FTIR Spectroscopy in Failure Analysis: Identifying the Unknown

What Is FTIR Failure Analysis?

Fourier Transform Infrared (FTIR) spectroscopy identifies materials and contaminants by measuring how a sample absorbs infrared light at different frequencies, producing a spectral “fingerprint” that’s compared against reference libraries. In failure analysis, FTIR is most often used to trace the root cause of field returns, warranty claims, or batch rejections back to a specific material or contamination source.

Test Procedure

• Isolate the region of interest — a contaminant, discolouration, inclusion, or suspect surface
• Collect a spectrum via transmission, reflectance, or attenuated total reflectance (ATR) sampling, depending on sample form
• Compare the resulting spectrum against reference libraries to identify chemical class or specific compound
• For internal contamination in a known polymer matrix, apply spectral subtraction — computationally removing the base polymer’s peaks to isolate the contaminant signal
• Correlate findings with the failure mode under investigation to determine relevance (not every detected difference is causally linked to the failure)

Applications in Failure Analysis

• Identifying foreign material or “black specks” in molded parts — thermally degraded polymer, carbonised screw/barrel residue, cross-contamination, or external particulates all look alike visually but differ chemically
• Detecting polymer degradation from heat, UV, or oxidative exposure via new functional groups in the spectrum
• Identifying chemical agents in contact with a failed part, distinguishing contamination from inherent material composition
• Confirming polymer identity for material substitution or counterfeit investigations

Detection Limits and Interpretation

FTIR can reliably detect contaminants down to roughly 100 ppm in favourable matrices, but a detected spectral difference doesn’t automatically mean it caused the failure — distinguishing a causally relevant contaminant from incidental variation is the harder, more experience-dependent part of the analysis.

Industry Specifications Referencing FTIR

• ASTM E168, E1252: general practices for infrared quantitative and qualitative analysis
• Common companion techniques: XPS for surface-only contamination, SEM/EDS for morphology and elemental mapping

Conclusion

FTIR is often the fastest, lowest-cost first step in a failure investigation because it narrows down the chemical identity of an unknown quickly — but it works best as part of a broader analytical workflow, not as a standalone verdict on root cause.