Temperature-induced inversion of elution order in the enantioseparation of sotalol on a cellobiohydrolase I-based stationary phase

The effect of temperature on the resolution of ( RS)-sotalol by immobilized cellobiohydrolase I (CBH I) was studied between 5 and 40°C and Van ’t Hoff plots of ln k versus 1/ T were acquired at different pH values of the aqueous mobile phase and in the presence of varying organic cosolvents. The elution order of the enantiomers reverses in the range between 17 and 28°C. Beyond this range, enantioseparations with comparatively high resolution factors are achieved either by decreasing or by increasing the temperature. The composition of the mobile phase influences the “crossover” temperature as well as the character of the global adsorption process of the ( R)-(−)-enantiomer. Under certain conditions, ( R)-(−)-sotalol exhibits an unusual endothermic adsorption behavior. Its retention time increases with increasing temperature. At room temperature (23°C) the enantiomeric elution order can also be regulated by the solvent additive.