Characterization of Microplastics in Environmental Samples by Laser Direct Infrared Imaging and User-Generated Libraries

Importance of the Topic

Microplastic pollution is recognized as a growing concern for aquatic, soil, air, and drinking water systems. Rapid and accurate identification of microplastics is essential for assessing environmental exposure, guiding remediation efforts, and informing regulatory standards.

Study Objectives and Overview

This study aimed to demonstrate the capabilities of the Agilent 8700 Laser Direct Infrared (LDIR) chemical imaging system for automated microplastic characterization. Beach-collected plastic fragments were converted into microplastic particles and analyzed to:

• Establish a user-generated spectral library of common polymers.
• Apply a fully automated particle analysis method to identify polymer types, sizes, and counts.
• Validate identifications using an Agilent Cary 630 FTIR spectrometer with ATR.

Methodology and Instrumentation

Sample Preparation and Library Generation
- Environmental plastic debris from Sorrento beach, Australia, was grated into irregular particles.
- Particles were suspended in ethanol and deposited onto infrared-reflective glass slides.
- A custom spectral library was built in Agilent Clarity software using pure polymer standards (e.g., PTFE, PMMA, PET, PC, PS, PP, PA).

Automated Particle Analysis
- The Agilent 8700 LDIR system employed two acquisition modes: rapid single-wavenumber scanning to locate particles and full-spectrum acquisition via a quantum cascade laser.
- The Clarity software’s “Particle-analysis” method was configured with default parameters for particle size detection (20–600 µm) and spectral matching against the user library.

Instrumentation Used

• Agilent 8700 LDIR chemical imaging system with QCL source and MCT detector.
• Agilent Clarity LDIR control software for library management and automated analysis.
• Agilent Cary 630 FTIR spectrometer with diamond ATR module for independent spectral confirmation.

Results and Discussion

Sample 1 (Red/White Plastic)
- Total scanned area: 3.04 × 3.06 mm²; 147 particles detected.
- Identified polymers: 74.8 % polypropylene, 17.0 % undefined, 6.8 % polyamide, 1.4 % polyacrylamide.
- Size distribution: majority between 20 and 200 µm; hit quality index (HQI) >0.8 for 71.4 % of particles.

Sample 2 (Yellow Film)
- Total scanned area: 3.76 × 4.42 mm²; 137 particles detected.
- Identified polymers: 85.4 % polyvinyl chloride, 10.9 % polyamide, 2.2 % polyacrylamide, 1.5 % undefined.
- Size distribution similar to sample 1; HQI >0.8 for 78.8 % of particles.

FTIR Confirmation
- Cary 630 ATR-FTIR analysis confirmed sample 1 as polypropylene blend (HQI 0.922) and sample 2 as PVC (HQI 0.969), aligning with LDIR results.

Benefits and Practical Applications

• Fully automated workflow yields rapid particle counts, size distributions, and polymer identifications with minimal user input.
• User-generated libraries can be expanded easily in Clarity software, supporting routine environmental monitoring.
• High confidence in polymer match (HQI >0.8) across a wide particle size range accelerates quality assurance in microplastic studies.

Future Trends and Opportunities

Advancements may include integration of expanded spectral libraries for complex environmental matrices, coupling LDIR with automated sampling for in situ monitoring, and combining chemical imaging data with machine learning to enhance classification accuracy and throughput.

Conclusion

The Agilent 8700 LDIR system, paired with user-generated libraries, offers an efficient and reliable approach for microplastic analysis in environmental samples. Automated particle detection and spectral matching deliver rapid, high-confidence identifications that are corroborated by ATR-FTIR. This workflow supports widespread laboratory adoption for environmental monitoring and research.

Reference

1. Laskar, S. et al. Plastics and Microplastics: A Threat to Environment. Environmental Technology & Innovation 2019, 14, 100352.