Trapped materials Charcoal

Various sample enrichment techniques are used to isolate volatile organic compounds from mammalian secretions and excretions. The dynamic headspace stripping of volatiles from collected material with purified inert gas and trapping of the volatile compounds on a porous polymer as described by Novotny [3], have been adapted by other workers to concentrate volatiles from various mammalian secretions [4-6]. It is risky to use activated charcoal as an adsorbent in the traps that are used in these methods because of the selective adsorption of compounds with different polarities and molecular sizes on different types of activated charcoal. Due to the high catalytic activity of activated charcoal, thermal conversion can occur if thermal desorption is used to recover the trapped material from such a trap. 

An inert gas is bubbled through the sample. The volatile hydrocarbons are transferred into the vapor phase and trapped over a sorbent bed containing 2,6-diphenylene oxide polymer (Tenax GC). A methyl silicone (3% OV-1 on Chromosorb-W, 60/80 mesh) packing protects the trapping material from contamination. Other adsorbents such as Carbopack B and Carbosieve S III may also be used. If pentane and other low boiling hydrocarbons need to be detected, the sorbent trap should be filled with activated charcoal, silica gel, and Tenax, respectively, in equal amounts. 

A chemical trap provides protection against various corrosive gases which attack the pump and pump oil as well as pollute the environment. These traps operate on the principle of chemical reactions between the exhaust gases and the chemical trapping reagents. The usual trapping materials are a mixture of activated charcoal and chemicals. Hydrogen chlorides in product gas can be neutralised by sodium or... 

Realisation of the first approach - trapping and offline analysis - employs a miniature gas-sampling tube packed with a mixture of Tenax (molecular sieve) and Carbopak (activated charcoal) absorbent material. Such tubes are routinely used for environmental monitoring of hazardous industrial atmospheres whereby operators during the normal course of their duties carry a small tube (about the size of a pen) clipped to their clothes. A pump may be used to draw gas through the tube at a controlled rate and, at the end of the work period, the tube is sealed and sent for analysis. Heating the sorbent tube drives off the trapped material into a gas chromatograph for separation and quantification. 

Xe, Kr and tritium (T) that are released from molten salt fuel could be effectively trapped in an activated charcoal bed and/or other trapping materials. The container vessels in which the trapping equipment is installed have thick and heat-resistant steel walls and they can be isolated from the off-gas lines by passively operating valves. The production rate of T is estimated at about 6.2><10 Bq/(100 MW day) in normal operation. More than 90% of the T is transferred into the secondary coolant salt and finally, about 98% of the T is transferred to the trapping equipment through an off-gas line [XXX-22]. In this way, the hazard of radioactive gas release from the core under internal and external events and combinations thereof can be decreased ... 

The discussion of headspace methods for blood alcohol and solid-phase micro extraction (SPME) in Section 4.2 introduced the concept of creating an enriched head-space above a sample. Headspace methods may be passive or active and may involve heating the sample. Dynamic headspace (DHS) methods, used in arson analyses, exploit the equilibrium at the liquid-sample interface by sweeping tire headspace with a constant stream of gas, usually helium. DHS is also referred to as purge-and-trap (FT), allhough the latter can also mean a specific t) of sample preconcentrator used in environmental analysis. The trap material can be thermally desorbed or desorbed wifii a solvent. The thermal method is preferred, but is not always possible. The choice of trapping or sorbent materials depends on fire application arson typically requires charcoal or charcoal combinations. 

The most common methods for trapping pesticide vapors from air use adsorbents. Common air sampling adsorbents include charcoal (derived from petroleum or coconut) and synthetic polymeric materials, such as cross-linked polystyrene and open-cell polyurethane foam. Charcoal has been used for the cumulative sampling of volatile... 

Air samples can be analyzed by passing a known volume of air through a Teflon filter to catch air particulates followed by an activated charcoal filter to trap any gas-phase materials. The Teflon filters are extracted with hexane, concentrated, and analyzed by GC/MS. The charcoal traps are desorbed with carbon disulfide, concentrated, and analyzed by GC/MS. No performance data were reported (Dannecker et al. 1990). 

In a sorption pump, the gas is trapped within the adsorbing material (zeolites or active charcoal) called molecular sieve. Zeolites are porous aluminium silicates which adsorb large amount of gas when cooled to low temperature (usually 77K). The pump is filled with zeolite and put in a bucket containing liquid nitrogen (see Fig. 1.11). 

In this context, extraction means any process by which a fluid (air or water) comes into contact with a material to which the pollutant has an affinity. The affinity can be a physical trapping modified by some form of surface energy or a solvent extraction process based on enthalpic principles. The result is that the fluid is pumped through the sorption medium and the pollutant is reduced or eliminated from the fluid. Despite limitations, the most common sorption medium is activated charcoal — a form of charcoal treated with oxygen to open millions of tiny pores between the carbon atoms. It is amorphous and is characterized by high adsorptivity for many gases and vapors. 

The word adsorb is important here. When a material adsorbs something, it attaches to it by chemical attraction. The huge surface area of activated charcoal gives it countless bonding sites. When certain chemicals pass next to the carbon surface, they attach to the surface and are trapped. 

Despite limitations, the most common sorption medium is activated charcoal — a form of carbon treated in such a way as to open a large number of pores. The surface energy of the material and the pores combine to produce a material that can first attract and then trap small organic molecules. The attraction is via adsorption rather than absorption. Adsorption applies to attachment to the surface absorption is a bulk effect. Extraction is a bulk phenomenon. Simply put, adsorption is a function of surface area while absorption is a mass effect. 

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. 

John watched the temperature and the amount of S-10 that collected in the cold trap. We then reversed the heating up process and slowly reduced both the heating current and the direct current through the pot. The fluorinator was a more difficult machine to rtm than the charcoal tests. The last stage was the slow one that required only one person during some of this phase the material in the cold trap was slowly vacuum-distilled into another bulb to remove any residual HF and SF. ... 

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