Ethylene Propylene Diene Monomer Rubber Analysis by using Pyrolysis-GCxGC-MS

Significance of the Topic

The analysis of ethylene–propylene–diene monomer (EPDM) rubber via pyrolysis coupled to comprehensive two-dimensional gas chromatography and high-resolution time-of-flight mass spectrometry (Py/GCxGC/HR-TOFMS) addresses critical needs in polymer research and quality control. Detailed profiling of pyrolysis fragments allows for a deeper understanding of polymer composition, additive content, and degradation pathways, which is essential for material development, failure analysis, and regulatory compliance.

Study Objectives and Overview

This study aimed to demonstrate the enhanced separation power and compound identification capabilities of a newly developed Py/GCxGC/HR-TOFMS system equipped with multiple ionization modes (electron ionization, field ionization, and photoionization). By applying this system to EPDM rubber pyrolysis, researchers sought to:

• Compare one-dimensional and two-dimensional GC separations under electron ionization.
• Assess the performance of soft ionization techniques (PI and FI) for molecular ion detection.
• Perform accurate mass analysis to elucidate unknown pyrolysis products.

Methodology and Instrumentation

The experimental setup combined pyrolysis with GCxGC and a high-resolution time-of-flight mass spectrometer capable of three ionization modes:

• Pyrolysis at 650 °C to generate volatile fragments.
• First GC dimension: BPX5 column (30 m × 0.25 mm, 0.25 µm film); second dimension: BPX50 column (2 m × 0.1 mm, 0.1 µm film).
• Oven program: 50 °C hold for 1 min, ramp 5 °C/min to 320 °C, hold for 10 min.
• Injection: split mode (100:1) at 300 °C; helium flow 1.8 mL/min.
• Modulation period: 5 s.
• Mass spectrometer settings: EI+ at 70 eV, PI+ using a deuterium lamp (10.8 eV), FI+ at –10 kV; mass range m/z 35–650.

Main Results and Discussion

Comprehensive GCxGC under electron ionization resolved over 1 000 distinct pyrolysis products from EPDM, compared to significant co-elution in one-dimensional GC. Soft ionization modes provided complementary molecular ion information:

• Photoionization and field ionization spectra exhibited strong molecular ion peaks with minimal fragmentation.
• Unknown compounds with low EI match factors were characterized by accurate mass measurements in PI and FI spectra.
• Accurate mass analysis of a target antioxidant fragment (compound A) matched the formula C23H26N2, identifying polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ).

Benefits and Practical Applications

The combination of GCxGC separation and multi-mode ionization enhances qualitative analysis by:

• Unraveling complex polymer matrices and additive profiles.
• Providing robust identification using EI library searches complemented by exact mass confirmation.
• Reducing ambiguity in compound assignment for regulatory, R&D, and quality assurance purposes.

Future Trends and Potential Applications

Advancements in pyrolysis-GCxGC-HR-TOFMS promise further improvements:

• Integration with machine learning for automated peak annotation and pattern recognition.
• Expansion of soft ionization techniques to access non-hydrocarbon additives and contaminant profiling.
• Application to broader polymer classes, environmental microplastic analysis, and forensic polymer investigations.

Conclusion

This work demonstrates that Py/GCxGC/HR-TOFMS, when combined with EI, PI, and FI ionization modes, delivers unparalleled separation and identification capabilities for EPDM pyrolysis products. The strategy of initial EI library searching followed by soft ionization and accurate mass measurement provides a comprehensive approach to polymer analysis and additive characterization.

Reference

• NIST Mass Spectral Library for electron ionization database searches.