Comprehensive Approach for Successful Microplastics Analysis

Importance of Topic

Microplastics are emerging environmental contaminants that require reliable analytical techniques to assess their abundance, size distribution, shape, and chemical identity. Quantitative and qualitative data on particles from a few micrometers up to several hundred micrometers underpin studies of environmental fate, risk assessment, and source attribution.

Objectives and Study Overview

This study demonstrates a comprehensive workflow for microplastics analysis in water samples by combining dynamic particle imaging and infrared spectroscopy. The goals are to measure particle counts, size distributions, shapes, and to perform polymer identification across size ranges from 5 µm to several hundred micrometers, following ASTM standards D8332, D8333, D8402, and the newly developed D8489.

Methodology and Instrumentation

Sample Preparation:

• Manual shredding of polypropylene (PP), polyethylene (PE), and polystyrene (PS) fragments.
• Mixing ~50 mg of shredded plastics in methanol and sieving through 212 µm and 100 µm meshes to create a synthetic D8333 mixture.

Dynamic Particle Analysis (ASTM D8489):

• Shimadzu iSpect™ DIA-10 for automated counting and imaging of 5–100 µm particles.
• Measurement medium: 50% methanol/50% glycerin; 250 µL sample aliquots; seven replicates.

Benchtop FTIR Spectroscopy for Larger Particles (>100 µm):

• Shimadzu IRTracer™-100 with QATR™ 10 attenuated total reflection attachment.
• Measurement parameters: 4 cm⁻¹ resolution, 30 scans, SqrTriangle apodization, DLATGS detector.

FTIR Microscopy for Intermediate Sizes (< few hundred µm):

• Shimadzu IRXross™ with AIMsight™ infrared microscope.
• Mapping conditions: 8 cm⁻¹ resolution, 5 scans, 50×50 µm aperture, 50 µm step, total mapping area 850×1,450 µm, T2SL detector.

Main Results and Discussion

Dynamic Imaging Results:

• Average total concentration: 3,479 count/mL (RSD 6.85%).
• Size‐class distributions (5–10 µm, 10–25 µm, 25–50 µm, 50–100 µm) showed repeatabilities from 6.7% to 19.5% RSD.
• Scattergrams illustrated area‐based diameters versus aspect ratios, confirming reliable shape characterization.

FTIR Identification of Larger Particles:

• Sixteen representative particles (67–382 µm) were identified by ATR‐FTIR as PP, PS, and PE, matching shredded material.

FTIR Microscopy Mapping:

• Two aliquots (~200 µL each) were filtered onto 15 µm stainless steel mesh; three 1.232 mm² areas measured per aliquot.
• Average counts per area: sample 1 = 10.7 particles; sample 2 = 8.3 particles.
• Estimated total particles per filter: sample 1 ~4,246; sample 2 ~3,317.

Benefits and Practical Applications

This integrated approach delivers:

• Rapid, high‐throughput quantification of microplastics size, count, and shape down to 5 µm.
• Robust polymer identification across broad size ranges using ATR‐FTIR and FTIR microscopy.
• Compliance with ASTM standardized workflows for sampling, analysis, and data comparability.

Future Trends and Applications

Advances may include automation of particle transfer to FTIR systems, higher‐resolution imaging of sub‐5 µm particles, machine‐learning algorithms for spectral classification, and in‐field portable instrumentation. Emerging standards will further harmonize results across laboratories and environmental matrices.

Conclusion

The combination of Shimadzu’s dynamic particle imaging and infrared spectroscopy platforms, guided by ASTM methods, provides a comprehensive, precise, and reproducible framework for microplastics characterization in water. This workflow addresses both quantitative and qualitative requirements, enabling better environmental monitoring and source tracking.

References

1. Shimadzu App News GCMS-2202, An Automated Workflow for Quantitative Analysis of Microplastics in Environmental Samples via Pyrolysis-GC/MS
2. Shimadzu App News 01-00396-en, Analysis of Microplastics Using AIRsight Infrared/Raman Microscope
3. WK 87463 Standard Test Method for Spectroscopic Identification and Quantification of Microplastic Particles in Water Using Infrared (IR) Spectroscopy
4. Shimadzu Whitepaper, New Standard Determination of Microplastics Particle and Fiber Size, Distribution, Shape and Concentration in Waters with High to Low Suspended Solids, Whitepaper-STP-DIA, September 2022
5. ASTM D8402, Standard Practice for Development of Microplastic Reference Samples for Calibration and Proficiency Evaluation in All Types of Water Matrices with High to Low Levels of Suspended Solids