Selective extraction techniques

Oil Fields. Oil field waters in the United States containing lithium have been identified in 10 states. The greatest concentrations are in waters from the Smackover formation of southern Arkansas and eastern Texas. Concentrations from this formation have been measured from 300—600 ppm in waters originating at a 2500—3300 m depth. Recovery of lithium from this resource would only be commercially feasible if a selective extraction technique could be developed. Lithium as a by-product of the recovery of petroleum (qv), bromine (qv), or other chemicals remains to be exploited (12). 

Owing to its relevancy in metabolite profiling analysis, several groups have investigated the suitability of different metabolite extraction procedures for GMO analysis. Selective extraction techniques, such as supercritical fluids... 

Another popular and selective extraction technique widely used in bioanalysis is solid phase extraction (SPE). SPE is a separation process utilizing the affinity of the analytes to a solid stationary phase. By manipulating the polarity and pH of the mobile phase, the analytes of interest or undesired impurities pass through stationary phase sequentially according to their physical and chemical properties. For a SPE procedure, a wash step refers to the elution of the unwanted impurities which are discarded and the elution step refers to the elution of the analytes of interest which are collected. While the fundamental remains the same in decades, the continuing invention and introduction of new commercial stationary phases and accessory devices have boosted the application of SPE in bioanalysis and many other fields. 

FIGURE 7.10 Relative roles of biogenic Mn oxide, Fe oxide, and organic material in controlling Pb adsorption to biofilms as determined using a novel selective extraction technique. (From Dong, D. et al., Water Res., 34, 427, 2000. With permission.)... 

Terrestrial materials (river sediments, lake sediments, and urban particulate matter) appear to have between 50% and 70% exchangeable Pb and Zn while marine sediments contain very little exchangeable metal but appreciably more reducible and much more residual Pb and Zn (Kersten and Forstner, 1995). This may not be too surprising as exchangeable metals are released once freshwater mixes with salt water and redistribution in the marine environment results in some precipitated phases (carbonates, Fe/Mn oxyhydroxides) and the relative increase in the lithogenic fraction. In future, the solid-phase identification techniques should be used to classify the sediments that are to be subjected to selective extraction techniques for the purpose of understanding the heavy metal phase associations. 

Selective hydrolysis (see Adams, 1965) at varying acid strengths may supply additional information about the nature (storage or structural) of the dissolved polysaccharides in seawater. For investigations of the composition of particulate matter, a selective extraction technique, to differentiate... 

AVS is not the sole partitioning phase for predicting the acute toxicity, especially for Cu, which may be strongly associated with sediment organic matter (e.g. Ankley et al., 1993). Although Huerta-Diaz et al. (1993) have presented experiments to measure the quantity of trace metals associated with AVS and pyrite in sediments, selective extraction techniques for prediction of solid phases controlling pore-water concentrations of trace metals in (partly) anaerobic sediments solid phases are still absent (Wallmann et al., 1993). 

Selective Extraction Techniques for Phosphorus in Sediments and Soiis... 

SFE is very suitable for extracting thermolabile compounds, as it allows the possibility to perform fast extractions at moderate temperatures (around Therefore numerous applications of the technique have been reported. A large field has been covered environmental matrices, plants, foods and fats, and polymers. As legislation will tend to restrict, or even ban, the use of many common solvents, recent extraction techniques will, in the future, undoubtedly supercede the traditional methods, as SFE considerably reduces the solvent volumes required, along with a reduction in the time devoted to the extraction step. SFE appears, undoubtedly, to be the most potentially selective extraction technique. 

The work by Ciferri and coworkers [128-130] focused on the supramolecular organization of aromatic rod-coil copolyamides in diluted (isotropic) and moderately concentrated (lyotropic) phases. Their diblock copolymers were based on a rigid block of poly(p-benzamide) (PBA) having a DP about 100, and different comparable lengths of flexible blocks, such as poly(m-phenylene isophthalamide) (MPD-I), poly(/n-benzamide) (MBA), or poly(ethylene glycol) (PEG). The use of end-capped prepolymers and selective extraction techniques assured a strict two-block sequence, the absence of free homopolymers not strongly bound to the copolymers, and a fractionation in terms of the rigid/flexible compositional distribution ratio. 

