Supercritical fluid extraction characteristics

Purifications of elfamycins have been described in the Hterature using Craig distribution (2,34), chromatography on Sephadex LH-20 (2,14,26) and Amberlite XAD-2 (10,17,19,26), supercritical fluid extraction (37), and chromatography on an Ito multilayer cod planet centrifuge (26,38). and nmr assignments of most elfamycins have been accompHshed (3,24,26,32). The characteristic uv spectra permits some differentiation (12) and bathochromic shifts associated with Al " complexation have been used to quantify efrotomycin (2, R = CH ) in feed premixes (39,40). 

Principles and Characteristics Supercritical fluid extraction uses the principles of traditional LSE. Recently SFE has become a much studied means of analytical sample preparation, particularly for the removal of analytes of interest from solid matrices prior to chromatography. SFE has also been evaluated for its potential for extraction of in-polymer additives. In SFE three interrelated factors, solubility, diffusion and matrix, influence recovery. For successful extraction, the solute must be sufficiently soluble in the SCF. The timescale for diffusion/transport depends on the shape and dimensions of the matrix particles. Mass transfer from the polymer surface to the SCF extractant is very fast because of the high diffusivity in SCFs and the layer of stagnant SCF around the solid particles is very thin. Therefore, the rate-limiting step in SFE is either... 

Principles and Characteristics In an attempt to develop a unified sample preparation system for extraction of various matrix/analyte combinations Ashraf-Khorassani et al. [498] have described a hybrid supercritical fluid extraction/enhanced solvent extraction (SFE/ESE ) system to remove both polar and nonpolar analytes from various matrices. The idea is that a single instrument that can perform extractions via pure C02 solvent, and all gradients thereof affords... 

On-line supercritical fluid extraction/GC methods combine the ability of liquid solvent extraction to extract efficiently a broad range of analytes with the ability of gas-phase extraction methods to rapidly and efficiently transfer the extracted analytes to the gas chromatograph. The characteristics of supercritical fluids make them ideal for the development of on-line sample extraction/gas chromatographic (SFE-GQ techniques. SFE has the ability to extract many analytes from a variety of matrices with recoveries that rival liquid solvent extraction, but with much shorter extraction times. Additionally, since most supercritical fluids are converted to the gas phase upon depressurization to ambient conditions, SFE has the potential to introduce extracted analytes to the GC in the gas phase. As shown in Fig. 13.8, the required instrumentation to perform direct coupling SFE-GC includes suitable transfer lines and a conventional gas chromatograph [162,163]. 

The characteristics of supercritical fluids make them ideal for the recovery of natural products (Molero et al., 1996). As a result, the food industry was among the first to implement supercritical fluid extraction (SFE) widely using CO2. Not only is this process environmentally benign, it is also nontoxic, a primary concern when manufacturing edible products. 

Supercritical fluid extraction (SFE) has been used for the recovery of analytes from hair this is a technique that offers several advantages due to the characteristics of low viscosity of supercritical fluid the speed of extraction, high extraction efficiency, and ultimately the ability to easily remove the extraction solvent. Also there is the possibility of working with automated systems that also allow the recycling of the solvent. The major limitation of this technique is the cost of the instrumentation [42],... 

Supercritical fluid extraction (SFE) is a suitable process for many separation problems. The regeneration of the supercritical fluid is as important as the extraction step itself Therefore this paper presents a method to do this in a more isobaric way than the customary pressure reduction regeneration. For the example of soil remediation we have investigated the activated carbon regeneration of supercritical carbon dioxide loaded with the low-volatile polycyclic aromatic hydrocarbon (PAH) pyrene. Characteristics of supercritical fluid extraction for soil remediation are elevated temperatures and pressures up to 370 K and 300 bar. For this reason adsorption isotherms of pyrene on activated carbon up to these conditions are measured first. Subsequently this method is used to regenerate carbon dioxide in a closed solvent cycle plant with a 4 1 extractor. An economic analysis using these results indicate that the soil remediation costs will decrease for about 20 - 30 % by means of an activated carbon adsorber. 

