Analysis of Microplastics on Aluminum-Coated Filters Using the Agilent 8700 Laser Direct Infrared (LDIR) Chemical Imaging System

Significance of the Topic

Microplastics are ubiquitous pollutants affecting ecosystems and human health. Reliable detection and characterization methods are vital for monitoring contamination, informing remediation efforts, and guiding policy decisions in environmental and industrial contexts.

Objectives and Study Overview

This study evaluates the performance of cost-effective aluminum‐coated polyester filters for direct analysis of microplastics using the Agilent 8700 Laser Direct Infrared (LDIR) chemical imaging system and Agilent Clarity software. Key goals include assessing filter usability, particle detection capability, repeatability, size accuracy, and polymer identification efficiency.

Methodology and Instrumentation

Aluminum‐coated filters (25 mm diameter, 0.8 µm pore size) were used in a vacuum filtration setup. Samples containing polystyrene microspheres or mixed microplastics were filtered, and the filters were placed in the LDIR system for analysis. The automated Particle Analysis workflow generated infrared (IR) images at 1442 cm⁻¹ and complementary high‐magnification visible images for validation. Repeatability tests involved ten sequential runs on a fixed 9 mm diameter region. Particle size accuracy was assessed using NIST‐traceable 20 µm and 50 µm polystyrene beads. Polymer identification performance was evaluated with a reference library and hit quality index (HQI) metrics.

Instrumental Setup

• Agilent 8700 LDIR Chemical Imaging System equipped with quantum cascade laser and rapid scanning optics
• Agilent Clarity software with automated Particle Analysis workflow and microplastics spectral library
• Aluminum‐coated polyester filters (25 mm, 0.8 µm pore size)
• Standard vacuum filtration apparatus with tweezers, retaining ring, and filter holder

Main Results and Discussion

• Particle Detection: Automated IR imaging detected 31 polystyrene microspheres versus 30 by visible imaging, demonstrating superior sensitivity of LDIR for small particles.
• Repeatability: Total particle counts (average 407) showed <1% variability across ten runs; size‐range and polymer‐specific counts also exhibited <1% variability.
• Size Accuracy: Measured averages for 50 µm and 20 µm beads were 55.1 µm (±3.7 µm) and 22.9 µm (±2.3 µm), confirming precise sizing.
• Polymer Identification: Polystyrene, polypropylene, polyethylene, and PET were identified with HQI scores >0.8 for 95–100% of particles, confirming reliable spectral matching.

Benefits and Practical Applications

The direct on‐filter analysis reduces sample handling and contamination risk, while aluminum‐coated filters offer a cost‐effective alternative to gold coatings. High throughput and automated workflows facilitate large‐scale environmental monitoring, quality assurance in water treatment, and rapid assessment of microplastic pollution in diverse matrices.

Future Trends and Applications

• Integration with machine learning algorithms for automated classification and quantification of emerging polymer types.
• Development of novel filter materials and coatings to enhance chemical resistance and reduce background signals.
• Adaptation of LDIR workflows for in situ or field‐deployable monitoring systems.
• Expansion of spectral libraries to include additives, degradation products, and nanoplastics.

Conclusion

Aluminum‐coated polyester filters combined with the Agilent 8700 LDIR system provide a robust, accurate, and cost‐effective solution for microplastics characterization. The method demonstrates excellent detection sensitivity, repeatability, size accuracy, and polymer identification performance, enabling high‐throughput and reliable environmental analysis.

References

1. Gerresten I. Plastic Pollution is One of the Defining Legacies of Our Modern Way of Life, BBC, 2023.
2. ASTM D8332-20. Standard Practice for Collection of Water Samples with High, Medium, or Low Suspended Solids for Identification and Quantification of Microplastic Particles and Fibers, ASTM International, 2020.
3. ASTM D8333-20. Standard Practice for Preparation of Water Samples with High, Medium, or Low Suspended Solids for Identification and Quantification of Microplastic Particles and Fibers Using Raman Spectroscopy, IR Spectroscopy, or Pyrolysis-GC/MS, ASTM International, 2020.
4. Draft Microplastics in Drinking Water Policy Handbook, State Water Resources Control Board, California, 2021.
5. Best Practice for On-Filter Analysis of Microplastics Using the Agilent 8700 LDIR Chemical Imaging System, Agilent Technologies White Paper, 2023.