FTIR talk letter (Vol. 43)

Importance of the Topic

Infrared spectroscopy remains a cornerstone technique in analytical chemistry for identifying organic materials, validating sample integrity, and monitoring environmental contaminants. Recent advances in software guidance, spectral interpretation protocols, and integrated instrumentation address key challenges in data quality, compound classification, and microplastics analysis.

Objectives and Study Overview

This summary integrates findings from three technical notes published by Shimadzu:

• An overview of the Spectrum Advisor feature added to LabSolutions IR v2.33 to assist analysts in diagnosing and correcting poor-quality FTIR data.
• Practical guidelines for distinguishing aliphatic unsaturated hydrocarbons (olefins) and aromatic compounds using characteristic infrared bands.
• A description of a product line for comprehensive microplastics (MPs) analysis, covering sample preparation, particle imaging, and polymer identification.

Methodology and Instrumentation

Key analytical approaches and equipment include:

• FTIR Sampling Modes: Transmission, specular/diffuse reflectance, and ATR methods evaluated by Spectrum Advisor.
• Interactive Software Tools: LabSolutions IR v2.33 with the Spectrum Advisor module and AMsolution for IR/Raman microscopy (AIMsight, AIRsight).
• Spectral Interpretation Protocols: Assignment of CH stretching (>3000 cm⁻¹), C=C stretching (1650 vs. 1600–1500 cm⁻¹), and C–H out‐of‐plane bending (1000–800 and 900–670 cm⁻¹) vibrations.
• Microplastics Workflow: The MAP-100 automated pretreatment unit, Plastic Analyzer FTIR system, and infrared microscopes for particle-level component determination.

Main Results and Discussion

Spectrum Advisor guides users through a stepwise process to identify noise sources, baseline distortions, and alignment errors by comparing reference spectra and recommending actions such as increasing scan numbers or performing auto background adjustments. For hydrocarbon analysis, diagnostic bands allow:

• Clear differentiation of olefins (C=C stretch at ~1650 cm⁻¹) versus aromatics (bands at ~1600 and ~1500 cm⁻¹).
• Structural identification of vinyl, cis- and trans-vinylene, and trisubstituted olefins via C–H out-of-plane bending in the 1000–800 cm⁻¹ region.
• Estimation of aromatic substitution patterns through peak positions in the 900–670 cm⁻¹ and overtone regions (2000–1660 cm⁻¹).

In butadiene rubbers, IR profiles in the 1000–800 cm⁻¹ window distinguish high-cis, low-cis, and high-trans isomer ratios. The microplastics portfolio streamlines analysis from automated particle isolation in environmental water samples to polymer verification using FTIR and microscope-based imaging.

Benefits and Practical Applications

This integrated approach delivers:

• Enhanced data quality assurance for FTIR users with varying expertise.
• Standardized spectral interpretation rules for rapid hydrocarbon classification.
• A turnkey pathway for environmental monitoring of microplastics, combining high throughput sample pretreatment with nondestructive compositional analysis.

Future Trends and Potential Applications

Emerging directions include:

• AI-driven real-time guidance for FTIR method optimization and error correction.
• Expansion of spectral libraries with machine-learning classifiers for complex polymer mixtures.
• Greater automation in microplastics imaging and polymer mapping, integrating hyperspectral and Raman modalities.

Conclusion

Shimadzu’s enhancements in software guidance, spectral interpretation, and instrument integration strengthen the reliability and throughput of IR-based analyses. These advances support diverse applications—from materials characterization to environmental contaminant monitoring—by reducing user dependency, clarifying spectral assignments, and facilitating comprehensive microplastics evaluation.

Reference

[1] Xu Yan, Karen Maruyama, “FTIR Analysis of Recycled Plastics Using the Spectrum Advisor Function,” Shimadzu Application News 01-00653-EN (Dec. 2023)
[2] N.B. Colthup, J. Opt. Soc. Am. 40, 397 (1950)
[3] P.J. Larkin, Infrared and Raman Spectroscopy: Principles and Spectral Interpretation, 2nd Ed., Elsevier (2017)
[4] T. Sone, J. Soc. Rubber Sci. Technol. Japan, 88, 178 (2015)