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Impact of GC Parameters on The Separation - Part 5: Choice of Column Temperature

by Jaap de Zeeuw, Restek Corporation, Middelburg, The Netherlands.

In parts 1, 2, 3 and 4 of this series we focused on the selection of stationary phase, column length, ID and the film thickness. Besides the column specific parameters, there are three non-column specific parameters that impact the separation. These are the type of carrier gas, its linear velocity and the temperature of the column. Here we look into the effects of temperature on separations as shown in Figure 1.

Oven Temperature
The temperature is a very important parameter to influence separation. As a rule of thumb, for every 15 °C higher or lower, the retention of a column decreases or increases by a factor of 2. That means if the last peak elutes at 100 °C after 10 minutes, it will elute at 5 minutes at 115 °C and at 20 minutes at 85 °C.

Looking at the resolution equation, as seen in Figure 2, temperature will mainly impact the k/k+1 term. When k is low, reducing the temperature will increase this term in a near linear way, which directly impacts the resolution in a linear way.

Figure 3 shows an example of the impact of temperature on retention and separation. Because the k-factor was very low at high temperature, separation is poor. By decreasing oven temperature the k factor increases, which strongly impacts the resolution between the C1-C5 isomers.