Reliable Identification of Microplastics of any Dimension, on any Filter

Significance of the Topic

Microplastic particles between 5 mm and 1 µm are widespread environmental contaminants that pose threats to aquatic life and human health. They serve as carriers for pathogens and persistent organic pollutants and can release toxic additives during degradation. Reliable identification of these particles is essential for accurate quantification and risk assessment.

Objectives and Study Overview

This application note presents a comprehensive analytical approach for detecting and identifying microplastic particles down to 5 µm on virtually any filter substrate. The study demonstrates the integration of visual microscopy and FTIR ATR measurements to ensure high-quality spectral data and unambiguous polymer identification.

Methodology

The workflow combines optical microscopy for rapid particle localization with ATR-FTIR spectroscopy for chemical characterization. Automated features such as crossed polarizers and dark-field illumination enhance contrast and facilitate detection of transparent or low-contrast particles. After locating each particle, a fully motorized knife-edge aperture is adjusted to isolate the target area, minimizing background interference. The ATR mode yields high-quality spectra irrespective of particle shape or filter material.

Used Instrumentation

• LUMOS II FTIR microscope with integrated ATR objective and motorized sample stage
• HYPERION FTIR microscope
• OPUS Spectroscopy Software
• B-KIMW polymer spectral library (Bruker)
• ATR-LIB-COMPLETE spectral database (>26 000 entries, Bruker)

Main Results and Discussion

Two case studies illustrate the method’s effectiveness: in bottled drinking water, a red fiber was isolated and identified as polyester, and inorganic particles were distinguished as silica. In a sediment sample, a thin filament was precisely measured and confirmed as polyamide. High-quality spectra enabled unambiguous library matching and accurate polymer classification.

Benefits and Practical Applications

• Simplified sample handling with automated microscopy and ATR measurement
• Ability to analyze particles down to 5 µm on diverse filter materials or complex matrices
• Accurate identification using comprehensive polymer and additive spectral libraries
• Reduced need for specialized filter substrates and extensive sample preparation

Future Trends and Opportunities

Advancements in automation and artificial intelligence are expected to enable high-throughput screening of microplastics. Integration with machine-learning algorithms may further streamline spectral interpretation and polymer classification. Coupling ATR-FTIR with complementary techniques, such as Raman spectroscopy or chemical imaging, could enhance sensitivity and expand the range of detectable materials.

Conclusion

The combined visual and ATR-FTIR microscope solution offers a robust, user-friendly approach for reliable identification of microplastic particles of any dimension on virtually any substrate. This workflow delivers high-quality spectral data, precise particle localization, and comprehensive polymer identification, supporting research and quality control efforts in environmental and industrial settings.

References

1. Nerland I L, Halsband C, Allan I, Thomas K V. Microplastics in Marine Environments – Occurrence, Distribution, and Effects. Norwegian Institute for Water Research; 2014.
2. Feng D Y, Zhang Y, Lemos B, Hongqiang R. Tissue accumulation of microplastics in mice and biomarker responses suggest widespread health risks of exposure. Scientific Reports. 2017.
3. Dris R, Gasperi J, Saad M, Mirande C, Tassin B. Synthetic fibers in atmospheric fallout: A source of microplastics in the environment? Marine Pollution Bulletin. 2016;104:290–293.
4. Barrows A P W, Cathey S E, Petersen C W. Marine environment microfiber contamination: Global patterns and the diversity of microparticle origins. Environmental Pollution. 2018;237:275–284.
5. Peng G, Xu P, Zhu Ba, Bai M, Li D. Microplastics in freshwater river sediments in Shanghai, China: A case study of risk assessment in mega-cities. Environmental Pollution. 2018;234:448–456.
6. Güven O, Gökdag K, Jovanovic B, Kıdeys A E. Microplastic litter composition of the Turkish territorial waters of the Mediterranean Sea, and its occurrence in the gastrointestinal tract of fish. Environmental Pollution. 2017;223:286–294.