Selected techniques extraction

A method which uses supercritical fluid/solid phase extraction/supercritical fluid chromatography (SE/SPE/SEC) has been developed for the analysis of trace constituents in complex matrices (67). By using this technique, extraction and clean-up are accomplished in one step using unmodified SC CO2. This step is monitored by a photodiode-array detector which allows fractionation. Eigure 10.14 shows a schematic representation of the SE/SPE/SEC set-up. This system allowed selective retention of the sample matrices while eluting and depositing the analytes of interest in the cryogenic trap. Application to the analysis of pesticides from lipid sample matrices have been reported. In this case, the lipids were completely separated from the pesticides. 

Specifically for triazines in water, multi-residue methods incorporating SPE and LC/MS/MS will soon be available that are capable of measuring numerous parent compounds and all their relevant degradates (including the hydroxytriazines) in one analysis. Continued increases in liquid chromatography/atmospheric pressure ionization tandem mass spectrometry (LC/API-MS/MS) sensitivity will lead to methods requiring no aqueous sample preparation at all, and portions of water samples will be injected directly into the LC column. The use of SPE and GC or LC coupled with MS and MS/MS systems will also be applied routinely to the analysis of more complex sample matrices such as soil and crop and animal tissues. However, the analyte(s) must first be removed from the sample matrix, and additional research is needed to develop more efficient extraction procedures. Increased selectivity during extraction also simplifies the sample purification requirements prior to injection. Certainly, miniaturization of all aspects of the analysis (sample extraction, purification, and instrumentation) will continue, and some of this may involve SEE, subcritical and microwave extraction, sonication, others or even combinations of these techniques for the initial isolation of the analyte(s) from the bulk of the sample matrix. 

In on-line extraction the process is coupled directly ( hyphenated ) to the analytical technique used for further analysis of the extract (either spectroscopy or, more frequently, chromatography, because of the limited selectivity of extraction). Common examples include SFE-GC, SFE-SFC, SFE-HPLC, SFE-FTIR,... 

MAP makes use of physical phenomena that are fundamentally different compared to those applied in current sample preparation techniques. Previously, application of microwave energy as a heat source, as opposed to a resistive source of heating, was based upon the ability to heat selectively an extractant over a matrix. The fundamental principle behind MAP is just the opposite. It is based upon the fact that different chemical substances absorb microwave energy... 

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. 

The analytes are typically extracted from the biological matrix using solvent extraction or solid phase extraction (SPE). Most analytes require some form of chemical derivatization prior to analysis by GC-MS techniques, whereas with LC-MS-MS no further treatment of the extract is required. The extracts obtained from urine are relatively dirty because of the many endogenous compounds that are present. It is for this reason that the very selective techniques of GC-MS-MS, GC-HRMS, or LC-MS-MS are required to detect some of the prohibited substances that have low detection levels. 

A simple way to increase the selectivity of extraction techniques is to derivatize the carbonyl compounds. 

In search of bioactive substances, researchers have directed their interest towards substances found in plants. Parts of plants which have been used in natural medicine have proved to be a rich source of bioactive compounds however, to make use of them, they have to be isolated and their properties deterrnined. Using selective techniques of extraction has resulted in obtaining concentrated preparations of bioactive substances. To achieve comprehensive knowledge of their properties, it was necessary to develop methods of isolation of individual components and testing these methods. This could be done with chromatographic techniques. Isolated compounds were tested in order to show which of them (and to what extent) are responsible for bioactivity of plant preparations from which they were obtained. Due to the fact that many of the substances have the opposite effect, it is frequently impossible to use extracts without isolating individual compounds. 

Activity coefficients at infinite dilution, of organic solutes in ILs have been reported in the literature during the last years very often [1,2,12,45,64, 65,106,123,144,174-189]. In most cases, a special technique based on the gas chromatographic determination of the solute retention time in a packed column filled with the IL as a stationary phase has been used [45,123,174-176,179,181-187]. An alternative method is the "dilutor technique" [64,65,106, 178,180]. A lot of y 3 (where 1 refers to the solute, i.e., the organic solvent, and 3 to the solvent, i.e., the IL) provide a useful tool for solvent selection in extractive distillation or solvent extraction processes. It is sufficient to know the separation factor of the components to be separated at infinite dilution to determine the applicability of a compound (a new IL) as a selective solvent. 

A protocol on lipid extraction modified from the pioneering work of Folch et al. (1957) is included in this unit for convenience (see Support Protocol). The authors laboratory uses this protocol for virtually all kinds of samples, and have found it to be effective with reproducibly high recoveries. Another very popular lipid extraction technique is the Bligh and Dyer method, which uses a 1 1 (v/v) mixture of chloroform/methanol (Bligh and Dyer, 1959). For more information on lipid extraction, the discussion by Nelson (1991) on solvent selection and extraction efficiency is recommended. 

Although supercritical extraction (SFE) has been known for some time, it is still a relatively new technique to the analytical chemist. Before developing an SFE method, the chemist must understand the composition of the matrix and the analyte properties. The key instrumental parameters affecting the extraction of analytes from the matrix include fluid density, temperature, and fluid composition. Both the make-up of the matrix and the analytes must be considered when selecting the extraction conditions. Consideration of the extraction parameters must be given with respect to their affect on the analytes of interest and on the compounds present in the matrix that may either coextract with the analytes or inhibit their extraction by physical or chemical means. 

This chapter considers methods of trace element speciation, and their application to soils, that involve selective chemical extraction techniques. It will be concerned firstly with extraction by single selective reagents and secondly with the development and application of sequential extraction procedures for soils and related materials. Sequential extraction procedures for sediments are discussed in depth in Chapter 11. Speciation in the soil solution and modelling aspects of its interaction with soil solid phases are comprehensively covered in Chapter 9 and will not be considered here. 

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

Every single regeneration problem has to be analysed individually, however, the following case study demonstrates how a selection of separation techniques, extraction and phase separation, can successfully be applied to regenerate a spent ionic liquid based electrolyte satisfactorily. As a case study the electrolyte 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ([BMP]Tf2N) was chosen, which is used for electrodeposition of aluminum as described in the literature [137, 138],... 

More widely applied to determine the potential, plant and human bioavailability are the methods of PTMs speciation which involve selective chemical extraction techniques. Estimation of the plant- or human-available element content of soil using single chemical extractants is an example of functionally defined speciation, in which the function is plant or human availability. In operationally defined speciation, single extractants are classified according to their ability to release elements from specific soil phases. Selective sequential extraction procedures are examples of operational speciation (Ure and Davidson, 2002). 

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. 

Dean JR and Xiong G. Extraction of organic pollutants from environmental matrices Selection of extraction technique. Trends Anal. Chem. 2000 19 553-564. 

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