Supercritical fluids solid-fluid

A method which uses supercritical fluid/solid phase extraction/supercritical fluid chromatography (SE/SPE/SEC) has been developed for the analysis of trace constituents in complex matrices (67). By using this technique, extraction and clean-up are accomplished in one step using unmodified SC CO2. This step is monitored by a photodiode-array detector which allows fractionation. Eigure 10.14 shows a schematic representation of the SE/SPE/SEC set-up. This system allowed selective retention of the sample matrices while eluting and depositing the analytes of interest in the cryogenic trap. Application to the analysis of pesticides from lipid sample matrices have been reported. In this case, the lipids were completely separated from the pesticides. 

Supercritical fluid Supercritical fluid, e.g. CO2 Liquid film coated on solid support Materials of mol. wt. overlapping with... 

Supercritical fluid solid chromatography (SFSC) may be abbreviated to fluid-solid chromatography (FSC), etc. 

When the analytes are to be retained in a sorbent, the sample (which can be solid, semi-solid, liquid or gaseous) is inserted in the solid state into the extraction cell. Samples in the latter three forms are supported on an appropriate material in order to ensure effective attack by the supercritical fluid. Solid supports are not used for liquid, gaseous and semi-solid samples only, however. Some research work conducted so far on solid samples has involved not natural samples but synthetic ones prepared from a selected sorbent (a natural matrix where the presence of the analytes of interest was previously excluded or a synthetic support such as polyurethane foam or glass wool) with which a solution containing the analytes was homogenized. Quantitative evaporation of the analyte solvent is mandatory as any residual solvent may alter the polarity of the supercritical fluid and hence its action to an extent dependent on the particular fluid and solvent properties, and also on the amount of solvent retained. 

Kurnik, R. T., and R. C. Reid. 1982. Solubility of solid mixtures in supercritical fluids. J. Fluid Phase Equilib. 8 93. 

Sie S T, Rijinders G W A 1967 High-pressure gas chromatography and chromatography with supercritical fluids. IV. Fluid-solid chromatography. Sep Sci 2 755-777... 

Combinations having a exchanger liquid-supercritical fluid supercritical fluid-solid ... 

Above the critical temperature and pressure, a substance is referred to as a supercritical fluid. Such fluids have unusual characteristics. They can diffuse through a solid like a gas and dissolve materials like a liquid. Carbon dioxide and water are the most commonly used supercritical fluids and hold the promise of many practical new applications (see Beyond the Classroom at the end of this chapter). 

One fluid phase in contact with one solid phase liquid-solid gas/vapor-solid supercritical fluid-solid (solid-fluid phase membrane contactors) (Fig. 26.2). 

Catalysis in a single fluid phase (liquid, gas or supercritical fluid) is called homogeneous catalysis because the phase in which it occurs is relatively unifonn or homogeneous. The catalyst may be molecular or ionic. Catalysis at an interface (usually a solid surface) is called heterogeneous catalysis, an implication of this tenn is that more than one phase is present in the reactor, and the reactants are usually concentrated in a fluid phase in contact with the catalyst, e.g., a gas in contact with a solid. Most catalysts used in the largest teclmological processes are solids. The tenn catalytic site (or active site) describes the groups on the surface to which reactants bond for catalysis to occur the identities of the catalytic sites are often unknown because most solid surfaces are nonunifonn in stmcture and composition and difficult to characterize well, and the active sites often constitute a small minority of the surface sites. 

D. C. Busby and co-workers. Supercritical Fluid Spray Application Technology A Pollution Prevention Technologyfor the Futures PP- 218—239 Proceedings of the 17th Water-Borne and High-Solid Coating Symposiums New Orleans, La., 1990. 

Analytical Supercritical Fluid Extraction and Chromatography Supercritical fluids, especially CO9, are used widely to extrac t a wide variety of solid and hquid matrices to obtain samples for analysis. Benefits compared with conventional Soxhlet extraction include minimization of solvent waste, faster extraction, tunabihty of solvent strength, and simple solvent removal with minimal solvent contamination in the sample. Compared with high-performance liquid chromatography, the number of theoretical stages is higher in... 

Supercritical fluid extraction (SFE) and Solid Phase Extraction (SPE) are excellent alternatives to traditional extraction methods, with both being used independently for clean-up and/or analyte concentration prior to chromatographic analysis. While SFE has been demonstrated to be an excellent method for extracting organic compounds from solid matrices such as soil and food (36, 37), SPE has been mainly used for diluted liquid samples such as water, biological fluids and samples obtained after-liquid-liquid extraction on solid matrices (38, 39). The coupling of these two techniques (SPE-SFE) turns out to be an interesting method for the quantitative transfer... 

