Supercritical fluid chromatography pumps

The major difference in supercritical fluid chromatography and conventional LC equipment is the pumping systems as well as the safety features installed to maintain higher pressure. Unique SFC equipment differences are ... 

Supercritical fluid chromatography are more complex that HPLCs. One of the fluids is usually a liquefied gas at high pressure. The instrument cannot use a single high pressure pump and a gradient valve to mix such fluids with normal liquids. Consequently, one always requires at least two high pressure... 

Supercritical fluid chromatography has at least one extra control variable compared to HPLC. Many people still associate the name SFC with syringe-pump-based systems in which pure carbon dioxide was used with pressure programming. Modern SFC sometimes still operates in this manner but only for nonpolar solutes. SFC is somewhat different from HPLC. It is useful to discuss the relative effects of different control variable on retention and selectivity. The relative effects of several control variables are represented schematically in Fig. 5. 

Supercritical fluid chromatography (SFC)ls Uses HPLC packed columns and a mobile phase of pressurized supercritical fluids (i.e., carbon dioxide modified with a polar organic solvent). Useful for nonpolar analytes and preparative applications where purified materials can be recovered easily by evaporating the carbon dioxide. HPLC pumps and GC-type detectors are often used. 

Ashraf-Khorassani, M. Levy, J.M. Addition of modifier in supercritical fluid chromatography using a microhore reciprocating pump. Chromatographia, 1995, 40, 78-84... 

More recently, liquid chromatography (LC), supercritical fluid chromatography (SEC), and CZE devices connected to mass spectrometers have been used to separate components of complex mixtures prior to mass analysis. When vaporized, the solvent from an LC represents a volume of 100-1000 times greater than that of a carrier gas used in GC. Interfaces developed commercially have solved the problem of eliminating this gas load by using combinations of heating and pumping, sometimes with... 

Generally, high-pressure pumps may work in two different modes constant flow and constant pressure. Usually, the constant-flow mode characterizes LC, while the constant-pressure mode is often used in capillary supercritical fluid chromatography (SFC). 

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