“CC-O-PTIR+Raman can expand capabilities for MP identification to cover atmospherically-sized particles and reduce analysis time, thereby improving understanding of atmospheric MP exposure and potential impacts on human health and the environment.”
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Reporting in Analytical Chemistry, researchers at University of Michigan have addressed a critical gap in atmospheric microplastics detection. Traditional infrared microscopy struggles to identify microplastics smaller than 20 μm due to the diffraction limit of IR radiation, yet atmospheric microplastics ≤10 μm represent a significant portion of airborne particles that pose inhalation risks to human health. This size limitation has prevented comprehensive analysis of atmospherically relevant microplastics, hampering understanding of exposure risks and environmental impacts.
The research team successfully demonstrated that computer-controlled optical photothermal infrared coupled with Raman (CC-O-PTIR+Raman) microspectroscopy can identify and classify microplastics by polymer type at atmospherically relevant sizes. The technique achieved submicron spatial resolution by monitoring elastic scattering of visible photons after IR absorption and photothermal expansion, enabling analysis of particles with diameters ≥0.8 μm. Testing included three sample types of increasing complexity: microplastics-only samples, microplastics mixed with atmospheric proxy particles, and microplastics added to real-world atmospheric particle samples.
The experimental results showed that CC-O-PTIR+Raman successfully distinguished high-density polyethylene, polypropylene, and polystyrene within the same sample and within samples containing atmospherically relevant standards. The technique demonstrated match fractions exceeding 80% between PTIR and Raman spectral classifications for the same particles, with particularly strong performance in identifying microplastics within complex environmental matrices. Analysis time was reduced by at least 30% compared to manual approaches, with automated analysis completing in 50 minutes compared to 1.25-2 hours for manual particle-by-particle analysis.
The O-PTIR technique proved essential for advancing microplastics research by extending detection capabilities into the underrepresented but atmospherically critical size regime below 10 μm. The combination of improved spatial resolution, automated analysis, and simultaneous PTIR and Raman spectral collection enables reliable characterization of microplastics in complex environmental samples. This advancement directly supports improved identification of atmospheric microplastics in ambient samples, enhancing understanding of microplastic concentrations and associated inhalation exposure risks that are critical for human health assessments.
Authors:
Rebecca L. Parham, Abbygail M. Ayala, Lauren Meagher, Madeline E. Clough, Eduardo Ochoa Rivera, Jia H. Shi, Ambuj Tewari, Anne J. McNeil, and Andrew P. Ault
