Selective solvent extraction

Several standard methods for the quantitative analysis of food samples are based on measuring the sample s mass following a selective solvent extraction. For example, the crude fat content in chocolate can be determined by extracting with ether for 16 h in a Soxhlet extractor. After the extraction is complete, the ether is allowed to evaporate, and the residue is weighed after drying at 100 °C. This analysis has also been accomplished indirectly by weighing a sample before and after extracting with supercritical GO2. 

Solvent extraction is generally employed in analysis to separate a solute (or solutes) of interest from substances which interfere in the ultimate quantitative analysis of the material sometimes the interfering solutes are extracted selectively. Solvent extraction is also used to concentrate a species which in aqueous solution is too dilute to be analysed. 

Table II. Selective Solvent Extraction, Calculated Mc PDMAAm, and Differential Scanning Calorimetry Data...

Cleare, M. J. Grant, R. A. Charlesworth, P. Separation of the platinum-group metals by use of selective solvent extraction techniques. Extr. Metall. 81, Pap. Symp. 1981, 34-41. 

Phenolsolvan A process for extracting phenols from coke-oven liquor and tar acids from tar by selective solvent extraction with di-isopropyl ether (formerly with -butyl acetate). Developed by Luigi in 1937. 

Thorium coprecipitated from acidified sample with Fe(OH)3, clean-up Th by selective solvent extraction, coprecipitated with Al(OH)3 and develop color by Arsenazo III reagent. After color development, coprecipitate Th with LaF3. 

Obviously to remove large amounts of asphaltic materials, substantial quantities of clay would be required in both the percolation and hot contacting methods, and the adsorption process then may become uneconomical in the treating of raw residua. With the exception of residual oils containing low concentrations of asphalts, oils to be treated with clay generally receive some pretreatment—for example, with sulfuric acid followed by neutralization of the acid oil, or selective solvent extraction. 

Separation of crude lipid extracts into individual lipid classes is difficult and time-consuming. In some cases a crude separation of lipids can be attained by selective solvent extraction. For more extensive purification of lipids, the researcher must turn to chromatography. Chromatographic methods can both resolve a complex lipid mixture into the various classes of lipids and separate the individual components of a single class of lipids. 

Polarographic methods have been extremely useful for the determination of the urinary excretion of the 1,4-benzodiazepines. An assay that employs selective solvent extraction and acid hydrolysis of diazepam and its major metabolites, iV-desmethyldiazepam and oxazepam, to their respective benzophe-nones has been employed to measure the urinary excretion of diazepam [183]. A pulse polarographic assay has been reported that will measure the urinary excretion of bromazepam following a single 12-mg dose [184]. The assay employs selective extraction of bromazepam and the 2-amino-5-bromobenzoyl-pyridine metabolite from the deconjugated metabolites, 3-hydroxybromazepam and 2-amino-3-hydroxy-5-bromobenzoylpyridine, into separate diethyl ether fractions. The residues of the respective extracts are dissolved in phosphate buffer (pH 5.4) and analyzed by pulse polarography, which yields two distinct... 

In this work both the prepolymers and the block copolymers were prepared in bulk and, therefore, it is not surprising that a large amount of homopolymer was obtained74,75. The subsequent characterization of the products was carried out, after a selective solvent extraction process, using NMR, IR, osmometry, viscosimetry and GPC. 

This reaction has the characteristics of a dead end polymerization, and the conversion of monomeric MMA to polymer can be controlled via the azo content of the polystyrene and the reaction temperature. The separation of the reaction products into homopolymer and block copolymer was achieved by selective solvent extraction thus, cyclohexane was used to dissolve the homopolystyrene, acetonitrile the homo-poly-MMA and the copolymer was completely soluble in benzene. The compositition of the crude product as a function of the ratio of MMA/prepolymer is shown in Fig. 4.5 58> ... 

Selective solvent extraction of volatiles will remove volatiles with very high yields although the extracts are always contaminated with non-volatile components. For example, acetonitrile extraction followed by co-extraction with pentane was used by Vemin (38). In our experiments the direct extraction of crushed crackers with Freon 113 or ethyl acetate contained too much residual lipid. Distillation of the solvent yielded a lipid concentrate low in aroma volatiles. Attempts to use gel filtration (Bio-Beads S-X12 from Bio-RAD) to remove the lipids but retain the odorous substances were also unsuccessful. 

Isolation of graft copolymers from homopolymers and unreacted cellulose nitrate was conducted by using selective solvent extraction technique. 

