Disruption in the helium supply chain continues to pressure analytical laboratories to find alternative solutions for their carrier gas requirements. The choice of the most suitable carrier gas for a specific GC or GC-MS application should keep into consideration some basilar concepts, with the ultimate purpose to separate the analytes of interest in a relatively short time and preserving the sample integrity for quantitative analysis.
Figure 1. Golay curves for carrier gases.Gas viscosity and diffusivity impact the separation efficiency and, consequently, corresponding optimum linear velocity, as represented by the Golay equation for the most common carrier gases: helium, hydrogen and nitrogen (Figure 1).
Other considerations are, of course, the inertness of the carrier gas, to avoid possible reaction with the sample or the stationary phase; the purity of the gas, limiting contaminants like oxygen or water, which are detrimental for the stationary phase; or organic impurities responsible for a high signal background.
Finally, it must be compatible with the detector in use. For example, different considerations need to be done if using a GC standalone or a GC-MS.
Helium has been — and still is — the most used carrier gas, combining high separation efficiency with high inertness and extended compatibility, however, its shortage and price increase is forcing laboratories to find alternatives when possible. Hydrogen is definitely the best alternative, offering high separation efficiency in a shorter analysis time, while nitrogen has a much lower diffusivity, leading to much longer analysis time. Nitrogen is a good alternative if some resolution can be sacrificed, but it is not an option when working with a GC-MS, since it is ionized very easily.
Migrating to hydrogen appears to be the most convenient approach to overcoming the helium shortage crisis: It offers high speed of analysis at a low cost ... and it is sustainable!
However, hydrogen is flammable, which poses safety risk concerns in the laboratory. Additionally, it is not an inert gas. Possible reactions have to be considered, especially in a hot injector or when working with a mass spectrometer detector.
Obviously, there are practical benefits in maintaining helium as a carrier gas, such as maintaining existing validated methods, maintaining unchanged GC-MS analytical performance and avoiding concerns about safety.
When helium is the best (or only) option, reducing consumption becomes mandatory.
Thermo Fisher Scientific developed a new option for its iConnect Split/Splitless inlet when mounted on the Thermo Scientific™ TRACE™ 1600 Series GC, the Thermo Scientific™ HeSaver-H2Safer™1. It offers several benefits, whether saving on helium consumption is required or hydrogen is a viable choice for the laboratory.
In the HeSaver mode, HeSaver-H2Safer extends the lifetime of a He cylinder 350% under 24/7 GC operation2 by limiting the maximum flow rate to fewer mL/min during analysis — just enough to feed the column for the chromatographic separation.
Using the H2Safer mode ensures safe operations without the need to install a H2 sensor, thanks to the limited maximum flow rate — even in case of column breakage. The fixed and limited consumption of hydrogen is also advantageous for optimum use of the hydrogen gas generators.
Whether you choose to migrate to hydrogen, or you prefer to reduce helium consumption, the HeSaver-H2Safer option is the solution for intelligent carrier gas management.