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

Significance of the topic

Microplastics are emerging contaminants found in water, food and natural habitats. Detailed characterization of their abundance, size, morphology and polymer type is critical to assess environmental distribution, inform risk assessments and guide mitigation strategies.

Objectives and study overview

This study evaluates a rapid, fully automated workflow for microplastic analysis using the Agilent 8700 Laser Direct Infrared (LDIR) chemical imaging system. Microplastics derived from polyethylene terephthalate (PET) bottles were analyzed by two sample preparation approaches: direct deposition on infrared-reflective glass slides and collection on gold-coated membrane filters.

Methodology and Used Instrumentation

Particles were generated by grinding a PET bottle into powder, dispersing in ethanol and aliquoting for two workflows. Key instrumentation and materials included:

• Agilent 8700 LDIR chemical imaging system with a tunable quantum cascade laser covering 1800–900 cm–1 fingerprint region
• Agilent Clarity software with automated Particle Analysis workflow and customizable microplastic spectral library
• IR-reflective glass slides for direct deposition
• Gold-coated polyester membrane filters (0.8 µm pore size) and vacuum filtration apparatus (–30 kPa)

Main results and discussion

On-slide analysis detected 7 949 particles (10–486 µm), with 95.2 % correctly identified as PET. Filter analysis on two 25 mm membranes detected 4 384 and 5 411 particles (11–413 µm), achieving 99.2 % and 98.4 % PET identification accuracy, respectively. Hit Quality Index (HQI) scores exceeded 0.8 for most PET matches, indicating high confidence across size ranges. Automated imaging provided visible and IR maps at 1 442 cm–1, enabling rapid particle boundary detection and classification.

Benefits and practical applications of the method

• High throughput: large area scanning yields thousands of particles in minutes
• Minimal training: fully automated IR microscopy reduces operator expertise requirements
• Reduced contamination risk: direct filter analysis avoids multiple transfer steps
• Flexible library management: users can build application-specific spectral libraries for diverse polymer types

Future trends and application possibilities

Expanding custom spectral libraries to include a broader range of polymers and additives will improve identification specificity. Integration with advanced data analytics and machine learning can enable real-time classification and source apportionment. The high-speed imaging approach may be extended to complex environmental matrices, food safety testing and quality control in plastic manufacturing.

Conclusion

The Agilent 8700 LDIR system delivers rapid, accurate microplastic characterization on reflective slides and filters, outperforming traditional FTIR and Raman microscopy in speed, area coverage and automation. Its accessible workflow and high confidence in polymer identification support large-scale environmental monitoring and research.

References

• XiaoZhi, L. Microplastics Are Everywhere—But Are They Harmful? Nature, 4 May 2021.
• Schymanski, D. et al. Analysis of Microplastics in Drinking Water and Other Clean Water Samples With Micro-Raman and Micro-Infrared Spectroscopy: Minimum Requirements and Best Practice Guidelines. Anal. Bioanal. Chem. 413, 5969–5994 (2021).
• Danence, L. et al. Quick and Easy Characterization of Microplastics in Surface Water and Treated Effluent, Agilent publication number 5994-3932EN.