Detection of Sulfur Compounds in Natural Gas According to ASTM D5504 with an Agilent Dual Plasma Sulfur Chemiluminescence Detector

Significance of the Topic

The reliable detection and quantification of sulfur compounds in natural gas are critical for maintaining process efficiency, ensuring safety through odorant monitoring, and meeting regulatory requirements. Accurate sulfur analysis supports refining, blending, and quality control across the petrochemical industry.

Objectives and Overview of the Study

This application evaluates the performance of an Agilent 7890B gas chromatograph equipped with an Agilent 8355 dual plasma sulfur chemiluminescence detector (SCD) under ASTM D5504 conditions. Key goals include assessing linearity, repeatability, and detection limits for 15 sulfur-containing analytes ranging from 0.15 to 10 ppm.

Instrumentation Used

• Agilent 7890B gas chromatograph with deactivated two-valve system
• Agilent DB-Sulfur SCD column, 70 m × 530 µm ID, 4.3 µm film thickness
• Agilent 8355 dual plasma SCD: base temperature 250 °C, burner 800 °C; upper H₂ flow 38 mL/min, lower H₂ flow 8 mL/min, oxidizer flow 60 mL/min, ozone generator 40 mL/min
• 10-port gas sample valve and deactivated purged ultimate union for sample introduction

Methodology

Sulfur standards spanning hydrogen sulfide to methyl/tert-butyl mercaptans and thiophene were blended in helium and diluted online using a six-port valve and a 50 µL sample loop. The oven program started at 30 °C (1.5 min), ramped at 15 °C/min to 250 °C (3 min hold). Helium served as carrier gas at 6 mL/min. Ten replicate injections per concentration established repeatability and calibration across five levels per analyte.

Main Results and Discussion

• Linearity: All 15 compounds exhibited equimolar responses with average R² ≈ 0.996 over 0.15–10 ppm.
• Repeatability: Peak-area RSDs were below 6.3 % at the lowest concentration (0.15 ppm) and improved to ~2 % at higher levels; later-eluting analytes and coelutions showed slightly higher variability.
• Detection Limits: Practical LODs ranged from 0.076 pg/sec (H₂S) to 6.2 pg/sec (1-propanethiol), roughly equivalent to 500 ppb; diethyl sulfide coeluted and was not resolved at 1.5 ppm.

Benefits and Practical Applications of the Method

The dual plasma SCD delivers linear, hydrocarbon-insensitive, equimolar responses, eliminating the need for compound-specific response factors. Its stable performance at low ppb levels makes it ideal for routine quality control, regulatory compliance, and safety monitoring of natural gas streams.

Future Trends and Potential Applications

Advances may include integrating continuous online monitoring, miniaturized GC-SCD systems for field use, coupling with mass spectrometry for enhanced specificity, and extending the methodology to other gaseous matrices such as biogas or refinery off-gases.

Conclusion

This study confirms that an Agilent 7890B GC with an 8355 dual plasma SCD meets ASTM D5504 requirements, offering excellent linearity, repeatability, and low detection limits for a broad suite of sulfur compounds in natural gas.

References

1. ASTM International. ASTM D5504-98: Standard Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography and Chemiluminescence. ASTM International, West Conshohocken, PA, 2016.