Headspace analysis cold trapping

Small solid seuaples can be analyzed directly by dynamic headspace sampling using a platinum coil and quartz crucible pyrolyzer and cold trap coupled to an open tubular column (341,369,379). This method has been used primarily for the analysis of mineral samples and of additives, catalysts and byproducts in finished polymers which yield unreliable results using conventional headspace techniques owing to the slow release of the volatiles to the headspace. At the higher temperatures (450-1000 C) available with the pyrolyzer the volatiles are more readily and completely removed from the sample providing for quantitative analysis. 

The headspace is the air above or around a fragrant substance that contains the volatile compounds. This can be collected for analysis when extraction of the volatiles from the material is not viable. This technique has been extensively developed for the collection and analysis of flower volatiles since many flowers do not yield an extract that reflects the odour of the fresh flower, while others are simply too rare to be available in sufficient quantity for extraction. Many different techniques have been applied to the collection of volatiles from the air above flowers including the use of cold traps, solvent traps, adsorbent materials... 

When analytes are under the limit of detection (LOD) of the technique is necessary to use enrichment techniques. In headspace analysis, for this purpose the target analytes must be separated from the headspace gas either by absorption into a liquid or by adsorption onto a solid adsorbent and also by condensation in a cold trap. (Kolb, 1999). Solvent free techniques are particularly desirable in case of trace analysis to avoid problems with solvent impurities. Consequently, cryogenic trapping is the preferred choice to improved detection limits in static headspace analysis... 

Volatile and aromatic components Cocoa volatile and aromatic components are analyzed by capillary GC, with samples derived from headspace enrichment or cold-trapping techniques. Analysis is similar to that of coffee volatiles FIDs are used and identification is by the use of reference compovmds. 

Fig. 1 Comparison of dynamic, static, and SPME headspace sampling, (a) Dynamic headspace sampling uses a sorbent or cold trap to concentrate volatile analytes before analysis by the GC. (b) Static headspace sampling uses direct transfer of a volume of gas from the headspace above the heated sample vial directly to the GC for analysis. Injection designs are illustrated in Fig. 2. (c) SPME headspace sampling uses a fiber support with solid-phase coating. The fiber is placed in the headspace and reaches equilibrium with the headspace volatile analytes. The SPME fiber is transferred by means of a syringe and thermally desorbed in the injector of the GC for analysis.

Raisanen [990] has described a device consisting of a cylindrical sample bottle holder, a dry carrier gas flow system, and a moisture transducer as a non-toxic replacement for Karl Fischer analysis of plastics. The sample of test material contained in a 20 mL septum bottle is heated to a preset temperature, usually just below the softening point of the resin. Evolved volatiles in the bottle headspace are passed through a cold trap filter to an analysis cell where the moisture content of the flowing gas is measured. High boilers are filtered out. A sophisticated algorithm, which makes use of the fact that as the sample approaches total dryness the rate of evolution of water is proportional to the water remaining in the sample, allows accurate determination of the... 

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