BMSS: Application of TD/Py-GCxGC-TOFMS for Analysis of Microplastics and Chemical Pollutants in Ambient Particulate Matter Samples

Importance of the Topic

This study addresses the growing concern over microplastic pollution and airborne chemical contaminants in urban environments. Understanding the concentrations and origins of these pollutants in inhalable particulate matter is critical for assessing human exposure risks and informing air quality management strategies.

Advanced analytical methods are needed to separate and identify both freely associated chemicals and polymer-derived markers within complex air filter samples.

Objectives and Study Overview

The main goal was to develop and apply a two-step thermal desorption (TD) and pyrolysis (Py) multidimensional gas chromatography–time-of-flight mass spectrometry (GC×GC-TOFMS) workflow. Key aims included:

• Quantifying “free” or adsorbed chemicals in PM10 samples via TD.
• Characterizing pyrolytic fragments from microplastic particles by Py.
• Differentiating chemical markers originating from ambient air versus those bound to or derived from polymer particles.
• Evaluating filter homogeneity and subsampling reproducibility using statistical comparison software.

Methodology

Ambient particulate matter with aerodynamic diameter <10 µm was collected over 24 hours on deactivated quartz filters at urban roadside sites in London. Filters were sub-sampled using 2 mm and 4 mm biopsy punches from outer, central, and direct middle regions. Each punch underwent two sequential analyses:

1. Thermal desorption at 50 °C ramped to 300 °C to release freely associated compounds.
2. Pyrolysis at 50 °C ramped to 600 °C for thermal fragmentation of polymer particles.

Linear retention indices were calculated using an n-alkane (C7–C30) standard. Data processing and statistical tile-based comparison were performed using ChromaTOF Tile software to assess subsampling variability and feature reproducibility.

Instrumentation Used

• LECO GC×GC QuadJet™ thermal modulator and dual-column GC×GC system (Rxi-5SilMS and Rxi-17SilMS columns).
• LECO Pegasus® BT4D time-of-flight mass spectrometer with electron ionization (70 eV).
• High-volume PM10 air samplers and deactivated quartz filters (47 mm Ø, 0.8 µm pore size).
• ChromaTOF Tile statistical software for chromatogram region comparison.

Key Results and Discussion

The two-step TD/Py-GC×GC-TOFMS approach achieved high-resolution separation and detection of thousands of chemical features. Major findings included:

• Detection of polystyrene pyrolyzates (styrene monomer, dimer, trimer) only during the pyrolysis step, confirming polymer particle presence.
• Identification of polymer-specific alkane, alkene, and alkadiene series from polyethylene and other plastics.
• Low subsampling variability in central and direct middle regions compared to outer filter zones, based on Fisher ratios from tile analysis.

These insights demonstrate the method’s ability to distinguish between background air pollutants and particle-bound polymer markers in PM10.

Benefits and Practical Applications

The developed workflow offers several advantages for environmental monitoring laboratories:

• Comprehensive profiling of both freely associated pollutants and microplastic-derived fragments in a single analytical sequence.
• Reduced sample preparation steps by combining TD and Py in one instrument platform.
• Robust subsampling strategy validated by statistical comparison, ensuring reproducible data from filter analyses.

Applications include air quality assessments, human exposure studies, and regulatory compliance testing for urban particulate pollution.

Future Trends and Applications

Emerging directions may include:

• Integration of high-throughput GC×GC-TOFMS with machine learning for automated pattern recognition of microplastic sources.
• Miniaturization of thermal desorption units for field-deployable monitoring of airborne microplastics.
• Expanded libraries of polymer pyrolyzates to cover novel and biodegradable plastic materials.

These developments could enhance real-time air quality surveillance and source apportionment studies.

Conclusion

The two-step TD/Py-GC×GC-TOFMS methodology proved effective for detailed chemical characterization of ambient PM10 samples, enabling discrimination between free pollutants and polymer-derived markers. Statistical tiling provided confidence in subsampling workflows, supporting reliable monitoring of microplastics and associated chemical contaminants in urban air.