Temperature effects in HPLC is not as significant as in gas chromatography. First, because we do not have same temperature range. Volatile solvents are not allow to rise temperature too mach, and the stability of the attached bonded ligands on the adsorbent surface may be influenced by the high temperature. So, main temperature range is from ambient temperature to 60 or 70 C.
According the equation (23) in the theory chapter, increasing the temperature will decrease the value of K or k', thus the actual retention time will decrease. For most of the systems these decrease will not exceed 50% of the component reduced retention time at ambient temperature.
Picture below illustrate the influence of the column temperature on the HPLC retention.
There are two other significant effects of separation under the elevated temperature.
Stabilisation of the column under the elevated temperature usually leads to the stabilisation of the retention times. Origin of this effect is not well understood yet, possible explanation is that the solvent viscosity decreased and more uniform stabilised temperature with absence of local temperature fluctuations due to the solvent friction lead to the more uniform adsorption-desorption process.
Another effect is the increase of the column efficiency. At the elevated temperature viscosity of liquids decrease and diffusion coefficient increase, thus, from the Van Deemter equation the second term will increase which will lead to the decrease of the efficiency at the very low flow rates (which is not important). The last term will decrease which will lead to the increasing of the efficiency at the common flow rates and it also widen the flow rate range with optimum efficiency.