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

Significance of the topic

The prevalence of microplastic particles in water, soil, air and drinking water poses increasing environmental and health concerns. Reliable, rapid and automated methods for detecting, identifying and quantifying microplastics are essential for environmental monitoring, regulatory compliance and research into pollution pathways and ecological impact.

Objectives and Study Overview

This study aimed to evaluate the performance of the Agilent 8700 LDIR chemical imaging system for characterizing microplastics collected from Sorrento beach, Australia. It also demonstrated the straightforward creation of a custom spectral library using Agilent Clarity software and validated the identification results using an Agilent Cary 630 FTIR–ATR system.

Methodology

Microplastic particles were generated by grinding two aged plastic debris samples and suspending the particles in ethanol before depositing them on infrared-reflective glass slides. A user-generated library of seven pure polymers (PTFE, PMMA, PET, PC, PS, PP, PA) was built by acquiring spectra of ground pellets via the 8700 LDIR system. The fully automated particle-analysis method in Agilent Clarity software performed rapid single-wavelength scanning to locate particles and full-spectrum acquisition for chemical identification. Identification confidence was reported as a Hit Quality Index (HQI).

Instrumentation

• Agilent 8700 LDIR chemical imaging system with quantum cascade laser (QCL) covering 1800–975 cm–1, MCT detector and high-speed optics
• Agilent Cary 630 FTIR spectrometer with diamond ATR module and ATR Polymers and Polymer Additives library for spectral confirmation

Key Results and Discussion

Sample 1 (red and white plastic) yielded 147 particles: 74.8% polypropylene, 17.0% undefined, 6.8% polyamide and 1.4% polyacrylamide. Sample 2 (yellow film) yielded 137 particles: 85.4% polyvinyl chloride, 10.9% polyamide, 2.2% polyacrylamide and 1.5% undefined. Most particles ranged from 20 to 200 μm. High identification confidence (HQI > 0.8) was achieved for over 70% of particles in both samples. FTIR–ATR analysis confirmed the primary polymer types with HQI values of 0.922 for polypropylene blends and 0.969 for PVC.

Benefits and Practical Applications

• Fully automated, high-throughput analysis reduces processing time from days to minutes per sample
• Low user interaction and easy custom library creation support routine environmental monitoring
• Provides both chemical identification and particle size distribution in a single workflow
• Scalable approach applicable to diverse environmental matrices and pollution studies

Future Trends and Potential Applications

• Expansion of custom libraries to cover emerging polymer additives and weathered materials
• Integration with complementary techniques (Raman imaging, microscopy) for multitechnique validation
• Development of miniature and portable LDIR instruments for in-field analysis
• High-throughput screening for regulatory compliance and ecosystem health assessment

Conclusion

The Agilent 8700 LDIR system coupled with user-generated spectral libraries provides a rapid, automated and reliable method for microplastic characterization. Validation by FTIR–ATR confirmed the accuracy of polymer identifications. This workflow supports routine environmental analysis and can be extended to broader applications in pollution monitoring and materials research.

Reference

• Laskar et al. Plastics and Microplastics: A Threat to Environment. Environmental Technology & Innovation 2019, 14, 100352. doi:10.1016/j.eti.2019.100352