Supercritical fluid extraction advantages

Supercritical Fluid Extraction. Supercritical fluid (SCF) extraction is a process in which elevated pressure and temperature conditions are used to make a substance exceed a critical point. Once above this critical point, the gas (CO2 is commonly used) exhibits unique solvating properties. The advantages of SCF extraction in foods are that there is no solvent residue in the extracted products, the process can be performed at low temperature, oxygen is excluded, and there is minimal protein degradation (49). One area in which SCF extraction of Hpids from meats maybe appHed is in the production of low fat dried meat ingredients for further processed items. Its apphcation in fresh meat is less successful because the fresh meat contains relatively high levels of moisture (50). 

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. 

Supercritical fluid extraction — During the past two decades, important progress was registered in the extraction of bioactive phytochemicals from plant or food matrices. Most of the work in this area focused on non-polar compounds (terpenoid flavors, hydrocarbons, carotenes) where a supercritical (SFE) method with CO2 offered high extraction efficiencies. Co-solvent systems combining CO2 with one or more modifiers extended the utility of the SFE-CO2 system to polar and even ionic compounds, e.g., supercritical water to extract polar compounds. This last technique claims the additional advantage of combining extraction and destruction of contaminants via the supercritical water oxidation process."... 

Supercritical fluid extraction (SFE) is a technique in which a supercritical fluid [formed when the critical temperature Tf) and critical pressure Pf) for the fluid are exceeded simultaneously] is used as an extraction solvent instead of an organic solvent. By far the most common choice of a supercritical fluid is carbon dioxide (CO2) because CO2 has a low critical temperature (re = 31.1 °C), is inexpensive, and is safe." SFE has the advantage of lower viscosity and improved diffusion coefficients relative to traditional organic solvents. Also, if supercritical CO2 is used as the extraction solvent, the solvent (CO2) can easily be removed by bringing the extract to atmospheric pressure. Supercritical CO2 itself is a very nonpolar solvent that may not have broad applicability as an extraction solvent. To overcome this problem, modifiers such as methanol can be used to increase the polarity of the SFE extraction solvent. Another problem associated with SFE using CO2 is the co-extraction of lipids and other nonpolar interferents. To overcome this problem, a combination of SFE with SPE can be used. Stolker et al." provided a review of several SFE/SPE methods described in the literature. 

One of the most studied technologies is supercritical fluid extraction with SC-CO2. The advantages of SC-CO2 include its low processing temperature, which minimizes thermal degradation the ease of separation with no solvent residue left in the final product and minimization of undesirable oxidation reactions. 

Figure 15.4 shows a schematic diagram of a supercritical fluid extraction apparatus. The advantages of supercritical fluid extraction (SFE) are as follows ... 

As its name suggests, supercritical fluid extraction (SEE) relies on the solubilizing properties of supercritical fluids. The lower viscosities and higher diffusion rates of supercritical fluids, when compared with those of liquids, make them ideal for the extraction of diffusion-controlled matrices, such as plant tissues. Advantages of the method are lower solvent consumption, controllable selectivity, and less thermal or chemical degradation than methods such as Soxhlet extraction. Numerous applications in the extraction of natural products have been reported, with supercritical carbon dioxide being the most widely used extraction solvent. However, to allow for the extraction of polar compounds such as flavonoids, polar solvents (like methanol) have to be added as modifiers. There is consequently a substantial reduction in selectivity. This explains why there are relatively few applications to polyphenols in the literature. Even with pressures of up to 689 bar and 20% modifier (usually methanol) in the extraction fluid, yields of polyphenolic compounds remain low, as shown for marigold Calendula officinalis, Asteraceae) and chamomile Matricaria recutita, Asteraceae). " ... 

Supercritical fluid extraction, offers also some desirable advantages including processing at low temperature, recovery of a solvent-free extract, and rapid extraction. However, very limited studies have been published on the use of supercritical fluids for the isolation of corticosteroids from biological samples. A combination of supercritical fluid extraction and liquid chromatography has been employed for the detection of dexamethasone residues in bovine tissues (448). 

Supercritical fluid extraction conditions were investigated in terms of mobile phase modifier, pressure, temperature and flow rate to improve extraction efficiency (104). High extraction efficiencies, up to 100%, in short times were reported. Relationships between extraction efficiency in supercritical fluid extraction and chromatographic retention in SFC were proposed. The effects of pressure and temperature as well as the advantages of static versus dynamic extraction were explored for PCB extraction in environmental analysis (105). High resolution GC was coupled with SFE in these experiments. 

Details of the instrumental design as well as results obtained using it are included in this report. The challenge is for instrument manufacturers to examine the features and produce equivalent instrumentation on a commercial basis. Only with this rapid, multiple sample analysis will the technique of supercritical fluid extraction be exploited to full advantage. 

Phenyl Metabolite of NUSTAR from Wheat The phenyl metabolite of NUSTAR was the extraction example used for twelve vessel multivessel extractor. As is illustrated in Table IV, the average recovery for these samples was 91.0%, with a relative standard deviation of 12.4%. Two samples were lost in this extraction example. The loss was attributed to overpressurization of the extraction system. The wheat sample which is ground with dry ice in a blender as a standard sample handling procedure for classical as well as the supercritical fluid extraction, frequently contains small fine particles. These particles can readily block the 0.45 pm frits at the end of the extraction vessel. The advantage of our system, is that the loss of one sample in the series does not interfere with the accurate extraction of the rest. 

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... 

The last two decades have seen an increased interest in the use of supercritical fluids in separation science. Supercritical C02 has often been employed as a naturally occurring medium for the separation, purification, and determination of organic substances in environmental samples. However, there are only limited reports on the use of supercritical fluid as solvent in the separation of metal ions from solutions as well as various solid matrices. The supercritical fluid extraction (SFE) technology offers several advantages over conventional solvent-based methods, including the ability to extract radionuclides directly from solids, easy separation of solutes from C02, and minimization of waste generation. It can easily be removed from the extracted substances by degasification under atmospheric pressure and temperature. 

Supercritical Fluid Chromatography, as well as Supercritical Fluid Extraction (SFE), are very often considered as niche detection techniques. However, it is obvious from Chapter 7.2 that SFC-NMR and SFE-NMR show the inherent advantage that no solvent suppression technique is needed and the whole proton chemical shift range can be used without any distortions of solvent signals and impurities. 

The extraction efficiency of supercritical fluids may be enhanced by mixing into it a small amount of a cosolvent such as acetone or methanol. Supercritical fluid extraction offers certain advantages over other extraction processes (1) it is relatively a fast process with greater extraction efficiency (2) sample concentration steps may be eliminated and (3) unlike LLE or Soxhlett extraction, a large amount of organic solvents is not required. 

To gain further information concerning the hexane fractions, on-line supercritical fluid extraction/SFC was coupled with on-line FTIR detection. FT1R should have an advantage in that it is more sensitive to aliphatic hydrocarbons than the UV detector. 

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