Solid extractants selectivity

Castillo M, Domingues R, Alpendurada MF, et al. 1997. Persistence of selected pesticides and their phenolic transformation products in natural waters using off-line liquid solid extraction followed by liquid chromatographic techniques. Anal Chim Acta 353 133-142. 

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]. 

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. 

Technique selection Since you are a mass spectrometrist, you decide a liquid-solid extraction of the solid followed by MS analysis can identify impurities in the carbon. 

S.B. Hawthorne, C.B. Grabanski, E. Martin and D.J. Miller, Comparison of Soxhlet extraction, pressurized liquid extraction, supercritical fluid extraction and subcritical water extraction for environmental solids recovery, selectivity and effects on sample matrix. J. Chromatogr.A 892 (2000) 421 133. 

The flexibility of the gas-solid extraction method stems from the choice of many adsorbing phases, each offering a particular selectivity. It is possible to stabilise certain molecules that would normally decompose upon contact with the sorbent by incorporating into the sorbent a reagent that carries out a specific derivatisation. For example, aldehydes can be converted into oxazolidines, which are stable and desorbable compounds, by reaction with 2-hydroxymethylpiperidine. 

Appropriate SPE sorbent selection is critical to obtaining efficient SPE recovery of semivolatile organics from liquids. Henry [58] notes that an SPE sorbent must be able to sorb rapidly and reproducibly, defined quantities of sample components of interest. Fritz [73] states that successful SPE has two major requirements (1) a high, reproducible percentage of the analytical solutes must be taken up by the solid extractant and (2) the solutes must then be easily and completely eluted from the solid particles. The sorption process must be reversible. In addition to reversible sorption, SPE sorbents should be porous with large surface areas, be free of leachable impurities, exhibit stability toward the sample matrix and the elution solvents, and have good surface contact with the sample solution [68,73],... 

Blasi et al. (2008) developed an experimental method for removing carbonyl compounds from wine. It used selective liquid-solid extraction, with phenylsulfonylhydrazine as a scavenging agent, bonded to a porous polymer support. The method was efficient for reducing the SO2 binding power of botrytized wines, without impairing their sensory qualities. 

Levels of drug and/or its metabolite have to be determined in plasma samples collected during the course of a toxicity study in order to evaluate the toxicokinetics of that compound. The UV absorption properties of the compound are used to determine the compound of interest. Since many of the endogenous compounds also show absorption in that wavelength range, a tailored sample work-up has to provide additional selectivity for the compound of interest. In addition, the plasma proteins have to be removed by the work-up in order to avoid blocking of the HPLC columns. Three principles are generally applied to remove the proteins from the sample Protein precipitation, liquid/liquid extraction and liquid/solid extraction. 

Solid phase extraction Selective adsorption and desorption... 

Conceptually, the solid material can be partitioned into fractions of different importance which can be extracted selectively (38). The procedures for determining the chemical species of trace metals in solid phases can be grouped into methods which affect the separation between residual and non-residual metals only and more elaborated methods making use of sequential extractions (39). 

A fourth experiment would be an evaluation of precision and recovery at one to four concentration levels (n — 6 to 24 plus a recovery standard), plus recovery of an internal standard (n — 3 plus recovery standard). Therefore, as a minimal method development exercise, 60—70 spiked samples would be prepared and extracted within 1 day. The experiments need to be performed sequentially because the results from each will impact how subsequent experiments are designed. Selectivity is assessed through the course of the method development. The analytical chemist with access to API LC/MS/MS will spend less time on solid-phase extraction selectivity development. 

