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

Importance of the Topic

Microplastic pollution poses a significant threat to aquatic ecosystems and human health. Rapid identification and quantification of microplastics are critical for environmental monitoring, regulatory compliance, and research into pollution sources and mitigation strategies. A reliable, high-throughput method that minimizes contamination and user expertise requirements can accelerate large-scale environmental assessments.

Objectives and Study Overview

This study evaluates a direct on-filter analysis approach for microplastics derived from polyethylene terephthalate (PET) bottles. By employing the Agilent 8700 Laser Direct Infrared Imaging (LDIR) system, the goal was to demonstrate fast, accurate, and automated detection of particles on gold-coated membrane filters, with minimal sample handling and reduced risk of contamination.

Methodology and Workflow

A powder of PET material was suspended in ethanol, diluted with deionized water, and vacuum-filtered onto gold-coated polycarbonate membranes. Filters were mounted onto microscope slides using adhesive patches and gently dried to ensure flatness. The Agilent Clarity software’s Particle Analysis workflow was used to

• automatically detect particles across the entire filter area,
• acquire mid-infrared spectra with a quantum cascade laser (QCL) source,
• and identify polymer type via library matching in minutes to hours.

Used Instrumentation

• Agilent 8700 LDIR chemical imaging system with QCL covering 1,800–900 cm⁻¹ fingerprint region
• Gold-coated polycarbonate membrane filters (25 mm, 0.8 µm pores)
• Vacuubrand ME 2 NT oil-free diaphragm vacuum pump with glass frit filtration base
• Agilent Clarity software for automated particle detection and identification

Main Results and Discussion

The LDIR system detected 978 particles (20–478 µm) on a single filter. Of these, 88% were confidently identified as PET (Hit Quality Index >0.8), 9% remained undefined, and 1% corresponded to cellulose, likely from sample handling. Trace contaminants such as polymethyl methacrylate and polyacrylamide were also observed. The gold-coated filter provided high-contrast visible and infrared images, and the direct on-filter method reduced analysis time to approximately 1.5 hours per filter.

Benefits and Practical Applications

• Rapid, full-area analysis of thousands of particles without sub-sampling
• Automated workflow requiring minimal operator training
• Reduced sample handling lowers contamination risk
• Versatile method for routine environmental monitoring and quality control

Future Trends and Potential Applications

• Extension of dedicated spectral libraries for a wider range of polymers and environmental matrices
• Simultaneous analysis of multiple filters on a single slide to increase throughput
• Integration with data analytics for pollution source tracking and size-based categorization
• Advances in QCL technology to improve detection limits below 20 µm

Conclusion

The Agilent 8700 LDIR system enables fast, accurate, and automated on-filter analysis of microplastics with minimal preparation and high identification confidence. Its ability to analyze large areas, combined with intuitive software and reduced contamination risk, makes it a valuable tool for environmental research and routine monitoring.

Reference

• 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.
• Li X. Microplastics Are Everywhere—But Are They Harmful? Nature. 4 May 2021.