Issues in the Analysis of Microplastics

Significance of the Topic

Microplastics are pervasive pollutants in marine and freshwater environments. Their small size and altered chemical signatures, resulting from UV exposure and thermal degradation, present significant challenges for accurate identification. Reliable analysis of these particles is critical for environmental monitoring, ecological risk assessment and regulatory compliance.

Objectives and Overview

This article outlines Shimadzu’s strategy for advanced microplastic analysis. It introduces the Plastic Analyzer system and its specialized spectral libraries for UV- and thermally-damaged plastics. Three illustrative case studies demonstrate how these tools, in combination with FTIR and Raman microscopy, improve the identification and quantification of degraded microplastic particles.

Methodology and Instrumentation

• Sample Collection: White plastic shards were gathered from a coastal shoreline. Waterborne microplastics were captured on PTFE filter paper.
• Spectral Analysis: FTIR spectroscopy with single-reflection ATR and infrared microscopic transmittance mapping were employed to acquire spectra and spatial distribution maps.
• Raman Microscopy: Infrared/Raman microscopy enabled analysis of particles down to a few micrometers.
• Library Matching: Acquired spectra were compared against two proprietary databases: UV-Damaged Plastics Library and Thermal-Damaged Plastics Library.
• Particle Sizing: AMsolution software provided length measurement functionality to determine individual particle dimensions.

Instrumentation

• Fourier Transform Infrared Spectrophotometer IRXross™ with Single-reflection ATR attachment.
• Plastic Analyzer Method Package, including UV-Damaged and Thermal-Damaged Plastics Libraries.
• Infrared Microscope AIMsight™ for micro-sized particle analysis.
• Infrared/Raman Microscope AIRsight™ for combined IR and Raman measurements.
• AMsolution Software for instrument control, spectral acquisition, mapping and particle measurement.

Key Results and Discussion

• Example 1: Standard spectral libraries yielded mixed matches for white shoreline shards, but the UV-Damaged Plastics Library accurately identified UV-degraded polypropylene (PP).
• Example 2: Infrared microscopic mapping of PTFE-filtered water samples showed a predominance of PP particles, with a minor fraction of polyethylene (PE).
• Example 3: Raman microspectroscopy on PTFE filters distinguished polyethylene (PE) and polystyrene (PS) particles as small as 5 μm, with precise sizing confirmed by software measurement.

Practical Benefits and Applications

• Improved qualitative and quantitative accuracy for degraded microplastics in environmental samples.
• Capability to analyze particle sizes ranging from a few micrometers to several hundred micrometers.
• Streamlined workflows for research, QA/QC and regulatory laboratories.
• Enhanced environmental monitoring and risk assessment through reliable data on microplastic composition and distribution.

Future Trends and Potential Applications

• Expansion of spectral libraries to cover a broader range of polymer types and degradation conditions.
• Integration of artificial intelligence for automated spectral matching and particle classification.
• Development of high-throughput imaging and mapping systems for large-scale environmental surveys.
• Coupling spectroscopic analysis with advanced separation and chemical profiling techniques to characterize additives and contaminants.

Conclusion

Dedicated spectral libraries for UV- and thermal-degraded plastics, combined with advanced FTIR and Raman microscopy, significantly enhance the reliability of microplastic analysis. Shimadzu’s Plastic Analyzer platform offers a comprehensive solution for identifying, mapping and sizing microplastics, supporting diverse applications in environmental research and regulatory compliance.