K. Haitonen and M. L. Riekkola, Detection of /3-blockers in urine by solid-phase extraction-supercritical fluid exti action and gas cliromatogi aphy-mass spectrometi y , 7. Chromatogr. B 676 45-52 (1996). 

D. L. Allen, K. S. Scott and J. S. Oliver, Comparison of solid-phase extraction and supercritical fluid exti action for the analysis of moipliine in whole blood , 7. Anal. Toxicol. 23 216-218 (1999). 

E. Pocumll, R. M. Marce, F. Bonnll, J. L. Bernal, L. Toribio and M. L. Serna, On-line solid-phase extraction coupled to supercritical fluid chromatography to determine phenol and nitrophenols in water , ]. Chromatogr. 755 67-74 (1996). 

Figure 15.14 Separation of explosives exnacted from water by using SPE-SFE-GC at several SEE trapping temperatures, peak identification is as follows NG, nitroglycerin 2,6-DNT, 2,6-dinitrotoluene 2,4-DNT, 2,4-dinitrotoluene TNT, triniti otoluene IS, 1,3-tiichloroben-zene. Adapted Journal of High Resolution Chromatography, 16, G. C. Slack et al., Coupled solid phase extraction supercritical fluid extraction-on-line gas cliromatography of explosives from water , pp. 473-478, 1993, with permission from Wiley-VCH.

G. C. Slack, H. M. McNair, S. B. Hawthorne and D. J. Miller, Coupled solid phase exti action-supercritical fluid exti action-on-line gas chromatography of explosives from water , ]. High Resolut. Chromatogr. 16 473-478 (1993). 

We will begin our discussion by describing (vapor + liquid) equilibrium, which we will extend into the supercritical fluid region as (fluid + fluid) equilibrium. (Liquid + liquid) equilibrium will then be described and combined with (vapor + liquid) equilibrium in the (fluid + fluid) equilibrium region. Finally, we will describe some examples of (solid + liquid) equilibrium. 

A number of analytical techniques such as FTIR spectroscopy,65-66 13C NMR,67,68 solid-state 13 C NMR,69 GPC or size exclusion chromatography (SEC),67-72 HPLC,73 mass spectrometric analysis,74 differential scanning calorimetry (DSC),67 75 76 and dynamic mechanical analysis (DMA)77 78 have been utilized to characterize resole syntheses and crosslinking reactions. Packed-column supercritical fluid chromatography with a negative-ion atmospheric pressure chemical ionization mass spectrometric detector has also been used to separate and characterize resoles resins.79 This section provides some examples of how these techniques are used in practical applications. 

The dense fluid that exists above the critical temperature and pressure of a substance is called a supercritical fluid. It may be so dense that, although it is formally a gas, it is as dense as a liquid phase and can act as a solvent for liquids and solids. Supercritical carbon dioxide, for instance, can dissolve organic compounds. It is used to remove caffeine from coffee beans, to separate drugs from biological fluids for later analysis, and to extract perfumes from flowers and phytochemicals from herbs. The use of supercritical carbon dioxide avoids contamination with potentially harmful solvents and allows rapid extraction on account of the high mobility of the molecules through the fluid. Supercritical hydrocarbons are used to dissolve coal and separate it from ash, and they have been proposed for extracting oil from oil-rich tar sands. 

Chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of which is stationary (the stationary phase), while the other (the mobile phase) moves in a definite direction. A mobile phase is described as a fluid which percolates through or along the stationary bed in a definite direction . It may be a liquid, a gas or a supercritical fluid, while the stationary phase may be a solid, a gel or a liquid. If a liquid, it may be distributed on a solid, which may or may not contribute to the separation process. ... 

Although critical pressures are many times greater than atmospheric pressure, supercritical fluids have important commercial applications. The most important of these is the use of supercritical carbon dioxide as a solvent. Supercritical CO2 diffuses through a solid matrix rapidly, and it transports materials well because it has a lower... 

Braga et al. ° compared the efficiencies of several processes, i.e., hydrodistillation, low pressnre solvent extraction, and Soxhlet and supercritical fluid extraction. For each process, the inflnences of several parameters (duration, temperature, nature of solvent) were also evalnated. These authors concluded that the Soxhlet method performed with ethanol/isopropanol 1/100 v/v for 2 hr and 30 min was the most effective. Snn et al. nsed solid phase extraction to concentrate (nine times) a... 

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