Frequently Asked Questions about Hydrogen Carrier Gas

Many gas chromatographers are considering hydrogen carrier gas instead of helium or nitrogen, but they might hesitate to do so because they have questions about performance, safety, or cost. This month's "GC Connections" focuses on these and other issues related to hydrogen in the gas chromatography laboratory.

Performance

For sheer column performance, hydrogen carrier gas offers some strong advantages over helium or nitrogen. Hydrogen yields higher plate numbers at rapid linear velocities and achieves higher velocities at lower pressures. At the same time, the presence of extra hydrogen can affect flame ionization and other detectors that use hydrogen fuel gas.

Does hydrogen carrier gas affect retention times? The answer is yes, and no. Retention times in gas chromatography (GC) are controlled by several factors: the distribution coefficient (K) of a solute in the column, which is not affected by the choice of carrier gas; the column dimensions of length, inner diameter, and stationary film thickness, all of which we will keep constant in this discussion; and the average carrier gas linear velocity (ū). As the linear velocity increases, isothermal retention times decrease in exact proportion, so doubling the velocity cuts retention times in half. We will look at the effects of changing carrier gas for three situations: constant velocity, constant inlet pressure, and constant flow rate, and then we will see what happens if the column is temperature programmed.