Column oven, supercritical fluid Columns

A schematic diagram of a chromatograph for SFC is shown in Figure 6.10. In general, the instrument components are a hybrid of components developed for gas and liquid chromatography that have been subsequently modified for use with supercritical fluids. Thus, the. fluid delivery system is a pump modified for pressure control and the injection system a rotary valve similar to components used in liquid chromatography. The column oven and... 

The solvating power of a supercritical fluid is manipulated by changing its density. An increase in density increases the solvating power of the supercritical fluid. In addition, the oven temperature can be varied to affect the selectivity of a supercritical fluid. The polarity of a supercritical fluid is altered by the addition of an organic modifier such as methanol or acetonitrile. Table 7.1 lists some of the commonly used organic modifiers added to carbon dioxide [2]. Supercritical fluids generally exhibit a high number of theoretical plates and selectivity when compared with HPLC or GC columns. 

Schematic of a supercritical fluid extractor. 1 = COj 2 = modifier 3 = pump 4 = oven 5 = mixing column 6 = extraction cell 7 = pressure regulator 8 = collection of the extract.

A supercritical fluid chromatograph consists of a gas supply, usually carbon dioxide, a pump, the column in an oven, a restrictor to maintain the high pressure in the column and a detector. In general there are two possible hardware setups ... 

As mentioned earlier, the pressures and temperatures required for creating supercritical fluids derived from several common gases and liquids lie well within the operating limits of ordinary HPLC equipment. Thus, as shown in Figure 29-1, instruments for SFC are similar in most aspects to the instruments for HPLC described in Section 28C. There are two important differences between the two techniques, however. First, a thermoslatted column oven, similar to that used in GC (Section 27B-3), is required to provide precise temperature control of the mobile phase second, a restrictor. 

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