A patented process has been developed for the production of electrode binder pitch from petroleum-based materials. Carbon anodes produced from the petroleum-based pitch and coke have been used successfully on a commercial scale by the aluminum industry. One stage of the process involves the pyrolysis of a highly aromatic petroleum feedstock. To study the pyrolysis stage of the process a small, sealed tube reactor was used to pyrolyze samples of feedstock. The progress of the reaction is discussed in terms of the formation of condensed aromatic structures, defined by selective solvent extraction of the reaction product. The pyrolysis of the feedstock exhibits a temperature-dependent induction period followed by reaction sequences that can be described by first-order kinetics. Rate constants and activation energies are derived for the formation of condensed aromatic structures and coke. 

The subdivision of the sample by selective solvent extraction is illustrated in the following scheme. 

This concept is an oversimplification of the complexity of the reaction system it is unlikely that the intermediate products are formed exclusively in sequential fashion, as suggested in Equation 4. The number of intermediate products in the sequence leading to coke is uncertain, but there are at least two—the / -resin precursors and the / -resins. As indicated earlier in the discussion, the / -resin precursors are probably found in the benzene soluble fraction. In work that will not be discussed in detail here, some evidence has been found for the existence of the / -resin precursors. When these are preformed in the decant oil and that material pyrolyzed, the induction period shown for -resins in Figure 1 is absent. In speculating on the number of distinct intermediate products in the reaction chain, we emphasize that the technique of selective solvent extraction can be a poor discriminator between the different sizes of condensed aromatic systems. We are therefore limited in our interpretation of the reaction sequences by not being able to identify the products of each stage. Thus, the reactions shown in Equations 5, 6, and 7 may represent the main sequence of reactions, but it is virtually impossible to isolate the products formed by stepwise addition of the decant oil aromatics. 

For liquid-liquid extraction, a selective solvent is required, which shows only a partial miscibility with the liquid stream to be separated. In Figure 2, a typical multistage counter-current liquid-liquid extraction process is shown for the separation of aliphatics from aromatics. In this process, with the help of the selective solvent (extractant) the desired components (aromatics) are extracted from the feed stream. Distillation is typically used for the recovery of the selective solvent from the extract and raffinate stream leaving the extraction column. 

The diverse production methods for high-purity tungsten are summarized in Fig. 5.39. The raw material is always APT with different purity depending on the uranium and thorium content. It depends on the ore deposit whether these two elements are present or not. If the concentrations are unacceptably high after dissolution, a selective solvent extraction process removes the main portion of these two elements. 

Although quite complex hybrid block copolymer architectures can now be synthesized, obtaining these materials in a state of high purity typically requires additional measures. As discussed above, many of the hybrid copolymers contain homopolymer impurities, which must be removed by selective solvent extractions or fractional precipitation when possible. Since conventional NCA polymerizations also usually give polypeptide segments with large chain length distributions, these samples are ideally also fractionated... 

New technology developed continuous operations so that plants became much larger and could make more consistent quality products at lower cost. These new process methods were based on the use of solvents continuous selective solvent extraction for aromatic removal was the process which replaced acid treatment and continuous solvent de-waxing replaced the very labour-intensive cold-pressing technique. Technology has developed further in the last 40 years. Catalytic hydrogenation processes have become the normal method for finishing base oils and a more severe form is used as an alternative to solvent extraction to control aromatics content. 

Specific volumes of stock solutions of polybutadiene (5% w/v) in n-heptane were introduced in test tubes or 500 ml three neck flasks charged with monomer and solvent (n-heptane and ethyl chloride) and thermo-equilibrated. Aliquots of Et2 A1C1 followed by f-BuCl were added. Reactions were terminated by addition of methanol. Polymers were recovered by precipitation in methanol, filtered and dried. Grafts and homopolymers were separated by selective solvent extraction using acetone and n-pentane. Pure grafts containing 15-60 wt% polystyrene were obtained. 

Solvent extraction is widely used for the isolation of single chemical species prior to a determination and the most important application of the technique is in the determination of metals present as minor and trace constituents in a variety of inorganic and organic materials. Thus the analysis of metallurgical and geological samples as well as petroleum products, foodstuffs, plant and animal tissue, and body fluids, in regard to their respective content of metals is carried out by selective solvent extraction and spectrometric determination of the metals as coloured complexes. 

Dipolar addition of nitrile sulfides to tetracyanoethylene produces mixtures of products, from which the mono- (353) and bis-l,2,4-thiadiazoles (354 and 355) are separable by selective solvent extraction. Equimolar... 

SEM / selective solvent extraction / FTIR / DMTA / WAXS thermal redistribution in internal mixer at 260°C / NMR / TLC / DSC internal mixer at 240°C / torque rheometry / SEM / GPC / mechanical properties / effects of mixing time / effects of PA amine and acid end-group concentrations internal mixer at 240°C / selective solvent extraction /... 

Polyarylate (90-10) / PETG (10-90) internal mixer at 235°C / torque variation / DSC / NMR / FTIR / selective solvent extraction Oh eta/., 1997... 

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