FTIR talk letter vol. 17

Significance of Topic

Rapid and non-destructive spectroscopic techniques play a key role in real-time monitoring of gas composition, thin-film coatings, and process control. Infrared (IR) and Raman methods offer complementary molecular information, while modern UV-VIS spectrophotometers extend analyses into the near-infrared, supporting research, industry QA/QC, and environmental monitoring.

Objectives and Overview of Articles

These articles present:

• Comparative analysis of gas chromatography and FTIR gas spectroscopy
• Automated FTIR quantitation in process control
• Specular reflection FTIR for thin films and coatings
• Q&A contrasting Raman and infrared spectroscopy
• Introduction to enhanced UV-VIS spectrophotometer models

Methodology and Instrumentation

Gas Analysis by FTIR:

• Transmission FTIR gas cell—integration times, resolution, pathlength adjustments
• Multipath gas cells for extended optical path and MCT detectors cooled by liquid nitrogen
• Standard gas calibration and pressure correction

Automated Quantitation System:

• FTIR interfaced with DCS and PLC for start/stop signals, 4–20 mA output
• Macro programming for background/sample alternation and endpoint detection

Specular Reflection FTIR:

• SRM-8000 specular reflectance attachment (10° incidence)
• Absolute reflectance accessory with V/W mirror arrangements
• Kramers–Kronig analysis for converting reflectance to absorption
• Interference fringe analysis for film thickness calculations

Raman Spectroscopy:

• 532 nm laser excitation, Raman shift spectra (cm⁻¹)
• Selection rules based on polarizability changes
• Complementary information to IR, glass-capillary and aqueous solution compatibility

UV-VIS Spectrophotometry:

• UV-2600 single monochromator (up to 1400 nm with integrating sphere)
• UV-2700 double monochromator for 8-Abs range and ultra-low stray light
• Compact design, energy saving, validation software included

Main Results and Discussion

FTIR gas analysis achieved ~1 min multi-component detection without carrier gas or sample pretreatment. Sensitivity differences among gases were linked to molecular dipole activity; multipath cells and integration control improved limits to ppm–ppb levels. Automated FTIR in a reaction furnace demonstrated reliable DCS control and unmanned operation. Specular reflection FTIR identified epoxy resins on aluminum, measured acrylic and polyester film absorption via K-K processing, and determined thickness (~26.4 µm) from interference fringes. Raman spectroscopy distinguished modes invisible to IR, notably C=C vibrations, confirming its complementarity. New UV-VIS models combined extended wavelength range, low noise, and high photometric range in a small footprint.

Benefits and Practical Applications

• Continuous, non-destructive gas monitoring in environmental and process control
• Direct thin-film analysis without sample destruction or special pretreatment
• Automated integration with plant control systems for endpoint detection
• Complementary IR/Raman datasets enhance substance identification in complex matrices
• Versatile UV-VIS platforms adaptable to research, QA/QC, and routine analysis

Future Trends and Opportunities

• Miniaturized and portable spectrometers for field and inline use
• Advanced detector technologies (e.g., uncooled MCT alternatives, quantum detectors)
• Enhanced multipath and waveguide cells for sub-ppm gas detection
• AI-driven spectral libraries and automated peak assignment
• Integration of IR, Raman, and UV-VIS into unified multi-modal platforms

Conclusion

Infrared gas analysis and specular reflection FTIR offer rapid, versatile, and non-invasive techniques for quantitative and qualitative monitoring of gases and surface films. Automated FTIR systems improve process control, while Raman spectroscopy provides complementary vibrational insights. Modern UV-VIS spectrophotometers extend analytical capabilities into the near-infrared with high sensitivity. Together, these technologies support advanced research and industrial applications.

Used Instrumentation

• FTIR spectrometer with gas cell and multipath accessories
• SRM-8000 specular reflectance attachment and absolute reflectance accessory
• MCT (HgCdTe) detector cooled by liquid nitrogen
• Raman microscope with 532 nm laser
• UV-VIS spectrophotometers UV-2600 and UV-2700
• Distributed control system (DCS) and PLC interfaces

References

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