Generally speaking，with the increase of temperature, the viscosity of the mobile phase decreases. The situation will lead to an increase in the transfer rate of the substances. Thus the chromatographic separation effect will be better than before.
Although the separation effect has been improved, the temperature in the meantime affects retention factor (k) and selectivity (a). Those factors may improve the resolution or reduce it.
The retention time tends to decrease with the increase of temperature. The analyte will tend to stay in the mobile phase at high temperature and elute faster. And the different compounds may also have different degrees of retention for temperature.
Certainly, one advantage of increasing temperature is that the HPLC column pressure during operation is reduced so that we can use larger column flow and finer packing.
The other factor influencing the separation effect of HPLC columns is the thermodynamic mismatch of the mobile phase.
If the HPLC column operates at 60℃, and the mobile phase flows into it at the room temperature, then the relative cold mobile phase will cause the deformation of the peak. The analyte tends to be in the mobile phase with high temperature.
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