Typical nonsieve, polar adsorbents are siUca gel and activated alumina. Kquilihrium data have been pubUshed on many systems (11—16,46,47). The order of affinity for various chemical species is saturated hydrocarbons < aromatic hydrocarbons = halogenated hydrocarbons < ethers = esters = ketones < amines = alcohols < carboxylic acids. In general, the selectivities are parallel to those obtained by the use of selective polar solvents in hydrocarbon systems, even the magnitudes are similar. Consequendy, the commercial use of these adsorbents must compete with solvent-extraction techniques. 

Latexes of synthetic resins are identified by ir spectrometry. Selective extraction with organic solvents is used to obtain purified fractions of the polymers for spectrometric identification. Polymeric films can be identified by the multiple internal reflectance ir technique, if the film is smooth enough to permit intimate contact with the reflectance plate. TAPPI and ASTM procedures have not been written for these instmmental methods, because the interpretation of spectra is not amenable to standardization. 

Standardized techniques atomic absorption (AAA) and photometric (FMA) of the analysis and designed by us a technique X-Ray fluorescence of the analysis (XRF) for metals definition in air of cities and the working areas of plants to production of non-ferrous metals are applied. The samples of aerosols were collected on cellulose (AFA-HA) and perchlorovinyl (AFA-VP and FPP) filters (Russia). The techniques AAA and FMA include a stage of an acid-temperature ashing of a loaded filter or selective extraction of defined elements from filter by approaching dissolvent. At XRF loaded filters were specimens. 

In summary, the development of materials for the extraction of pesticides from water samples has progressed from simple liquid-liquid extraction for the principal active compound to sophisticated SPE media capable of exclusively trapping the target pesticide and metabolites selectively. The development of alkyl bonded phase silica cartridges and extraction disks combined with on-line extraction techniques is currently the principal means used for the extraction and trace enrichment of pesticides and metabolites from water. 

Solubilizing all or part of a sample matrix by contacting with liquids is one of the most widely used sample preparation techniques for gases, vapors, liquids or solids. Additional selectivity is possible by distributing the sample between pairs of immiscible liquids in which the analyte and its matrix have different solubilities. Equipment requirements are generally very simple for solvent extraction techniques. Table 8.2 [4,10], and solutions are easy to manipulate, convenient to inject into chromatographic instruments, and even small volumes of liquids can be measured accurately. Solids can be recovered from volatile solvents by evaporation. Since relatively large solvent volumes are used in most extraction procedures, solvent impurities, contaminants, etc., are always a common cause for concern [65,66]. 

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. 

It is the difficult task of the analytical chemist to select the sample preparation technique best-suited for the problem at hand. The more tools there are in the toolkit, the larger the chances of finding a sample preparation technique that offers the desired characteristics. The goal of any extraction technique is to obtain extraction efficiency for the analyte which meets the analytical requirements in the shortest possible time. In some analytical procedures little sample handling is needed [46-49]. 

The polymer/additive system in combination with the proposed extraction technique determines the preferred solvent. In ASE the solvent must swell but not dissolve the polymer, whereas MAE requires a high dielectric solvent or solvent component. This makes solvent selection for MAE more problematical than for ASE . Therefore, MAE may be the preferred method for a plant laboratory analysing large numbers of similar samples (e.g. nonpolar or polar additives in polyolefins [210]). At variance to ASE , in MAE dissolution of the polymer will not block any transfer lines. Complete dissolution of the sample leads to rapid extractions, the polymer precipitating when the solvent cools. However, partial dissolution and softening of the polymer will result in agglomeration of particles and a reduction in extraction rate. 

Classical LLEs have also been replaced by membrane extractions such as SLM (supported liquid membrane extraction), MMLLE (microporous membrane liquid-liquid extraction) and MESI (membrane extraction with a sorbent interface). All of these techniques use a nonporous membrane, involving partitioning of the analytes [499]. SLM is a sample handling technique which can be used for selective extraction of a particular class of compounds from complex (aqueous) matrices [500]. Membrane extraction with a sorbent interface (MESI) is suitable for VOC analysis (e.g. in a MESI- xGC-TCD configuration) [501,502]. 

The main characteristics of the ideal extraction method are given in Table 3.47, which at the same time are also criteria for comparison of sample preparation techniques. It is unlikely that a unique best method can be defined, which is analyte and matrix independent. Extraction is affected by polymer functionality, molecular weight and cross-linking. Selective extraction of some additives is basically not possible. Hence, the goal of an ideal extraction would be the complete extraction of all additives from the polymer for subsequent chromatographic separation. 

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. 

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