Although the preferred method of calculating a spectrum is to perform an ab initio calculation on an extended solid, extracting frequencies and displacements across the Brillouin zone, on a fine A-grid, this approach can be computationally very expensive. In plane wave codes like CASTEP [18], CPMD [19], TWSCF [20], VASP [21], ABINIT [22], and some others, the number of plane waves that are taken into consideration, the selected correlation fimctional and the choice of pseudopotential will all have an impact on the quality of the calculations. Some codes (e.g. ABINIT) alleviate the problem by permitting frozen phonon calculations at the symmetry zone boundary, i.e. (0,0,0), (l/2,0,0), (l/2,l/2,0) and (l/2,l/2,l/2) and so determine the dynamical matrix at these points. The code then interpolates values of the d3mamical matrix for all the points within the Brillouin zone and uses these to calculate the solution to the vibrational problem inside the zone. 

Haeberlin (5) expressed the prevailing attitude of the spectroscopist in 1976 with the statement, "Narrow is beautiful." Although this attitude still prevails, it has long been recognized that a wealth of information is contained in NMR line shapes broadened by specific interactions in solids. Extracting that information has been difficult, since a variety of mechanisms contribute to the line shape, and each must be selectively removed from the others to decipher the... 

Besides the theoretical interest in the unusual phase behavior encountered in these systems, the principles involved can be applied in operations wherein the nonideality is intentionally created. The magnitude of solubility of a compound of low volatility in a gas above its critical temperature. .. is sufficient to consider the gas as an extracting medium, that is fluid-liquid or fluid-solid extraction analogous to liquid-liquid extraction and leaching. In this case the solute is removed and the solvent recovered by partial decompression. Thus compression of a gas over a mixture of compounds could selectively dissolve one compound, permitting it to be removed from the mixture. Partial decompression of the fluid elsewhere would drop out the dissolved compound, and the gas could be reused for further extraction. 

SFE was also more selective as compared to the liquid solid extraction (LSE) with isopropanol, chloroform, and isopropanol-chloroform. Glycolipids and phospholipids were found in the LS extract but they were not extracted by SFE. The SF extracts were also cleaner than the LS extracts and did not require the various clean up procedures required by the latter extraction method. The SF extracts were richer in fatty acids whereas, the isopropanol-chloroform combined extracts were richer in the more polar and hi molecular weight lipids. 

Although careful method development may lead to good extraction selectivity, additional clean-up after completed extraction is still often needed for complicated samples, especially when using MAE or PLE. For some MAE applications, only a filtration step is needed, whereas for others, solid-phase extraction or liquid-liquid extraction steps are needed to prepare for the final analysis. Also in PLE further clean-up is normally needed, but here the possibilities are better for a simultaneous clean-up inside the extraction cell resulting in final extracts directly suited for analysis as discussed above. 

Liquid-liquid extraction is a process by which one or more components of a mixture, usually in water, are selectively transferred to another, usually organic liquid. Liquid-solid extraction involves the use of a liquid to selectively remove components from a solid. The majority of laboratory scale extractions are batch extractions, involving separatory funnels. The theory and general techniques are discussed in Chapter 9. 

An extraction is the selective transfer of a compound or compounds from one liquid (usually water) to another immiscible liquid (usually organic) or from a solid to a liquid. The former process is called a liquid-liquid extraction and the latter is called a liquid-solid extraction. More recently, with the development of reactive solid phases, materials are extracted from liquids by a solid. This is called solid phase extraction and is discussed in Chapter 12. 

IRMS LC MDGC MS MSA NIF NMR OAV OSV PCA RAS RP SDE SFE SIM SNIF SPME TIC TLC Stable Isotope Ratio Mass Spectrometry Liquid Chromatography MultiDimensional Gas Chromatography Mass Spectrometry Multivariate Sensory Analysis Nasal Impact Frequency Nuclear Magnetic Resonance spectroscopy Odor Activity value Odor Spectrum Value Principal Component Analysis Retronasal Stimulation Reversed Phase Simultaneous steam Distillation Extraction Supercritical Fluid Extraction Selected Ion Monitoring Surface of Nasal Impact Frequency Solid Phase Micro Extraction Total Ion Current Thin Layer Chromatography... 

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