Characterization of petroleum samples via thermal analysis coupled to APCI MRMS

Significance of the Topic

Thermal analysis coupled with atmospheric pressure chemical ionization ultra-high resolution mass spectrometry (TG-APCI MRMS) addresses a critical need in petroleomics by enabling direct, temperature-resolved characterization of high-viscosity and solid petroleum fractions. This approach offers molecular-level insights into complex mixtures, including polar and heteroatom-containing species that are challenging to access by conventional gas chromatography or direct infusion methods.

Objectives and Study Overview

The study aimed to demonstrate the capabilities of TG-APCI MRMS for a range of petroleum samples: a fatty acid methyl ester standard mix (FAME), diesel fuel, heavy fuel oil (HFO), and a crude oil. Key goals included mapping the temperature evolution of molecular species, distinguishing desorption and pyrolysis phases, and assigning elemental compositions with high mass accuracy.

Methodology and Instrumentation

A Netzsch TG 209 thermo balance was coupled via a 260 °C heated transfer line to a Bruker GC-APCI II ion source, which fed ions into a 7 T Bruker Apex Qe FT-ICR-MS. Samples (≈1 mg) were placed in an aluminum crucible and heated from 20 °C to 600 °C at 10 K/min. Evolved gases were ionized by APCI in positive mode, and spectra (m/z 100–1000) were acquired at ~260 000 resolving power (m/z 200). Data processing included peak picking, calibration in Bruker Data Analysis, and elemental assignment (C6–100H6–200N0–2O0–10S0–2) using custom MATLAB scripts.

Major Results and Discussion

• Survey plots of temperature vs. m/z revealed hundreds of features for diesel and thousands for HFO and crude oil, spanning m/z 100–750.
• Diesel samples were dominated by CH, CHO1, and CHO2 classes, while HFO and crude oil showed significant CH and CHS species.
• Double bond equivalent (DBE) distributions tracked over temperature illustrated the emergence of desorption (≤300 °C) and pyrolysis (>300 °C) products, with pyrolysis fragments shifting toward lower m/z and providing structural clues.
• Distinct desorption and decomposition phases were visible in total ion chromatograms, extending the analytical range beyond conventional GC limits.

Benefits and Practical Applications

• Minimal sample preparation and low sample mass (<2 mg) requirements.
• High temperature range (up to 600 °C) enables analysis of heavy fractions and pyrolysis fragments.
• Enhanced detection of polar and heteroatom-containing species via APCI.
• Complementary to GC-APCI and direct infusion, with temperature-resolved molecular profiles useful for fuel quality control, degradation studies, and structural elucidation.

Future Trends and Opportunities

Advances may include integration with chromatographic separation prior to TG, development of multimodal ionization workflows, machine learning–driven data interpretation of complex thermal profiles, and extension to other challenging matrices such as bio-oils, polymers, and environmental samples.

Conclusion

TG-APCI MRMS provides a powerful platform for petroleomics by combining thermal desorption/pyrolysis with ultra-high resolution mass spectrometry. The method delivers detailed, temperature-resolved compositional maps of complex petroleum samples and offers unique structural insights through pyrolysis fragments. High mass accuracy is essential for reliable elemental assignments in these intricate mixtures.

Reference

1. Rüger C. P. et al. Analytical Chemistry 2015, 87(13), 6493–6499.
2. Schwemer T. et al. Analytical Chemistry 2015, DOI:10.1021/acs.analchem.5b02114.
3. Smit E. et al. Energy Fuels 2015, DOI:10.1021/acs.energyfuels.5b00831.