Characterization of petroleum samples via thermal analysis coupled to APCI MRMS

Importance of the Topic

Thermal analysis coupled with atmospheric pressure chemical ionization high-resolution mass spectrometry offers a unique route to dissect the complex molecular makeup of petroleum fractions. It extends standard gas chromatographic techniques by accessing higher boiling components and pyrolysis products, thus providing structural insights that are otherwise difficult to obtain.

Study Objectives and Overview

This study aims to demonstrate the capabilities of combining thermogravimetric analysis with a GC-APCI II ion source and a 7 T Fourier transform ion cyclotron resonance mass spectrometer for the detailed characterization of various petroleum samples. A fatty acid methyl ester standard mix, diesel fuel, heavy fuel oil, and crude oil were examined under a controlled temperature program to resolve desorption and pyrolysis processes systematically.

Methodology and Instrumentation

• A thermo balance (TG 209, Netzsch) coupled via a heated transfer line to a Bruker GC-APCI II source.
• Apex Qe 7 T MRMS in positive ion mode, resolving power ~260 000 at m/z 200.
• Temperature ramp from 20 °C to 600 °C at 10 K/min; direct sample loading in aluminum crucibles; ~1 mg per run.
• Analytes: FAME standard mix, DIN EN 590 diesel, heavy fuel oil, Greek crude oil, diluted as needed in dichloromethane.
• Data processing via Bruker DataAnalysis and custom MATLAB scripts; elemental formulas assigned within 2 ppm tolerance (C6–100, H6–200, N0–2, O0–10, S0–2).

Main Results and Discussion

The evolved gas analysis revealed hundreds of molecular features for diesel and thousands for heavy fuel oil and crude oil, spanning m/z 100–750. Class distribution indicated CHxO–rich species in diesel and CHxS classes in heavy fuel oil. Temperature-resolved double bond equivalent plots highlighted aromatic and polyaromatic distributions. Thermal profiles distinguished a low-temperature desorption phase (<300 °C) of volatile constituents and a higher-temperature pyrolysis phase (>300 °C) yielding fragment ions from larger structures. Overlapping desorption and pyrolysis signals underscored the method’s ability to deconvolute complex thermal behavior.

Benefits and Practical Applications

• Minimal sample requirements (<2 mg) and no elaborate preparation.
• Capability to analyze viscous and solid fractions directly.
• Temperature-resolved molecular insight, including pyrolysis fragments for structural elucidation.
• Complementary to direct infusion and GC-based approaches, with enhanced detection of polar and medium-polar species via APCI.

Future Trends and Potential Applications

The integration of thermal analysis high-resolution MS is poised to advance petroleomics, environmental monitoring, and quality control of fuels. Future work may involve coupling with alternative ionization methods, real-time reaction monitoring, and leveraging machine learning for automated pattern recognition and class assignments in complex mixtures.

Conclusion

Thermogravimetric analysis paired with GC-APCI MRMS offers a powerful platform for temperature-resolved, molecular-level characterization of petroleum samples. The method’s high resolution, broad mass range, and ability to probe pyrolysis products make it a valuable complement to existing analytical techniques for complex hydrocarbon mixtures.

Reference

1. Rüger CP, Miersch T, Schwemer T, Sklorz M, Zimmermann R. Hyphenation of Thermal Analysis to Ultrahigh-Resolution Mass Spectrometry Using Atmospheric Pressure Chemical Ionization for Studying Composition and Thermal Degradation of Complex Materials. Anal Chem. 2015;87(13):6493–6499.
2. Schwemer T, Rüger CP, Sklorz M, Zimmermann R. Gas Chromatography Coupled to Atmospheric Pressure Chemical Ionization FT-ICR Mass Spectrometry for Improvement of Data Reliability. Anal Chem. 2015. DOI:10.1021/acs.analchem.5b02114.
3. Smit E, Rüger CP, Sklorz M, de Goede S, Zimmermann R, Rohwer ER. Investigating trace polar species in diesel using high-resolution mass spectrometry and selective ionization techniques. Energy Fuels. 2015; DOI:10.1021/acs.energyfuels.5b00831.