Analysis of Microplastics Using AIMsight Infrared Microscope

Significance of the Topic

The proliferation of microplastic pollution in aquatic environments poses severe ecological and health concerns. Identifying the polymer composition and size distribution of microscopic plastic particles is essential for tracking sources, assessing environmental fate, and developing mitigation strategies.

Objectives and Study Overview

This study demonstrates the application of the AIMsight infrared microscope for qualitative identification, spatial mapping, and size measurement of environmental microplastics collected on PTFE filters. It aims to assess the instrument’s sensitivity, mapping capabilities, and integrated software functions.

Methodology and Instrumentation

• Sample Collection: Microplastics were concentrated onto PTFE filter papers from water samples. PTFE was chosen due to minimal infrared absorption except near 1200 cm⁻¹.
• Instrument Setup: An IRTracer-100 spectrometer coupled with the AIMsight infrared microscope was configured for transmission mode analysis. Measurement parameters included an 8 cm⁻¹ spectral resolution, 10 accumulations, Square Triangle apodization, 30 μm × 30 μm aperture, 30 μm step interval, and a mapping area of 1560 μm × 1110 μm. A T2SL detector captured the spectra.
• Spectral Libraries: Degraded plastic spectra were compared against the Shimadzu UV-Damaged Plastic Library to identify polyethylene and polypropylene.
• Image Analysis: The AMsolution software’s length measurement function processed wide-field and 15× reflective objective images to quantify particle dimensions.

Main Results and Discussion

• Spectrum Identification: Two distinct microplastic spectra matched UV-aged polyethylene (550 h) and polypropylene (125 h) standards. Characteristic CH2 rocking and CH3 bending peaks at 718 cm⁻¹ and 1373 cm⁻¹ were used for compound discrimination.
• Spatial Mapping: Chemical imaging revealed the heterogeneous distribution of PE and PP on the filter surface. Peak height corrections provided clear false-color maps with higher concentrations shown in red.
• Size Measurement: The length measurement tool efficiently measured particle dimensions directly from microscope images, enabling statistical assessment of microplastic sizes.

Benefits and Practical Applications

• High Sensitivity: The microscope’s high signal-to-noise ratio (30000:1) allows rapid analysis of sub-tens-of-microns particles.
• Integrated Workflow: Combines qualitative identification, spatial mapping, and size analysis in a single platform.
• Environmental Monitoring: Facilitates routine surveys to assess microplastic pollution levels and polymer types.
• Quality Control: Applicable to QA/QC laboratories and industrial materials verification where trace particle analysis is required.

Future Trends and Potential Applications

• Extension to smaller particles using combined infrared/Raman microscopy for sub-micron analysis.
• Expansion of spectral libraries to include a wider range of environmental polymer variants and weathering products.
• Integration with automated particle detection algorithms for high-throughput monitoring.
• Development of field-deployable systems for real-time microplastic mapping in environmental waters.

Conclusion

The AIMsight infrared microscope, paired with specialized software and spectral libraries, offers a robust approach for the identification, spatial mapping, and sizing of environmental microplastics. Its high sensitivity and integrated analysis capabilities support comprehensive microplastic monitoring and research.

References

• Shimadzu Corporation, Application News No. 01-00396
• Shimadzu UV-Damaged Plastic Library