The Use of GCxGC-TOFMS and Classifications for the Quantitative Determination of Different Compound Classes in Complex Isoparaffinic Hydrocarbon Samples

Importance of the Topic

Accurate quantification of different hydrocarbon classes in complex isoparaffinic mixtures is a major challenge in fields such as petrochemical analysis, quality control and environmental monitoring. Traditional one-dimensional GC coupled with mass spectrometry struggles to resolve the hundreds to thousands of isomeric and cyclic alkanes present. Comprehensive two-dimensional GC (GC×GC) combined with high-speed time-of-flight MS (TOFMS) enhances separation capacity, enabling reliable classification and quantitation of compound groups within complex hydrocarbon matrices.

Objectives and Study Overview

This study demonstrates how GC×GC-TOFMS, paired with a classification workflow, can differentiate and quantify linear, branched (isoparaffins) and cyclic hydrocarbons spanning a wide carbon number range. Two samples containing more than 1 000 components each were analyzed to build and validate classification templates and to assess reproducibility across different hydrocarbon mixtures.

Methodology and Instrumentation Used

A GC×GC system with a non-polar primary column and a mid-polarity secondary column was employed. Key elements include:

• Instrumentation: LECO Pegasus® 4D TOFMS
• Columns: 30 m × 0.25 mm ID Rtx-Wax (0.25 µm film) and 1.2 m × 0.10 mm ID Rtx-5 (0.10 µm film)
• Carrier gas: Helium at 1 mL/min (constant flow)
• Oven programs: 1st dimension 40 °C→140 °C at 2 °C/min; 2nd dimension 65 °C→165 °C at 2 °C/min
• Modulation period: 5 s; mass range: 45–450 m/z; acquisition rate: 100 spectra/s

Major Results and Discussion

GC×GC-TOFMS produced well-resolved two-dimensional chromatograms, where linear alkanes, isoparaffins and cyclic compounds occupy distinct bands. A classification template was constructed by assigning retention zones and characteristic mass defects for each carbon number class (e.g., C6, C6i, C6c). Application to Sample 1 yielded precise relative abundances for each class, with branched hydrocarbons dominating (~80 %), cyclic ~19 % and linear ~1 %. The same template applied to Sample 2 produced highly consistent class distributions, validating template robustness.

Benefits and Practical Applications of the Method

By grouping compounds based on chromatographic space rather than identifying every isomer, analysts achieve rapid, reproducible quantitation without exhaustive library matching. This approach streamlines hydrocarbon profiling in fuels, lubricants, environmental extracts and process streams, supporting quality control, regulatory compliance and R&D.

Future Trends and Potential Applications

Advances in data processing and automation will further simplify template generation and transfer between laboratories. Extension to more complex matrices—such as aromatics, sulfur‐ and nitrogen-containing species—can yield comprehensive fingerprints for forensic, environmental and petrochemical applications. Integration with chemometric tools could enable predictive modeling of sample origin and properties.

Conclusion

GC×GC-TOFMS combined with classification templates offers a powerful, efficient route for quantitative determination of hydrocarbon classes in complex samples. Once established, classification workflows deliver rapid, reproducible analyses, outperforming one-dimensional methods in resolution and accuracy.

Reference

• Classification Summary Table Tutorial v1.0, LECO Corporation