Identification of microplastics with Raman microscopy

Significance of the Topic

Microplastics are a pervasive environmental concern due to their small size and persistence in marine ecosystems. Rapid and reliable identification of these particles is essential for assessing pollution sources, understanding ecological impacts, and guiding mitigation strategies.

Objectives and Study Overview

This study demonstrates the application of portable Raman microscopy for quick identification of microplastic particles collected from surface estuary waters. The focus is on evaluating spectral analysis with a 1064 nm excitation source to distinguish common polymers.

Methodology and Instrumentation

Water samples were collected from Delaware Bay, fixed with formaldehyde, and size‐fractioned using stainless steel sieves (5000, 1000, 300 μm). Following drying, samples underwent wet peroxide oxidation and density separation to isolate microplastics. Particles were sorted by type under a stereomicroscope prior to spectroscopic analysis.

Used Instrumentation

• i-Raman EX portable Raman spectrometer with 1064 nm laser excitation (laser power <165 mW, spot size 42 μm)
• BAC151C video microscope with 50× objective (working distance 9.15 mm)
• BWID software for spectral library matching and calculation of hit quality index (HQI)

Results and Discussion

Secondary microplastics such as irregular blue fragments (≈4.5 mm) were identified as polyethylene with HQI 95.7. Primary microplastics included spherical beads matched to polystyrene (HQI 98.2) and thin colored fibers identified as polypropylene (HQI 74.9). Additional peaks in fiber spectra revealed the presence of copper phthalocyanine green pigment, aiding source attribution. A summary of identifications showed 11 polyethylene, 4 polypropylene, 2 polystyrene, and 5 inconclusive samples, with black particles and sample degradation posing challenges.

Benefits and Practical Applications

Raman microscopy enables on‐site analysis of particles under 100 μm, with 1064 nm excitation reducing fluorescence from dyes. The HQI algorithm streamlines polymer matching against reference libraries, facilitating rapid screening in environmental monitoring and laboratory QA/QC.

Future Trends and Potential Applications

Advancements may include integration of multivariate analysis for complex mixtures, automated particle mapping, and coupling with imaging platforms. Standardization of protocols and expansion of spectral libraries will enhance comparability across studies. Portable Raman instruments could support real‐time field surveys and large‐scale screening programs.

Conclusion

Portable 1064 nm Raman microscopy proves effective for unambiguous identification of microplastics in environmental samples. The approach offers rapid, non‐destructive analysis with minimal fluorescence interference and reliable library matching.

Reference

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