SUPERCRITICAL FLUID CHROMATOGRAPHY 2 Column Selection

Figure 7.7 Typical SFC separation of estrone (1), equilin (2), a-estradiol (3), /3-estradiol (4), and d-equilenin (5) on a SB-cyanopropyl-50 column. [Reprinted from Ref. 5, J. Pharm. Biomed. Anal. 10, Jagota and Stewart,, Supercritical Fluid Chromatography of Selected Oestrogens, p. 667 (1992) with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, UK.]...

An on-line supercritical fluid chromatography-capillary gas chromatography (SFC-GC) technique has been demonstrated for the direct transfer of SFC fractions from a packed column SFC system to a GC system. This technique has been applied in the analysis of industrial samples such as aviation fuel (24). This type of coupled technique is sometimes more advantageous than the traditional LC-GC coupled technique since SFC is compatible with GC, because most supercritical fluids decompress into gases at GC conditions and are not detected by flame-ionization detection. The use of solvent evaporation techniques are not necessary. SFC, in the same way as LC, can be used to preseparate a sample into classes of compounds where the individual components can then be analyzed and quantified by GC. The supercritical fluid sample effluent is decompressed through a restrictor directly into a capillary GC injection port. In addition, this technique allows selective or multi-step heart-cutting of various sample peaks as they elute from the supercritical fluid... 

ViUeneuve, M.S., Anderegg, R.J. Analytical supercritical fluid chromatography using fully automated column and modifier selection valves for the rapid development of chiral separations. J. Chromatogr. A 1998, 826, 217-225. 

To apply a screening approach to proactive method development, analyses of selectivity samples under a variety of mobile phase conditions are conducted on different HPLC columns. HPLC columns should be as orthogonaT as possible and variations in solvent composition should be designed to maximize the probability of selectivity differences. Alternate separation techniques, such as ion exchange chromatography (IC), supercritical fluid chromatography (SFC), or capillary electrophoresis (CE) may also be used to obtain orthogonality. 

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... 

The use of supercritical fluid chromatography for carotene separation has been examined and optimized, especially in regard to temperature, pressure, and organic modifiers in the supercritical fluid (71). With an RP column it was possible to resolve an a-carotene-cis isomer from an all-trans carotene as well as two cis isomers of /3-carotene from an all-trans /3-carotene. As with HPLC, only polymeric C,8 columns were able to resolve the cis isomers of a- and /3-carotene from the all-trans isomers. Supercritical fluid chromatography offers the advantage not only of an efficient separation but also of fast analysis. Indeed, the use of SFC with ODS-based columns for the analysis of carotenoid pigments affords a threefold reduction of analysis time compared to HPLC (72). The elution order of carotenoids and their cis isomers was found to be the same as in RP-HPLC. The selectivity of the system could further be increased by adding modifiers (e.g.,... 

Supercritical fluid chromatography offers high selectivity and efficiency. Method development is faster and easier than HPLC. The future of SFC lies in the use of both capillary and packed columns. Although capillary... 

O. Gyllenhaal and J. Vessman, Packed-column supercritical fluid chromatography of omeprazole and related compounds selection of column support with triethylamine and methanol-modified carbon dioxide as the mobile phase, J. Chromatogr., 628 215 (1993). 

Supercritical fluid chromatography has some of the same characteristics of both HPLC and gas chromatography (GC). Packed column SFC uses the same column technology as HPLC, and when used with binary or tertiary solvents, has a broad range of applicability [1]. This range is much broader than GC, because compounds need not be volatile or thermally stable. As in GC, SFC can be coupled to most modern chromatographic detectors, such as element-specific detectors. These detectors are often very selective for... 

Supercritical fluid chromatography is a very important chromatographic technique still underestimated and underutilized. It presents characteristics similar to both GC and HPLC, although having its own characteristics. Whereas the column temperature control is the way to achieve a good separation in GC and the solvating power of the mobile phase is controlling factor in HPLC, in SFC the density of the fluid is the major factor to be optimized. Both packed (LC-like) and capillary (GC-like) columns have been used in this technique, which has found applications in practically all areas in which GC or HPLC has shown to be the selected separation technique. 

Villeneuve, M.S. Anderegg, R.J. Analytical Supercritical Fluid Chromatography Using Fully Automated Column and Modifier Selection Valves for the Rapid Development of Chiral Separations, 7. Chromatogr. A 826, 217-225 (1998). 

Sandra, P Medvedovici, A. Kot, A. David, F. Selectivity Tuning in Packed Column Supercritical Fluid Chromatography, pp. 177-194 in Anton, K. Berger, C., eds., Supercritical Eluid Chromatography with Packed Columns. Dekker, New York (1998). 

Sandra P, Medvedovici A, Kot A, David F. Selectivity tuning in packed column SFC. In Anton K, Berger C, eds. Supercritical Fluid Chromatography with Packed Columns. Chromatographic Science Series. Vol. 75. New York Marcel Dekker, 1998, Chap 6. 

Supercritical fluid chromatography is compatible with both HPLC and GC detectors. As a result, optical detectors, flame detectors and spectroscopic detectors can be used. The FID is the most common detector used. However, the mobile phase composition, column type and flow rate must be taken into account when the detector is selected. Some care must also be taken such that the detector components are capable of withstanding the high pressures of SFC. 

Packed-column supercritical fluid chromatography (PSFC) is currently competitive with LC and GC as it combines the speed and efficiency of GC with the extensive selectivity adjustment capabilities of LC, thereby facilitating the determination of polar and thermolabile compounds. Thus, carbamate pesticides have been determined by PSFC in river water and soil. ... 

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