Supercritical fluid chromatography temperature

The most common mobile phase for supercritical fluid chromatography is CO2. Its low critical temperature, 31 °C, and critical pressure, 72.9 atm, are relatively easy to achieve and maintain. Although supercritical CO2 is a good solvent for nonpolar organics, it is less useful for polar solutes. The addition of an organic modifier, such as methanol, improves the mobile phase s elution strength. Other common mobile phases and their critical temperatures and pressures are listed in Table 12.7. 

Supercritical fluid extraction (SFE) has been extensively used for the extraction of volatile components such as essential oils, flavours and aromas from plant materials on an industrial as well as an analytical scale (61). The extract thus obtained is usually analysed by GC. Off-line SFE-GC is frequently employed, but on-line SEE-GC has also been used. The direct coupling of SEE with supercritical fluid chromatography (SEC) has also been successfully caried out. Coupling SEE with SEC provides several advantages for the separation and detection of organic substances low temperatures can be used for both SEE and SEC, so they are well suited for the analysis of natural materials that contain compounds which are temperature-sensitive, such as flavours and fragrances. 

Figure 12.22 SFC-GC analysis of aromatic fraction of a gasoline fuel, (a) SFC trace (b) GC ttace of the aromatic cut. SFC conditions four columns (4.6 mm i.d.) in series (silica, silver-loaded silica, cation-exchange silica, amino-silica) 50 °C 2850 psi CO2 mobile phase at 2.5 niL/min FID detection. GC conditions methyl silicone column (50 m X 0.2 mm i.d.) injector split ratio, 80 1 injector temperature, 250 °C earner gas helium temperature programmed, — 50 °C (8 min) to 320 °C at a rate of 5 °C/min FID detection. Reprinted from Journal of Liquid Chromatography, 5, P. A. Peaden and M. L. Lee, Supercritical fluid chromatography methods and principles , pp. 179-221, 1987, by courtesy of Marcel Dekker Inc.

Supercritical fluid chromatography (SFC) refers to the use of mobile phases at temperatures and pressures above the critical point (supercritical) or just below (sub-critical). SFC shows several features that can be advantageous for its application to large-scale separations [132-135]. One of the most interesting properties of this technique is the low viscosity of the solvents used that, combined with high diffusion coefficients for solutes, leads to a higher efficiency and a shorter analysis time than in HPLC. 

If simple sample pretreatment procedures are insufficient to simplify the complex matrix often observed in process mixtures, multidimensional chromatography may be required. Manual fraction collection from one separation mode and re-injection into a second mode are impractical, so automatic collection and reinjection techniques are preferred. For example, a programmed temperature vaporizer has been used to transfer fractions of sterols such as cholesterol and stigmasterol from a reversed phase HPLC system to a gas chromatographic system.11 Interfacing gel permeation HPLC and supercritical fluid chromatography is useful for nonvolatile or thermally unstable analytes and was demonstrated to be extremely useful for separation of compounds such as pentaerythritol tetrastearate and a C36 hydrocarbon standard.12... 

In supercritical fluid chromatography (SFC) the mobile phase is a supercritical fluid, such as carbon dioxide [15]. A supercritical fluid can be created either by heating a gas above its critical temperature or compressing a liquid above its critical pressure. Generally, an SFC system typically has chromatographic equipment similar to a HPLC, but uses GC columns. Both GC and LC detectors are used, thus allowing analysis of samples that cannot be vaporized for analysis by GC, yet cannot be detected with the usual LC detectors, to be both separated and detected using SFC. SFC is also in other... 

Supercritical fluid chromatography employs supercritical fluid instead of gas or liquid to achieve separations. Supercritical fluids generally exist at conditions above atmospheric pressure and at an elevated temperature. As a fluid, the supercritical state generally exhibits properties that are intermediate to the properties of either a gas or a liqiud. Chapter 16 discusses various advantages of SFC over GC and HPLC and also provides some interesting applications. 

Supercritical fluid chromatography is the name for all chromatographic methods in which the mobile phase is supercritical under the conditions of analysis and the solvating properties of the fluid have a measurable effect on the separation. SFC has some advantages over GC and HPLC it extends the molecular weight range of GC, thermally labile compounds can be separated at lower temperatures, compounds without chromophores can be sensitively detected, and the use of open-tubular and packed columns is feasible. SFC can be employed in both the analysis of natural pigments and synthetic dyes, however it has not been frequently applied in up-to-date analytical practice. 

A variety of modern instrumental analytical techniques have attracted considerable attention in the last decades as alternative separation and analysis methods with respect to HPLC. This includes, in particular, supercritical fluid chromatography (SFC), which utilizes condensed carbon dioxide (above or near its critical temperature of... 

Finally, supercritical fluid chromatography, in which a supercritical fluid is used as the mobile phase, was introduced by Klesper [164-166]. SFE directly coupled to SFC provides an extremely powerful analytical tool. The efficient, fast and selective extraction capabilities of supercritical fluids allows quantitative extraction and direct transfer of the selected solutes of interest to be accomplished to the column, often without the need for further sample treatment or cleanup. Extraction selectivity is usually achieved by adjusting the pressure of the supercritical fluid at constant temperature or, less often, by changing the temperature of the supercritical fluid at constant pressure. SFE coupled with packed column SFC has found... 

Supercritical fluid chromatography is a form of chromatography in which the system is held near the critical temperature of the mobile phase and pressure utilized to effect solvency and hence migration. 

Supercritical fluid chromatography (SFC) is an intermediate chromatographic technique between GC and HPLC. It depends upon the fact that when a fluid becomes supercritical (both the temperature and pressure are at or above its critical point) it develops some of the solvating properties of a liquid whilst retaining the low viscosity of a gas. Hence, mass transfer (essential to efficient chromatography) is more akin to that of GC than HPLC, but many compounds can be chromatographed at temperatures much lower than what would be required by GC, so some thermally labile compounds are amenable to SFC where they would degrade under GC conditions [28]. 

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