Adsorbents, extraction procedures

Adsorbents, extraction procedures, organic pollutants, 113 Aerosol, problems in measuring, coal combustion, 312-317 Aerosol carbon data, results and discussion, carbon isotope tracers, 270-275... 

Samples that contain two phases present a special problem depending on the site of the materials of interest. If the substances are known to be associated with one phase only, the sample procedure is simply to separate the two phases by filtration or centrifugation and treat the sample as a liquid or solid sample depending on the phase that contains the materials to be determined. However, if the materials of interest are distributed between the two phases, some in solution and some adsorbed on the surface of the solid, then special extraction procedures will be necessary. 

Solid-phase microextraction (SPME) consists of dipping a fiber into an aqueous sample to adsorb the analytes followed by thermal desorption into the carrier stream for GC, or, if the analytes are thermally labile, they can be desorbed into the mobile phase for LC. Examples of commercially available fibers include 100-qm PDMS, 65-qm Carbowax-divinylbenzene (CW-DVB), 75-qm Carboxen-polydimethylsiloxane (CX-PDMS), and 85-qm polyacrylate, the last being more suitable for the determination of triazines. The LCDs can be as low as 0.1 qgL Since the quantity of analyte adsorbed on the fiber is based on equilibrium rather than extraction, procedural recovery cannot be assessed on the basis of percentage extraction. The robustness and sensitivity of the technique were demonstrated in an inter-laboratory validation study for several parent triazines and DEA and DIA. A 65-qm CW-DVB fiber was employed for analyte adsorption followed by desorption into the injection port (split/splitless) of a gas chromatograph. The sample was adjusted to neutral pH, and sodium chloride was added to obtain a concentration of 0.3 g During continuous... 

In this method volatile organic matter in seawater is concentrated on a Tenax GC solid adsorbent trap and dry-ice trap in series. The trapped organic material is then desorbed and oxidised to carbon dioxide, which is measured with a non-dispersive infrared analyser. A dynamic headspace method was used for the extraction with the assistance of nitrogen purging. Dynamic headspace analysis [184] is an efficient extraction procedure. The efficiency of extraction... 

Finally, toxicity (defined in terms of a standard extraction procedure followed by chemical analysis for specific substances) is a characteristic of all chemicals, whether petroleum or nonpetroleum in origin. Toxic wastes are harmful or fatal when ingested or absorbed, and when such wastes are disposed of on land, the chemicals may drain (leach) from the waste and pollute groundwater. Leaching of such chemicals from contaminated soil may be particularly evident when the area is exposed to acid rain. The acidic nature of the water may impart mobility to the waste by changing the chemical character of the waste or the character of the minerals to which the waste species are adsorbed. 

In operationally defined speciation the physical or chemical fractionation procedure applied to the sample defines the fraction isolated for measurement. For example, selective sequential extraction procedures are used to isolate metals associated with the water/acid soluble , exchangeable , reducible , oxidisable and residual fractions in a sediment. The reducible, oxidisable and residual fractions, for example, are often equated with the metals associated, bound or adsorbed in the iron/manganese oxyhydroxide, organic matter/sulfide and silicate phases, respectively. While this is often a convenient concept it must be emphasised that these associations are nominal and can be misleading. It is, therefore, sounder to regard the isolated fractions as defined by the operational procedure. Physical procedures such as the division of a solid sample into particle-size fractions or the isolation of a soil solution by filtration, centrifugation or dialysis are also examples of operational speciation. Indeed even the distinction between soluble and insoluble species in aquatic systems can be considered as operational speciation as it is based on the somewhat arbitrary definition of soluble as the ability to pass a 0.45/Am filter. 

The most widely applied procedure is indirect quantification by extracting the fractions from the adsorbent layer in the presence of an internal standard, transmethylating, and subjecting the methyl esters of the fatty acids to gas chromatography (GC) analysis. Information is simultaneously obtained on the composition of the fractions and their absolute amounts. In practice, the sample is resolved on a preparative plate, each distinct zone is carefully scraped off, a standard solution of the internal standard (usually an odd-chain fatty acid methyl ester) is added, and the material is extracted with a suitable polar solvent such as diethyl ether or a chloroform-methanol mixture. More complicated extraction procedures are sometimes needed for polar complex lipids. Fatty acid methyl esters... 

Sample preparation represents a formidable challenge in the chemical analysis of the real-world samples. Not only is the majority of total analysis time spent in sample preparation, but also it is the most error-prone, least glamorous, and the most labor-intensive task in the laboratory. The components to be separated from the matrix are usually taken up with an auxiliary substance such as a carrier gas, an organic solvent, or an adsorbent. These separation processes can be regarded as extraction procedures (i.e., liquid-liquid extraction, liquid-solid extraction, Soxhlet extraction, solid-phase extraction, supercritical fluid extraction, solid-phase microextraction, etc.). 

