Associated with Evolved Volatiles

Thermal-programmed solid insertion probe mass spectrometry (TP-SIP-MS) has been proposed [247,248], in which the solid insertion probe consisting of a water-cooled microfumace enters the mass spectrometer via an airlock. The sample is contained in a small Pyrex tube (i.d. 1 mm, length 20 mm). The TIC trace gives a characteristic evolved gas profile for each compound in a mixture of materials, and the mass spectra associated with each TIC peak give a positive identification of that component as it is vaporised. TP-SIP-MS is appropriate for analysis of small solid particles which are volatile, or produce volatile decomposition products. The technique is a form of evolved gas analysis. 

Besides the system described previously, other instrumental setups are reported or manufactured, including double-oven bidimensional systems, systems allowing the monitoring of the separation in the first dimension even when the heart-cut is taken, etc. Also, two independent GC systems have been used for the analysis of complex samples [40b], mainly associated with programmed temperature pyrolysis. When two groups of compounds of very different volatility are generated in pyrolysis, the volatiles that evolve... 

The volatile components or the labile groups from a polymer will be released at lower temperatures (or at the beginning of the heating time), while the polymer backbone will decompose at higher temperatures. Each point in the total ion trace (TIT) has an associated mass spectrum that allows the characterization of this process. Thermal analysis (TA) associated with the MS analysis of the evolving pyrolysates is a useful tool for polymer analysis, but the main focus in this process is not relat to an actual pyrolysis. 

It is apparent from these studies that stress MS of polymeric and composite materials is a practical method to analyze for compounds trapped within the matrix. The technique is not meant to replace existing thermal desoprtion GC/MS techniques but is complementary to them. The primary advantages of stress MS as a way to characterize indigenous volatile compounds are that labile compounds can be detected and that information on the distribution of the compounds in the sample can be obtained. However, this method is not as sensitive as conventional methods in which the evolved volatile compounds are concentrated prior to analysis. Furthermore, it is necessary to interpret the mass spectrum of the mixture of compounds. Nevertheless, the diflBculties associated with the determination of impurities of unreacted compounds in an intractable polymeric matrix warrants the continued development of stress MS. 

The endotherm observed at temperatures lower than 125 °C represents the loss of adsorbed water associated with low molecular mass volatile gas. The second broad endotherm at 300-465 °C is due to the formation of a metaplastic system. The large exotherm at 465-510 °C is attributed to a primary carbonization stage as a result of the formation of semi-coke. In the pyrolyzed gas evolved in the primary carbonization stage, Hj, CH4 and CjCyC, HjO, etc, are detected on the gas chromatogram. The second carbonization stage at about 510-750 °C is a transient process from semi-coke to coke (C J, ethylene C3, propylene C3, propane). 

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