Effect of the temperature

Temperature effects in HPLC are not as significant as in gas chromatography. First, because we do not have same temperature range. Volatile solvents are not allowed to rise to higher temperatures too much, and the stability of the attached bonded ligands on the adsorbent surface may be influenced by the high temperature. So, the main temperature range is from ambient temperature to 60 or 70 C.

According the equation (23), 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.

Stabilization of the column under the elevated temperature usually leads to the stabilization of the retention times. Origin of this effect is not well understood yet. Possible explanation is that the solvent viscosity decreased and more uniform stabilized 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 the diffusion coefficient increase. 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. It also widens the flow rate range with optimum efficiency.