GC/TOFMS analysis of high boiling point compounds - cholesterol and Irganox® 1010

Importance of the Topic

Cholesterol and polymer antioxidants such as Irganox 1010 represent challenging high boiling point analytes in gas chromatographic mass spectrometric analysis due to thermal stability requirements and detection sensitivity. Soft ionization methods and advanced time-of-flight detection enhance the ability to observe intact molecular ions and reduce background interference.

Objectives and Study Overview

This study explores the application of gas chromatography coupled with time-of-flight mass spectrometry (GC TOFMS) to analyze high boiling point compounds using electron ionization and field ionization. By comparing both ionization techniques for cholesterol and Irganox 1010, the work aims to demonstrate improved qualitative capabilities and baseline performance.

Methodology

• Sample Preparation: 1 mg/mL solutions of cholesterol and Irganox 1010 in methanol.
• Gas Chromatography Conditions: DB 1HT column (7 m x 0.25 mm, 0.10 μm), injector at 380 °C, constant flow of 2 mL/min, split injection (80:1 for EI, 10:1 for FI), oven ramp from 120 °C to 380 °C.
• Ionization Approaches: Hard ionization by electron energy at 70 eV for EI, and soft field ionization at cathode potential of -10 kV.

Instrumentation Used

• Gas Chromatograph: JEOL DB 1HT column with high temperature capability.
• Mass Spectrometer: JMS T100GC AccuTOF GC with TOF detection up to m/z 1400.
• Interface and Source Temperatures: GC interface at 350 °C; EI source at 300 °C; FI source at 250 °C.
• Acquisition Settings: Mass range m/z 35 to 1400; spectral interval 0.4 seconds; emitter current 35 mA for FI.

Main Results and Discussion

• Chromatographic Performance: GC EI analyses showed rising baselines at high temperatures due to column bleed, partially obscuring late eluting compounds. GC FI delivered flat baselines and clear detection of cholesterol around 240 °C and Irganox 1010 at the final temperature of 380 °C.
• Mass Spectral Features: EI spectra were dominated by fragment ions and lacked molecular ions for Irganox 1010. Conversely, FI spectra produced strong molecular ion peaks as base peaks with minimal fragmentation for both analytes.
• Analytical Advantages: The combination of FI and EI enabled confident identification through intact molecular ions and complementary fragmentation patterns.

Benefits and Practical Applications

• Enhanced Qualitative Analysis: Soft ionization preserves molecular ions, aiding accurate mass determination and structural confirmation.
• Improved Sensitivity and Clarity: Reduced background noise in FI improves peak detection of high boiling analytes.
• Versatility: The dual ionization strategy supports a broad range of compounds from lipids to polymer additives, beneficial for research, QA QC, and industrial analytics.

Future Trends and Potential Applications

• Integration with High Resolution Mass Spectrometry for enhanced exact mass analysis.
• Automation and high throughput screening of thermo labile and high molecular weight compounds.
• Expansion to chemical ionization modes to further tailor ionization selectivity for complex mixtures.
• Development of specialized high temperature columns and injection systems for ultra high boiling analytes.

Conclusion

The study confirms the feasibility of GC TOFMS analysis of high boiling point compounds using both electron and field ionization. Field ionization significantly reduces baseline interference and preserves molecular ion information, while electron ionization provides detailed fragmentation. Together, these methods enhance the confidence and versatility of qualitative analyses for challenging analytes.

Reference

• JEOL MS Data Sheet No 040 and No 123 Mass Spectrometry Application Group JEOL Ltd 2008