationary phases and greater resolving power. One of the original attractions of this technique was that it would be possible to separate non-volatile compounds (otherwise analysed by HPLC) with a degree of resolution found in gas chromatography. At one stage it was even widely touted as supplanting HPLC for many applications. However, for a variety of reasons, the drive to develop this technique lost its momentum and within a few years only relatively few manufacturers were developing or supporting this technology. One of the factors was that there were technical disagreements as to the relative merits of packed and capillary SFC systems, particularly since all early units were based on either converted HPLC or GC systems. Of these, capillary systems predominated, but unfortunately this hampered further research and development, since they were generally less forgiving to the inexperienced user.