Analysis of Tetrahydrothiophene (THT) in Natural Gas Using the Agilent 990 Micro GC

Importance of the Topic

Natural gas is odorless yet poses significant fire and explosion hazards when leaked. To enable early leak detection, odorants are routinely added. Tetrahydrothiophene (THT) is a widely used sulfur-based odorant in Europe and China, valued for its strong smell, stability, and noncorrosive properties. However, factors such as adsorption to pipeline surfaces or contaminants in the gas can reduce odorant concentration over time, making frequent and accurate monitoring essential for safety and cost control.

Objectives and Study Overview

This application note demonstrates the capability of the Agilent 990 Micro GC, equipped with a CP-Sil 19CB column, to quantify trace levels of THT in simulated natural gas. The study aims to achieve rapid analysis with high sensitivity, good signal-to-noise ratio, and excellent repeatability, enabling reliable odorant monitoring at concentrations below regulatory limits (10–40 mg/m³ in Europe and 20 mg/m³ in China).

Methodology and Instrumentation

The 990 Micro GC system was fitted with a 6 m CP-Sil 19CB straight channel. Key operating parameters included:

• Column pressure: 200 kPa
• Column temperature: 90 °C
• Carrier gas: Helium
• Injection time: 255 ms

The standard test mixture contained n-hexane (4.95 ppm), tert-butyl mercaptan (5.17 ppm), THT (4.01 ppm), and n-nonane (3.94 ppm). Chromatograms were recorded to evaluate retention times, resolution, and peak repeatability.

Used Instrumentation

• Agilent 990 Micro GC
• CP-Sil 19CB straight channel (6 m)
• Helium carrier gas supply

Main Results and Discussion

The 4 ppm THT peak eluted at 49.6 s, while octane and nonane eluted at 31.3 s and 52.7 s, respectively. Resolution between THT and n-nonane was 2.1, ensuring clear separation. Signal-to-noise ratio for THT exceeded 20 under test conditions, suitable for trace-level detection. Ten replicate injections showed exceptional repeatability with retention time RSD of 0.019% and area RSD of 2.5%. The mid-polarity CP-Sil 19CB column also reduced heavy hydrocarbon retention, achieving complete analysis within approximately one minute.

Benefits and Practical Applications

This method offers a fast, sensitive, and reproducible approach for monitoring THT in natural gas supply chains. It supports regulatory compliance, enhances safety by early leak detection, and allows optimization of odorant dosing to minimize costs without compromising effectiveness.

Future Trends and Applications

Future developments may focus on integrating the Micro GC system into on-line monitoring platforms within distribution networks, coupling with remote data acquisition, and expanding analyses to additional odorants or trace contaminants. Advances in miniaturization and detector technology could further enable field-deployable, real-time odorant monitoring.

Conclusion

The Agilent 990 Micro GC with a CP-Sil 19CB column provides a robust and efficient solution for trace quantitation of THT in natural gas. Its rapid analysis time, high sensitivity, and excellent repeatability make it an ideal tool for routine quality control and safety assurance in industrial gas handling.

References

1. Van Loon, R. Analysis of Tetrahydrothiophene (THT) in Natural Gas Using Agilent 490 Micro GC, Agilent Technologies Application Note, publication number 5990-8528EN, 2011.