FTIR Letter Vol. 45

Význam tématu

Four interconnected contributions illustrate recent advances in FTIR spectroscopy for environmental analysis, instrument development, spectral interpretation, and detector technology. Monitoring microscopic elastomer particles and tire and road wear particles (TRWPs) is critical to assess their ecological impact. High-performance, compact FTIR platforms with moisture-resistant beam splitters and liquid-nitrogen-free detectors expand analytical capabilities. Enhanced spectral classification of carbonyl-containing compounds further improves material identification.

Cíle a přehled článků

• Develop an FTIR microscopy method for identifying and quantifying elastomer particles ≥20 µm in sediments, including TRWPs.
• Introduce the IRSpirit-ZX FTIR spectrophotometer, highlighting its ZnSe beam splitter for humidity-robust performance.
• Provide practical infrared spectral analysis guidelines for different carbonyl functional groups (carboxylic acids, esters, ketones, aldehydes).
• Present the TEC MCT (Peltier-cooled MCT) detector option for FTIR microscopy, eliminating the need for liquid nitrogen.

Použitá metodika a instrumentace

• Sample pretreatment for sediment: KOH/MeOH digestion, high-density floatation, centrifugation, filtration through 5 µm silicon membranes.
• FTIR microscopy: transmission mode imaging with YCALOS software for spectral matching, plus ATR confirmation for TRWPs.
• Instrument platforms: IRSpirit-TX and IRSpirit-LX with KBr beam splitters; IRSpirit-ZX with ZnSe beam splitter for moisture resistance.
• Spectral analysis: identification of carbonyl classes via characteristic infrared peaks and band progressions for fatty acid derivatives.
• Detector options for microanalysis: T2SL (10×10 µm), TEC MCT (25×25 µm), DLATGS (100×100 µm) with corresponding wavenumber ranges and cooling requirements.

Hlavní výsledky a diskuse

• The FTIR microscopy method reliably identified 11 elastomer types and TRWPs ≥20 µm. Application to Tokyo Bay sediments yielded 1.7×10^5 particles/g dry weight, dominated by natural/nitrile rubber.
• Transmission FTIR microscopy proved effective for black particles up to 90 %, as thin particles transmit sufficient infrared light.
• Comparative analysis showed ZnSe beam splitters maintain transmittance under high humidity, whereas KBr degrades rapidly by deliquescence, affecting spectral accuracy.
• Carbonyl spectral rules: carboxylic acids show broad OH bands at 3 300–2 500 cm⁻¹; esters exhibit strong C–O–C bands at 1 300–1 200 and 1 150–1 000 cm⁻¹; ketones feature C–C–C asymmetric bands at 1 250–1 025 cm⁻¹ (aliphatic) or 1 325–1 215 cm⁻¹ (aromatic); aldehydes display weak Fermi resonance peaks near 2 720 cm⁻¹.
• TEC MCT detector enables high-sensitivity micro-FTIR without liquid nitrogen, with spectra comparable to liquid-nitrogen-cooled detectors for small aperture measurements.

Přínosy a praktické využití metody

• Allows unbiased quantitation of sub-100 µm elastomer particles in environmental matrices, supporting ecological risk assessments.
• Compact, user-friendly FTIR instruments with automated guidance (IR Pilot) and spectral advisors streamline routine analyses.
• ZnSe-based FTIR systems reduce maintenance in humid laboratories and field stations.
• Liquid-nitrogen-free detectors cut operational costs and simplify microscopy workflows.
• Infrared fingerprint rules for carbonyls assist researchers in rapid functional-group identification across polymers, additives, and degradation products.

Budoucí trendy a možnosti využití

• Integration of transmission FTIR microscopy with pyrolysis-GC/MS for comprehensive elastomer profiling and validation.
• Expansion of FTIR microscopy methods to airborne and waterborne micro-particles, including road dust and wastewater effluent.
• Development of larger, more diverse spectral libraries covering novel elastomer chemistries and environmental degradation products.
• Adoption of Peltier-cooled detectors in portable FTIR systems for on-site environmental monitoring and quality control.
• Advancements in AI-driven spectral interpretation to automate functional-group classification and particle identification.

Závěr

Collectively, these contributions demonstrate significant improvements in FTIR-based analysis of environmental microparticles, instrument robustness for challenging conditions, refined spectral interpretation strategies for carbonyl functionalities, and accessible detector technology. The combination of advanced sample preparation, compact moisture-resistant spectrometers, automated software, and novel detectors positions FTIR microscopy as a versatile tool for environmental chemistry, materials research, and industrial quality assurance.

Reference

1. Scholz N.L. et al., PLoS ONE, 2011, 6, e2803.
2. Tian Z. et al., Science, 2020, 371, 185–189.
3. Yamamoto K., Furumai H., J. Jpn. Soc. Civ. Eng. G, 2022, 78, III-349–III-358.
4. ISO/TS 20596:2017b, Pyrolysis-GC/MS method for TRWPs.
5. Jeong S. et al., STOTEN, 2024, 942, 173796.
6. Rauert C. et al., Environ. Sci. Technol. Lett., 2021, 8, 231–236.
7. Kameda Y. et al., Environ. Pollut., 2021, 284, 117516.
8. JIS K6230:2018, Rubber identification by IR spectroscopy.
9. Rachi S., Kameda Y., Fujita E., Proc. JSWE, 2022, 56th AM, 460.
10. JRMA statistics, rubber product shipment (2022).
11. Unice K.M. et al., Environ. Sci. Technol., 2013, 47, 8138–8147.