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

Significance of the topic

FTIR spectroscopy offers detailed molecular information but the choice of sampling interface greatly influences data quality and sample integrity. Portable FTIR instruments with interchangeable interfaces enable non-destructive, rapid analysis of diverse solids without extensive preparation, addressing limitations of traditional ATR methods on brittle or uneven samples.

Objectives and overview of the study

The study evaluates ATR, diffuse reflectance and 45° specular reflectance interfaces on an Agilent 4300 handheld FTIR across three sample types: modern white acrylic paints, a silicate rock and cured concrete. Comparisons focus on spectral detail, reproducibility and sample preservation under identical instrumental settings (64 scans, 4 cm⁻¹ resolution, sub-40 second acquisition time).

Methodology

• Instrument: Agilent 4300 handheld FTIR spectrometer
• Sampling interfaces: ATR, 45° specular reflectance, diffuse reflectance
• Acquisition parameters: 64 scans per spectrum, 4 cm⁻¹ resolution, acquisition time under 40 seconds
• Samples: 14 paint formulations on fibre–cement board; eleven locations on a monolithic silicate rock; CEM I concrete cured for 60 days, including thermal treatments at 150 °C, 300 °C, 600 °C and 900 °C

Used Instrumentation

• ATR interface with diamond crystal requiring intimate contact
• 45° specular reflectance module capturing light reflected at a fixed angle
• Diffuse reflectance module allowing non-contact or minimal contact measurements with scattered light collection

Main results and discussion

Paint analysis unveiled that only diffuse reflectance spectra contained sufficient detail to distinguish formulations, including identification of carbonate fillers around 2500 cm⁻¹. ATR spectra lacked depth and reproducibility and caused surface damage, while 45° specular reflectance delivered intermediate performance with high reproducibility.

Geological samples showed ATR failure due to uneven surface and specular reflectance failure due to low reflectivity. Diffuse reflectance provided clear silicate fingerprint peaks (950–1300 cm⁻¹), carbonate features and hydroxyl bands, enabling rapid mapping of compositional variations across the rock surface.

In concrete analysis, ATR required destructive pulverization and still yielded less information than diffuse reflectance collected directly on the polished sample surface. Diffuse spectra differentiated binder, aggregates and fines and captured spectral changes associated with thermal degradation. Thermal treatment studies correlated mid-IR spectral changes in hydroxyl, carbonate and silicate regions with mass losses observed by TGA, demonstrating non-destructive monitoring of concrete chemistry upon heating.

Contributions and practical applications

• Non-destructive, in situ analysis of paints, minerals and concrete without sample preparation
• High reproducibility and depth of information using diffuse reflectance
• Rapid interface switching for multi-modal measurements in field and laboratory settings
• Capability to monitor real-time ageing, weathering and thermal degradation processes

Future trends and possibilities for use

Advances in portable FTIR instrumentation and diffuse reflectance optics will expand real-time, on-site QA/QC across heritage conservation, construction monitoring and geosciences. Integration with chemometric models and hyperspectral imaging may enable detailed spatial mapping and automated material classification without sample destruction.

Conclusion

Diffuse reflectance measurements with a handheld FTIR deliver superior spectral detail, reproducibility and sample integrity compared to ATR and specular reflectance. Interchangeable interfaces on portable instruments facilitate versatile, non-destructive analysis of complex solids, underscoring the value of reflectance techniques for broad analytical applications.

References

1. Positive and Non-destructive Identification of Acrylic Based Coatings – Agilent publication 5991-5965EN
2. Coating Analysis: Non-Destructive Spectroscopic Modelling of an Industrial 2K Epoxy Resin Coated Panel Undergoing Accelerated Weathering – Agilent publication 5991-6976EN
3. M. Saafi, P. L. Tang, J. Fung, M. Rahman and J. Liggatt, Enhanced properties of graphene/flyash geopolymeric composite cement, Cement and Concrete Research, 2015, 67, 292–299.
4. P. L. Tang, M. Alqassim, N. N. Daéid, L. Berlouis and J. Seelenbinder, Non-destructive Handheld Fourier Transform Infrared (FT-IR) Analysis of Spectroscopic Changes and Multivariate Modelling of Thermally Degraded Plain Portland Cement Concrete and its Slag and Fly Ash-Based Analogs, Applied Spectroscopy, 2016, 70(5), 923–931.
5. BS EN 197-1:2011 Part 1 Composition, Specifications and Conformity Criteria for Common Cements, British Standards Institution, 2011.