Reduce Helium Consumption by 68% Using Nitrogen Purge Gas for VOCs in Water

Reducing Helium Consumption in VOC Water Analysis by Nitrogen Purge Gas

Significance of the topic

Monitoring volatile organic compounds (VOCs) in water is critical for environmental compliance and public health. Conventional purge-and-trap GC-MS methods rely heavily on helium, a finite and increasingly costly resource. Adapting EPA Method 524.4 to use nitrogen purge gas addresses supply constraints, lowers operational costs, and supports sustainable laboratory practices.

Objectives and study overview

This work evaluates the performance and resource savings of replacing helium purge gas with nitrogen in the analysis of purgeable organics in water using EPA Method 524.4. Key goals include:

• Quantifying helium consumption reduction per sample.
• Verifying chromatographic resolution of critical VOCs on an Rtx-VMS column.
• Assessing compliance with Method 524.4 performance criteria.

Methodology

Water samples spiked with VOC standards were processed via purge-and-trap. The optimized sequence comprised:

• Purge: 11 min at 40 mL/min of nitrogen.
• Dry purge: 1 min at 50 mL/min.
• Thermal desorption: 1 min at 260 °C.

The total gas volume for each sample remained near 720 mL. Helium usage was limited to GC functions, while nitrogen served as the purge gas.

Used instrumentation

• Purge-and-trap system: EST Encon Evolution with Vocarb 3000 trap.
• Gas chromatograph: Agilent 7890A.
• Mass spectrometer: Agilent 5975C MSD in scan mode (47–300 amu).
• Analytical column: Rtx®-VMS, 30 m × 0.25 mm ID, 1.4 µm film.
• Nitrogen gas generator: Parker Balston® HPN2-1100 ultra-high purity.

Main results and discussion

Switching to nitrogen purge gas yielded a 68 % reduction in helium usage, saving approximately 490 mL per sample. Chromatographic performance on the narrow-bore Rtx-VMS column met all resolution criteria of Method 524.4. Key analytes such as o-xylene, styrene, 1,1,1-trichloroethane and carbon tetrachloride were baseline-resolved, demonstrating that nitrogen purge does not compromise analytical quality.

Benefits and practical applications

The nitrogen-based approach offers:

• Substantial cost savings on helium purchases and improved budget predictability.
• Independence from helium supply fluctuations.
• Compliance with EPA Method 524.4 without modification to existing GC-MS platforms.
• Enhanced column efficiency and sharper peak shapes due to the narrow column bore.

Future trends and applications

Laboratories are likely to adopt on-site nitrogen generation more broadly, extending this strategy to other purge-and-trap methods and applications. Advances in column chemistry may further optimize separations under nitrogen. Integrating green chemistry principles will drive broader replacement of finite laboratory gases.

Conclusion

By adopting nitrogen as the purge gas in EPA Method 524.4 and employing an Rtx-VMS column, laboratories can achieve significant helium savings while maintaining method performance. This approach enhances sustainability, reduces costs, and secures analytical workflows against helium shortages.

Reference

• U.S. Environmental Protection Agency. Method 524.4, Measurement of Purgeable Organic Compounds in Water by Gas Chromatography/Mass Spectrometry Using Nitrogen Purge Gas, May 2013.