From Collection to Analysis: A Practical Guide to Sample Preparation and Processing of Microplastics

Importance of the topic

Microplastics (1 µm–5 mm) are ubiquitous pollutants that pose risks to ecosystems and human health. Reliable, standardized analytical workflows are essential to generate comparable data across studies and to support environmental monitoring, regulatory compliance, and risk assessment.

Objectives and overview of the study

This guide outlines a practical workflow for the preparation and analysis of microplastics using the Agilent 8700 Laser Direct Infrared (LDIR) chemical imaging system. It covers critical aspects including laboratory setup, sample digestion, density separation, filtration, and analytical methods for different matrices: bottled drinking water, environmental water, soil and sediment, and infant formula.

Methodology and instrumentation

Key methodological steps and instruments:

• Laboratory setup: laminar flow hood with HEPA filters, filtered Milli-Q water, cotton lab coats, and strict contamination control.
• Sample digestion: oxidative (H₂O₂, Fenton’s reagent), acidic (HCl, HNO₃), alkaline (NaOH, KOH), or enzymatic treatments to eliminate organic matter without degrading polymers.
• Density separation: use of saturated salt solutions (NaCl, CaCl₂, NaI, ZnCl₂) to float microplastics based on polymer densities (0.85–1.45 g/cm³).
• Filtration: gold- or aluminum-coated polyester (PETG) filters (0.8 µm, 25 mm) or polycarbonate membranes, with direct transfer onto low-e slides for analysis.
• Instrumentation: Agilent 8700 LDIR system for 20–500 µm particles; Agilent Cary 630 FTIR for >500 µm; vacuum filtration apparatus; sieves; tweezers; low-e slides; vacuum pump.

Main results and discussion

LDIR-based workflows enable rapid, automated detection, counting, sizing, and chemical identification of microplastics directly on filters or low-e slides. Case studies demonstrate:

• Bottled water: direct filtration of entire samples and on-filter LDIR analysis with minimal preparation.
• Environmental water: H₂O₂ digestion at 55 °C, density separation in CaCl₂ or ZnCl₂, and transfer to slides yielded clear infrared spectra for reliable identification.
• Soil and sediment: drying, sieving, digestion, density separation, and filtration recovered microplastics efficiently across size ranges.
• Infant formula: 68 % HNO₃ digestion, heating, ethanol sonication, and direct on-filter LDIR characterization enabled analysis in a complex food matrix.

Benefits and practical applications

• Reproducible sample preparation with built-in QA/QC controls minimizes contamination and sample loss.
• Automated LDIR imaging accelerates throughput and reduces handling errors.
• Applicable to diverse environmental and food samples, supporting monitoring, research, and quality assurance.

Future trends and possibilities

• Development of globally standardized protocols and certified reference materials.
• Integration of machine learning and advanced spectral libraries for improved polymer identification.
• Portable or miniaturized infrared imaging systems for field-based monitoring.

Conclusion

The combination of robust digestion, density separation, filtration, and automated LDIR imaging provides a comprehensive, high-throughput solution for accurate microplastic analysis. This workflow supports consistent data generation across laboratories and contributes to global efforts addressing microplastic pollution.

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