An Alternative Application for a Highly Oxygen-Selective Capillary GC Plot Column

Significance of the Topic

The determination of trace sulfur species in hydrocarbon streams is critical for regulatory compliance, process control and prevention of catalyst poisoning. Low‐molecular‐weight thiols, sulfides and disulfides at ppm levels pose analytical challenges in complex matrices such as gasoline and liquefied gases. A highly oxygen‐selective capillary column with affinity for sulfur analogs can create sufficient retention shifts to resolve these compounds from abundant hydrocarbons, enabling accurate quantification and improved refinery throughput.

Objectives and Overview of the Study

This application work aimed to demonstrate selective retention and baseline resolution of low‐molecular‐weight sulfur compounds using an Agilent J&W GS-OxyPLOT capillary column. Three sample types—a liquid sulfur standard in base gasoline, a gaseous sulfur blend in nitrogen, and a liquefied gas-liquid sulfur mix in n-butane—were evaluated to assess retention behavior, resolution from matrix components and feasibility of low ppm detection.

Methodology and Instrumentation

Standard mixtures of sulfur analytes were prepared: a 14‐component liquid mix in gasoline, an 11‐component gas blend in N₂, and a five‐component liquefied gas mix in n-butane. Each was injected onto capillary columns using split injection into an Agilent 6890N gas chromatograph. Dual detection (FID and pulsed flame photometric detector) was employed for simultaneous hydrocarbon and sulfur response. Oven programs and flow conditions were optimized to exploit the differential retention offered by the GS-OxyPLOT phase.

Used Instrumentation

• Gas Chromatograph: Agilent 6890N Network GC System
• Columns:
  • Agilent J&W GS-OxyPLOT, 0.53 mm × 10 m, 10 µm film thickness
  • Agilent J&W DB-1, 0.53 mm × 25 m, 1 µm or 0.53 mm × 10 m, 0.5 µm
• Detectors:
  • Flame Ionization Detector (FID): 250–350 °C, H₂ 30–40 mL/min, air 300–450 mL/min, N₂ makeup 15–30 mL/min
  • Pulsed Flame Photometric Detector (FPD): 250 °C, H₂ 50 mL/min, air 60 mL/min, N₂ makeup 60 mL/min
• Carrier Gas: Helium or hydrogen in constant flow mode (0.9–4.7 mL/min)
• Injection: Split ratios 10:1–25:1, injection port at 250 °C, volumes 1–25 µL

Main Results and Discussion

On a nonpolar DB-1 column, sulfur analytes coeluted with light hydrocarbons, preventing selective quantification. In contrast, the GS-OxyPLOT phase provided strong retention of sulfur species while most hydrocarbon matrix compounds eluted early. Liquid gasoline tests showed clear separation of mercaptans, sulfides and thiophenes except for potential overlap of tert-butanethiol with toluene. Gas and liquefied gas tests confirmed effective retention shifts, with large-volume injections yielding no baseline distortion despite some detector overloading in the FID trace.

Benefits and Practical Applications of the Method

• Low‐ppm level quantification of sulfur species in complex hydrocarbon streams
• Prevention of catalyst deactivation in refining and petrochemical processes
• Compliance with stringent emission and fuel quality regulations
• Flexibility to analyze liquid, gaseous and liquefied gas matrices

Future Trends and Potential Applications

Advancements may include coupling the GS-OxyPLOT column with mass spectrometry for enhanced selectivity and sensitivity. Miniaturized or automated GC systems could enable field‐deployable monitoring. Expansion to other heteroatom‐containing analytes (nitrogen or oxygen species) and integration into on-line process analyzers will further broaden applicability in modern petrochemical operations.

Conclusion

The Agilent J&W GS-OxyPLOT capillary column provides sufficient selectivity to shift retention of low‐molecular‐weight sulfur compounds away from hydrocarbon matrices, enabling accurate low‐ppm quantification. Method design must consider potential aromatic interferences, but the approach is practical for routine monitoring of sulfur in gasoline, gas and liquefied gas streams.

References

• Vickers AK. GS-OxyPLOT: A PLOT Column for the GC Analysis of Oxygenated Hydrocarbons. Agilent Technologies Technical Overview, publication 5989-6447EN, March 2007.
• Zou Y, Cai M. Investigation of the Unique Selectivity and Stability of Agilent GC-OxyPLOT Columns. Agilent Technologies, publication 5989-8771EN, June 2008.
• ASTM D7059-04. Standard Test Method for the Determination of Methanol in Crude Oils by Multi-Dimensional Gas Chromatography. ASTM International, July 2004.
• March J. Advanced Organic Chemistry: Mechanisms and Structure. 4th ed. John Wiley & Sons; 1992.