Temperature Control
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.
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