Best Practice for On-Filter Analysis of Microplastics Using the Agilent 8700 Laser Direct Infrared (LDIR) Chemical Imaging System

Significance of the Topic

Microplastics are pervasive environmental contaminants formed by the breakdown of larger plastic items through weathering, wear, and improper disposal. Ranging from 1 to 5 mm, these particles have been detected in drinking water, wastewater, food, and air, raising concerns about their potential impacts on human health and ecosystems. Reliable identification, characterization, and quantification methods are essential to support risk assessment, regulatory compliance, and pollution mitigation.

Objectives and Overview of the White Paper

This white paper presents best practices for on-filter analysis of microplastics using the Agilent 8700 Laser Direct Infrared (LDIR) Chemical Imaging System. It describes contamination control procedures, sample handling, automated particle detection, and data reporting workflows designed to deliver accurate, reproducible results across laboratories.

Used Instrumentation

• Agilent 8700 LDIR Chemical Imaging System with Clarity software
• Polyester gold-coated membrane filters (0.8 µm pore size)
• Agilent Cary 630 FTIR spectrometer with diamond ATR module and MicroLab software

Methodology and Sample Preparation

Key steps to minimise contamination and ensure filter flatness include:

• Laboratory environment: controlled airflow, natural‐fiber lab coats, lint removal, minimal glove usage, and strict hand hygiene
• Glassware and equipment: cleaning with high-purity water or ethanol, blank analysis to monitor background contamination
• Filter handling: use supplied tweezers, avoid damaged or reused filters, maintain surface flatness within 10 µm over 3 × 3 mm regions
• Filtration: gentle vacuum application (700 mbar) on a clean support stem, careful drying, and secure placement in the filter holder
• Sample mounting: insertion of the flat filter holder into the LDIR system without tilting, ensuring flatness thresholds for reliable imaging

Data Acquisition and Processing

The Clarity Particle Analysis workflow automates particle detection, image capture, and spectral matching. Critical parameters include:

• Pre-scan at 1,442 cm^–1 to verify sample loading and select the analysis area
• Auto Scan for unattended detection and optional high-magnification imaging
• Hit Quality Index (HQI) classification: low (0.65–0.75), medium (0.75–0.85), high (0.85–0.99)
• Configurable minimum particle size (default 20 µm)
• Comprehensive reporting: total and size-categorized particle counts, polymer types, infrared spectra, and visible images

Benefits and Practical Applications

By following these guidelines, laboratories achieve fast, objective, and repeatable microplastic analysis for environmental monitoring, quality assurance, and research. The combination of LDIR imaging for small particles and FTIR confirmation for larger fragments provides a robust approach for polymer identification and source tracing.

Future Trends and Potential Applications

• Standardisation through interlaboratory studies to harmonise methods and reporting metrics
• Advanced software tools for cloud‐based data sharing, real-time analytics, and machine learning-driven classification
• Expansion of spectral libraries to include novel and weathered polymers
• Development of portable or field-deployable LDIR units for in situ microplastic monitoring

Conclusion

Strict contamination control, meticulous sample preparation, and automated chemical imaging ensure high-quality microplastic analysis. The Agilent 8700 LDIR system, complemented by FTIR verification, offers a comprehensive solution for reliable detection, identification, and quantification of microplastics in diverse sample matrices.

References

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4. Kadac-Czapska K., Knez E., Grembecka M. Food and Human Safety: the Impact of Microplastics. Crit. Rev. Food Sci. Nutr. 2022.
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6. Van Mourik LM. et al. Results of WEPAL-QUASIMEME/NORMAN’s First Global Interlaboratory Study on Microplastics. Sci. Total Environ. 2021;772:145071.
7. Belz S. et al. Current Status of the Quantification of Microplastics in Water – Results of a JRC/BAM Inter-Laboratory Comparison Study on PET in Water. EUR 30799 EN. Publications Office of the European Union; 2021.
8. 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. 2021;413:5969–5994.
9. Alwan W., Robey D. Characterization of Microplastics in Environmental Samples by Laser Direct Infrared Imaging and User-Generated Libraries. Agilent Technologies Application Note. 2022.