Gas Chromatography - Tandem Techniques - Modern GC/IR Systems > Thermogravimetric Analysis (TGA) Coupled with GC/IR and GC/MS > Page 61


Samples of pyrolysis products from the TGA instrument were either taken directly by a light pipe interface, to the FTIR spectrometer or the products were collected in a Tenax trap. The products were recovered by rapidly heating the trap to 275C in the capillary injector of the gas chromatograph, and the carrier gas stream transferred the solutes to the GC column. The trap was then cooled back to room temperature after injection. The column was maintained at 60C until the sample had been injected and then programmed from 60 to 200C at 8C per minute. The column used was 30 m long, 0.32 mm I.D., and carried a film of 5% phenyl silicone, 1 mm thick as the stationary phase. Samples of the pyrolysis or oxidation products were taken at regular intervals and their IR spectra obtained.


A stacked plot of the spectra, taken over the heating period between 8 and 14 minutes, is shown in the upper diagram in figure 50. The spectrum obtained by combining all the spectra taken during the TGA analysis between the temperatures of 290C and 310C is also shown in figure 50. It is seen that no carbonyl adsorption bands are present indicating that a simple evaporation procedure was taking place and little or no oxidation was evident.


The stacked plot of the spectra taken during a TGA analysis that was carried out in air, over a heating period extending between 6 and 14 minutes is shown in the lower part of figure 50. It is seen that the spectra are quite different and the sample, was not merely being volatilized but oxidized. This unambiguously confirmed by the strong adsorption peak for carbon dioxide shown by the spectra that arises from the oxidation of the sample.