Question

In gas chromatography, what is the effect on retention time (longer, shorter, or unchanged) of the following?

a. Loss of stationary phase by column bleeding.

b. Operating the column at higher temperature.

c. Operating the column at a higher head pressure.

d. Clipping off 5% of the column to remove non-volatile contaminants.

e. Changing the carrier gas from He to N2, if flow, temperature, and the column are the same.

Answer 1

Here the Answer is the (b) Operating the column at higher temperature.

A excessively high column temperature results in very short retention time but also in a very poor separation because all components mainly stay in the gas phase. However, in order for the separation to occur the components need to be able to interact with the stationary phase. If the compound does not interact with the stationary phase, the retention time will decrease. At the same time, the quality of the separation deteriorates, because the differences in retention times are not as pronounced anymore. The best separations are usually observed for temperature gradients, because the differences in polarity and in boiling points are used here.

So Operating the column at higher temperature decrease the retention time, but also deteriorate the quality of the separation.