As noted earlier, control of the column’s temperature is critical to attaining a good separation in gas chromatography. For this reason the column is located inside a thermostated oven. In an isothermal separation the column is maintained at a con- stant temperature, the choice of which is dictated by the solutes. Normally, the tem- perature is set slightly below that for the lowest boiling solute so as to increase the solute’s interaction with the stationary phase.
One difficulty with an isothermal separation is that a temperature favoring the separation of low-boiling solutes may cause unacceptably long retention times for higher boiling solutes. Ovens capable of temperature programming provide a solu- tion to this problem. The initial temperature is set below that for the lowest boiling solute. As the separation progresses, the temperature is slowly increased at either a uniform rate or in a series of steps.