Automated Characterization of a Diesel Sample Using Comprehensive Two-Dimensional GC (GCxGC) and Time-of-Flight Mass Spectrometry (TOFMS) Detection (Pegasus 4D System)

Significance of the Topic

Diesel fuel comprises a highly complex mixture of hydrocarbons and heteroatomic species, each contributing to performance, emissions, and regulatory compliance. Comprehensive two-dimensional gas chromatography (GCxGC) coupled with time-of-flight mass spectrometry (TOFMS) offers the resolution and speed needed to profile thousands of components that traditional one-dimensional methods cannot separate fully.

Objectives and Overview

This study aimed to achieve full chemical class pattern identification in an untreated diesel sample by integrating GCxGC separation with rapid TOFMS detection. The goal was to demonstrate automated characterization of over 6,000 compounds, highlighting class-specific organization in the chromatogram and resolving overlapping species.

Methodology and Used Instrumentation

GCxGC separations were conducted on an Agilent 6890 GC equipped with a LECO thermal modulator. Key parameters included:

• Primary column: DB-PONA, 50 m × 0.2 mm i.d., 0.5 µm film; oven ramp from 100 °C (0.2 min) to 240 °C (66.7 min) at 1.5 °C/min
• Secondary column: DB-WAX, 2 m × 0.1 mm i.d., 0.1 µm film; oven ramp from 110 °C (1 min) to 240 °C (74.5 min) at 1.5 °C/min
• Injection: 0.2 µL, split ratio 100:1, inlet 250 °C, He carrier at 1.5 mL/min
• Thermal modulation: 30 °C offset, 5 s cycle with 0.6 s hot pulse

Mass spectral detection used the LECO Pegasus 4D GCxGC-TOFMS with EI at 70 eV, mass range 35–500 u, source at 225 °C, and acquisition at 100 spectra/s.

Main Results and Discussion

The combined GCxGC-TOFMS system resolved more than 6,000 components in the diesel sample. The primary non-polar column organized analytes by carbon number, while the secondary polar column separated them by polarity, producing distinct bands for hydrocarbon classes. Unique m/z plots allowed discrimination of co-eluting species, such as substituted benzothiophenes, biphenyls, and naphthalenes, enhancing confidence in class identification even in overlapping regions.

Benefits and Practical Applications

The coupling of GCxGC with high-speed TOFMS offers:

• Automated, high-throughput profiling of complex mixtures
• Enhanced peak capacity for regulatory and quality control testing
• Class-based fingerprinting for petroleum product comparison and authentication
• Improved detection of trace heteroatom-containing compounds

Future Trends and Potential Applications

Advances in software for automated peak deconvolution, machine learning classification, and increased detector speed will further streamline comprehensive analyses. Integration with real-time monitoring, expanded mass range, and hybrid detectors could extend applications to biofuels, environmental forensics, and advanced refining processes.

Conclusion

Comprehensive two-dimensional GC combined with TOFMS provided the resolution and speed required for automated, detailed characterization of a complex diesel sample. This methodology delivers organized chromatograms by chemical class and overcomes limitations of conventional one-dimensional approaches, establishing a robust platform for petroleum analysis and beyond.