Supercritical fluid chromatography solvents

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 Chromatography. Supercritical fluid chromatography (sfc) combines the advantages of gc and hplc in that it allows the use of gc-type detectors when supercritical fluids are used instead of the solvents normally used in hplc. Carbon dioxide, -petane, and ammonia are common supercritical fluids (qv). For example, carbon dioxide (qv) employed at 7.38 MPa (72.9 atm) and 31.3°C has a density of 448 g/mL. 

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... 

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. 

Supercritical fluid chromatography pressure gradient solvent delivery system Pierce Chemicals Life Science Laboratories Ltd Sedgewick Road Luton... 

Matthijs, N., Maftouh, M., Vander Heyden, Y. Chiral separation strategy in polar organic solvent chromatography and performance comparison with normal-phase liquid and supercritical-fluid chromatography. J. Sep. Sci. 2006, 29, 1353-1362. 

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. 

Packed-column SFC also is suitable for preparative-scale enatioseparations. Compared with preparative LC, sub- or supercritical fluid chromatography results in easier product and solvent recovery, reduced solvent waste and cost, and higher output per unit time. Because of its reduced sample capacity, SFC usually allows the separation of 10-100 mg samples per run. Chromatographers can compensate for these sample amounts by using shorter analysis times and repetitive injections (Wolf and Pirkle, 1997). 

Supercritical fluid chromatography (SFC) is a relatively recently developed chromatographic technique. Because of its ability to deal with compounds that are either polar or of high molecular weight, much attention has recently focused on applications of SFC to the analysis of different analytes using a variety of fluids or fluid mixtures to provide differing solvent capabilities and select vities. As a result there is a large amount of research currently underway both in SFC method development and in hardware development. 

Supercritical fluid chromatography provides increased speed and resolution, relative to liquid chromatography, because of increased diffusion coefficients of solutes in supercritical fluids. (However, speed and resolution are slower than those of gas chromatography.) Unlike gases, supercritical fluids can dissolve nonvolatile solutes. When the pressure on the supercritical solution is released, the solvent turns to gas. leaving the solute in the gas phase for easy detection. Carbon dioxide is the supercritical fluid of choice for chromatography because it is compatible with flame ionization and ultraviolet detectors, it has a low critical temperature. and it is nontoxic. 

For volatile materials vapor phase chromatography (gas chromatography) permits equilibration between the gas phase and immobilized liquids at relatively high temperatures. Tire formation of volatile derivatives, e.g., methyl esters or trimethylsilyl derivatives of sugars, extends the usefulness of the method.103104 A method which makes use of neither a gas nor a liquid as the mobile phase is supercritical fluid chromatography.105 A gas above but close to its critical pressure and temperature serves as the solvent. The technique has advantages of high resolution, low temperatures, and ease of recovery of products. Carbon dioxide, N20, and xenon are suitable solvents. 

Supercritical fluid chromatography (SFC) has also been used in phospholipid analysis. According to Lafosse et al., phospholipid classes can be separated by SFC using a simple isocratic solvent consisting of 78.4/21.6 (w/w) mixture of carbon dioxide and a mixture of methanol, water, and triethylamine (95/4.95/0.05) in combination with a Zorbax Sil stationary phase detection was performed by evaporative light-scattering (20). 

Use of Solvatochromic Dyes To Correlate Mobile Phase Solvent Strength to Chromatographic Retention in Supercritical Fluid Chromatography... 

Several researchers have combined the separating power of supercritical fluid chromatography (SFC) with more informative spectroscopic detectors. For example, Pinkston et. al. combined SFC with a quadrupole mass spectrometer operated in the chemical ionization mode to analyze poly(dimethylsiloxanes) and derivatized oligosaccharides (7). Fourier Transform infrared spectroscopy (FTIR) provides a nondestructive universal detector and can be interfaced to SFC. Taylor has successfully employed supercritical fluid extraction (SFE)/SFC with FTIR dectection to examine propellants (8). SFC was shown to be superior over conventional gas or liquid chromatographic methods. Furthermore, SFE was reported to have several advantages over conventional liquid solvent extraction (8). Griffiths has published several... 

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