GC064 Carrier Gas and Flow Rate

With packed columns and thick film megabore columns, nitrogen is the chosen carrier gas, since the B term in van Deemter equation (which corresponds to longitudinal diffusion in the gas phase) dominates. Since nitrogen is heavier than helium, it minimizes this term and more efficiency is attained.

In capillary columns, particularly those with thin films, hydrogen is the best carrier gas. Since the separations are usually good enough, the emphasis is placed on speed. Hydrogen can be used at faster-than-optimal flow rates, with a minimal loss in efficiency. High-speed analysis is not possible with packed columns or with thick capillary columns.

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