Supercritical total extraction

Figure 3.13 Total extractables from nylon-6 by SFE as a function of extraction time. After Ezzell and Thompson [399]. Reproduced by permission of Supercritical Conferences...

Supercritical fluid extraction (EPA 3540, for total recoverable petroleum hydrocarbons EPA 3561 for polynuclear aromatic hydrocarbons) is applicable to the extraction of semivolatile constituents. Supercritical fluid extraction involves heating and pressuring a mobile phase to supercritical conditions (where the solvent has the properties of a gas and a liquid). The supercritical fluid is passed through the soil sample, and the analytes are concentrated on a sorbent or trapped cryogenically. The analytes are eluted with a solvent and analyzed using conventional techniques. Carbon dioxide is the most popular mobile phase. 

Supercritical fluid extraction of total recoverable petroleum hydrocarbons (TRPH)... 

Carotenoids A large number of solvents have been used for extraction of carotenoids from vegetables matrices, such as acetone, tetrahydrofuran, n-hexane, pentane, ethanol, methanol, chloroform [427-431], or solvent mixtures such as dichloromethane/methanol, tetrahydrofuran/methanol, -hexane/acetone, or toluene or ethyl acetate [424,432-435], SPE has been used as an additional purification step by some authors [422,426], Supercritical fluid extraction (SEE) has been widely used, as an alternative method, also adding CO2 modifiers (such as methanol, ethanol, -hexane, water, methylene chloride) to increase extraction efficiency [436-438], In addition, saponification can be carried out, but a loss of the total carotenoid content has been observed and, furthermore, direct solvent extraction has been proved to be a valid alternative [439],... 

The pure oleoresin produced by solvents normally contains only pure curcumin, in a crystalline form. It is hardly soluble in liquid- and supercritical CO2- Even at an extraction pressure of 450 bar, and with 2 hours extraction time at 65°C, only 20% of the initial curcumin can be extracted. On the other hand, all the volatile oil and fatty oil is extracted, and a fat-free curcumin-starch mixture with a very low flavour-content can be produced. The total extraction yields are between 5 to 12%, with mostly fatty oil and volatile oil, and about 10% curcumin in the extract. 

Extraction of fat by supercritical carbon dioxide was investigated as an important option for minimizing the expanded use of frequently flammable and carcinogenic solvents in food analysis. Unfortunately, the presence of moisture in foods has an adverse effect on the quantitative extraction of fat by supercritical fluid extraction (SEE). Hence, samples have to be lyophilized first. The total fat content of freeze-dried meat and oilseed samples was found to be comparable to values derived from Soxhlet-extracted samples (26). Besides, only small amounts of residual lipids could be recovered by an additional extraction of the SFE-extracted matrix by the Bligh and Dyer solvent extraction procedure. As far as the minor constituents are concerned, it was found that the extraction recovery ranged from 99% for PC to 88% for PA. Hence, Snyder et al. concluded that SFE can be used as a rapid, automated method to obtain total fat, including total phospholipids, from foods (26). 

Methods of extracting the fat-soluble vitamin from food matrices include alkaline hydrolysis, enzymatic hydrolysis, alcoholysis, direct solvent extraction, and supercritical fluid extraction of the total lipid component. 

Supercritical fluid extraction system - Hewlett Packard Model 7680A totally automated system with unlimited-capacity reciprocating pump, specially designed extraction chamber with safety interlocks, a variable restrictor nozzle and analyte collection trap. The operation of the extractor is controlled by a personal computer which is a Microsoft Windows-based system. An animated status screen provides real-time monitoring of the extraction process. Table II gives the SFE conditions for the HP extractor. 

Agemian and Bedak [42] have described a semi-automated method for the determination of total arsenic in soils. Chappell et al. [43] have described an inexpensive but effective method for the quantitative determination of arsenic species in contaminated soils. Chappell found that the extraction efficiency varied with the ratio of soil to acid and with the concentration of the acid. Rurikova and Beno [346] accomplished speciation of arsenic(III) and arsenic(V) in soils by cathodic stripping voltammetry. Wenclawiak and Krah [347] used reactive supercritical fluid extraction in speciation studies of inorganic and organic arsenic in soils. In this method, derivatisation with thioglycollic acid methyl ester was performed in supercritical carbon dioxide. Various other workers have discussed the determination of arsenic in soils [44-46]. 

The method of analysis involves extraction of 1 L of aqueous sample (liquid-liquid extraction) or 25 g of soil (sonication or Soxhlett extraction or supercritical fluid extraction) or an appropriate amount of the sample with methylene chloride. The extract is dried, concentrated to a volume of 1 mL, and injected into a capillary GC column for separation and detection by FID. For quantitation, the area or height response of all peaks eluting between C-10 and C-28 are summed and compared against the chromatographic response of the same peaks in a 2 Fuel or Diesel Oil standard. A 10-component n-alkanes mixture containing even numbered alkanes ranging between 10 and 28 C atoms has been recommended as an alternative calibration standard. These alkanes occur in all types of diesel oils, and each compound constitutes approximately a 1% total mass of diesel fuel, i.e., 1 g of diesel fuel contains about 10 mg each of any of the above alkanes. Therefore, when using the latter as a calibration standard, the result must be multiplied appropriately by 100. 

