Analytes, recovered after extraction

Extraction discs (0.5 mm thick, 25 to 90 mm diameter) constitute a variation of column-based SPE. These discs allow rapid extraction of large volumes of sample, which is not possible using a small column. The discs are made of bonded-phase silica particles, a few micrometres in diameter, trapped in a porous Teflon or glass fibre matrix. The discs are operated in a similar way to a paper filter on a vacuum flask. After extraction, the analyte is recovered by percolating a solvent through the filter. The major application of this technique is the isolation of trace amounts of compound dispersed in an aqueous medium. 

Large (stoichiometric) amounts of analyte are required to manufacture MIPs. This is an important issue if the (analyte) template is expensive, difficult to isolate, or toxic. In principle, the analyte could be recovered after template extraction although this process can also be cumbersome. 

The performance of SLM extraction is characterized by two measures the enrichment factor (Ec) and the extraction efficiency (E). E measures how much of the analyte in the sample is recovered on the acceptor side after extraction E = (CA/CS) x (VJV%), and Et reflects how many times the concentration in the acceptor is increased compared to the initial sample concentration Ee = (CA/CS). CA and Cs are the final acceptor and initial sample concentrations, respectively. Similarly, VA and Vs are the acceptor and sample volumes, respectively. A more comprehensive elaboration of SLM principles63 and mass transfer kinetics,62 64 as well as the role of the octanol-water partition coefficient in SLM extraction of ionizable compounds,65 is given elsewhere. 

Ashton and Chan [ 1 ] have reviewed the techniques for the collection of seawater samples preservation, storage, and prevention of contamination are all discussed. The most appropriate measurement techniques, preconcentration and extraction, method validation, and analytical control are all covered. The apparent aluminium content of seawater stored in ordinary containers such as glass and polyethylene bottles decreases gradually, e.g., to half in 2.5 h. But if the samples are acidified with 0.5ml/l concentrated sulfuric acid the aluminium content remains constant for at least one month. Accordingly, samples should be acidified immediately after collection. However, the aluminium could be recovered by acidifying the stored samples and leaving them for at least five hours. 

Relative extraction efficiencies of polar polymeric neutral, cation, and anion exchange sorbents (HLB, MCX, and MAX) for 11 beta antagonists and 6 beta agonists in human whole blood were probed.109 Initial characterization of MCX and MAX for acidic and basic load conditions, respectively, showed that both the agonists and antagonists were well retained on MCX, while they were recovered from MAX in the wash with either methanol or 2% ammonia in methanol (see Table 1.6). Blood samples were treated with ethanol containing 10% zinc sulfate to precipitate proteins and the supernatants loaded in 2% aqueous ammonium hydroxide onto the sorbents. After a 30% methanol and 2% aqueous ammonia wash, the analytes were eluted with methanol (HLB), 2% ammonia in methanol (MCX), or 2% formic acid in methanol (MAX). The best recoveries were observed with MCX under aqueous conditions or blood supernatant (after protein precipitation) spiked sample load conditions (see Table 1.7). Ion suppression studies by post-column infusion showed no suppression for propranolol and terbutaline with MCX, while HLB and MAX exhibited suppression (see Figure 1.6). 

Application of the MAS to drinking water should considerably broaden the scope of organic compounds detected and measured, relative to previously available analytical methods. This conclusion is especially true for the polar compounds of relatively low MW (<500) however, a few of these compounds are not recovered well by the MAS extraction and isolation techniques or are not gas chromatographable, even after derivatization. HPLC methods offer the most promise for separation and analysis of these compounds as well as those of high molecular weight. 

The application of MIPs prepared using triazines as templates to the SPE of water samples requires drying of the cartridge after the sample application in order to remove water traces, which would disrupt the interactions between the analytes and the sorbent. In the protocol described by Matsui et al. [19] the aqueous sample was applied to the MIP cartridge, which was then carefully dried prior to a selective dichloromethane wash (entry D in Tables 15.1 and 15.2). HPLC-UV analysis of wastes and extracts showed that all the impurities were washed off without significant elution of simazine (4) and that the analyte was quantitatively recovered in the eluate. 

Table IV shows the results of three laboratory runs of the solvent extraction step (after the plutonium was removed by anion exchange). The major elements are shown before solvent extraction, after solvent extraction, in the 7M HNO wash, and in the final strip product. The americium remaining in the organic after stripping is also shown. Although there were some analytical discrepancies, the data show that americium was effectively recovered (except in Test 1, for which we have no explanation). Americium was decontaminated from aluminum and magnesium in all three runs.

Extraction or separation of dissolved chemical component [X]A from liquid phase A is accomplished by bringing liquid solution of [X]B into contact with a second phase B that is totally immiscible. A distribution of the component between the immiscible phases occurs. After the analyte is distributed between the two phases, the extracting analyte is released and/or recovered from phase A for analysis. The theory of chemical equilibrium leads us to a reversible distribution coefficient as follows ... 

Extraction procedures should recover essentially aU of the analyte from the sample and leave behind as many of the impurities as possible. Cleanup procedures are designed to reduce matrix interferences while not losing any of the analyte and increasing its concentration as much as possible. General, practical aspects of modem sample preparation methods have been described in earlier arti-cles, but not their use in TLC. The purpose of this entry is to review the procedures used prior to TLC analysis and illustrate analytes and samples for which each has been applied successfully details of the TLC methods after sample preparation will not be given but can be found in the cited references. 

Solid phase extraction is a useful separation and preconcentration procedure for the determination of trace metals in fuels. It is based on the partition between a liquid (sample) and a solid phase (sorbent), which can be unloaded, load on chemically modified with organofunctional groups (Koen et al., 2006). After pre-concentration the analyte is recovered by elution with an appropriate solvent or directly determined in the solid phase. 

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