Analysis of Gas Oil by GC/APCI FTMS

Significance of the Topic

Gas oil is a complex petroleum distillate whose composition and impurity profile have important environmental and regulatory implications, particularly for sulfur and nitrogen content. High–resolution mass spectrometry coupled with chromatographic separation provides the necessary specificity and sensitivity to identify and quantify trace heteroatom‐containing species that impact fuel quality and emissions.

Objectives and Article Overview

This application note demonstrates the use of gas chromatography–atmospheric pressure chemical ionization Fourier transform mass spectrometry (GC/APCI FTMS) to separate, detect, and quantify low‐abundance sulfur‐containing compounds in gas oil. The study focuses on distinguishing isomeric series of alkylated benzothiophenes and dibenzothiophenes and comparing GC/APCI results with direct infusion measurements.

Methodology and Instrumentation

The workflow involves a splitless injection of 1 µL of gas oil diluted 1:100 in dichloromethane onto an HP-5 ms GC column (30 m × 0.25 mm ID, 0.25 µm film). The temperature gradient of 5–10 °C/min enables separation of homologous series. The eluent is ionized by APCI in positive‐ion mode and analyzed by a 12 T solariX FT‐ICR mass spectrometer. Spectra are acquired at 1 Hz over m/z 73–1000 with 2 MW data points, achieving resolving power ~300,000 at m/z 200 and sub‐ppm mass accuracy. Extracted ion chromatograms (EICs) with 1 mDa tolerance are used to resolve isomers and isobars.

Used Instrumentation

• Bruker solariX 12 T FT‐ICR MS
• GC/APCI ion source (Bruker)
• Agilent HP-5 ms capillary column (30 m × 0.25 mm, 0.25 µm film)
• Bruker DataAnalysis 4.0 software

Main Results and Discussion

Base peak chromatograms and RT vs. m/z survey plots reveal a highly complex mixture with numerous isomeric and isobaric components. GC/APCI FTMS successfully separates and identifies multiple alkyl‐benzothiophene and alkyl‐dibenzothiophene isomers across a broad carbon number range (C8–C19). Comparison with direct infusion APCI shows differing carbon number distributions, attributed to GC separation of lower‐boiling species and reduced ion suppression. High resolving power enables separation of isobars differing by only 3.4 mDa (e.g., C3 vs. SH4), demonstrating the method’s capacity to deconvolute closely spaced species.

Benefits and Practical Applications

• Sensitive detection and accurate mass measurement of volatile and semi‐volatile hydrocarbons.
• Effective separation of isomeric heteroatom species for improved identification.
• Quantification of trace sulfur compounds in compliance with environmental regulations.
• Enhanced dynamic range to detect low‐abundance impurities in complex matrices.

Future Trends and Potential Applications

Advances in GC/APCI FTMS may include automated quantification workflows for fuel quality control and regulatory monitoring, expansion to nitrogen‐ and oxygen‐containing species, and integration with chemometric or machine‐learning tools for rapid spectral deconvolution. Miniaturization and higher throughput instrumentation could further broaden industrial adoption.

Conclusion

GC/APCI FTMS on a 12 T FT‐ICR MS platform provides an effective, high-resolution approach to profile complex gas oil mixtures, enabling the separation and quantification of isomeric sulfur compounds with unparalleled mass accuracy and resolving power. This methodology supports stringent impurity monitoring and fuel characterization needs.

Reference

Bruker Daltonik GmbH. Application Note FTMS-41: Analysis of Gas Oil by GC/APCI FTMS (2010).