Property of supercritical fluids:
One remarkable property of supercritical fluids which is related to their high densities (0.2- 0.5 g/cm3) is their capability to dissolve large non-volatile molecules. Another property which is associated with many supercritical fluids is that the dissolved analyte can be easily recovered by allowing the solutions to equilibrate with the atmosphere at a relatively low temperature. This is significant if the analyte happens to be thermally unstable. An important point that goes in the favour of several supercritical fluids is that they are inexpensive and non- toxic. They can be easily allowed to evaporate in atmosphere with no harmful effects.
As a matter of fact supercritical fluid chromatography is a hybrid of gas and liquid chromatography. It merges some of the benefits of both liquid and gas chromatography. Within supercritical fluid chromatography, the mobile has a low viscosity and high self diffusion coefficient. A mobile phase could be further modified through addition of polar modifier in small amounts. In this kind of chromatography both packed and open tubular columns are used. In open tubular columns, the internal coating is of siloaxanes of various types and that of bonded phases.