The characterization of closely related polymeric materials by thermogravimetry—mass spectrometry

The potential of a new technique in forensic science, thermogravimetry—mass spectrometry, is illustrated by its application to the examination of acrylic fibres and white alkyd gloss paints, small samples of which are difficult to differentiate even by a combination of current techniques. A simple interface allowing the coupling of a magnetic sector mass spectrometer to a thermobalance is described. This combination allows up to five experimental parameters to be determined simultaneously either for classification of the material under investigation or for the detailed direct comparison of samples. The thermobalance allows the temperatures at which weight losses occur and their relative proportions to be determined; the basic parameter obtained from the mass spectrometer is the total ion current trace. From this, single qualitative mass spectra may be chosen for examination and ions, whose presence or absence may be diagnostic or which vary characteristically throughout the analysis, can be selected. The variations of these ions may then be examined by computer-generated mass thermograms (analagous to mass chromatograms in g.c.—m.s.) or, if computer facilities are not available, by multiple ion detection. The residue from the analysis can be used for trace element analysis, e.g. by energy-dispersive x-ray fluorescence spectrometry.