Analysis of Microplastics Using AIRsight Infrared/Raman Microscope

Significance of the Topic

The widespread presence of microplastics in aquatic environments poses risks to ecosystems and human health. Accurate identification of polymer types and size distributions is essential for tracing pollutant sources and assessing ecological impact. Integrating infrared and Raman microscopy streamlines analysis and enhances detection limits for particles down to sub-micron dimensions.

Objectives and Overview

This study demonstrates the use of a combined infrared/Raman microscope (AIRsight™) for qualitative and dimensional analysis of environmental microplastics. It compares micro-infrared spectroscopy and micro-Raman spectroscopy on a single platform, evaluates measurement protocols, and illustrates a novel image-based length measurement feature.

Methodology and Instrumentation

Samples of microplastics were collected by filtering water through PTFE filter paper, which exhibits minimal infrared absorption except around 1200 cm⁻¹. The intact filter was placed on the AIRsight stage for analysis.

• Infrared measurements: IRXross™ module with 8 cm⁻¹ resolution, 30-scan accumulation, Happ-Genzel apodization, 25 µm aperture, T2SL detector, transmission mode.
• Raman measurements: 785 nm excitation to minimize fluorescence, 100× objective, 5 sec exposure, 40-scan accumulation, CCD detector.

Main Results and Discussion

Infrared spectra of the largest particles matched UV-irradiated polypropylene, confirming polymer type despite PTFE background absorption. Raman spectra unambiguously identified smaller particles as polyethylene and polystyrene. Combining both techniques allowed reliable identification across a size range from ~100 µm down to below 10 µm. A built-in image-based length measurement tool provided particle dimensions of 97 µm, 10 µm, and 5 µm for three representative particles.

Benefits and Practical Applications

The AIRsight microscope enables both spectroscopic modalities on one stage without sample transfer, reducing analysis time and contamination risk. The integrated length measurement function adds quantitative size data to chemical identification, supporting environmental monitoring, regulatory compliance, and source attribution in microplastics research.

Future Trends and Possibilities

Ongoing developments may include automated particle mapping and classification workflows, expanded spectral libraries for weathered polymers, and coupling with imaging algorithms for high-throughput microplastics screening. Integration with AI-driven spectral interpretation could further accelerate environmental assessments.

Conclusion

This work demonstrates a unified infrared/Raman approach for comprehensive microplastics analysis, combining spectral identification and size measurement in a single instrument. The methodology enhances detection limits, streamlines workflows, and offers robust data crucial for environmental science and quality control.

Reference

Zenjiro Osawa: Principles of Chemiluminescence Method and Applications to Polymer Degradation, Material Life, Vol. 3, No. 1, pp. 32–39 (1991)