Extraction selectivities

Principles and Characteristics A sample can contain a great number of compounds, but analysts are usually interested only in the qualitative presence (and the quantitative amount) of a small number of the total compounds. Selectivity is an important parameter in analytical separations. The total analytical process clearly benefits from selectivity enhancement arising from appropriate sample preparation strategies. Selective separation of groups or compound classes can simplify a mixture of analytes before analysis, which in turn enhances analytical precision and sensitivity. Selective fractionation, in some cases, allows easier resolution of the compounds of interest, so analysts can avoid the extreme conditions of high-resolution columns. 

Selectivity in extraction can be defined as the ability to extract only the analyte(s) of interest, while leaving 

Selective extractions are not only of interest to solvent extraction, but also to thermal extractions. For example, selective in situ detection of polymer additives is possible using laser mass spectrometry, notably UV laser desorption/MS [561]. The proper matching of extraction technique to a sample determines the success of the operation and enhances the precision and accuracy of the analysis. 

Analysis by 13C NMR has shown that the 7 and 10 MPa scC02 extracts of sorbitan ester (a complex 

With suitable adjustments to the temperature, also subcritical water extraction (SWE) or pressurised hot water extraction (PHWE) allows selective extraction of polar (chlorinated phenols), low-polarity (PCBs and PAHs) and nonpolar (alkanes) organic compounds from industrial soils [418]. 

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Two further examples of type I ternary systems are shown in Figure 19 which presents calculated and observed selectivities. For successful extraction, selectivity is often a more important index than the distribution coefficient. Calculations are shown for the case where binary data alone are used and where binary data are used together with a single ternary tie line. It is evident that calculated selectivities are substantially improved by including limited ternary tie-line data in data reduction. 

Fig. 1. Liquid—Hquid extraction selectivity 0> olefins , paraffins.

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. 

AH commercial copper extractants selectively extract copper from weakly acidic aqueous leach solutions by the general reaction... 

Cytochalasin B (from dehydrated mould matter) [14930-96-2] M 479.6. Purified by MeOH extraction, reverse phase Cl8 silica gel batch extraction, selective elution with 1 1 v/v hexane/tetrahydrofuran, crystn, subjected to TLC and recrystallised [Lipski et al. Aruil Biochem 161 332 1987]. 

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. 

Three classes of carbamoylmethylphosphoryl extractants were studied for their ability to extract selected tri-, tetra-, and hexavalent actinides from nitric acid. The three extractants are dihexyl-N,N-diethylcarbamoylmethylphosphonate (DHDECMP), hexyl hexyl-N,N-diethylcarbamoylmethylphosphinate (HHDECMP), and octyl(phenyl)-N,N-diisobutylcarbamoylmethylphos-phine oxide 0< >D[IB]CMP0. The above three extrac-trants were compared on the basis of nitric acid and extractant dependencies for Am(III), solubility of complexes on loading with Nd(III) and U(VI), and selectivity of actinide(III) over fission products. 

Enzyme-mediated extractions — Selective enzyme-mediated extraction of cap-sacinoids and carotenoids from Chili Guajillo Puja using ethanol as a solvent was... 

Tables 3.4 and 3.16 show the main characteristics of SFE. The technique has important advantages especially in cases where loss or degradation of target analytes is likely to occur. The generation of oxidation products will not present any problems. Some authors have claimed that selectivity can be introduced in modern SFE instrumentation [320]. Extraction selectivity and efficiency can be controlled by the nature of the supercritical medium (Selectivity 1). Another opportunity for selectivity concerns the density of the...

Extraction selectivity (tuneable solvent strength p, T, modifier)... 

Pandey, B. D. Bagchi, D. Kumar, V. Co extraction—selective stripping for the recovery of nickel and copper from the leach liquor of ocean nodules. Can. J. Chem. Eng. 1994, 72, 631-636. 

Oligomerization of nucleobases can be advantageous to reinforce the H-bonding supramolecular motifs when supramacromolecular polymers are desired. Moreover the different interconverting outputs that may form by oligomerization define a dynamic polyfunctional diversity which may be extracted selectively under the intrinsic stability of the system or by interaction with external factors by polymerization in the solid state. 

Efficiency of Extraction. Selectivity of Extraction. Extraction Systems. Extraction of Uncharged Metal Chelates. Methods of Extraction. Applications of Solvent Extraction. 

Activated carbon, activated charcoal. A form of carbon that has (a) a porous or honeycomb-like structure and therefore a large surface area and (b) high adsorbdvity (certain molecules stick to it). Used to strip out impurities or extract selected compounds. 

In the European Community (EC) countries, two additional criteria for extractant selection are thought to be important. The first is related to... 

Table 12.5 Comparison of the Extraction Selectivity of Two p-terr-butylcalix(6)arene, Uranophiles, Bearing 6 Carboxylates 1(6) or 6 Hydroxamates 2(6) Groups on the Lower Rim...

Finally, supercritical fluid chromatography, in which a supercritical fluid is used as the mobile phase, was introduced by Klesper [164-166]. SFE directly coupled to SFC provides an extremely powerful analytical tool. The efficient, fast and selective extraction capabilities of supercritical fluids allows quantitative extraction and direct transfer of the selected solutes of interest to be accomplished to the column, often without the need for further sample treatment or cleanup. Extraction selectivity is usually achieved by adjusting the pressure of the supercritical fluid at constant temperature or, less often, by changing the temperature of the supercritical fluid at constant pressure. SFE coupled with packed column SFC has found... 

Keywords sou geochemistry, partial extraction, selective extraction, Matagami, Perseverance zinc deposit. 

Since, according to Eq. 17.14, M2+ must compete with 2H+ for Q, we can set the pH low enough to ensure that only copper(II) forms major amounts of an uncharged di(hydroxyquinolinato) complex, which can then be extracted selectively into, say, chloroform. When this is complete, the pH could be increased enough to permit selective extraction of NiQ2, etc. The metal ions can be stripped from the extractant by the reverse process, i.e., by equilibration with sufficiently concentrated aqueous acid. 

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