Pyrolysis-GC-Orbitrap MS - a powerful analytical tool for identification and quantification of microplastics in a biological matrix

Importance of the Topic

The ubiquity of plastic pollution in the environment, particularly the emergence of micro- and nanoplastics, poses growing risks to marine ecosystems and human health. Detecting and quantifying plastic polymers in complex biological samples is critical for assessing exposure pathways, toxicological effects, and regulatory compliance. Advanced analytical tools that combine sensitivity, selectivity, and throughput are needed to address these challenges.

Objectives and Study Overview

This work evaluates the potential of a pyrolysis–gas chromatography system coupled to a high-resolution Orbitrap mass spectrometer for both qualitative identification and quantitative determination of eight common plastic polymers in a decomposed fishmeal matrix. The study aims to demonstrate linearity, mass accuracy, selectivity, and applicability in complex biological samples.

Methodology and Instrumentation

Sample Preparation:

• Custom standards of PE, PP, PA, PC, PVC, PET, PS, PMMA and mixtures (10–100 µg each) weighed into pyrolyzer cups.
• Biological matrix (fishmeal) digested with 10% KOH at 50 °C and 30% H₂O₂ at 40 °C then spiked with 2.7 µg PS and 2.5 µg PMMA.
• 10 µL tetramethylammonium hydroxide (25% v/v) added as methylation agent.

Instrumental Setup:

• Frontier Lab Multi-Shot Pyrolyzer EGA/PY-3030D with Auto-Shot Sampler AS-1020E at 600 °C pyrolysis temperature.
• Thermo Scientific TRACE 1310 GC with TraceGOLD TG-5SilMS capillary column (30 m × 0.25 mm × 0.25 µm).
• Thermo Scientific Exactive GC Orbitrap mass spectrometer operated in EI full-scan mode, 70 eV, resolution 60 000 FWHM, mass range 50–650 Da, transfer line 320 °C, ion source 280 °C.
• Data acquired with lockmass correction and processed in Thermo TraceFinder software (deconvolution, spectral matching, quantification).

Main Results and Discussion

• Linearity: PS and PMMA standards (0.05–50 µg) yielded R² > 0.999 and residual %RSD < 15%.
• Mass Accuracy: Sub-ppm mass deviations (<1 ppm) maintained across all concentrations and matrices.
• Selectivity: High-resolution extracted-ion chromatograms (±2 ppm) resolved pyrolysis fragments of eight polymers; low-resolution windows (±100 mmu) showed interferences.
• Quantification in Fishmeal: Back-calculation of spiked PS and PMMA showed deviations of +7.4% and −12.0%, respectively, without internal standards.
• Non-Targeted Identification: Orbitrap full-scan data enabled detection of additional pyrolysis products (e.g., α-methylstyrene) with library matching and deconvolution (>97% confidence).

Benefits and Practical Applications

• Simultaneous qualitative screening and accurate quantification in one run.
• High throughput due to automated pyrolysis sampling and rapid GC–MS analysis.
• Low detection limits for microplastics down to tens of nanograms per sample.
• Enhanced confidence in polymer identification via sub-ppm mass accuracy and spectral deconvolution.
• Applicable to environmental monitoring, food safety, and regulatory testing.

Future Trends and Opportunities

• Extension to a broader range of polymers and additives in soils, sediments, and biota.
• Integration of isotope-labeled internal standards for improved quantification accuracy.
• Miniaturized or field-deployable pyrolysis-GC-Orbitrap platforms for in situ monitoring.
• Advanced data-processing workflows incorporating machine learning for automated pattern recognition of unknown pyrolysis products.
• Combined multi-omics approaches to link polymer identification with biological effects.

Conclusion

This study demonstrates that pyrolysis–GC coupled with high-resolution Orbitrap mass spectrometry provides a powerful, versatile, and robust platform for the qualitative and quantitative analysis of microplastics in complex biological matrices. Its exceptional linearity, mass accuracy, and selectivity pave the way for routine environmental and food-safety applications.

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