Using Hydrogen as a Carrier Gas for GC

Choosing a Carrier Gas for GC

The aim within the laboratory should be to achieve the best separation in the shortest time period. The most commonly used gases as carrier gas for GC are nitrogen, hydrogen and helium.The differences between the gases are evident when comparing their van Deemter curves. This is illustrated in the Van Deemter Equation (Figure 1).

Although it displays the lowest minimum plate height compared with that of helium or hydrogen, nitrogen has a much narrower velocity range and a steeper van Deemter curve, so at higher flow rates, solute efficiency drops off dramatically (Figure 1). Analysis times with helium are about 1/2 the value when using nitrogen and there is only a very small sacrifice in efficiency. The helium Van Deemter curve is much flatter than the nitrogen curve, thus changes in the average linear velocity do not decrease efficiency by a large amount. Hydrogen is the fastest carrier gas (uopt), with an optimum linear velocity of 40cm/sec, and exhibits the flattest Van Deemter profile. Hydrogen’s high uopt (optimal linear velocity) results in the shortest analysis times. Also, the wide range over which high efficiency is obtained makes hydrogen the best carrier gas for samples containing compounds that elute over a wide temperature range.