Natural Polymer Analysis by using Pyrolysis-GCxGC-MSー”Urushi” analysis with GCxGC/EI and GCxGC/PI

Significance of the Topic

Pyrolysis coupled with comprehensive two-dimensional gas chromatography and high-resolution time-of-flight mass spectrometry (Py/GCxGC-HR-TOFMS) offers unparalleled separation and identification of complex natural polymers like Urushi lacquer film. This method enables detailed profiling of thermal decomposition products and enhances our understanding of polymer structure and composition in cultural heritage and industrial contexts.

Objectives and Overview

The study aimed to apply a novel GCxGC-HR-TOFMS system equipped with a combined electron ionization (EI) and photoionization (PI) source to analyze Urushi lacquer film. Key goals included optimizing pyrolysis conditions, characterizing main components, and demonstrating the technique’s ability to resolve co-eluting species.

Methodology

Samples of Japanese lacquer film were thermally decomposed using pyrolysis at 500 °C followed by comprehensive two-dimensional gas chromatography and high-resolution TOFMS.
Key procedural steps:

• Pyrolysis at 500 °C to maximize release of Urushiol-related compounds
• First-dimension GC column: BPX5 (30 m × 0.25 mm, 0.25 µm)
• Second-dimension GC column: BPX50 (3 m × 0.1 mm, 0.1 µm)
• Modulation period: 8 s
• Oven program: 50 °C (1 min) to 300 °C at 3 °C/min (6 min hold)
• Ionization modes: EI (70 eV) and PI (10.8 eV D₂ lamp)
• Mass range: m/z 35–650; data rates: EI 50 Hz, PI 25 Hz

Instrumentation

System: JMS-T200GC “AccuTOF™ GCx” HR-TOFMS with combined EI/PI ion source; pyrolyzer: JEOL pyrolysis unit.

Main Results and Discussion

The method successfully identified Urushiols as primary constituents in both EI and PI datasets. Optimization at 500 °C provided enhanced signal for thermal decomposition products compared to 400 °C. Over 1,000 compounds were detected using automated peak finding. Two-dimensional extracted ion chromatograms at m/z 123.044 (C₇H₇O₂) revealed distinct series of alkyl catechols and alkyl orcinols, which co-elute in one-dimensional GC but are effectively separated by GCxGC due to polarity differences. PI spectra provided clear molecular ion signals for key analytes such as 3-pentadecyl catechol (C₂₁H₃₆O₂) and 3-pentadecenyl catechol (C₂₁H₃₄O₂), enabling accurate mass measurement with sub-2 mDa error.

Benefits and Practical Applications

This approach offers:

• Enhanced separation of minor and co-eluting compounds in complex polymers
• Accurate molecular ion information via soft PI ionization
• Comprehensive profiling of thermal degradation products for quality control
• Application in cultural heritage conservation, polymer authentication, and industrial QA/QC

Future Trends and Applications

Advances may include integration of machine learning for peak deconvolution, hybrid ionization strategies for broader analyte coverage, and real-time Py/GCxGC analysis. Further development of HR-TOFMS platforms with improved sensitivity could expand non-targeted investigations of diverse polymeric and biopolymeric materials.

Conclusion

The combined Py/GCxGC-HR-TOFMS with EI/PI ionization demonstrates powerful capabilities for detailed analysis of Urushi lacquer film. The method achieves high-resolution separation of complex thermal decomposition products, accurate mass determination, and distinguishes structurally similar compound series, establishing a valuable tool for polymer analysis.

References

• MSTips 245. 2024. Natural Polymer Analysis by using Pyrolysis-GCxGC-MS: “Urushi” analysis with GCxGC/EI and GCxGC/PI. JEOL Ltd.