Characteristic Specifications of Coupled Thermal Analysis - Gas Analysis Installations
Erwin W. Kaisersberger NETZSCH-Gerätebau GmbH, Wittelsbacherstr. 42, D-95100 Selb, Germany
A common functional basis of coupled systems is the gas flow through the thermal analyzer to a continuously working gas analyzer. For a continuous and therefore precisely temperature- and time-correlated gas analysis combined with thermal analysis techniques, mass spectrometry (MS) and Fourier transform infrared spectrometry (FTIR) are the methods of choice. With some restrictions, gas chromatography (GC) can also be operated in a quasi-continuous mode together with thermogravimetry. The dominant factors in the performance of a coupled system are the selection of the type of gas, the gas flow conditions (especially around the sample and on the further gas flow path through the coupling interface to the gas analyzers and detectors).
The construction materials of the transfer systems, the geometry and direction of flow paths, the pressure conditions and the temperature distribution are all studied for their influence on the sample gas transfer to the detectors.
The coupling interfaces for combinations with quadrupole mass spectrometers, based on capillaries, orifices and Skimmers, will be discussed with reference to their function as single- or double-step pressure reduction systems, with reference to the dilution effect, and also with reference to the transfer time as a function of the distance between sample, coupling interface and quadrupole mass filter.
The design, arrangement, construction materials and heating of FTIR gas cells will be highlighted for their influence on total performance of coupled systems.
New aspects in the coupling of GC-MS to thermogravimetry for fast, quasi-continuous operation are introduced and compared with the normal discontinuous gas analysis by GC-MS.
Finally, an overview on the various coupled gas analysis systems will be presented, allowing selection of the appropriate method for a given application.
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