GC-APCI IMS of Diesel

Importance of the Topic

This study addresses the challenge of profiling sulfur species in diesel fuel, crucial for environmental compliance and fuel performance. Sulfur compounds in diesel contribute to emissions and reduce product value, making their precise detection and quantification vital for the refining industry.

Study Objectives and Overview

The work evaluates the integration of gas chromatography with atmospheric pressure chemical ionization (GC-APCI), ion mobility separation, and high-resolution mass spectrometry to differentiate aromatic sulfur compounds from a complex hydrocarbon matrix. Diesel samples were compared before and after hydrodesulfurization to assess changes in sulfur speciation.

Methodology

Samples of untreated and treated diesel were diluted in isooctane without further cleanup. Chromatographic separation was performed on a nonpolar column under a temperature program. Ionization was achieved by APCI, followed by drift tube ion mobility for size and shape separation, and time-of-flight high-resolution mass analysis.

Instrumentation

• Agilent 7890B gas chromatograph equipped with a GC-APCI interface
• Agilent 6560 ion mobility Q-TOF mass spectrometer operating in positive ion mode

Key Results and Discussion

The addition of ion mobility enabled clear resolution of isobaric interferences such as column bleed and coeluting hydrocarbons, as seen in mobility-filtered spectra. Mass defect filtering highlighted aromatic sulfur species with mass defects below 0.1 Da, enabling selective extraction of dibenzothiophenes. Kendrick mass defect plots further grouped homologous series differing by CH2 units, facilitating the identification of alkylated dibenzothiophenes and related hydrocarbon series. Comparison of pre- and post-treatment samples showed a marked reduction in sulfur-containing aromatics after hydrodesulfurization.

Benefits and Practical Applications

The combined GC-APCI IMS-Q-TOF approach enhances specificity and sensitivity in complex matrices without extensive sample preparation. Its ability to separate structural isomers and remove background noise streamlines sulfur profiling in diesel, supporting refinery process optimization and quality control.

Future Trends and Potential Applications

Advances in ion mobility separation and high-resolution detection are expected to further improve throughput and structural characterization of trace components. Integration with automated data analysis and machine learning may enable real-time monitoring of fuel composition and extension to other heteroatom classes in petrochemical and environmental analyses.

Conclusion

This study demonstrates that GC-APCI combined with ion mobility and high-resolution mass spectrometry provides a powerful platform for detailed sulfur speciation in diesel fuel. The multidimensional separation yields high peak capacity and reliable identification of challenging aromatic sulfur compounds.

References

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3. Kendrick E. A mass scale based on CH2=14.0000 for high-resolution mass spectrometry of organic compounds. Anal Chem. 1963;35:2146-2154.
4. Hughey CA et al. Kendrick mass defect spectroscopy: A compact visual analysis for ultrahigh-resolution broadband mass spectra. Anal Chem. 2001;73:4676-4681.