Pyrogram
Definition
The gas chromatographic trace of volatile fragments produced by pyrolysis of a polymer; acts as the polymer-class fingerprint in Py-GC-MS.
- Produced by
- Pyrolysis of a polymer sample
- Technique
- Py-GC-MS, pyrolysis gas chromatography mass spectrometry
- Function
- Polymer-class fingerprint
- Common application
- Paint layer and coating comparison
Common questions
Why is a pyrogram useful when FTIR alone cannot identify a polymer?+
Some polymers, additives, and copolymer blends produce overlapping or weak infrared absorption bands that FTIR cannot fully resolve. Py-GC-MS breaks the polymer down into characteristic volatile fragments, giving a more specific chemical fingerprint for comparison.
Can two different paint samples from unrelated sources produce similar pyrograms?+
Samples sharing the same resin type, such as two alkyd-based paints from different manufacturers, can produce broadly similar pyrograms. Analysts typically combine Py-GC-MS results with FTIR and cross-sectional layer structure to strengthen a comparison.
Is pyrolysis a destructive test on evidence?+
Yes. The sample is thermally decomposed during the run, so analysts document and photograph the specimen and reserve a portion of the original sample before pyrolysis whenever evidence quantity allows it.
Related terms
- ASTM E2937
- ASTM International standard guide for identification of paint binders by pyrolysis-GC-MS; specifies pyrolysis conditions, GC column, oven program, and diagnostic ion reporting.
- ATR (Attenuated Total Reflectance)
- An FTIR sampling mode in which the sample is pressed against a diamond or ZnSe crystal and the evanescent wave probes the...
- Backscattered Electron (BSE) Imaging
- An SEM imaging mode sensitive to atomic number and crystallographic texture; can reveal grain-boundary elongation patterns in the sub-surface cold-worked zone after...
- ENFSI EPG Protocol
- European Network of Forensic Science Institutes Expert Working Group on Paint protocol; the European standard for paint comparison examination sequence and reporting.
- FTIR Microspectroscopy
- Fourier-transform infrared spectroscopy collected from a microscope-focused spot of 10-20 µm diameter; the primary technique for paint binder characterisation.
- IRUG Database
- Infrared and Raman Users Group spectral database; covers historic pigments, artists' materials, and museum-object coatings. Primary reference for art-investigation paint analysis.
- Likelihood Ratio Reporting
- A Bayesian framework for reporting paint-comparison conclusions, expressing the probability of the observed data given the hypothesis of common source versus the...
- Microtome Cross-Section
- A thin section of a paint chip cut perpendicular to the layer planes, allowing each layer to be examined separately by microscopy...
- Py-GC-MS
- Pyrolysis gas chromatography mass spectrometry. Thermal decomposition of a paint sample, separation of fragments, mass spectral identification. Definitive identification of polymer binders.
- Raman Microspectroscopy
- A vibrational spectroscopy technique using a focused laser beam to excite molecular vibrations in an ink sample. Non-destructive. Primary method for toner...
- SEM-EDS
- Scanning electron microscopy with energy-dispersive X-ray spectroscopy; provides elemental composition of each paint layer at 1-5 µm spatial resolution.