Handheld FTIR spectroscopy applications using the Agilent ExoScan 4100 FTIR with diffuse sample interface

Importance of the Topic

The capability to conduct rapid, non-destructive infrared analysis outside the laboratory on samples with irregular surfaces is essential for geologists, conservation scientists, quality-control technicians and industrial analysts.
A portable FTIR system with a diffuse reflectance interface extends IR spectroscopy to applications previously inaccessible to handheld devices, delivering immediate qualitative and quantitative results.

Objectives and Overview

This application note evaluates the Agilent 4100 ExoScan FTIR spectrometer equipped with a diffuse reflectance sample interface for onsite analysis of geological specimens, fabrics, paints and plastics.
The study demonstrates how efficient optics and an extended focus depth enable direct measurement of rough, curved or fragile surfaces without sample preparation.

Methodology and Instrumentation

The Agilent 4100 ExoScan FTIR integrates:

• A diffuse reflectance interface that illuminates samples at normal incidence and collects diffusely scattered light collinear with the incoming beam.
• A high-efficiency lens design to capture weak scattered signals over a wide collection angle and maintain several millimeters of focus depth.
• Scanning parameters: 8 cm⁻¹ resolution, 32 co-added scans, acquisition times under 10 seconds for most samples.
• MicroLab software for real-time spectral library matching and quantitative calibration.

Key Results and Discussion

The instrument delivered high-quality IR spectra for various challenging materials:

• Mineral identification directly on rock surfaces: franklinite, esperite, willemite, calcite, margarosanite and wollastonite exhibited distinct vibrational bands suitable for library searches despite the presence of inverted reflectance peaks from high molar absorptivity.
• Polymer coating verification: four visually similar coatings were accurately distinguished in under 15 seconds per measurement using a custom spectral library.
• Quantitative soil analysis: sulfate concentrations between 3,500 and 10,000 ppm were quantified via the overtone band near 2,200 cm⁻¹, producing linear calibration curves.
• Multi-component soil assays: simultaneous determination of carbonate, quartz, gibbsite, kaolinite, gypsum and organic matter in a single spectrum demonstrated the method’s versatility.

Benefits and Practical Applications

The handheld ExoScan FTIR with diffuse reflectance offers:

• Onsite, non-destructive qualitative identification and quantitative measurement without sample alteration.
• Rapid field decision-making in mineral exploration, roadbed assessment and product verification.
• High tolerance for surface irregularities and variable sample-to-instrument distances.
• Preservation of finished goods and field samples by avoiding contact-based sampling.

Future Trends and Potential Applications

Advances in miniaturized IR optics, combined with expanded spectral libraries and machine-learning algorithms, will further enhance in-field material characterization.
Integration with GPS, cloud-based data management and remote collaboration tools is expected to streamline decision workflows in mining, cultural heritage conservation and industrial QA/QC.

Conclusion

The Agilent 4100 ExoScan FTIR with its diffuse reflectance interface transforms handheld IR spectroscopy by enabling reliable onsite analysis of difficult samples.
Its combination of efficient light collection, extended depth of field and intuitive software supports both qualitative identification and quantitative assays in under 10 seconds per measurement.

References

• Fuller E.L., Griffiths P.R., Anal. Chem., 50, 1906 (1978).
• Agilent Technologies, Application Note 5990-7793EN, May 1, 2011.