LABTips: Switching from Helium to Hydrogen Carrier Gas for GC

While there are several different gasses that can be used as a mobile phase in gas chromatography (GC), helium has long prevailed as the most popular choice due to a number of factors including inertness, safety, purity and overall excellent performance.¹ Despite its advantages, the use of helium carrier gas for GC analysis also comes with its challenges, including persistent supply chain issues and higher cost compared to alternatives such as hydrogen. The globe is currently experiencing its fourth major helium shortage since 2006, dubbed “Helium Shortage 4.0,” which was spurred by events including the unexpected shutdowns of major helium plants in Texas and Russia, and exacerbated by the war in Ukraine.² These challenges have led many labs to consider switching from helium to an alternative carrier gas, with hydrogen being one of the most promising alternative choices.

The shortage of helium is not the only reason to consider switching from helium to hydrogen carrier gas for GC. Hydrogen is more abundant and less expensive overall, and also has a higher optimum linear velocity than helium, which offers labs the opportunity to operate their GC at a higher flow rate without sacrificing efficiency.³ However, laboratories may be hesitant to make the switch for a number of reasons. Unlike the inert helium, hydrogen is combustible and has the potential to cause an explosion. Additionally, transferring methods from helium to hydrogen carrier gas requires planning, time and, often, additional costs. Laboratories may be concerned that altering a well-established helium method to one that uses hydrogen will impact the accuracy and reliability of results. Here are some tips for tackling the challenge of method transfer and for how to make the most out of hydrogen as a carrier gas.

1. Put Safety First

Due to its combustibility, many labs are understandably wary about using hydrogen for their GC applications. Knowing the safety risks of hydrogen in greater detail can help laboratories make more informed decisions about switching, as well as develop more effective safety procedures for when hydrogen is used in the lab.

Hydrogen can combust at concentrations from 4% to 74.2% by volume at atmospheric pressure, has very low ignition energy and has the highest burning velocity of any gas.¹ Additionally, hydrogen can self-ignite when allowed to rapidly expand from high pressure, and burns with a nonluminous flame that may not be visible under bright lighting. While it is unlikely that a small hydrogen leak could accumulate to a concentration of 4% in a properly-ventilated laboratory,the risk of explosion is greater if hydrogen builds up in the GC oven or mass spectrometer. Rapid expansion from high-pressure hydrogen cylinders is also a concern.

 Thus, switching from helium to hydrogen requires increased vigilance and safety training that ensures all operators are aware of the hazards and how to mitigate them.⁴ Preventing and detecting leaks is critical, so thorough leak inspections should be performed regularly. Operators must ensure that the gas supply is shut off when the GC system is not in use. Prior to making the switch, hazards such as potential ignition sources should be identified and addressed. A hydrogen sensor and alarm inside the column oven offers additional protection against gas buildup in this high-risk area.

Compared to hydrogen gas generators, high-pressure gas cylinders pose a higher risk of releasing high concentrations of hydrogen into the air and potentially causing an explosion. When cylinders are used, it is crucial that they are properly stored in a well-ventilated area, are not exposed to direct sunlight or temperatures greater than 40°C, and are properly secured using a stand or chain to prevent them from falling over.⁵ Tubing leading from the cylinder to GC should be checked for leaks before every operation and hydrogen should never be released directly from the cylinder into the air. Laboratories seeking to use hydrogen for their GC operations should consider investing in a hydrogen gas generator, which greatly reduces the risk, as these generators operate at low pressure, store minimal volumes of gas at once and often include automatic shut-down features that prevent more gas from being released when a leak or other malfunction is detected.⁶

2. Start Simple

The task of converting a helium carrier gas-based method to one that uses hydrogen gas may seem overwhelming due to the physical, chemical and mathematical principles behind factors such as resolution, efficiency, retention time, peak shape and more. However, most modern GC instruments are designed to make changing carrier gasses relatively simple, and the digital age has made it easier than ever to access knowledge and resources that can further ease the process and answer questions chromatographers may have along the way.

First, laboratories should always ensure that any regulated methods they are currently using with helium allow for hydrogen to be used as an alternative, as not all methods allow for the use of another carrier gas.⁷ Chromatographers should also look for application notes and examples in literature of analyses similar to theirs that have been successfully performed using hydrogen gas, as these can help to guide a smoother transition between methods.

When first making the change, a good starting point is to keep most parameters the same, and compare chromatograms from before and after just changing the gas to gain a baseline understanding of how the change affects performance.⁸ In some cases, simply switching the gas source and switching the instrument to hydrogen carrier gas mode — while using the same column, linear velocity and temperature program as with helium — will yield similar results and retention times to what you were seeing before.

Keep in mind that, unlike in liquid chromatography (LC) analysis, GC analysis does not rely on chemical reactions between the carrier gas and analyte, so replacing the mobile phase is not as complex as it may seem at first glance. Looking at a Van Deemter plot, you can also see that the efficiency of helium and hydrogen is very similar at average linear velocities between 20-30 cm/sec. Although hydrogen can be used at higher linear velocities than helium, keeping the linear velocity constant at first allows for a direct comparison of the gasses’ performance.⁷

One caveat is the conversion of GC-mass spectrometry (MS) methods, which requires additional hardware changes and conditioning, and may result in more pronounced problems with sensitivity and peak shape when hydrogen is first introduced. The lower viscosity of hydrogen compared to helium requires greater vacuum pump efficiency to maintain vacuum levels, and loss of vacuum conditions will negatively impact sensitivity in addition to risking build-up of hydrogen in the detector.⁹ Hydrogen may also interact differently within the ion source than helium and is more likely to displace contaminants which can lead to very noisy spectra upon first changing gasses.

