Alternative sampling devices

Generally, any of these filters satisfied the requirements for collection of most of the particulates to be analyzed. However, certain analytes and their associated analytical methods gave better results with alternative filters. The filter cassette was also tested as part of the total sampling device. Some substances were partially collected on the cassette, and the substance had to be rinsed from the cassette with solvent to avoid loss. 

On-line SFE-GC has also been used as an alternative to thermal desorption gas chromatography of Tenax sampling devices for quantitative analysis of volatile organic compounds (VOC). The SFE-GC approach allows the analytes to be recovered from the adsorbent sampling devices at mild temperatures, which prevents thermal decomposition and other problems associated with high temperature desorption. This work is described in detail elsewhere (Wright,B.W. Kopriva, A.J. Smith, R.D. submitted for publication). 

In the alternative, open-circuit type of chamber (Hg. 11.4b), air is drawn through the chamber at a metered rate and sampled for analysis on entry and exit.Thus, carbon dioxide production, methane production and oxygen consumption can be estimated. As the differences in composition between inlet and outlet air must be kept small if conditions for the animal are to be kept normal, very accurate measures of gas flow and composition are required. Modern equipment, based on infrared analysers, meet this criterion, and open-circuit chambers have now largely replaced closed-circuit chambers.AMth some chambers it is possible to alternate between closed- and open-circuit operation. Closed-circuit operation for perhaps 30 minutes, with no gas absorption, produces appreciable changes in the composition of the chamber air. Then a brief period (about 3 minutes) of open-circuit operation allows the chamber air to be flushed out through a flow meter and sampling device. 

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