For it was stated that as the column

For the analysis of hydrocarbon
mixtures in GC, the main objective is to obtain the lowest theoretical plate
height which translates to the best possible column efficiency. By adjusting
the column head pressure (which changes the phase velocity) for each run of a
mixture of samples we can determine the flow rate at which all samples share a
high efficiency at a certain flow rate. This can be done by constructing Van
Demeter plots for each hydrocarbon and locating where all three graphs
interact. This point is the flow rate at which you will receive the best
possible plate height. In the beginning of this report, it was stated that as
the column pressure decreased, the peaks would narrow but the resolution would
decrease as a consequence. Although for the most part the data did show a
slight drop in resolution with a lowering of pressure, the peaks actually
broadened as well. The reasoning for this would be as the CHP is lowered, the
linear velocity does so as well. As a result of this, the various compounds
spent more time in the stationary phase than the gas phase which meant that it
took longer for them to reach the detector, and a wider peak was the result. 

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