Separation selectivity, solvent extraction

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. 

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. 

Over thirty different elements have been determined in medical and biological materials by atomic absorption spectroscopy. The popularity of the technique is due to a number of factors, including sensitivity, selectivity, and ease of sample preparation. With biological fluids, often no preparation at all is required. The techniques employed usually involve simple dilution of the sample with water or with an appropriate reagent to eliminate interference. Alternatively, the element to be determined is separated by solvent extraction. Either an untreated sample, a protein free filtrate, or an ashed sample is extracted. 

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... 

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> ... 

The selective extraction of a radioactive nuclide as a nonpolar compound or complex from an aqueous solution by an immiscible organic solvent Is frequently the most satisfactory method for making a fast radiochemical separation In either macro or trace concentrations. Separations by solvent extraction are simple, convenient, clean, and rapid. They usually require apparatus as uncomplicated as a separatory funnel and may readily be adapted to remote handling procedures. 

Recovery of vanadium with peroxygens involves both oxidation and com-plexation. In solution, conversion of lower oxidation states into vanadium(V) allows separation by solvent extraction (Figure 6.18).269 This chemistry can be used for vanadium by-products in uranium extractions. With hydrogen peroxide, vanadium(IV) is not oxidized in acidic solution, but rather in alkaline conditions, e.g. 60 °C at pH 9 (Figure 6.19).270 Use of excess hydrogen peroxide readily forms peroxo complexes and this is of value in selective dissolution of vanadium from secondary sources. 

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. 

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. 

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... 

PA-6 (100-0) / SAN (0-100) or ABS / SMA (14 or 25% MA) (0-10) or imidized acrylate copolymer with 1 % MA content or SAN-co-IPO (1% oxazoline) double-extrusion on SSE / torque rheometry / mechanical properties / selective solvent extraction / SEM / lap shear adhesion / SAN + SMA double-extruded in separate step followed by extrusion with PA Triacca etal., 1991... 

To simplify asphalt analysis, a common practice is to fractionate the material to divide it into groupings of simpler constitution. A large number of methods have been proposed, but most are based on either selective solvent extraction or chromatographic separation or, frequently, a combination of solvent precipitation and chromatographic separation. 

PA/PS blends have also been compatibilized through block copolymer formation between amine-terminated PA and anhydride-terminated PS. Anhydride end-groups were introduced into PS through reaction of either anion-terminated PS or hydroxy-terminated PS with trimellitic anhydride acid chloride. For example, Park et al. (1992) blended 80 parts PA-6 with 10-16 parts PS and 4-10 parts anhydride-terminated PS in an internal mixer at 240 °C. The blends were characterized by torque rheometiy, SEM, selective solvent extraction, DSC, morphological stability to annealing, and lap shear adhesion. The effect of mixing protocol on properties was studied. Properties were also compared to those for blends compatibilized by added PA-PS graft copolymer that had been synthesized in a separate step. 

It is seen that the spectrum of a sample may consist of the basic polymer spectrum on which are superimposed the spectra of the additives, fillers, lubricants, fire retardants, catalyst residues, contaminants, etc. in proportions relating to their concentrations in the sample. Hence, there are many reasons why difficulties may be encountered when examining polymeric samples. Obviously, there are advantages if the problem can be made simpler, perhaps by separation, eg. use of chromatography or solvent extraction etc. With certain polymeric samples, it may be possible to use selective solvent extraction but, in some of these samples, this may result in fine particles of carbon black remaining in suspension and being difficult to remove. 

Although it is not widely used, selective solvent extraction is practiced by small operations to neutralize very high FFA content oils. Selective solvent or liquid-liquid extraction of FFAs from TAGs is based on the differences in solubility of FFA and TAG in various organic solvents. Phase separation and selective extraction of FFAs (0-50%) in peanut oil could be achieved by use of aqueous isopropyl alcohol (IPA) (75% and 80%). Phase separation was found to be depended on the fatty acid content in the mixture and... 

Pu (86 years) is formed from Np. Pu is separated by selective oxidation and solvent extraction. The metal is formed by reduction of PuF with calcium there are six crystal forms. Pu is used in nuclear weapons and reactors Pu is used as a nuclear power source (e.g. in space exploration). The ionizing radiation of plutonium can be a health hazard if the material is inhaled. 

The principal direct appHcation of furfural is as a selective solvent. It is used for separating saturated from unsaturated compounds in petroleum refining, for the extractive distillation of butadiene and other hydrocarbons in the manufacture of synthetic mbber and for the production of... 

Ion exchange (qv see also Chromatography) is an important procedure for the separation and chemical identification of curium and higher elements. This technique is selective and rapid and has been the key to the discovery of the transcurium elements, in that the elution order and approximate peak position for the undiscovered elements were predicted with considerable confidence (9). Thus the first experimental observation of the chemical behavior of a new actinide element has often been its ion-exchange behavior—an observation coincident with its identification. Further exploration of the chemistry of the element often depended on the production of larger amounts by this method. Solvent extraction is another useful method for separating and purifying actinide elements. 

The choice of separation method to be appHed to a particular system depends largely on the phase relations that can be developed by using various separative agents. Adsorption is usually considered to be a more complex operation than is the use of selective solvents in Hquid—Hquid extraction (see Extraction, liquid-liquid), extractive distillation, or azeotropic distillation (see Distillation, azeotropic and extractive). Consequentiy, adsorption is employed when it achieves higher selectivities than those obtained with solvents. 

Unique adsorption selectivities are employed in the separation of Cg aromatic isomers, a classical problem that caimot be easily solved by distillation, crystallisation, or solvent extraction (10). Although -xylene [106-42-3] can be separated by crystallisation, its recovery is limited because of the formation of eutectic with / -xylene [108-58-3]. However, either -xylene, / -xylene, (9-xylene [95-47-6] or ethylbensene [100-41-4] can be extracted selectively by suitable modification of seoUtic adsorbents. 

Selectivity. Solvent selectivity is intimately linked to the purity of the recovered extract, and obtaining a purer extract can reduce the number and cost of subsequent separation and purification operations. In aqueous extractions pH gives only limited control over selectivity greater control can be exercised using organic solvents. Use of mixed solvents, for example short-chain alcohols admixed with water to give a wide range of compositions, can be beneficial in this respect (6). 

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