In this project, the feasibility of catalyst regeneration by supercritical fluid extraction was studied. A spent catalyst from an industrial naphtha hydrotreater was extracted with tetrahydrofuran, pyridine, carbon dioxide, and sulfur dioxide under subcritical and supercritical conditions. The coke reduction and changes in the catalyst pore characteristics were measured and to a limited extent the catalyst activity was evaluated. It is shown that by supercritical extraction, the coke content of spent hydrotreating catalysts can be reduced and the catalyst pore volume and surface area can be increased. 

Polysiloxanes are readily fractionated by supercritical-fluid-extraction techniques because of their excellent solubility characteristics. Indeed, poly(dimethylsiloxane)s with molecular weights up to 100,000 g/mol have been dissolved by supercritical fluids (14). In the present study on amino-terminated polysiloxanes, similar results were obtained. However, the desired molecular weight of difunctionalized precursors for segmented copolymer systems generally is less than 20,000 g/mol. 

In more recent years, supercritical fluid extraction has been found to be useful for the extraction of low to moderately polar compounds. The requirements in any particular case depend on the characteristics of the matrix, the drug, and the drug metabolites. The concentration range of the drug is also obviously important, as it will determine the methods selected for the separation and analytical procedures. 

Dynamic factors are among the key variables to be optimized in an SFE process. In addition to extracting the analytes, the primary function of the supercritical fluid is to transport the solutes to the collecting vessel or to an on-line coupled chromatograph or detector. Ensuring efficient transportation of the analytes following separation from the matrix entails optimizing three mutually related variables, namely the flow-rate of the supercritical fluid, the characteristics of the extraction cell and the extraction time. These factors must be carefully combined in order to allow the flow-cell to be vented as many times as required. 

Because all three types of chromatography can be coupled to SFE, the choice in each case should be dictated by the characteristics of the analytes to be isolated and determined. If GC can be used, it is to be preferred on account of its consolidated status and the high sensitivity and flexibility of the detectors with which it is compatible. Analysing supercritical fluid extracts by HPLC provides one special advantage over GC as most... 

The impact of the extraction conditions using various solvents on the recoveries has never been studied in detail, and the results have never been compared. The introduction of modern extraction methods, such as microwave-assisted extraction, supercritical fluid extraction, and solid-phase extraction, probably will improve the efficiency of extraction, even in the instance of unstable pigments and pigment mixtures. The majority of TLC separations were carried out on traditional silica layers. As the chemical structures and, consequently, the retention characteristics of pigments are highly different, a wide variety of eluent systems has been employed for their separation, consisting of light petroleum, ethyl formate, ethyl acetate, benzene, toluene, chloroform, methanol, n-butanol, formic or acetic acid, and so forth. 

A well-known extraction system is supercritical fluid extraction. It can be applied to matrices of different composition. This technique demonstrates the influence of matrix characteristics and common extraction variables on equilibrium analyte distribution.63 These factors assure, for supercritical fluid extrachon, the optimum conditions for efficient extraction of the matrix. 

What are some characteristics that make supercritical fluid extraction attractive ... 

Supercritical Fluid Extraction. The properties of cryogenic fluids under supercritical conditions give them considerable potential for regenerating spent adsorbents. The solution characteristics of the fluid should be compatible with the adsorbed components and, when the fluid is pumped through the adsorbent bed, it will dissolve the adsorbed spiU components. The supercritical fluid can be evaporated easily due to its volatility, and in some cases both the solvent and the contaminant from the spill can be recovered. The high solvation character of the supercritical fluids is due to low intermolecular distances between the solvent molecules. This novel process is expensive at present and therefore the spilled material should be high value added and recoverable, such as pharmaceutical products. 

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