Rapid, Large-Area, On-Filter Analysis of Microplastics from Plastic Bottles Using Laser Direct Infrared Imaging

Importance of the Topic

Microplastics generated from consumer plastics pose serious threats to aquatic ecosystems and human health. Rapid, reliable methods for identifying and quantifying microplastic particles are essential to support environmental monitoring, regulatory compliance, and research into pollution sources and fate.

Objectives and Study Overview

This study evaluates a direct on-filter analysis approach for microplastics derived from polyethylene terephthalate (PET) bottles. Using gold-coated polycarbonate membrane filters, the method employs the Agilent 8700 Laser Direct Infrared Imaging (LDIR) chemical imaging system to deliver fast, accurate identification of microplastic particles on large-area samples.

Methodology and Instrumentation

Sample Preparation

• PET bottle material ground to fine powder and dispersed in ethanol
• Aliquots diluted in de-ionized water and vacuum-filtered onto 25 mm, 0.8 μm gold-coated membrane filters
• Filters mounted on adhesive microscope slides after controlled drying

Instrumentation

• Agilent 8700 LDIR system with tunable quantum cascade laser covering the 1,800–900 cm–1 infrared fingerprint region
• Dual-camera setup for low and high magnification visible imaging
• Agilent Clarity software with automated Particle Analysis workflow and custom microplastics spectral library

Main Results and Discussion

The automated workflow detected 978 particles (20–478 μm). Identification results showed 88% PET, 9% undefined, and 1% cellulose, with trace contaminants (e.g., poly-methyl-methacrylate). High-confidence matches (Hit Quality Index > 0.8) confirmed spectral quality. Direct on-filter analysis provided sharp infrared and visible images, minimized sample handling, and reduced contamination risks. Detection of particles below 20 μm remains challenging due to beam size limitations but can be improved with enhanced spectral libraries and optimized focus parameters.

Benefits and Practical Applications

This LDIR approach offers significant time savings compared to traditional FTIR and Raman microscopy. Fully automated identification requires no specialized microscopy training and supports high-throughput environmental testing, quality assurance, and polymer research. The large scan area allows comprehensive mapping of representative filter surfaces.

Future Trends and Opportunities

Opportunities for method enhancement include expanding spectral libraries to cover diverse polymer types, refining detection of sub-20 μm particles, and integrating multiple filters on a single slide for parallel analysis. Advances in machine learning and spectral deconvolution could further improve identification accuracy and throughput.

Conclusion

The Agilent 8700 LDIR system enables rapid, direct on-filter analysis of microplastics with high accuracy, minimal preparation steps, and automation suitable for routine environmental monitoring. This technique addresses key limitations of existing microscopy methods and advances the field of microplastic analysis.

References

1. Eriksen M et al. Plastic Pollution in the World’s Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea. PLoS ONE 2014, 9.
2. XiaoZhi L. Microplastics Are Everywhere—But Are They Harmful? Nature, 4 May 2021.