Adsorbents solid, volatile

Volatile compounds can be isolated from a solid or liquid food sample by purging the sample with an inert gas (e.g., N2, CO2, He) and adsorbing the volatiles on a porous, granulated polymer (Tenax GC, Porapak Q, Chromosorb 105), followed by recovery of the compounds. Water is retarded to only a negligible extent by these polymers (Table 5.9). The desorption of volatiles is usually achieved stepwise in a temperature gradient. At low temperatures, the traces of water are removed by elution, while at elevated temperatures, the volatiles are released and flushed out by a carrier gas into a cold trap, usually connected to a gas chromatograph. 

A technique for separating volatile analytes from liquid samples in which the analytes are subsequently trapped on a solid adsorbent. 

Both solvent-extracted and expelled coffee oils can be sprayed directly onto soluble coffee solids. The oil is adsorbed without degradation, provided moisture and oxygen are absent. However, the most volatile compounds do tend to leave the coffee powder and fill the head space of the container. 

Its inert behavior towards numerous chemical compounds and its adsorbent properties (responsible for the retention of volatile or sublimable organic compounds), make graphite the choice support for thermal reactions. Among its impurities, magnetite was revealed to be an active catalyst, and some reactions can be performed without any added catalyst. Two processes are then possible, the graphite-supported reaction ( dry process), and the reaction in the presence of a small amount of graphite (solid-liquid medium). 

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... 

These adsorptions appear to be inconsistent with the evolution of carbon dioxide and other volatiles out of the charring solid in the pyrolysis process. The adsorptive properties develop as pyrolysis frees sites for adsorption debris escaping from thermally decomposing lignocellulosics leaves the char residue with a highly reactive, eagerly adsorbing inner surface. 

Bidleman, T.F., N.F. Burdick, J.W. Westcott, and W.N. Billings. 1983. Influence of volatility on the collection of airborne PCB and pesticides with filter-solid adsorbent samplers. Pages 15 18 in D. Mackay, S. Paterson, S.J. Eisenreich, and M.S. Simmons (eds.). Physical Behavior ofPCBs in the Great Lakes. Ann Arbor Science, Ann Arbor, MI. 

The volatile substances were extracted from portions of 0. lg hair using solid-phase micro extraction (SPME). The method uses a fibre coated with an adsorbent that can extract organic compounds from the headspace above the sample. Extracted compounds are desorbed upon exposure of the SPME fibre in the heated injector port of a gas chromatograph (GC). 

Analysing volatile acids in aqueous systems, resulting mainly from the presence of water, have been reported [19]. The volatile acids high polarity as well as their tendency to associate and to be adsorbed firmly on the column require esterification prior to gas chromatographic determination. The presence of water interferes in esterification so that complex drying techniques and isolation of the acids by extraction, liquid solid chromatography, distillation, and even ion exchangers had to be used [20-23],... 

Solid-phase microextraction has also been used for to determine volatile organic compounds in soil [26]. Target compounds were adsorbed directly from a head-space sample above a soil layer onto a fused-silica fibre. Vacuum distillation coupled with gas chromatography-mass spectrometry [27], head-... 

More recently, solid phase microextraction (SPME) [22] has been applied to the analysis of bug pheromones, using two techniques. In the first, headspace volatiles are trapped on the SPME fiber, analogous to trapping on SuperQ [e.g., 23]. Alternatively, if the source of the pheromone is known, the SPME fiber can be wiped on the cuticle to directly adsorb the compounds [24]. In either case, the fiber is then thermally desorbed directly into a GC or GC-MS. Whereas this method is excellent for analysis, with good recoveries, it does not provide a sample that can be used for bioassays or for isolation of an active compound. 

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