Why not use nitrogen instead of helium or hydrogen?
Nitrogen (the “other” carrier gas) has a minimum plate height that is about 10% lower (better) than either helium or hydrogen, see Figure 2. This means that if we were to operate at the optimum velocity, then nitrogen would deliver around 10% more theoretical plates. The effect on peak resolution is negligible, however, because resolution is related to the square root of the plate number. What is not so good about nitrogen is the much narrower velocity range over which the plate height remains close to optimum, from about 8 to 20 cm/s in this case. The optimum linear velocity depends upon the solute and temperature, so for different solutes, and as the temperature changes during programming, the optima for each solute will appear at velocities somewhat different than the theoretical minimum. With nitrogen it is more likely that, for a given solute, the plate height will be farther from optimum than with carrier gases like helium or hydrogen for which the plate height does not depend as
