Extracting organic compounds

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... 

Strachan WMJ. 1974. Chloroform-extractable organic compounds in the international great lakes. In Keith LH, ed. Identification and Analysis of Organic Pollutants in Water. Ann Arbor, MI Ann Arbor Science, 479, 487-488. 

SPME can be used to extract organic compounds from a solid matrix as long as target compounds can be released from the matrix into the headspace. For volatile compounds, the release of analytes into the headspace is relatively easy because analytes tend to vaporise once they are dissociated from their matrix. For semi-volatile compounds, the... 

The volatile substances were extracted from portions of 0. lg hair using solid-phase micro extraction (SPME). The method uses a fibre coated with an adsorbent that can extract organic compounds from the headspace above the sample. Extracted compounds are desorbed upon exposure of the SPME fibre in the heated injector port of a gas chromatograph (GC). 

Organic solvents at STP and under supercritical conditions are the most common extractants for soil organic matter. Supercritical C02 and, to a lesser extent, N20 have also been used to extract both native and organic contamination from soil. Humus is extracted using aqueous solutions, but otherwise, water is rarely used to extract organic compounds from soil. A list of common soil organic matter extractants is given in Table 12.2. 

Carbon dioxide is the most common inorganic extractant used for the extraction of organic compounds in soil. Under pressure, it remains in the liquid state and can be used to extract organic compounds from soil. When the pressure is released, the carbon dioxide becomes a gas and is thus removed from the extracted components. An additional benefit is that liquid carbon dioxide is converted to gas at relatively low temperatures, thus limiting the loss of... 

Common surfactants such as Tween, Triton,5 and sodium dihexyl sulfosuc-cinate, among many others, have been used to extract organic compounds from soil. In the field, they have been particularly useful in the remediation of soils contaminated with halogenated organic compounds, oils, and other hydrocarbon compounds [24],... 

Lopez-Avila V, Bauer K, Milanes J, et al. 1993. Evaluation of Soxtec extraction procedure for extracting organic compounds from soils and sediments. J AOAC International 76 864-880. 

Liquid-Solid Extraction Organic Compounds in Drinking... 

Ethers are good for extracting organic compounds from aqueous solutions because the density of ethers is less than water, causing the ether layer to float on top of the water layer. 

Environmental Waters and Waste Waters. This medium is multi-phasic and covers a wide range of constituents, including aqueous and nonaqueous liquids and dissolved and suspended solids. The protocol (Figure 3) is limited to solvent-extractable organic compounds however, not all compounds will be recoverable and/or stable under the protocol s methods. An overall scheme was developed and incorporated in the protocol to link the variety of components of this medium to the other protocols. 

Solvent extraction of the plant material is still by far the most popular method for extracting organic compounds or organometallic compounds from plant materials, crops and fruit and vegetables prior to final analysis, see Table 1.5. 

Guo, Z.G., Sheng, L.F., Feng, J.L., Fang, M., 2003b. Seasonal variation of solvent extractable organic compounds in the aerosols in Qingdao, China. Atmos. Environ. 37, 1825-1834. 

Zheng, M., Fang, M., Wang, F., To, K.L., 2000. Characterization of the solvent extractable organic compounds in PM2.5 aerosols in Hong Kong. Atmos. Environ. 34, 2691-2702. 

Rubio, S. and D. Perez-Bendito. 2003. Supramolecular assemblies for extracting organic compounds. Trends Anal. Chem. 22 470-485. 

Solvent selection depends largely on the nature of the analytes and the matrix. Although the discussions in Chapter 2 can be used as a guideline to account for the solvent-analyte interactions, the matrix effects are often unpredictable. There is no single solvent that works universally for all analytes and all matrices. Sometimes, a mixture of water-miscible solvents (such as acetone) with nonmiscible ones (such as hexane or methylene chloride) are used. The water-miscible solvents can penetrate the layer of moisture on the surface of the solid particles, facilitating the extraction of hydrophilic organics. The hydrophobic solvents then extract organic compounds of like polarity. For instance, hexane is efficient in the extraction of nonpolar analytes, and methylene chloride extracts the polar ones. 

It should be noted that microwave-assisted extraction (MAE) discussed in this chapter is different from microwave-assisted acid digestion. The former uses organic solvents to extract organic compounds from solids, while the latter uses acids to dissolve the sample for elemental analysis with the organic contents being destroyed. Microwave-assisted digestion of metals is covered in Chapter 5. 

Liquid-liquid extraction (LLE) is the traditional method to extract organic compounds from water. The low molecular weight compounds are transferred from one liquid phase to another immiscible or partially immiscible liquid by shaking them in a separation funnel. LLE is still a common method, but has several drawbacks such as low selectivity, labor intensivity, and the use of large amount, of organic solvent. LLE has been used to extract hydrolysis products of degradable polyesters such as PLA and its copolymers from the buffer solution [115]. 

This method is suitable for the determination of extractable organic compounds at 0.05 to 100 mg/kg but is most appropriate for organic compounds with a vapor pressure greater than 10 mm Hg at 25°. 

Supercritical fluids such as carbon dioxide can be used as solvents to extract organic compounds from aqueous solutions. In order to achieve recoveries of these products often in low concentration, cosolvents as methanol or other alcohols have been added to improve the solubility and the selectivity of the primary fluid. To optimize the extract recovery, the knowledge of phase equilibria of the ternary system carbon dioxide-methanol-water is required at different temperatures and pressures. 

Headspace solid-phase microextraction (HS-SPME) is a rapid and solvent-free modification of the SPME technique in which a fine fused silica fiber with a polymeric coating is inserted into a headspace gas to extract organic compounds and directly transfer them into the injector of a gas chromatograph for thermal desorption and analysis. In this technique, the quantity of compounds extracted onto the fiber depends on the polarity and thickness of the stationary phase as well as on extraction time and concentration of volatiles in the sample. 

Most of the carbon in the Allende C3V chondrite is present in elemental form, rather than as polymer or extractable organic compounds (Breger et al., 1972). It was originally called amorphous carbon , since it is amorphous to x-rays. However, recent work shows it to be carbyne (Whittaker et al., 1980 Hayatsu et al., 1980b) a triply bonded, linear allotrope of elemental carbon. Carbyne exists in at least 10 varieties, ranging between graphite and diamond in hardness and density (Whittaker, 1978 and references therein). 

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