FTIR talk letter vol. 17

Significance of the topic

The advances in spectroscopic techniques described here address critical needs in industrial and research laboratories for rapid, non-destructive, multi-component analysis of gases, thin films, coatings, and bulk materials. Continuous gas monitoring by FTIR can replace or complement gas chromatography for process control. Specular reflectance FTIR enables characterization of films and coatings without sample destruction. The complementary nature of infrared and Raman spectroscopy expands molecular identification capabilities, and the latest UV-Vis spectrophotometers extend measurement range into the near-infrared while improving throughput and energy efficiency.

Objectives and overview of the article

This article presents four key topics: 1) FTIR gas analysis methods, 2) specular reflection FTIR for thin films and substrates, 3) comparison between Raman and infrared spectroscopy, and 4) features of new single- and double-monochromator UV-Vis systems. Each section outlines the methodology, instrumentation details, performance advantages, limitations, and application examples, with a focus on practical implementation in QA/QC, process monitoring, and materials research.

Methodology and Instrumentation

• FTIR gas analysis: gas cell configurations (multipath cells, optical pathlengths from cm to meters), MCT detectors cooled by liquid nitrogen for ppt-level sensitivity, number of scans and resolution trade-offs, flow cells for real-time monitoring, macro programs for automated control via DCS/PLC and 4–20 mA outputs.
• Specular reflection FTIR: SRM-8000 attachment at 10° incidence for relative reflectance, absolute reflectance accessory using V/W mirror arrangements, Kramers-Kronig analysis (Maclaurin and double-FFT methods) to derive absorption coefficient, interference fringe analysis for film thickness measurement.
• Raman vs IR: Raman microscope (∼1 μm spot) with 532 nm laser excitation, benefits of glass transparency and minimal water interference; infrared microscope measurements (∼10 μm) with extensive spectral libraries.
• UV-Vis spectrophotometers: UV-2600 single monochromator with extended range to 1400 nm using an integrating sphere, compact footprint, energy savings and built-in validation; UV-2700 double monochromator with ultra-low stray light and 8-Abs photometric range using Lo-Ray-Ligh gratings.

Main results and discussion

• FTIR gas analysis enables highly rapid (∼1 min) non-destructive, multi-component quantitation without pretreatment, though sensitivity varies by molecular polarity and overlap of absorption bands; key combustion gases (CO, CO₂, SO₂, NOₓ, HCl, HF, HCN) have specific calibration peaks in the mid-IR.
• Flow-cell measurements capture dynamic concentration changes in real time but require optimization of cell volume for temporal resolution, temperature control to prevent adsorption, and moisture removal to avoid interference.
• Specular reflectance FTIR yields reflection absorption spectra for thin coatings, differential spectra for thick films, and fringe patterns for thickness determination; K-K processing recovers true absorption but demands low-noise data acquisition.
• Raman and IR provide complementary molecular fingerprints: IR highlights polar bonds (C=O, C–O), Raman emphasizes symmetric stretches (C=C); each has unique instrumentation costs, sample preparation, and library resources.
• UV-Vis systems combine high throughput, wide dynamic range, and flexible accessories to support applications from routine QA to advanced research.

Benefits and practical applications of the methods

• In-line FTIR gas monitoring for combustion control, reaction endpoints, emission tracking, and environmental compliance.
• Automated FTIR integration with plant DCS/PLC enables unattended operation and feedback loops for furnace control.
• Specular reflectance FTIR for non-destructive analysis of paint coatings, metal films, and polymer layers in manufacturing and failure analysis.
• Complementary use of Raman and IR spectroscopy for comprehensive identification of pharmaceuticals, polymers, and contaminants.
• UV-Vis spectrophotometry with extended NIR capability for color measurements, transmittance/reflectance studies, and concentration assays in chemical, food, and biomedical fields.

Future trends and potential applications

Integration of FTIR and Raman sensors into compact, fiber-optic platforms for remote and in-process measurements is anticipated. Machine learning algorithms will enhance spectral deconvolution and predictive maintenance. The trend toward modular, multi-technique spectrometers that combine UV-Vis, IR, Raman, and fluorescence in a single platform will streamline analytical workflows. Advances in detector technology may improve sensitivity and reduce cooling requirements, broadening field-deployable applications.

Conclusion

The methodologies reviewed offer robust solutions for rapid, non-destructive analysis across gas, film, and bulk materials. Optimizing cell design, detector choice, and data processing ensures high sensitivity and precision. Complementary pairing of IR and Raman expands molecular coverage, while modern UV-Vis systems address broad wavelength demands. Together, these spectroscopic tools form an integrated analytical framework for industrial process control, quality assurance, and advanced research.

References

• David Welti (1970) Infrared Vapour Spectra. Heyden & Son Ltd.
• IR and Raman Spectroscopy, Introduction to Spectroscopy Series, Vol. 6. Spectroscopical Society of Japan, Kodansha.
• Masayuki Tanaka and Norio Teramae. IR Spectroscopy (Instrument Analysis Techniques Series), Kyoritsu Shuppan.
• Mitsuo Tasumi. FT-IR Fundamentals and Actualities. Tokyo Kagaku Dojin.
• Yukihiro Ozaki (Ed.). NIR Spectroscopy. Japan Scientific Societies Press.
• Sadtler Database. Bio-Rad Laboratories, Inc.