Wasson Chromatography Corner 28

Importance of the Topic

Global helium shortages and rising costs have challenged routine gas chromatography methods that rely on helium as a carrier gas. Developing robust alternative carrier gas strategies helps laboratories maintain compliance with standard test methods such as ASTM D3606 and D5599, reduce operational expenses, and ensure sustainable analytical operations in petrochemical and environmental testing.

Aims and Study Overview

This application note demonstrates how an existing Agilent gas chromatograph was adapted to use hydrogen and nitrogen carrier gases instead of helium. Two primary analyses are presented:

• Separation and quantification of oxygenates and light hydrocarbons in gasoline blends following ASTM D3606 and D5599 criteria.
• Simultaneous analysis of oxygenates and C4 hydrocarbon streams using dual injection trains equipped with flame ionization detectors.

Methodology and Instrumentation

An Agilent GC system was configured with two parallel analysis trains, each featuring a Deans switch to backflush heavy components to vent. The front train targeted oxygenates using an oxygenate flame ionization detector (O-FID), while the back train analyzed remaining hydrocarbons with a standard FID. Three carrier gases were evaluated:

• Helium as the industry standard reference.
• Hydrogen to assess resolution and detection limits in oxygenate and hydrocarbon separations.
• Nitrogen to test compatibility and performance under method requirements.

Key instrumentation elements included packed and capillary columns meeting ASTM requirements, thermal conductivity detection for benzene and toluene, and flow ramp programming to accommodate lower maximum flows when using nitrogen.

Main Results and Discussion

Helium provided baseline performance for oxygenate and C4 stream separations. Hydrogen achieved acceptable resolution and detection limits for oxygenates but induced side reactions with high levels of olefins, leading to reduction of isobutylene into isobutane and the appearance of transient peaks during repeat runs. Nitrogen delivered chromatograms comparable to helium for both oxygenate and hydrocarbon analyses. Its lower maximum flow was managed by low column flow and high split flow injection followed by a programmed flow ramp. The study confirmed:

• Nitrogen is a reliable helium substitute for routine oxygenate and C4 hydrocarbon analyses.
• Hydrogen may be viable for oxygenate detection but requires careful monitoring to avoid reduction reactions in olefinic samples.

Benefits and Practical Applications

The helium‐free configurations guarantee method compliance with ASTM D3606 and D5599. By employing nitrogen or hydrogen, laboratories can:

• Reduce dependency on scarce helium supplies and avoid supply chain disruptions.
• Lower operational costs associated with high‐purity helium cylinders.
• Maintain detection limits and separation quality for oxygenates, benzene, toluene, and C4 hydrocarbons.

Future Trends and Potential Applications

Ongoing advancements may include:

• Automated flow control and real‐time gas switching to further optimize carrier gas use.
• Development of new column chemistries tailored for hydrogen or nitrogen carriers.
• Integration of advanced detectors that combine selectivity with reduced sensitivity to carrier gas impurities.

Conclusion

This work demonstrates that nitrogen and hydrogen can effectively replace helium in critical ASTM D3606 and D5599 gas chromatographic methods. Nitrogen emerged as the most straightforward substitute, delivering equivalent performance without reaction artifacts. Hydrogen may be used with caution where unsaturated compounds are minimal. Implementing these alternatives ensures continuous, cost‐effective chromatographic analysis in helium‐constrained environments.