Fundamental studies on the adsorption of supercritical fluids at the gas-solid interface are rarely cited in the supercritical fluid extraction literature. This is most unfortunate since equilibrium shifts induced by gas phase non-ideality in multiphase systems can rarely be totally attributed to solute solubility in the supercritical fluid phase. The partitioning of an adsorbed specie between the interface and gaseous phase can be governed by a complex array of molecular interactions which depend on the relative intensity of the adsorbate-adsorbent interactions, adsorbate-adsorbate association, the sorption of the supercritical fluid at the solid interface, and the solubility of the sorbate in the critical fluid. As we shall demonstrate, competitive adsorption between the sorbate and the supercritical fluid at the gas-solid interface is a significant mechanism which should be considered in the proper design of adsorption/desorption methods which incorporate dense gases as one of the active phases. 

For the toluene extractions, the work-up procedure was as described previously (j> ). In the supercritical water experiments, most of the extract was insoluble in water, after cooling and lowering of the pressure, and precipitated out in the condenser and receiver from which it was collected by washing with acetone and then THF. The remainder of the extract was found in the aqueous suspension which was evaporated to dryness on a rotary evaporator and the residue extracted with acetone and THF. The solvents were removed under reduced pressure from the combined acetone and THF solutions to give the total extract. This was then extracted with hot toluene and the cooled solution filtered to give the preasphaltene fraction. After the toluene was removed under reduced pressure from the filtrate, the residue was re-dissolved in a small volume of toluene and a 20 fold excess of pentane added to precipitate the asphaltene which was filtered off. The pentane and toluene were then removed from the filtrate under reduced pressure to give the oil. For the NaOH extractions, the NaOH solutions were neutralised with HC1. The insoluble extract was washed with water and then extracted with THF. Removal of the THF gave the total extract. 

The ratio of solvent solute is also important as noted by Stuart and Wills (2000b). They noted that as the solvent solute ratio increased from 2 1 to 8 1, alkamide in the extract increased from 37 to 68% for the roots and from 27 to 53% for the aerial parts. As the ratio of solvent solute increases, so does the ethanol level thus enhancing alkamide recovery. In SF extractions, the addition of ethanol (10-12%) as a modifier to the supercritical carbon dioxide enhances the total extract or oleoresin yield but does not significantly influence the alkamide concentrations (Catchpole et al., 2002). Sun et al. (2002) also noted that a 5% ethanol addition did not significantly affect the alkamide recovery. 

Supercritical fluid extraction(SFE) combined with five types of bioassay tests is extensively applied to explore some bioactive substances from thirty types of natural resources available in Korean peninsula. To evaluate comparatively the economic viability of the SFE, organic liquid solvent extraction(LSE) with n-hexane, chloroform and methanol was also performed. To characterize the extracts, GC and HPLC are employed. Also, the column chromatography is used to isolate some target compounds from the total extracts. For all the samples, the optimum SFE condition for each sample which gives maximum yield and cytotoxicity were discussed. 

In the Orient, numerous natural products have long been used in folk medicine. Also, in recent years some pharmaceutical industries and universities in Korea are placing their efforts on the quantification of cytotoxic phytochemicals from the natural resources. As a part of those efforts, the present authors are involved on the two-fold critical evaluations of the possible implementation of the supercritical fluid extraction(SFE) to obtain extracts from the natural resources one is the establishment of the optimum SFE condition for each sample resource which gives maximum extraction yield and cytotoxicity, and the other is the high-purity isolation of some specific compounds from the SFE total extracts. 

Supercritical fluid extraction and microwave-assisted extraction have been recently applied to the extraction of essential oils. Both techniques are based on the application of high pressures and temperatures for the total extraction of analytes. Supercritical fluid extraction has... 

Sample preparation represents a formidable challenge in the chemical analysis of the real-world samples. Not only is the majority of total analysis time spent in sample preparation, but also it is the most error-prone, least glamorous, and the most labor-intensive task in the laboratory. The components to be separated from the matrix are usually taken up with an auxiliary substance such as a carrier gas, an organic solvent, or an adsorbent. These separation processes can be regarded as extraction procedures (i.e., liquid-liquid extraction, liquid-solid extraction, Soxhlet extraction, solid-phase extraction, supercritical fluid extraction, solid-phase microextraction, etc.). 

There are many publications showing the applications of SFE to the determination of polymer additives. Antioxidants such as Irganox 2246, BHT and others, as well as UV stabilizers such as Tinuvin P, have been effectively extracted with supercritical CO2. Extraction conditions varied from 15 to 25 MPa at 60°C and with a total time of 30 min [1], If microwaves are applied to extract these compounds, a mixture of sol-... 

The crushed seeds of Crotalaria spectabilis were first contacted with supercritical carbon dioxide and, as expected, the oils comprising the bulk of the seed material were preferentially extracted. The addition of ethanol and water as co-solvents in the fluid phase led to the appearance of monocrotaline in the extract. Monocrotaline contents as high as 24% of the total extract could be obtained with carbon dioxide-ethanol mixtures. 

Supercritical CO. Extraction Results. The extent of lipid extraction from freeze dried algae was influenced by the total COj volume passed through the system, by the operating pressure, and by the ratio of non-polar to polar lipids present in the batches. 

Selective extracts obtained in the pressure range around 100 bar contain only small volatile molecules like mono- and sesquiterpenes. Thus they are similar to conventional steam distillates (essential oils). Total extracts recovered in the pressure range around 300 bar contain in addition higher molecular weight lipophilic constituents like fatty oils, resins and waxes and thus are comparable to classical hexane extracts (oleoresins). Consequently supercritical C02-extraction is the only procedure which produces completely different extracts from one and the same raw material on the same equipment. 

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