Does hydrogen deliver higher plate numbers or separation efficiency at high separation speeds?
The carrier gas influences column efficiency, or plate number, in a couple of ways. The theoretical optimum linear velocity is influenced directly by solutes’ gas–gas diffusion rates — higher diffusion will increase the optimum velocity. For example, the gas–gas diffusion rate of n-octane in helium at 130 C is 0.383 cm2 /s, while in hydrogen it increases to 0.467 cm2 /s, therefore, we would expect the optimum velocity to increase with hydrogen carrier compared to helium. This is the case, as shown in Figure 2, where the optimum for hydrogen is almost 40 cm/s, while for helium the optimum is closer to 30 cm/s. The minimum theoretical plate heights for hydrogen and helium are close to each other, however, and so at the optimum linear velocity little difference in the theoretical plate number would be expected for significantly retained peaks.
