Microplastic Analysis Using the AIM-9000 Infrared Microscope

Importance of the Topic

Microplastics, defined as plastic fragments smaller than 5 mm, pose significant environmental and health risks due to their persistence and capacity to sorb toxic contaminants. Reliable identification and spatial mapping of these particles are vital for assessing pollution sources, tracking distribution pathways, and guiding mitigation strategies in marine and terrestrial ecosystems.

Objectives and Study Overview

This study demonstrates the qualitative and mapping analysis of both primary microplastics derived from consumer products and secondary microplastics collected from aqueous environments. The aim is to evaluate the performance of the AIM-9000 infrared microscope coupled with an FTIR spectrophotometer in characterizing different polymer types at the microscale.

Methodology and Instrumentation

Primary microplastics were extracted from a commercial scrub by dissolving the matrix in water, followed by repeated filtration. Individual particles (~50 µm) were isolated and compressed in a diamond cell for transmission FTIR microspectroscopy. Secondary microplastics suspended in water were collected on a PTFE filter, exploiting its minimal IR absorbance background. Infrared transmission mapping was then performed over a 1.8 mm × 2.6 mm area with 50 µm aperture and step intervals.

Instrumentation Used

• FTIR Spectrophotometer: IRTracer-100
• Infrared Microscope: AIM-9000
• Detector: MCT
• Spectral Resolution: 8 cm⁻¹
• Accumulations: 40 (qualitative), 1 (mapping)
• Aperture Size: 50 µm × 50 µm

Key Results and Discussion

Qualitative analysis of the scrub sample confirmed the presence of polystyrene (PS) by its characteristic IR bands. Mapping of environmental microplastics revealed three polymer types: polyethylene (PE, CH₂ rocking at 718 cm⁻¹), polypropylene (PP, CH₂ stretching at 2839 cm⁻¹), and polyethylene terephthalate (PET, C=O stretching at 1724 cm⁻¹). False-color distribution maps highlighted particle clusters and compositional heterogeneity, demonstrating the system’s sensitivity and spatial resolution.

Benefits and Practical Applications

The infrared microscope approach enables rapid, non-destructive identification and localization of microplastics down to tens of micrometers. It supports environmental monitoring, quality control in industrial processes, and research into microplastic transport and fate. The method’s minimal sample preparation and use of standard spectral libraries facilitate routine analysis in analytical laboratories.

Future Trends and Potential Applications

Further developments may include automated particle recognition algorithms, integration with Raman microspectroscopy for complementary chemical information, and expansion of reference databases for emerging polymer additives. Miniaturization and field-deployable IR imaging systems could enable on-site screening in remote or sensitive environments.

Conclusion

The combined FTIR-microscope system provides a robust platform for both qualitative and mapping analyses of microplastic particles. High sensitivity, spatial specificity, and compatibility with standard spectral libraries make it a valuable tool for environmental and industrial applications.

References

1. Ministry of the Environment, Japan. Annual Report on the Environment, the Sound Material-Cycle Society and Biodiversity in Japan 2017, Part II, Chapter 4, Section 7: Preservation of the Marine Environment.
2. Ministry of the Environment, Japan. 2016 New Year Symposium on Marine Litter: Documentation on Water/Soil/Ground Environment and Marine Litter.