Recent Developments in GC Analysis of Low Molecular Weight Sulfur and Oxygen Containing Species in Fuels and Feed Stocks

Importance of the Topic

Reliable detection and quantitation of trace sulfur and oxygen-containing compounds in fuels and feed stocks are vital for refinery operation, catalyst protection, environmental compliance and process safety. Sulfur species can rapidly deactivate cracking catalysts and contaminate downstream products, while oxygenates (alcohols, ethers, ketones) serve as regulated additives or pollutants requiring stringent monitoring.

Objectives and Study Overview

This work presents recent advances in multidimensional gas chromatography (2D-GC) using the GS-OxyPLOT porous layer open tubular column coupled to electronic pressure control. The goals are to improve selectivity and sensitivity for C1–C5 oxygenates in high-ethanol gasoline streams and low-molecular-weight sulfur species in hydrocarbon matrices, and to align performance with emerging ASTM proposed methods.

Methodology and Instrumentation

Chromatographic separation employs a primary nonpolar DB-1 column for hydrocarbon classes followed by a GS-OxyPLOT megabore (10 m×0.53 mm×10 µm) secondary column. A valve switch traps target analytes on the GS-OxyPLOT phase, then thermal desorption through programmed heating separates oxygenates and sulfur compounds from the hydrocarbon background. Carrier gas is helium at constant flow, injection is 1 µL split, and detection uses a flame ionization detector (FID).

Used Instrumentation

• Gas chromatograph: Agilent 6890 with electronic pressure control
• Primary column: DB-1 (25 m×0.53 mm×1 µm)
• Secondary column: GS-OxyPLOT PLOT capillary (10 m×0.53 mm×10 µm)
• Detector: FID, H₂ 40 mL/min, air 450 mL/min, makeup N₂ 30 mL/min
• Oven program: 60 °C hold, ramp to 120 °C at 10 °C/min, then to 310 °C at 25 °C/min

Main Results and Discussion

• GS-OxyPLOT exhibits strong adsorption of polar oxygenates and selective retention of low-boiling sulfur species, while nonpolar hydrocarbons elute with minimal retention.
• Retention time shifts relative to DB-1 enable clear resolution of trace oxygenates (methanol, ethanol, MTBE, ethers, aldehydes, ketones) and sulfur compounds (mercaptans, thiophenes, sulfides).
• Demonstrated alignment with proposed ASTM methods for C1‒C5 oxygenates in reformulated gasoline and for methanol in crude oil (ASTM D7059).

Benefits and Practical Applications

• Enhanced selectivity reduces hydrocarbon interferences and improves quantitation limits for trace analytes.
• Modular 2D-GC approach streamlines analyses of mixed hydrocarbon/oxygenate/sulfur streams.
• Compatibility with existing FID systems facilitates rapid implementation in QA/QC laboratories and refineries.

Future Trends and Applications

Integration with automated valve switching and mass spectrometric detection may further extend compound coverage and sensitivity. Development of tailored PLOT phases and standardized 2D-GC protocols is expected to support emerging biofuel analyses and real-time process monitoring in petrochemical operations.

Conclusion

The GS-OxyPLOT column, combined with 2D-GC and electronic pressure control, offers a robust solution for simultaneous analysis of low-molecular sulfur and oxygenates in complex fuel matrices. Its high selectivity, broad temperature stability and alignment with ASTM guidelines make it a valuable tool for modern analytical laboratories.