Dynamic supercritical-fluid extraction

These results therefore suggest a careful evaluation of the pros and cons of supercritical fluids. Another study that included PCBs showed good agreement between Soxhlet extraction and dynamic supercritical fluid extraction of soil samples with the added advantage that no cleanup step was needed with the latter (van der Velde et al. 1992). A combined extraction using C02 and acetylation with acetic anhydride and triethylamine has been used for the analysis of chlorophenolic compounds in soil (Lee et al. 1992) and air-dried sediment samples (Lee et al. 1993). This is both rapid and gives results comparable to those using conventional methods of steam distillation. 

Wagner, B., Nishioka, M., Tuma, D., Maiwald, M., and Schneider, G.M. (1999) Sample purification for spectroscopic high-pressure investigations by dynamic supercritical fluid extraction, J. Supercrit. Fluids, in press. 

Supercritical fluid extraction can be performed in a static system with the attainment of a steady-state equilibrium or in a continuous leaching mode (dynamic mode) for which equilibrium is unlikely to be obtained (257,260). In most instances the dynamic approach has been preferred, although the selection of the method probably depends just as much on the properties of the matrix as those of the analyte. The potential for saturation of a component with limited solubility in a static solvent pool may hinder complete recovery of the analyte. In a dynamic system, the analyte is continuously exposed to a fresh stream of solvent, increasing the rate of extraction from the matrix. In a static systea... 

There are basically three methods of liquid sampling in GC direct sampling, solid-phase extraction and liquid extraction. The traditional method of treating liquid samples prior to GC injection is liquid-liquid extraction (LLE), but several alternative methods, which reduce or eliminate the use of solvents, are preferred nowadays, such as static and dynamic headspace (DHS) for volatile compounds and supercritical fluid extraction (SFE) and solid-phase extraction (SPE) for semivolatiles. The method chosen depends on concentration and nature of the substances of interest that are present in the liquid. Direct sampling is used when the substances to be assayed are major components of the liquid. The other two extraction procedures are used when the pertinent solutes are present in very low concentration. Modem automated on-line SPE-GC-MS is configured either for at-column conditions or rapid large-volume injection (RLVI). 

Dynamic headspace-extraction stripping and purge-and-trap methodology are used most often for determination of M-hcxanc in water and hazardous wastes. Dynamic headspace extraction techniques have been applied to water samples (Roberts and Burton 1994) and sediment (Bianchi et al. 1991). Detection limits of 0.5 g/L were reported for lake water (Roberts and Burton 1994) and 20 ng/kg (ppt) for sediment (Bianchi et al. 1991). Supercritical fluid extraction (SFE) is a relatively new technique that has been applied to -hcxane in soil (Yang et al. 1995). Membrane extraction of M-hexane from water samples has been developed to provide online, continuous monitoring (Wong et al. 1995 Xu and Mitra... 

Supercritical fluid extraction is a potential technique for the purification of pharmaceutical products containing residual solvents. The solubilities of three inhibitors of inflammatory activity, Ketoprofen, Piroxicam, and Nimesulide, in supercritical CO2, measured using a dynamic saturation technique, were reported at pressures between 100 bar and 220 bar and at two temperatures 312.5 K and 331.5 K. The solubilities exhibit a clear dependence on the solvent density, and this has been used to provide a simple and precise correlation of the data (Macnaughton et al., 1996). 

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. 

Static/Dynamic Selection Valve. This valve is the key feature of our design in that it eliminates the use of a restrictor. Restrictors are the most common means of controlling the pressure or density of a supercritical process. With no restriction, flow is dead-ended (i.e. restricted) via a switching valve in our invention. Supercritical fluid extractions are then conducted in a static (no flow) mode. 

Influence of matrix on the supercritical fluid extractability of cocaine using COj, COj + MeOH and COj + HjO/TEA (85 15 v/v). SFE conditions 400 atm, 110 C, 10 min static, 15 min dynamic mode 100 pL modifier. (From Morrison, J. F., MacCrehan, W. A., Selavka, C. M., submitted. With permission from the National Institute of Standards and Technology.)... 

