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

Significance of the Topic

Fourier transform infrared spectroscopy is a versatile and widely used tool for material characterization in fields ranging from art conservation to construction quality control. Selecting the optimal sampling interface is critical to obtaining reliable, detailed spectral data from diverse solid samples without damaging valuable or brittle materials.

Objectives and Study Overview

This study compares three portable FTIR sampling interfaces—attenuated total reflectance, 45° specular reflectance, and diffuse reflectance—using an Agilent 4300 handheld instrument. The analysis focuses on three sample types: modern white acrylic paints, silicate rock fragments, and 60-day cured concrete, including thermally treated blocks.

Methodology

Spectra were collected at 4 cm-1 resolution over 64 scans in under 40 seconds per measurement. Paint samples comprised 14 formulations on cement fiber board. Geological samples involved 11 measurement locations on a monolithic silicate rock. Concrete blocks cured for 60 days were analyzed intact and after thermal treatment at 150, 300, 600, and 900 °C. Each technique was evaluated for spectral detail, reproducibility, and sample preservation.

Used Instrumentation

• Agilent 4300 handheld FTIR
• Interchangeable ATR, 45° specular reflectance, and diffuse reflectance interfaces
• Spectral resolution of 4 cm-1 and 64 scans per spectrum

Key Results and Discussion

• Paint Analysis: Diffuse reflectance captured the richest spectral detail, including carbonate filler peaks, enabling clear discrimination among 14 white acrylic formulations. ATR spectra lacked key features and required damaging sample contact; specular reflectance offered intermediate detail with high reproducibility.
• Geological Samples: Only diffuse reflectance yielded meaningful spectra from a rough silicate rock surface. ATR failed due to poor contact and specular reflectance was hindered by low surface reflectivity.
• Concrete Analysis: ATR required grinding to powder for contact, altering sample composition. External specular reflectance was ineffective on polished concrete. Diffuse reflectance successfully characterized intact and powdered concrete, revealing binder, aggregate, and sand features.
• Thermal Treatment Monitoring: Diffuse reflectance tracked hydroxyl band consolidation, carbonate decomposition at ~840 °C, and silicate structural changes in thermally treated concrete blocks. These spectral shifts correlated with mass loss events observed by thermal gravimetric analysis.

Benefits and Practical Applications

• Non-destructive sampling preserving valuable and brittle specimens
• No sample preparation enabling rapid in situ analysis
• High reproducibility with minimal user-induced variance
• Greater sampling depth and spectral detail beyond surface layers
• Portable field deployment for real-time monitoring of coating weathering and concrete curing

Future Trends and Applications

Portable FTIR with diffuse reflectance is poised for expanded use in art conservation, geology, and construction QA/QC. Integration of multivariate data analysis and real-time processing will support on-site decision making. Extension to powders, composites, and environmental monitoring will broaden its industrial and research applications.

Conclusion

Diffuse reflectance sampling outperforms ATR and specular reflectance for portable FTIR analysis of paints, minerals, and concrete by delivering superior spectral detail, reproducibility, and truly non-destructive measurement. The Agilent 4300 handheld FTIR with interchangeable interfaces offers a flexible solution for rapid material characterization in laboratory and field environments.

References

1. Positive and Non destructive Identification of Acrylic Based Coatings Agilent publication number 5991 5965EN
2. Coating Analysis Non Destructive Spectroscopic Modelling of an Industrial 2K Epoxy Resin Coated Panel Undergoing Accelerated Weathering as per ASTM G155 Protocol Agilent publication number 5991 6976EN
3. 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
4. Tang PL Alqassim M Daéid NN Berlouis L Seelenbinder J Non destructive Handheld Fourier Transform Infrared 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 I Composition Specifications and Conformity Criteria for Common Cements