Comparison of Portable FTIR Interface Technologies for the Analysis of Paints, Minerals & Concrete

Significance of the Topic

FTIR spectroscopy is a well-established technique for detailed molecular analysis of solids. The choice of sampling interface influences the depth of information, sample integrity and operational ease. While ATR is widely adopted for its simplicity, its limited penetration depth and sample contact requirements can undermine analysis of brittle or uneven materials. Exploring alternative interfaces such as diffuse and specular reflectance can expand FTIR’s applicability to coatings, minerals and construction materials without destructive sample preparation.

Study Objectives and Overview

This application note compares three FTIR sampling modes (ATR, 45° specular reflectance, diffuse reflectance) on paint, geological and concrete samples using a handheld Agilent 4300 FTIR. The aim is to evaluate spectral quality, reproducibility, sample impact and suitability for in situ non-destructive analysis of complex solid matrices.

Methodology and Instrumentation Used

The Agilent 4300 handheld FTIR was fitted with interchangeable interfaces: ATR, 45° specular reflectance and diffuse reflectance. Spectra were acquired with 64 scans at 4 cm−1 resolution in under 40 seconds per spectrum. Samples included modern white acrylic paint on cement fibre board, a silicate-based rock measured at multiple surface locations, and ordinary Portland cement concrete cured for 60 days. Powdered concrete was also prepared to enable ATR measurements for direct comparison.

Main Results and Discussion

• Paint Analysis
  • Diffuse reflectance spectra provided the most detailed fingerprint, revealing filler peaks (~2500 cm−1) and subtle binder variations across 14 paint formulations.
  • Specular reflectance yielded reproducible spectra but with slightly less detail than diffuse reflectance.
  • ATR spectra showed limited information and suffered from surface damage and high variance due to sample deformation under contact pressure.
• Geological Samples
  • ATR and specular reflectance failed to produce meaningful spectra on the uneven rock surface without destructive grinding.
  • Diffuse reflectance captured silicate bands (950–1300 cm−1) and hydroxyl features (3000–4750 cm−1) across 11 locations, illustrating compositional variability.
• Concrete Analysis
  • ATR required powdering and risked thermal alterations, while specular reflectance was ineffective on low-reflectance surfaces.
  • Diffuse reflectance delivered richer spectral detail of the mortar and aggregate phases without sample preparation.
  • Thermal treatment studies (150–900 °C) showed predictable changes: consolidation of hydroxyl bands, carbonate decomposition (~2500 cm−1), and silicate structural transformations correlating with TGA mass-loss events.

Benefits and Practical Applications

• Non-destructive in situ measurements preserve sample integrity, essential for heritage conservation and real-time monitoring.
• Diffuse reflectance minimizes user-induced error by eliminating contact pressure requirements.
• Enhanced spectral detail facilitates discrimination of coatings, mineralogy mapping and monitoring of concrete cure and degradation.

Future Trends and Opportunities

Increased adoption of portable diffuse reflectance FTIR may drive advances in on-site quality control, heritage science and construction diagnostics. Coupling with chemometric modelling and real-time data analytics can further improve material classification and lifecycle monitoring. Emerging nanostructured interfaces could extend depth profiling and sensitivity for complex composites.

Conclusion

The comparative study demonstrates that diffuse reflectance FTIR outperforms ATR and 45° specular reflectance for diverse solid samples. It provides greater spectral information, reproducibility and non-destructive in situ capability. The handheld Agilent 4300 FTIR with interchangeable interfaces offers a versatile platform for rapid field analyses across paints, minerals and concrete.

References

• Agilent Technologies. Positive and Non-destructive Identification of Acrylic Based Coatings. Publication 5991-5965EN.
• Agilent Technologies. Non-Destructive Spectroscopic Modelling of an Industrial 2K Epoxy Resin Coated Panel. Publication 5991-6976EN.
• Saafi M, Tang PL, Fung J, Rahman M, Liggatt J. Enhanced Properties of Graphene/Flyash Geopolymeric Composite Cement. Cement and Concrete Research. 2015;67:292–299.
• Tang PL, Alqassim M, Daéid NN, Berlouis L, Seelenbinder J. Non-destructive Handheld FT-IR Analysis of Thermally Degraded Concrete. Applied Spectroscopy. 2016;70(5):923–931.
• BS EN 197-1:2011. Composition, Specifications and Conformity Criteria for Common Cements. 2011.