Earlier fluorometric methods for analysis of urinary free catecholamines have been replaced by HPLC methods that allow selective quantitation of epinephrine, norepinephrine, and dopamine. Preliminary extraction of urine is stid required and numerous preanalytical cleanup techniques are available. An alumina extraction procedure is typically coupled with ion-exchange or adsorption chromatography. Alumina pretreatment usually involves a batch extraction technique in which catechols are first adsorbed at pH 8.6 and then eluted with boric acid, which forms a complex with cis-diol groups. Purification on boric acid affinity gels provides an alternative procedure for selective adsorption of catecholamines. 

Perot et al. [7] in collaboration with Rhodia have studied the deactivation of industrial catalysts HBEA and HY during the acylation of veratrole and anisole. After reaction, the spent catalysts were extracted with methylene chloride. This Soxhlet extraction makes possible the elimination of compounds that were not strongly adsorbed on the zeolites. The composition of the residue obtained after evaporation of methylene chloride was practically the same as that of the reaction mixture at the end of the experiment. By this extraction procedure, approximately 80% of the compounds remaining on the catalysts after reaction were recovered. After Soxhlet extraction, the catalyst samples were recovered and dissolved with hydrofluoric acid. The organic compounds released by the catalysts were extracted again by methylene chloride and, after evaporation of solvent, the residues contained di- and triketones as well as cyclization compounds, the structures of which are presented in Scheme 14.1. 

A novel approach to increase the overall extraction yield of a microbial product has been developed. The primary isolation steps of fermentation derived microbial products generally involve procedures including solid removal, wash and volume reduction using either solvent extraction or ion-exchange. These steps can be further simplified by the use of whole broth extraction. In the case of using solid phase adsorbents, extraction performance can be drastically affected by the size and the nature of the adsorbent used. If the adsorbent size is large, it exhibits internal diffusional resistance (pore diffusion) and the resultant mass transfer resistance reduces the overall rate of adsorption... 

Cabernet Sauvignon grape skins (50g) were extracted twice with 100 mL of methanol. Extract was combined and evaporated under reduced pressure to remove methanol. Residue was reconstituted to 20 mL with water. Five milliliters of water solution was passed through a preconditioned C-18 Sep-Pak cartridge (Waters Corporation). The adsorbed pigments were washed with 5 mL of water and eluted with 2 mL of 0.01% HCl methanol. The eluant was stored at -20 °C prior to HPLC analysis. Cabernet Sauvignon grape skins were also extracted with 75% acetone with 0.2% acetic acid to compare anthocyanin profiles in different extraction procedures. 

An intermediate polar compound like trimethylphenol can be analysed with both the systems. A lower recovery with the first method will be obtained if soil with a high organic matter has to be analysed. In that case the phenol is more strongly adsorbed to the soil matrix. The washing step in the second method will also reduce the recovery. An alternative is making use of the extraction procedure for the chlorophenols. This procedure makes use of the weakly acidic character of the phenols. 

An unusual extraction procedure is shown in Scheme 6 for the purification of soraphen Aj from a myxobacterium. An adsorbent resin was added to a large-scale fermentation vessel prior to inoculation so that the metabolite was continuously adsorbed as it was produced. Not only did this simplify the isolation, but it also resulted in increased production of the compound by the organism, possibly because adsorbent effectively removed metabolite from the system, thus reducing any feedback inhibition. The eluate from the resin was sufficiently clean that it required only solvent extraction prior to a crystallization step that yielded reasonably pure soraphen A[ (8). 

This chapter has four sections that focus on laboratory-scale capture steps solids removal, solvent extraction, solid phase adsorption, and expanded bed adsorption. Although these techniques are widely applicable, most of this chapter is aimed at extraction of microbial fermentation broth. Techniques specific to initial extraction of plants and marine organisms can be found in Chapters 12 and 13, respectively. The first section describes laboratory-scale procedures for batch filtration and centrifugation. The second section describes solvent-extraction procedures with either water-miscible or -immiscible solvents. The third section describes using adsorbents for solid-phase extraction. The fourth section describes a technique known as expanded bed adsorption, which is unique in that it enables resin-column recovery of product directly from unclarified fermentation broth. 

A six-step extraction method was used to operationally discriminate the chemical species of P (e.g., authigenic apatite and refractory organic P). The six-step extraction procedure separates the major reservoirs of sedimentary P into six pools, including loosely adsorbed P (LSor-P), iron-bound inorganic P (Fe-P), leachable organic P (Lea-OP), authigenic apatite (CFAP), detrital apatite (FAP), and refractory organic P (Ref-OP). The location of studied cores was as shown in Fig. 3.35. 

Zasavica/Sava confluence, and downstream sites of the river Zasavica in order Modran , Valjevac , Sumareva , Ravnjanska , Rajevica , Gajica . A sequential extraction procedure was applied for partitioning of metals into five fractions. The examined river sediment samples are very interesting because of their great surface area and content of highly adsorbing minerals that are adsorbing toxic heavy metals, for example lead and cadmium. 

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