Depending on the way the sample and extractant are brought into contact, supercritical fluid extraction can be implemented in two different operational modes, viz. static and dynamic. 

Supercritical fluid extractions can be performed statically or dynamically. During static extractions the extraction cell is pressurized and heated to the desired temperature. The supercritical fluid remains in the extraction cell and... 

Because tocopherols and tocotrienols and their esters are lipid-soluble compounds, they are soluble in organic solvents and can be extracted with them. Simple extraction of vitamers from cereal products and other foods containing high amounts of fiber and other polysaccharides may be less effective because of the complex matrix. Inclusion of the vitamers in the matrix by various interactions may hinder the penetration of the solvent into the sample, thus lowering its extraction power. To improve the extraction of lipids from cereals, dynamic extraction with hot solvents (Balz et al., 1992 Zhou et al., 1999), and modem techniques such as supercritical fluid extraction, may be used. 

In this chapter, we present the results of computational studies on the above mentioned novel inorganic systems namely AlPOs, carbon nanotubes and supercritical fluid extraction from the adsorbed phase over ceramics. Multi-technique computational methods such as Computer Graphics (CG), molecular mechanics (MM), quantum chemistry (QC) and molecular dynamics (MD) were applied. The attempts made to design synthetic sorbents at molecular level are reviewed. 

Supercritical fluid extraction is also a suitable technique for enhancing the quality of essential oils obtained by conventional extraction methods, by means of fractionation and deterpenation. Thus, the separation of citrus oils into different clssses of substances by supercritical CO2 has been widely investigated. Temelli et al. reported a method for the extraction of terpene hydrocarbons from cold-pressed Valencia orange oil with supercritical CO2, using both static and dynamic flow approaches (65). Another article has reported the SFE of terpenes from cold-pressed orange oil in a temperature range from 40°C to 70°C and pressures from 83 to 124 bar (66). The determination and elimination of psoralens from lemon peel oil by SFE has also been conducted (67). The procedure included the increase of CO2 density in successive steps. 

Supercritical fluid extraction (SFE) with solid-phase trapping has been used for the extraction of DBDE and PBBs together with PCBs and chlorinated benzenes from sediment samples, with CO2 as the supercritical fluid. ° Before the extraction, the sediment sample can be mixed with copper powder and sodium sulphate for the removal of moisture and sulphur. Usually, the extraction combines static and dynamic extraction. The time required for the extraction ranges from 40 to 60 min, the extraction temperature is around 120°C and the pressure 374 bar. Compared with Soxhlet extraction, SFE gives similar yields, but the extracts are generally much cleaner and it might not be necessary to clean the extracts before GC analysis. 

An essential oil (EO) is internationally defined as the product obtained by hydro-, steam-, or dry-distillation of a plant or of some of its parts, or by a suitable mechanical process without heating, as in the case of Citrus fruits (AFNOR, 1998 Council of Europe, 2010). Vacuum distUladon solvent extraction combined offline with distillation simultaneous distillation extraction supercritical fluid extraction microwave-assisted extraction and hydro-distiUation and static, dynamic, and high concentration capacity headspace sampling are other techniques used for extracting the volatile fraction from aromatic plants, although the products of these processes cannot be termed EOs (Faleiro and Miguel, 2013). 

Neither MAE nor ASE is currently in a configuration that would readily lead to the automation of sample preparation. Supercritical fluid extraction can be used as online system that can then be connected to the chromatographic and detection systems. Connected online with the GC/MS, SFE was successfully used for the determination of PAHs in marine sediments. Using either CO2 alone or modified with toluene or MeOH in the extraction, the PAHs were cryofocused in the accumulation cell of the GC and then directly chromatographed. For the study of PAHs in marine sediments, a new extraction technique, which consists of the combination of ASE (dynamic and static mode) and SFE (dynamic mode), was developed, with an extraction time longer than in ASE but shorter than in SFE, and... 

Favati, F., Florentini, R.and De Vitis, V. (1994) Supercritical fluid extraction of sunflower oil Extraction dynamics and process optimization, Proceedings of the 3rd International Symposium on Supercritical Fluids, Institut National Polytechnique de Lorraine, Nancy, France, pp. 305-310. 

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