Therefore, greater planning is needed to ensure the pumping capacity of the system is not exceeded, that ion source issues can be addressed and time can be allowed for proper conditioning of the system to the new gas, which can take days.⁹ You may want to consider changing out the ion source to a source optimized for hydrogen carrier gas use, as well as initially switching to a lower internal diameter column to prevent excessively low or negative inlet pressures.

3. Take Advantage of Hydrogen’s Inherent Benefits

Once you have gotten your GC up and running with a new carrier gas, you can seize the opportunity to leverage hydrogen’s specific advantages for increased throughput. A fast, easy and effective way to do this is to use a method translator tool that performs the necessary calculations for you based on your initial method parameters, providing you with optimal parameters to maximize speed and efficiency. Method translation may be included in your GC software but free online tools are also available.¹⁰ For example, the free online EZGC Method Translator from Restek allows method translation from helium to hydrogen carrier gas, including for GC-MS, and provides recommended flow rates and oven programs to achieve a desired balance of speed and resolution.¹¹

By switching from helium to hydrogen carrier gas, analysis times can potentially be reduced by a factor of up to 1.5 to 2 with minimal reduction in separation efficiency.¹² Additionally, the faster elution times achievable with hydrogen allows more flexibility to operate at lower temperatures, which can potentially extend column lifetimes.¹³ Because high-purity hydrogen can be generated on demand from water, as opposed to helium, which requires cylinders, laboratories can further benefit from great convenience, space savings and, ultimately, additional cost savings with the options of acquiring a hydrogen generator for their GC applications.

With ongoing helium supply issues, more methods are being developed and validated for use with hydrogen carrier gas, and many manufacturers offer resources and services to address clients’ method conversion needs. While switching to hydrogen may not be the best solution for every lab, staying informed about alternative gas options can help lab managers stay prepared for potential future shortages.

References

1. Heseltine, J. Hydrogen as a Carrier Gas for GC and GC-MS. LCGC North America. 2010, 28 (1), 16-27. https://www.chromatographyonline.com/view/hydrogen-carrier-gas-gc-and-gc-ms
2. "Helium shortage 4.0 continues, and it's not just bad for party balloons," Article by Deena Zaidi, CTVNews.ca (2022). https://www.ctvnews.ca/sci-tech/helium-shortage-4-0-continues-and-it-s-not-just-bad-for-party-balloons-1.6090014
3. Wallace, R.F.; Sidisky, L.M. Hydrogen: A Carrier Gas Alternative to Helium. Reporter US. 2008, 26 (3). https://www.sigmaaldrich.com/US/en/technical-documents/protocol/analytical-chemistry/gas-chromatography/hydrogen-a-carrier
4. "Hydrogen as an alternative to Helium for gas chromatography," Application Note by Peter Adam, The Linde Group (2012). http://hiq.linde-gas.com/en/images/Application%20Note_HiQ%20Hydrogen%20as%20an%20alternative%20to%20Helium%20for%20GC_tcm899-90120.pdf
5. "High-Pressure Gas Cylinder Precautions," Shimadzu. https://www.shimadzu.com/an/service-support/technical-support/handling-precautions/gas-chromatography/bombe5/index.html
6. "Three Key Reasons Why Gas Generators Are the Safest Options in Laboratories," Blog Post by Ellie Jones, Parker (2018). https://blog.parker.com/site/usa/en-US/details-home-page/three-key-reasons-why-gas-generators-are-the-safest-option-in-laboratories-us
7. "Converting from Helium to Hydrogen for carrier gas," Webinar presented by Ed Connor, Peak Scientific (2020). https://www.peakscientific.com/converting-from-helium-to-hydrogen/
8. "Life in the Fast Lane: Switch from Helium to Hydrogen in One Easy Step," Webinar presented by Lee N. Polite, Axion Labs (2021). https://www.youtube.com/watch?v=jST8GDgUrrk
9. "The LCGC Blog: Hydrogen Carrier Gas for Gas Chromatography Mass Spectrometry (GC-MS) — a Practical Guide," Blog Post by Tony Taylor, The LGCG Blog (2022). https://www.chromatographyonline.com/view/the-lcgc-blog-hydrogen-carrier-gas-for-gas-chromatography-mass-spectrometry-gc-ms-a-practical-guide
10. "The Great Helium Shortage of 2022: What Can I Do to Keep My Lab Running?," Article by Nicole M. Lock, Labcompare (2022). https://www.labcompare.com/10-Featured-Articles/585657-The-Great-Helium-Shortage-of-2022-What-Can-I-Do-to-Keep-My-Lab-Running/
11. EZGC Method Translator and Flow Calculator, Restek. https://ez.restek.com/ezgc-mtfc
12. "Benefits and Considerations of Converting to Hydrogen Carrier Gas," Article by Jaap de Zeeuw and Jim Whitford on behalf of Restek Corp, Petro Online (2013). https://www.petro-online.com/article/analytical-instrumentation/11/restek-corp/benefits-and-considerations-of-converting-tonbsphydrogen-carrier-gasnbsp/1338
13. "Hydrogen as carrier gas," Shimadzu. https://www.shimadzu.eu/Hydrogen-as-carrier-gas