Gas extraction techniques

Kelley S, Turner G, Butterfield AW, Shepherd TJ (1986) The source and significance of argon isotopes in fluid inclusions from areas of mineralization. Earth Planet Sci Lett 79 303-318 Kendrick MA, Burgess R, Pattrick RAD, Turner G (2001a) Halogen and Ar-Ar age determinations of inclusions within quartz veins from porphyry copper deposits using complementary noble gas extraction techniques. Chem Geol 177 351-370... 

This procedure was compared with sequential extractive techniques employing alkaline hydrolysis of dried plant tissue followed by extraction of the acidified mixture with ethyl acetate. Fractions were individually evaluated for phytotoxic properties. Selected fractions from those showing a positive response were analyzed by gas-liquid chromatography. Structural identification and characterization of the individual components in these selected fractions were accomplished by gas chromatography-mass spectrometry. 

The classical Soxhlet extraction technique has seen some improvements, mainly in the submersion of the whole extraction thimble into the boiling extraction solvent, degree of automation, and in reduction of solvent volume. In a recently introduced universal extraction system (Biichi) four SLE methods are contained in one device Soxhlet Standard, Soxhlet warm, hot extraction and continuous flow. It is possible to use solvents with boiling points of up to 150 °C inert gas can be supplied during the extraction process. 

Various models of SFE have been published, which aim at understanding the kinetics of the processes. For many dynamic extractions of compounds from solid matrices, e.g. for additives in polymers, the analytes are present in small amounts in the matrix and during extraction their concentration in the SCF is well below the solubility limit. The rate of extraction is then not determined principally by solubility, but by the rate of mass transfer out of the matrix. Supercritical gas extraction usually falls very clearly into the class of purely diffusional operations. Gere et al. [285] have reported the physico-chemical principles that are the foundation of theory and practice of SCF analytical techniques. The authors stress in particular the use of intrinsic solubility parameters (such as the Hildebrand solubility parameter 5), in relation to the solubility of analytes in SCFs and optimisation of SFE conditions. 

Complex matrixes typically cannot be analysed directly to obtain the selectivity and sensitivity required for most trace analysis applications. To circumvent this problem, solid-phase micro extraction techniques were used to preconcentrate analytes selectively prior to gas chromatography/ion trap mass spectrometry analysis. 

Krause, A.A. and Niemczyk, H.D. Gas-liquid chromatographic analysis of chlorthal-dimethyl herbicide and its degradates in turfgrass thatch and soil using a solid-phase extraction technique, J. Environ. Sci Health, B25(5) 587-606, 1990. Kresheck, G.C., Schneider, H., and Scheraga, H.A. The effect of DzO on the thermal stability of proteins. Thermod3mamic parameters for the transfer of model compounds from HzO to DzO, J. Phys. Chem., 69(9) 3132-3144, 1965. 

Often the products of nuclear reactions have very short half-lives. This is especially true for the heaviest elements obtained by bombardment of heavy targets with heavy ions. To identify and characterize such short-lived nuclides, fast separations are required solvent extraction techniques are well suited to provide the required fast separations. For example, the SISAK method [68] has been successfully used in conjunction with in-line gas jet separators at heavy ion accelerators to identify short half-life actinide isotopes produced by collision of heavy atoms. The Sisak method involves use of centrifugal contactors, with phase residence times as low as tenths of a second, in conjunction with in-line radiometric detection equipment. 

A new, fast, sensitive, and solventless extraction technique was developed in order to analyze beer carbonyl compounds. The method was based on solid-phase microextraction with on-fiber derivatization. A derivatization agent, 0-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBOA), was absorbed onto a divinyl benzene/poly(dimethylsiloxane) 65- xm fiber and exposed to the headspace of a vial with a beer sample. Carbonyl compounds selectively reacted with PFBOA, and the oximes formed were desorbed into a gas chromatograph injection port and quantified by mass spectrometry. This method provided very high reproducibility and linearity When it was used for the analysis of aged beers, nine aldehydes were detected 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, pentanal, hexanal, furfural, methional, phenylacetaldehyde, and (E)-2-nonenal. (107 words)... 

Fuel. The nuclear fuel cycle starts with mining of the uranium ore, chemical leaching to extract the uranium, and solvent extraction with tributyl phosphate to produce eventually pure uranium oxide. If enriched uranium is required, the uranium is converted to the gaseous uranitim hexafluoride for enrichment by gaseous diffusion or gas centrifuge techniques, after which it is reconverted to uranium oxide. Since the CANDU system uses natural uranium, I will say no more about uranium enrichment although, as I m sure you appreciate, it is a major chemical industry in its own right. 

Following extraction and cleanup, anabolic compounds can be separated by thin-layer, liquid, or gas chromatographic methods. Thin-layer and gas chromatography are the principal separation techniques prior to the end-point measurement. Because most molecules are stable and volatile enough after appropriate derivatization, liquid chromatography has not been able to keep pace with gas chromatography techniques. 

The gas chromatographic technique is explained on the basis of a physical process with correlations to distillation,liquid-liquid extraction, countercurrent distribution, and other separation techniques to give the reader a better appreciation of the basic process of chromatography. Explanation of fundamentals is followed by chapters on columns and column selection, theory and use of detectors, instrumentation necessary for a gas chromatographic system, techniques used for qualitative and quantitative analyses, and data reduction and readout. Subsequent chapters cover specialized areas in which gas chromatographic literature is more scattered and data collection and evaluation are more important. 

M Amelio, R Rizzo, F Varazini. Determination of sterols, erythrodiol, uvaol and alkanols in olive oils using combined solid-phase extraction, high-performance liquid chromatographic and high-resolution gas chromatographic techniques. J Chromatogr 606 179-185, 1992. 

The hydride generation ICP-mass spectrometric technique [75] had a sensitivity of 6.4 ng/g selenium in plant material and was applied to digests of corn, kale and rice. In the isotope dilution mass spectrometric technique [77], the samples were spiked with 76-selenium solution and digested on a heating block at 150 °C with a mixture of nitric acid and hydrogen peroxide. Solid-phase microextraction was used to extract selenium from plant material prior to the gas chromatographic techniques [76]. See also Sects. 7.34.1 and 7.34.2. 

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