Helium’s availability and low price for decades have made it the default carrier gas for a majority of GC applications. However, more recent market and supply volatility has forced GC users to consider other gases as a replacement option. Hydrogen, nitrogen, and argon are all potential options for carrier gas and detector gas, depending on the application.
Nitrogen (N2) – Some users are considering nitrogen as a replacement for carrier gas. It is readily available (nitrogen comprises 79.1% of Earth’s atmosphere), relatively inexpensive, and inert. Two nitrogen atoms make up the molecule (N2), giving it similar properties to a noble gas.
For Flame Ionization Detector (FID) gas chromatography applications, nitrogen as a make-up gas improves the shape of the flame, which enhances sensitivity of the analysis. However, as a carrier gas, Nitrogen must be used at slower flow rates to achieve adequate resolution between peaks. Its disadvantages include a narrow optimum linear velocity range and a low optimum linear velocity that requires more analysis time.
Argon (Ar) – Argon is the third most common gas in the atmosphere after nitrogen and oxygen, although it makes up less than one percent of the atmosphere (roughly 0.9%). It is a noble gas and completely inert, nonreactive with every other substance. Commercially, it is produced only as a byproduct of industrial air separation, thus supply is limited, and the cost is comparatively high.
With its relatively high density, Argon can be effective for purging applications. It also offers good performance for arc welding and window insulation where its low thermal conductivity is an advantage. It has been used to replace helium as a coolant for photovoltaic panels, for example. But in most GC applications, it is typically less ideal than the alternatives.
Hydrogen (H2) – Hydrogen offers multiple advantages for gas chromatography. It has a higher optimal linear velocity and can be operated at higher flow rates. Analytes elute earlier with hydrogen than with helium, which speeds up analysis times, thus increasing sample throughput while still maintaining high sample quality.
The potential downside of hydrogen is a slightly increased risk: it is a flammable gas that requires some precautions to ensure safe use. The risks can be easily mitigated, however. Hydrogen’s lower explosive limit (LEL) is 4.1% concentration in air.
Because of its lightness, hydrogen rises and dissipates quickly. Even in a small laboratory, the large volume of air compared to the relatively low rate of helium production or consumption during typical GC analysis means the danger of reaching the LEL is quite low. Installation of hydrogen gas detectors can further mitigate the risk.
Advantages of Hydrogen as a Carrier Gas
For many applications, using hydrogen in place of helium is a viable solution. The two gases are equally compatible with the range of materials used for GC equipment and supplies, including several metals (aluminum, brass, copper, and stainless steel) and polymers/plastics (e.g., PA, PTFE, PCTFE, PVDF, and PFA). Metals and materials age differently over time, leading GC manufacturers to prefer stainless steel with hydrogen carrier gas.
Hydrogen can improve GC throughput and results: it provides a faster elution and analysis time than helium and generates sharper peak shapes.
To learn more about hydrogen as a carrier gas—and how a VICI DBS hydrogen gas generator can provide a safe, cost-effective, and convenient source of high-purity gas for GC applications, read the white paper.
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