Identification of Components of Polymer Extracts by Gas Chromatography with EI and CI High Resolution Time-of-Flight Mass Spectrometry

Importance of Topic

Profiling extractable components from polymer materials is critical for ensuring product quality, safety, and regulatory compliance. Comprehensive chemical characterization supports detection of residual monomers, additives, degradation products, and contaminants, which is essential in industries ranging from medical devices to packaging.

Objectives and Study Overview

This study aimed to achieve a full chemical profile of a polymer extract by combining gas chromatography with electron impact (EI) and chemical ionization (CI) high-resolution time-of-flight mass spectrometry (GC-HRT). The goal was to overcome limitations of library matching and low-abundance molecular ions in conventional nominal-mass GC-MS analyses and to confidently identify over 20 components in the extract.

Methodology and Instrumentation Used

Sample Preparation:

• Polymer beads (2 g) were extracted with 15 mL HPLC-grade acetonitrile at 37 °C for 24 h, followed by filtration through a 0.45 µm PTFE filter.
• A 1 mL aliquot of the filtrate was analyzed by GC-MS.

Gas Chromatography:

• Instrument: Agilent 7890 GC with 7693 autosampler.
• Column: Restek Rxi-5Sil MS (30 m × 0.25 mm × 0.25 µm).
• Carrier gas: Helium at 1.0 mL/min; injection split 3:1 (0.5 µL) for EI, splitless (1 µL) for CI.
• Oven program: 60 °C (2 min) to 190 °C at 10 °C/min (1 min), then to 250 °C at 50 °C/min (10 min).

Mass Spectrometry:

• Instrument: LECO Pegasus GC-HRT.
• EI source at 70 eV, 250 °C; CI source at 140 eV, 225 °C with 5% NH₃ in methane reagent gas.
• Mass range: m/z 50–650 for EI; 180–1400 for CI, acquisition rate 6 spectra/s.
• High-resolution TOF flight path (RFWHM ≈ 25 000); internal calibration with PFTBA.

Key Results and Discussion

1. EI Profiling:

• Detected methylated cyclosiloxanes D4–D8 with characteristic [M–CH₃]⁺ fragment ions at mass accuracy ~0.92 ppm.
• D9 and D10 lacked the [M–CH₃]⁺ signal due to increased stability of larger homologs.

2. CI Confirmation:

• HR-CI pseudomolecular ions enabled formula confirmation for cyclosiloxanes D4–D17, with average mass accuracy of 0.43 ppm.
• Additional components identified included butylated hydroxytoluene (BHT), a diisocyanate, a dilactone, and a tetralactone, each confirmed by protonated and ammoniated molecular ions within ±0.3 ppm.
• Extracted ion chromatograms and deconvoluted “Peak True” spectra resolved co-eluting or isobaric interferences, ensuring unambiguous assignments.

Benefits and Practical Applications

• Complementary EI and CI ionization maximizes structural information and preserves molecular ions for formula determination.
• High-resolution accurate-mass measurements allow confident identification of trace and labile compounds.
• Approach is well suited for quality control, process monitoring, and detection of adulterants in polymer-based materials.

Future Trends and Potential Applications

Advances may include integration of alternative reagent gases for tailored CI chemistries, automated deconvolution workflows, expanded high-resolution mass spectral libraries, and real-time monitoring of polymer manufacturing. Further applications could target broader polymer classes, biocompatible materials, and compliance with evolving regulatory standards.

Conclusion

The integrated GC-EI/CI GC-HRT approach delivers a comprehensive chemical profile of polymer extracts, leveraging high-resolution accurate-mass data and complementary ionization modes to identify and confirm over 20 components with high confidence. This methodology enhances analytical capabilities for research, quality assurance, and regulatory compliance in polymer analysis.