FTIR Microspectroscopy
Definition
Fourier-transform infrared spectroscopy collected from a microscope-focused spot of 10-20 µm diameter; the primary technique for paint binder characterisation.
- Spot size
- 10 to 20 micrometres diameter
- Detector type
- Coupled to an IR microscope, often with an MCT detector
- Primary use
- Paint binder and layer characterisation
- Sample form
- Thin section or diamond-cell flattened cross-section
Common questions
Why is a microscope needed instead of bulk FTIR?+
A standard FTIR sample compartment averages the whole pellet or crystal, but automotive and architectural paint chips are built from stacked layers only tens of micrometres thick. The microscope focuses the beam so each layer can be measured separately without contamination from the layers above or below it.
What can it not tell you about a paint sample?+
It identifies binder chemistry and some inorganic pigments but is poor at distinguishing pigments of similar composition or trace organic dyes present at low concentration; those cases usually need Raman spectroscopy or Py-GC-MS alongside 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.
- 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.
- Pyrogram
- The gas chromatographic trace of volatile fragments produced by pyrolysis of a polymer; acts as the polymer-class fingerprint in Py-GC-MS.
- 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.