Characterization of Plastics Using Mass Spectral Reference Libraries Developed From Pyrolysis-APGC-QToF MS

Significance of the Topic

Understanding the chemical composition of polymeric materials is critical in quality control, recycling, and environmental monitoring. Pyrolysis coupled with gas chromatography and high-resolution mass spectrometry offers reproducible fragmentation patterns for complex plastics that cannot be easily dissolved. Developing in-house spectral libraries enhances the speed and confidence of polymer identification.

Study Objectives and Overview

This application note explores the construction of mass spectral reference libraries from pyrolyzed polymer standards using two analytical platforms: traditional electron ionization (py-GC-EI-MS) and soft ionization with atmospheric pressure GC and quadrupole time-of-flight mass spectrometry (py-APGC-QToF MS). The performance of each library is evaluated by matching spectra from real plastic and biobased plastic samples.

Methodology

Polymer standards (~0.1 mg) were pyrolyzed in quartz wool–packed capillaries at ramp rates of 20 °C/ms to 750 °C. Separation occurred on an Rtx-5MS column (30 m × 0.25 mm, 0.25 µm) with a split ratio of 75:1 and an oven program from 45 °C (5 min) to 300 °C at 20 °C/min. Data were acquired in full scan mode:

• py-GC-EI-MS: 70 eV, m/z 10–650, scan time 0.1 s
• py-APGC-QToF MS: APGC positive ionization, m/z 10–1500, MSE acquisition (low energy 6 V; high energy 15–45 V), scan time 0.2 s

MassLynx 4.2 software was used for data processing and NIST library integration.

Used Instrumentation

• Pyrolyzer: CDS 5000
• Gas chromatograph: Agilent-style split/splitless inlet with Rtx-5MS column
• Mass spectrometers: Xevo TQ-GC (EI) and Xevo G2-XS QTof (APGC)

Main Results and Discussion

In-house libraries built from averaged spectra of pure polymers yielded forward and reverse match scores above 800—considered reliable for identification. Recycled PET containers matched PET standards with scores of 865 on py-GC-EI-MS and 818 on py-APGC-QToF MS. Biobased PLA straws produced scores of 863/868 (forward/reverse) on EI and 851/852 on QToF, confirming PLA as the primary component.

Benefits and Practical Applications

• Soft ionization preserves molecular ions, improving elemental composition confirmation.
• High-resolution accurate mass facilitates structural elucidation.
• Custom libraries accelerate routine screening of commercial and recycled plastics.

Future Trends and Opportunities

Expansion of spectral libraries to include novel biopolymers and copolymers will broaden applicability. Integration with machine learning could enhance automated identification. Coupling pyrolysis-MS with complementary techniques such as FTIR imaging or ambient ionization may provide multi-modal analysis of polymer surfaces and additives.

Conclusion

Both py-GC-EI-MS and py-APGC-QToF MS enable construction of reliable pyrolyzate libraries for polymer identification. Soft ionization QToF offers additional confidence through molecular ion detection and high-resolution fragmentation data, making it a valuable tool for detailed polymer analysis.

References

1. Suge S., Ohtani H., Watanabe C. Pyrolysis-GC/MS Data Book of Synthetic Polymers. 2011.
2. Peacock P. M., McEwen C. N. Mass Spectrometry of Synthetic Polymers. Anal. Chem. 2006;78(12):3957–3964.
3. Sanig R., Cojocariu C., Jones R. Pyrolysis-gas chromatography-high resolution mass spectrometry with soft ionization for increased confidence for polymer characterization. Waters Application Note 720007599, April 2022.
4. NIST/EPA/NIH Mass Spectral Library Compound Scoring: Match Factor, Reverse Match Factor, and Probability, Jordi Labs.