Determination of Trace Amounts of Sulfur Compounds in Gases by GC-SCD

Significance of the Topic

The ability to detect trace levels of sulfur compounds in hydrogen is critical for ensuring catalyst longevity and performance in proton exchange membrane (PEM) fuel cells. Sulfur contamination at parts-per-billion levels can poison catalysts, reducing fuel cell efficiency and lifespan. Meeting stringent international standards such as ISO/DIS 14687 and DIN EN 17124 requires highly sensitive and reliable analytical methods.

Objectives and Study Overview

This application note describes the development and validation of a gas chromatographic method coupled with sulfur chemiluminescence detection (GC-SCD) for quantifying hydrogen sulfide (H₂S), carbonyl sulfide (COS), carbon disulfide (CS₂) and mercaptans in pure hydrogen. The goal was to achieve a total sulfur quantification limit below 4 ppb, demonstrate equimolar response, verify system reproducibility, evaluate carryover, and address consumable aging effects.

Methodology and Instrumentation

Sample preparation involved dilution of high-purity sulfur gas standards using a gas mixing pump and injection of 20 mL sample loops into the GC valve box. Pre-column focusing of volatile sulfur species was achieved via a liquid nitrogen cryo-trap. Sulfur chemiluminescence detection (SCD-2030) provided selective and equimolar response across analytes. All gas lines and valve surfaces were Sulfinert® treated to prevent adsorption or reaction losses.

• Gas chromatograph: Nexis GC-2030
• Detector: Nexis SCD-2030 sulfur chemiluminescence
• Valve system: Top mounted valve box LVO-2030
• Cryo-trap: MicroJet Cryo-Trap (Frontier Laboratories)
• Columns: SH-Q-Bond (1 m×0.32 mm×10 µm) and SH-I guard column (5 m×0.32 mm)
• Software: LabSolutions LCGC

Main Results and Discussion

Trapping optimization at 5 minutes for 20 mL sample volumes allowed complete desorption and a total run time of approximately 7 minutes, enabling six analyses per hour. Calibration with COS standards from 1.3 to 13 ppb exhibited excellent linearity, and equimolar detector response eliminated the need for separate calibrations for each sulfur species. Ten replicates of 3.9 ppb COS yielded relative standard deviations below 2 % for both peak area and concentration. Carryover tests with a 6.3 ppm TBM injection showed no residual signals in subsequent hydrogen blanks, confirming negligible memory effects.
Investigation of SCD pyrotube aging revealed an eight-fold loss in sensitivity after three months of operation. Incorporation of a post-sample internal standard (TBM) injection loop effectively corrected for detector drift and extended calibration stability.

Practical Benefits and Applications

This GC-SCD methodology meets and exceeds international hydrogen impurity limits, enabling reliable quality control in hydrogen production, distribution and fuel cell research. Key advantages include:

• Trace quantification below 4 ppb total sulfur
• Equimolar response simplifies calibration routines
• Rapid cycle time with high sample throughput
• Minimal carryover ensures consistent results
• Internal standard option for long-term accuracy

Future Trends and Potential Applications

Advances in detector design may further enhance sensitivity and reduce maintenance intervals. Integration of on-line sampling and real-time monitoring systems could support continuous hydrogen quality assurance in large-scale production facilities. Expanding SCD applications to other trace sulfur matrices such as biogas and natural gas is also feasible. Coupling with advanced data analytics and machine learning may improve predictive maintenance and process optimization.

Conclusion

The combination of Nexis GC-2030 and SCD-2030 with cryogenic trapping delivers a robust, reproducible, and highly sensitive solution for trace sulfur analysis in hydrogen. Equimolar detection, low detection limits, negligible carryover and internal standard correction provide a comprehensive approach to meet stringent fuel cell fuel quality standards.

References

1. ISO/DIS 14687(en) Hydrogen fuel quality — Product specification.
2. DIN EN 17124:2019-07 Hydrogen fuel — Product specification and quality assurance.
3. Wösthoff Digamix gas mixing pump product information.
4. Shimadzu Application News: Equimolar Sensitivity Measurement by SCD-2030.