Determination of Microplastics using Pyrolysis Gas Chromatography Mass Spectrometry

Importance of the Topic

Microplastics and nanoplastics are pervasive pollutants in aquatic environments, entering the food chain through ingestion by fish and shellfish and resisting conventional wastewater treatment. Accurate identification and quantification of these particles are critical for environmental monitoring and human health assessment. Traditional spectroscopic techniques can be hindered by pigments and additives, making pyrolysis-GC/MS a valuable complementary approach.

Objectives and Study Overview

This study evaluates an automated pyrolysis GC/MS workflow to identify microplastics in environmental and consumer product samples. Goals include:

• Demonstrating smart ramped pyrolysis (SRP) for rapid optimization of pyrolysis conditions.
• Characterizing plastic types in Great Lakes plastic and sediment samples.
• Exploring fractionated pyrolysis to resolve complex matrices in a commercial facial scrub.

Methodology and Instrumentation

Sample preparation involved placing sub-milligram fragments or aqueous suspensions onto quartz wool in quartz tubes. Sediment samples were filtered in-tube and dried prior to analysis. A Gerstel Multipurpose Sampler (MPS) equipped with a Thermal Desorption Unit 2 (TDU 2), Cooled Injection System 4 (CIS 4) and PYRO insert performed automated pyrolysis. Key parameters:

• Column: Agilent DB-5MS UI, 30 m × 0.25 mm × 0.25 µm, He carrier at 1.0 mL/min.
• Thermal ramp: 40 °C to 320 °C at 10 °C/min.
• Smart ramped pyrolysis: 300 → 800 °C at 5 °C/s.
• Fractionated pyrolysis: discrete steps at 120, 300, 600 °C.

Results and Discussion

Plastic pieces from Great Lakes samples were identified predominantly as polyethylene (PE) and polypropylene (PP), with mixed PE/PP in some multicolor fragments. SRP yielded pyrograms equivalent to optimal pulsed pyrolysis in a single run, streamlining method development. Sediment extracts produced markers for styrene (polystyrene), methyl methacrylate (polyacrylate), siloxanes, phthalates, phenol, and phthalic anhydride, reflecting diverse polymer sources.

Analysis of a facial scrub by fractionated pyrolysis separated compound classes:

• 120 °C fraction: skin conditioners (glycerol, 1,3-butanediol), preservatives (2-phenoxyethanol), fatty acids.
• 300 °C fraction: long-chain acids, amides, siloxanes, sulfur dioxide (dextran sulfate degradation).
• 600 °C fraction: polymer markers such as polyethylene oligomers.

This approach clarified complex formulations and identified microplastic beads among cosmetic additives.

Benefits and Practical Applications

The automated MPS/TDU/CIS/PYRO system enables high-throughput analysis of limited-mass samples, reduces pyrolysis optimization to a single SRP run, and offers fractionated pyrolysis for matrix simplification. It supports environmental monitoring, quality control in consumer products, and research on microplastic pollution.

Future Trends and Opportunities

Advances may include coupling SRP with high-resolution mass spectrometry for enhanced compound identification, development of standardized protocols for nanoplastic detection, integration with chemometric tools for source attribution, and deployment in field-portable instruments for real-time monitoring.

Conclusion

The GERSTEL MPS workflow with smart ramped and fractionated pyrolysis delivers rapid, reliable identification of microplastics and associated additives in environmental and consumer samples. It addresses challenges of pigment interference and complex matrices, facilitating comprehensive microplastic analysis.

Used Instrumentation

• Gerstel Multipurpose Sampler (MPS)
• Gerstel Thermal Desorption Unit 2 (TDU 2)
• Gerstel Cooled Injection System 4 (CIS 4) with PYRO insert
• Agilent DB-5MS UI GC column
• Mass spectrometer detector

References

• Whitecavage J., Stuff J.R., Vernarelli L. Determination of Microplastics using Pyrolysis Gas Chromatography Mass Spectrometry. GERSTEL Application Note No. 212, 2020.