Changing from Helium to Nitrogen and Maintaining the Separation Efficiency in the Same Analysis Time

Importance of the Topic

The global shortage and rising cost of helium and safety concerns surrounding hydrogen have prompted the exploration of nitrogen as an alternative carrier gas in gas chromatography. Efficient separation, analysis time, and temperature programming are critical for routine GC methods, and replacing helium without compromising these parameters can yield substantial cost savings and ensure consistent availability of carrier gas.

Objectives and Study Overview

This study aimed to demonstrate that nitrogen can replace helium as a carrier gas in existing GC methods while maintaining separation efficiency, analysis time, and temperature programs unchanged. By employing chromatogram modeling, van Deemter analysis, and method translation software, the authors compared a conventional 30 m × 0.25 mm column under helium with a 20 m × 0.15 mm column under nitrogen in both efficiency-optimized and speed-optimized modes.

Methodology

Van Deemter curves were used to model the optimum linear velocities for helium, hydrogen, and nitrogen, illustrating that nitrogen’s slower optimum can be offset by reducing column diameter and length. Method translation calculations determined matching hold-up times and temperature programs for the smaller column under nitrogen. Practical experiments analyzed complex samples such as fragrances and pesticides to validate the model predictions in both efficiency- and speed-optimized conditions.

Instrumentation Used

• Gas chromatograph configured for capillary columns
• Columns: 30 m × 0.25 mm × 0.25 µm Stabilwax phase; 20 m × 0.15 mm × 0.15 µm Stabilwax phase
• Carrier gases: helium and nitrogen
• Method translation software: Restek EZ-GC Method Translator

Main Results and Discussion

Modeling showed that a 20 m × 0.15 mm column under nitrogen matches the separation efficiency and analysis time of a 30 m × 0.25 mm column under helium when flows are translated. Practical GC runs confirmed identical chromatograms, void times, and temperature profiles, with only a slight increase in inlet pressure and a 30 % reduction in peak intensity under nitrogen. Both efficiency-optimized and speed-optimized conditions delivered comparable performance, although the latter incurred a minor loss of theoretical plates. The approach is broadly applicable, especially for non-polar phases, but reduced loadability of smaller columns may limit trace-level analyses.

Benefits and Practical Applications

• Elimination of dependence on helium supply
• Significant cost reductions in carrier gas usage
• No change required to existing oven temperature programs
• Seamless method transfer with minimal revalidation
• Compatibility with common detectors

Future Trends and Possibilities

Further integration of method translation software will streamline carrier gas conversion workflows. Advances in column technology and nitrogen generators may expand the applicability to trace analysis. Software-automated optimization and real-time modeling could enable dynamic carrier gas selection, while emerging detectors may adopt nitrogen-compatible interfaces.

Conclusion

Replacing helium with nitrogen in GC methods is feasible by switching to a 20 m × 0.15 mm column and using method translation to preserve separation, analysis time, and temperature programs. This strategy offers cost savings, guaranteed gas supply, and simplified method transfer with only modest increases in pressure and slight sensitivity loss.

References

1. J. de Zeeuw, Chromatography Today, Nov/Dec 2012, p.24–27.
2. Restek blog post, method translation details, 2014.
3. J. de Zeeuw, PetroOnline, June/July 2013, p.30–31.
4. Restek EZ-GC Method Translator user guide.
5. Restek blog post on non-polar phase optimization, 2015.