Quantitation of PAH in Engine Oils Using GCxGC-TOFMS

Importance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) in engine oils pose environmental and regulatory challenges due to their persistence and toxicity. Accurate quantitation and identification of PAHs and their alkylated derivatives in complex petroleum matrices are essential for quality control, environmental monitoring, and compliance with emission standards.

Objectives and Study Overview

This study aimed to develop robust quantitation methods for a standard set of PAHs using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GCxGC-TOFMS) and apply these methods to a range of engine oil samples (unused, used under various driving conditions, and new oil). It also sought to evaluate the improved deconvolution capabilities of GCxGC and identify non-targeted sulfur- and oxygen-containing species.

Methodology and Instrumentation

The analytical approach combined enhanced chromatographic separation with high-speed mass spectral acquisition to resolve PAHs from coeluting matrix interferences.

• Sample Preparation: Liquid injection of diluted engine oil samples (split 20:1 at 320 °C).
• GCxGC Separation: Agilent 7890 GC with dual stage quad jet thermal modulator; Rxi-PAH primary column (60 m × 0.25 mm, 0.10 µm) and Rxi-1HT secondary column (0.6 m × 0.25 mm, 0.10 µm); temperature program: 1.5 min at 80 °C, 10 °C/min to 300 °C, 3 °C/min to 320 °C (held 10 min); secondary oven +10 °C.
• Mass Spectrometry: LECO Pegasus BT 4D TOFMS; ion source 300 °C; transfer line 350 °C; mass range 45–500 m/z; acquisition rate 200 spectra/s; modulation period 2.5 s.

Key Results and Discussion

Calibration curves for 16 PAHs exhibited excellent linearity (R2 > 0.995) over 5–2500 ppb. Quantified PAH levels in used oils corresponded with expected combustion efficiencies: highest concentrations in short-trip used oils, lowest in long-trip used oils. GCxGC-TOFMS deconvolution distinctly separated coeluting compounds (e.g., nonadecane vs. 2,6-dimethylnaphthalene) that were unresolved by one-dimensional GC. Automated library matching enabled tentative identification of oxygen- and sulfur-containing compounds in used oil samples.

Benefits and Practical Applications

The combined GCxGC and TOFMS platform offers:

• High chromatographic resolution and peak capacity for complex samples.
• Accurate quantitation of regulated PAHs with minimal interference.
• Enhanced deconvolution for reliable qualitative profiling.
• Capability to identify non-targeted heteroatom species for comprehensive oil characterization.

Future Trends and Potential Applications

Advances may include integration with high-resolution accurate-mass detectors, real-time on-line monitoring of industrial streams, application of machine learning for automated spectral deconvolution, expansion to other complex matrices (e.g., environmental samples, waste oils), and miniaturized portable GCxGC systems for field analysis.

Conclusion

GCxGC-TOFMS using the Pegasus BT 4D system provides a robust, sensitive, and high-throughput solution for quantitative and qualitative analysis of PAHs in engine oils. The enhanced separation and mass spectral deconvolution capabilities enable accurate determination of target analytes and identification of additional species in complex petroleum matrices.

References

Kelly CN, Alonso DE, Fell LM, Binkley JE. Quantitation of PAH in Engine Oils Using GCxGC-TOFMS. LECO Corporation Application Note.