Supercritical Fluid Chromatography carbon dioxide solvent

Supercritical or near-critical fluids can be used both for extraction and chromatography. Many chemicals, primarily organic species, can be separated and analyzed using this approach [6], which is particularly useful in the food industry. Substances that are useful as supercritical fluids include carbon dioxide, water, ethane, ethene, propane, xenon, ammonia, nitrous oxide, and a fluoroform. Carbon dioxide is most commonly used, typically at a pressure near 100 bar. The required operating pressure ranges from about 43 bar for propane to 221 bar for water. Sometimes a solvent modifier is added (also called an entrainer or cosolvent), particularly when carbon dioxide is used. 

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. 

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). 

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. 

The combination of two techniques, simulated moving bed and supercritical fluid chromatography (SFC), leads to an apparatus with unique features. Besides the known advantages of the SMB process, like reduced solvent consumption, and its continuity the use of supercritical carbon dioxide as mobile phase offers an easy product recovery by depressurizing the supercritical fluid. Clavier et al. 

Since the cost of the mobile phase often represents more than half of the total cost of the separation (except the lower cost of carbon dioxide in supercritical fluid chromatography, SFC), it is worthwhile to minimize the solvent consumption and also to increase the concentration of the product in the eluted fractions. Regeneration of the mobile phase is an economical choice at high solvent consumption rates. Regeneration may include distillation of the used mobile phase followed by adjustment of the mobile phase composition if necessary. 

SFE with carbon dioxide offers several advantages compared to classical solvent extraction methods (1) it is very selective (2) it is fast, because of lower viscosity and approximately 10 times higher diffusion coefficients and (3) CO is neither flammable nor explosive and is nontoxic. SFE is suitable for oxidizable and temperature-sensitive samples. In addition, no reactions occur between extraction medium and. sample compounds and on-line coupling is possible with both. supercritical fluid chromatography (SFC) and gas chromatography. 

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