To identify the composition of the peaks in the TIC, mass spectral libraries and the analyst's knowledge of mass spectra can be employed. There are a number of factors that should be considered when comparing pyrograms including the presence or absence of peaks, their retention time, shape, and relative intensity. When comparing the TIC between questioned and known samples, a visual comparison of the TIC from the questioned and known samples can be made by overlaying them on a light box or displaying the TICs on the same graph. Variable peak height between samples may be another consideration when regarding paint heterogeneity. An architectural paint which contains a large quantity of components that do not degrade with pyrolysis (usually pigments) will require a larger sample than a less ‘filled’ automotive paint.
Another consideration when evaluating the sample size is the type of paint. Referring back to the inherent heterogeneity of paint, a small particle may not be representative of the coating as a whole.
If the questioned paint particle is small, it may be necessary to analyze a number of known paint particles of the same relative size to assess not only the viability of the Py-GC or Py-GCMS analysis on a particle of that size but also the variation within the known particles given the size limitation. Sample size is an important consideration when using the Py-GC or Py-GCMS. The TIC is then compared between the questioned and known samples. The mass spectrometer (present in the Py-GCMS) then detects and aids in the identification of the individual components resulting in a signal displayed as the total ion chromatograph (TIC). The polymer is thermally degraded by the pyrolyzer, and the resulting complex mixture is separated by the gas chromatograph. Pyrolysis- gas chromatograph (Py-GC) and the pyrolysis-gas chromatograph-mass spectrometry (Py-GCMS) examine the polymeric portion of the paint. Bender, in Encyclopedia of Forensic Sciences (Second Edition), 2013 Pyrolysis-Gas Chromatograph and Pyrolysis-Gas Chromatograph-Mass Spectrometer