Analysis of Dibenzothiophenes in Diesel by GC-APCI Ion Mobility High-Resolution MS

Importance of the Topic

Diesel fuel contains sulfur heterocycles such as dibenzothiophenes, which contribute to harmful emissions and catalyst poisoning. Accurate speciation and quantification of these compounds at trace levels support regulatory compliance, engine performance optimization, and environmental protection.

Study Objectives and Overview

This work demonstrates a workflow combining gas chromatography (GC), atmospheric pressure chemical ionization (APCI), ion mobility separation, and high-resolution mass spectrometry (HRMS) to resolve and quantify dibenzothiophene isomers in complex diesel matrices. Key goals include enhanced selectivity, sensitivity, and confidence in compound identification.

Methodology

• Sample Preparation: Diesel samples diluted and spiked with isotope-labeled standards for calibration.
• Chromatographic Separation: Capillary GC column optimized for sulfur heterocycles; temperature program tailored for isomeric resolution.
• Ionization and Mobility: APCI source generating [M+H]+ ions introduced into drift cell for mobility separation based on collisional cross section.
• Mass Analysis: Orthogonal time-of-flight (TOF) HRMS providing accurate mass measurements (<2 ppm) to distinguish closely related species.

Instrumental Setup

• Gas Chromatograph with programmed temperature control.
• Atmospheric Pressure Chemical Ionization Interface.
• Ion Mobility Spectrometer for drift time measurement.
• High-Resolution TOF Mass Analyzer.

Key Results and Discussion

GC-APCI-IM-HRMS achieved baseline separation of dibenzothiophene isomers, with drift time differences of 0.1–0.3 ms. Accurate mass data confirmed elemental compositions and suppressed interferences from co-eluting compounds. Method detection limits reached low ppb levels, with linear dynamic range spanning three orders of magnitude. Matrix effects were minimized through mobility filtering, improving quantitation accuracy.

Practical Benefits

• Enhanced Selectivity: Mobility separation resolves isomeric and isobaric interferences.
• Improved Sensitivity: APCI offers soft ionization, reducing fragmentation and background noise.
• Regulatory Compliance: Low detection limits align with tightening sulfur content standards.
• Versatility: Approach adaptable to other polar and nonpolar sulfur compounds.

Future Trends and Applications

Advances in ion mobility resolution and machine-learning–based drift time prediction will further streamline identification workflows. Integration with two-dimensional separations (e.g., GC×GC) and targeted data-independent acquisition could expand coverage to complex fuel blends and biodesulfurization products.

Conclusions

The GC-APCI-IM-HRMS platform provides a powerful tool for detailed sulfur speciation in diesel, combining chromatographic, mobility, and high-resolution mass information to achieve high confidence in trace-level analysis. This method supports environmental monitoring, quality control, and research into cleaner fuel technologies.