Analysis of SF6 Insulation Gas Using a GC-BID System

Significance of the Topic

Sulfur hexafluoride (SF6) is a broadly used insulation and tracer gas valued for its outstanding dielectric strength and chemical inertness. However, it is also one of the most potent greenhouse gases, driving demand for precise purity and leak detection analyses. High-sensitivity, reliable methods are essential for quality control in electrical equipment manufacturing and maintenance, for environmental monitoring, and to meet international emission-reduction commitments.

Objectives and Study Overview

This application note demonstrates how a gas chromatography system equipped with a barrier discharge ionization detector (BID) can analyze (1) trace impurities in high-purity SF6, (2) low-concentration SF6 in air, and (3) decomposition products from electrical equipment. The study aims to showcase performance in sensitivity, quantitation accuracy, linearity, and operational simplicity without reliance on radioisotope detectors.

Instrumentation

• Gas chromatograph: Shimadzu Nexis GC-2030
• Detector: Shimadzu BID-2030 (barrier discharge ionization detector)
• Sample introduction: MGS-2030 gas sampler (3.0 mL) and gas-tight syringe (200 µL)
• Columns: MICROPACKED-ST (2.0 m × 1.0 mm I.D., df = 10 µm) for impurity and decomposition analyses; SH-Rt-Msieve 5A (30 m × 0.53 mm I.D., df = 50 µm) for trace SF6

Methodology

Split injection (ratios 1:4 and 1:7) at 150 °C introduced gas samples into the GC. Carrier gas (He) flow was controlled either by constant flow (7 mL/min) or constant linear velocity (45 cm/s). Temperature programs optimized separation from ambient gases to hydrocarbons and inorganic impurities. Detector and discharge gas (He at 50 mL/min) temperatures were set at 280 °C to maintain stable ionization and high sensitivity.

Key Results and Discussion

Analysis of a high-purity SF6 sample revealed trace contaminants including H2 (0.9 ppm), CO and CH4 (0.9–1.7 ppm), CO2 (21 ppm), N2O (2.0 ppm), C2H2, C2H4, C3H6, and C3H8 (1.0–2.4 ppm). In atmospheric air spiked with SF6, a 0.1 ppm peak was detected with signal-to-noise of 24 and demonstrated excellent linearity (R2 = 0.9998) from 0.1 to 50 ppm. Decomposition products CF4 (310 ppm) and SOF2 (107 ppm) from electrical equipment were clearly separated, illustrating the system’s versatility.

Benefits and Practical Applications

• Universal, high-sensitivity detection of both electrophilic and non-electrophilic trace components without radioisotopes
• Robust quantitation across low- and high-concentration ranges
• Streamlined workflow for quality control of SF6 reuse and leak testing in power utilities
• Capability to analyze diverse gas samples (ambient, high-purity, decomposition) on a single GC system

Future Trends and Opportunities

Advances may include integration with automated sampling networks for real-time greenhouse gas monitoring, miniaturized multidetector systems for on-site leak detection, and expansion to other critical industrial gases. Coupling BID-GC with data-driven analytics could further enhance diagnostic capabilities in predictive maintenance and environmental compliance.

Conclusion

The GC-BID approach provides a sensitive, stable, and versatile platform for comprehensive analysis of SF6 and related gases. It addresses challenges in purity verification, environmental monitoring, and equipment maintenance while supporting regulatory and sustainability goals.

Reference

R. Kubota and S. Uchiyama, Analysis of SF6 Insulation Gas Using a GC-BID System, Shimadzu Application Note No. G300, First Edition, March 2018.