Solid sorbent material

The solid sorbent material must also be heated and cooled for regeneration and absorption cycles. Because the solid C02 sorbents operate at higher temperatures than the liquid absorption systems, they provide opportunities for simultaneous WGS reaction with C02 removal improving the CO conversion in sorbent-enhanced reaction process (SERP). A number of studies have been reported on the SERP concept and are currently underway as discussed in later sections. 

Selection of Collection Media. The methods developed for HCCP, HCBD, and 1,2-DCP involve the collection of the analytes from air on solid sorbent materials in small Pyrex tubes. Each tube is 7 cm long by 6 mm o.d. and 4 mm i.d. The recommended sampling tubes contain two beds of sorbent material—one layer for sorption and a second, smaller, backup layer to monitor breakthrough if the capacity of the sorbing layer is exceeded. 

Analytes may accumulate in the sorption phase either by adsorption onto the surface of solid sorbent materials or by absorption in absorbent liquids or polymers that behave like subcooled liquids.The advantage of solid adsorbents is the potential to select materials with a high affinity and selectivity for target analytes. However, the sorption capacity of adsorbents is usually limited, and the description of adsorption/desorption kinetics of analytes to adsorbents is complex. Typically, the adsorbent materials used in passive samplers are similar to those used in solid-phase extraction techniques. 

Ceramic dosimeter Various solid sorbent materials Microporous ceramic material PAHs, BTEX, chlorinated hydrocarbons Integrative sampling in groundwater Up to 1 year Solvent extraction or thermal desorption 54... 

Separation of DEHP from environmental samples is usually by extraction with an organic solvent such as acetonitrile, chloroform, ethyl acetate, hexane, or methylene chloride. Air samples are drawn through a solid sorbent material (e.g., charcoal or XAD-2 resin) and desorbed with carbon disulfide (NIOSH 1985b) or ether/hexane (Rudel et al. 2001). A purge and trap method might be used for separation of DEHP from the fat in foods (van Lierop and van Veen 1988). Detector options are identical to those mentioned above (Section 7.1). Detection limits for these methods are generally in the ppb range. 

Solid sorbent materials have the ability to adsorb water vapor until an equilibrium condition is attained. The total weight of water that can be adsorbed in a particular material is a function of the temperature of the material and of the relative humidity of the air (see Adsorption). To regenerate the sorbent, its temperature must be raised or the relative humidity7 lowered. The solid sorbents most commonly used are silica (qv), alumina (see Aluminum COMPOUNDS), and molecular sieves (qv). 

Numerous articles can be found on the use of sorbent materials such as silica, stainless steel beads, and common solid-phase extraction materials for collection of supercritical fluid-extracted analytes.38 2 In this scenario the fluid is usually allowed to expand into a gas, which is forced through a packed bed of solid sorbent material. The analytes are bound or simply deposited and cryogenically trapped onto the sorbent and are later eluted with appropriate solvents. The advantage of this technique is that further cleanup can be performed by carefully selecting the eluting solvent. 

A unit operation is any single step in an overall process that can be isolated and that also tends to appear frequently in other processes. For example, a car s carburetor is a single unit operation of the engine, just as the heart is a unit operation of the human body. The concept of a unit operation is based on the idea that general analysis will be the same for all systems because individual operations have common techniques and are based on the same scientific principles. In separations, a unit operation is any process that uses the same separation mechanism. For example, adsorption is a technique in which a solid sorbent material removes speciflc components, called solutes, from either gas- or liquid-feed streams because the solute has a higher affinity for the solid sorbent than it does for the fluid. The mathematical characterization of any adsorption column is the same regardless... 

Few studies have completely determined alkyl nitrates in the field, mainly because of the complexity of the analysis and the time required for sample pretreatment. Typical reported atmospheric concentrations for some alkyl nitrates are in Table 19.4. The values for the higher alkyl nitrates (C s 4) are the sums for all isomers. As the very low values indicate, sample preconcentration is necessary to achieve low detection limits with BCD or mass spectrometry. Sample concentration most commonly employs solid sorbent materials to trap the alkyl nitrates. Pumping of large volumes of air (100 to 1000 m ) through charcoal or silica gel is followed by... 

Extraction of pesticide residues from liquid samples can be performed using a solid sorbent material. Currently available sorbent extraction techniques include (1) solid-phase extraction (SPE), (2) solid-phase microextraction (SPME), and (3) stir-bar sorptive extraction (SBSE). In the case of solid samples, a liquid extraction of pesticide residues (transfer into a solution) usually precedes the sorption step thus, it should be considered rather as a clean-up than an extraction. Matrix solid-phase dispersion (MSPD) represents a unique SPE approach that combines extraction and clean-up of solid or semisolid food samples in one step. In MSPD, the sample is mixed with a sorbent (Florisil, Cig, Cg) that serves as a solid support in sample disruption and dispersion. The resulting mix is packed into a column from which the analytes are eluted while separated matrix components are retained by the sorbent. The main drawbacks of this approach comprise rather small sample sizes ( 0.5g) and a relatively high consumption of expensive sorbents. 

In SPE, a solid sorbent material (e.g., resin or alkyl bonded silica) packed into a cartridge or imbedded... 

Andersen KB, Hansen MJ, Feilberg A (2012) Minimisation of artefact formation of dimethyl disulphide during sampling and analysis of methanethiol in air using solid sorbent materials. J Chromatogr A 1245 24... 

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