Pyrolysis-Gas Chromatography-High Resolution Mass Spectrometry with Soft Ionization for Increased Confidence of Polymer Characterization

Importance of the topic

Polymer characterization by pyrolysis-GC–MS is widely used for materials that resist dissolution, but conventional electron ionization often yields extensive fragmentation and limited molecular information. Soft ionization combined with high-resolution mass spectrometry addresses these limitations by preserving molecular ions and providing accurate mass data for structural elucidation, essential for analyzing sustainable plastics, recyclates, and complex polymeric formulations.

Objectives and Study Overview

This study compares classical pyrolysis-GC with EI-tandem quadrupole MS against pyrolysis with atmospheric pressure GC ionization (APGC) coupled to QToF MS. It evaluates the benefits of soft ionization and high-resolution accurate mass acquisition for polymer standards and biobased plastic bags, and highlights software tools for compound identification.

Methodology

Samples included polymer standards and commercial biobased plastic bags loaded into quartz-wool-filled capillaries and analyzed in triplicate on two platforms:

• Pyrolysis at up to 750 °C (20 °C/ms ramp) using a CDS 5000 pyrolyzer.
• Gas chromatographic separation on an Rtx-5MS column (30 m × 0.25 mm × 0.25 µm) with an oven gradient from 45 °C to 300 °C.
• Mass spectrometry data acquired in full-scan or MSE mode over m/z 10–1500.

Data processing and putative identification were performed with MassLynx 4.2 and MassFragment software.

Instrumentation

• CDS 5000 pyrolyzer
• Waters Xevo TQ-GC with EI source
• Waters Xevo G2-XS QTof with APGC source
• RESTEK Rtx-5MS GC column
• MassLynx 4.2 and MassFragment software

Main Results and Discussion

APGC-QToF produced more information-rich pyrograms, revealing additional peaks and higher oligomers (e.g., polystyrene tetramer at m/z 416.2504) not seen with EI. Soft ionization enabled detection of molecular ions such as protonated Nylon-6 pyrolysis products (m/z 194.2374) and erucamide in bioplastic samples. MSE acquisition provided simultaneous low- and high-energy spectra, supporting accurate mass determination of precursors and fragments and facilitating structural elucidation of unknown compounds.

Benefits and Practical Applications

Key advantages include:

• Enhanced sensitivity and selectivity through molecular ion detection
• Time-efficient soft ionization without source replacement or reagent gases
• High-resolution accurate mass data for reliable elemental composition and structural insights
• Automated fragment assignment using MassFragment accelerates identification of unknowns

These features support detailed compositional analysis of post-consumer recyclates, industrial polymers, and biobased materials.

Future trends and applications

Continued integration of soft-ionization HRMS is expected to extend regulatory monitoring of additives and contaminants, advance library-free identification workflows, and combine with machine learning for automated polymer profiling. Development of expanded spectral databases and ambient pyrolysis interfaces may further improve throughput and applicability to diverse polymer waste streams.

Conclusion

Pyrolysis-APGC-QToF MS with soft ionization and MSE acquisition offers a powerful, time-efficient approach for confident polymer characterization. By preserving molecular ions and delivering accurate mass information for both precursors and fragments, this method overcomes the limitations of conventional EI-MS and streamlines the analysis of complex polymeric samples.

References

1. Welle F., Franz R. Recycling of Post-Consumer Packaging Materials into New Food Packaging Applications—Critical Review of the European Approach and Future Perspectives. Sustainability 2022;14:824.
2. Tsuge S., Ohtani H., Watanabe C. Pyrolysis-GC/MS Data Book of Synthetic Polymers. 2011.
3. Peacock P.M., McEwen C.N. Mass Spectrometry of Synthetic Polymers. Anal. Chem. 2006;78(12):3957–3964.
4. Stevens D.M., Cabovska B., Bailey A.E. Detection and Identification of Extractable Compounds from Polymers. Waters Application Note 720004211. 2012.
5. Hill A.W., Mortishire-Smith R.J. Automated Assignment of High-Resolution Collisionally Activated Dissociation Mass Spectra Using a Systematic Bond Disconnection Approach. Rapid Commun. Mass Spectrom. 2005;19(21):3111–3118.