Analysis of Sulfur Compounds in Light Petroleum Liquids by Gas Chromatography and Sulfur Selective Detection according to ASTM D5623

Importance of the topic

Speciation of sulfur compounds in light petroleum is critical due to the corrosive and odorous nature of sulfur species, their capacity to poison catalysts in downstream refinery operations and impact product quality and environmental compliance.

Objectives and overview of the study

This application note details the determination of volatile sulfur compounds in gasoline liquids using a gas chromatography method with a PAC SeNse sulfur chemiluminescence detector, following ASTM D5623. The study aims to deliver a rapid (<30 min), sensitive and interference-free analysis with high repeatability and linear equimolar response.

Methodology and used instrumentation

• Sample introduction via liquid sampling valve (LSV) or syringe into split/splitless inlet
• Separation on a thick-phase methyl silicone capillary column under temperature programming
• Dual plasma furnace for combustion of sulfur compounds to SO₂ with subsequent reduction and ozone chemiluminescence detection
• PAC SeNse SCD detector with ozone generator, photomultiplier tube and precise flow and temperature control

Main results and discussion

• Separation efficiency: Eighteen sulfur compounds (e.g. ethanethiol, thiophene, benzothiophene) were baseline-resolved using optimized GC conditions and two calibration mixes.
• Retention time repeatability: Ten consecutive runs yielded retention time RSD below 0.05 min across all target compounds, meeting ASTM D5623 criteria.
• Recovery and repeatability: Analysis of NIST SRM 2299 (Sulfur in Gasoline) achieved an average total sulfur recovery of 12.35 ppm (target 13.6 µg/g) with RSD of 1.77%, demonstrating excellent accuracy and precision.
• Linearity: Response linearity over three orders of magnitude (30 ppb to 100 ppm wt S) showed R² > 0.9999 and consistent response factors (RSD ~2%).
• Detectability: Calculated limits of detection around 50 ppb (split 1:10, 1 µL injection); all compounds at ~40 ppb clearly distinguished from baseline.

Benefits and practical applications

Rapid, robust sulfur speciation supports quality control in refineries and fuel production, helps meet regulatory limits, protects downstream catalysts and enables targeted process optimization.

Future trends and potential applications

Integration with online process monitoring, miniaturized portable detectors for field use, coupling with automated sampling for high-throughput labs, and extension to heavier petroleum streams are anticipated developments.

Conclusion

The GC-SCD system with PAC SeNse detection under ASTM D5623 offers a robust, sensitive and repeatable solution for sulfur compound analysis in light petroleum liquids, delivering fast results with low detection limits and high data quality suitable for routine QA/QC environments.

Used instrumentation

• Gas chromatograph with split/splitless inlet (He carrier gas)
• Thick-phase methyl silicone capillary column, temperature-programmed
• PAC SeNse sulfur chemiluminescence detector with dual plasma furnace and ozonator
• Liquid sampling valve (LSV) and automated liquid sampler (ALS)
• Photomultiplier tube for photon detection