Analysis and experimental demonstration of temperature step gradients in preparative liquid chromatography

The amount of substance adsorbed on solid surface depends on temperature. Therefore, the migration velocities of the solutes in a chromatographic column can be altered by introducing temperature gradients. Such gradients designed to change retention behaviours can be exploited to improve the separation performances in preparative chromatography. To describe key process features, we used analytical solutions of the equilibrium model with instant stepwise shift of temperature. To achieve a more realistic description, the equilibrium dispersion model was additionally applied to treat finite column efficiencies. The effect of temperature gradients was illustrated experimentally using two identical columns sequentially connected. Temperature of the second column was modulated by thermostats. Wide pulse injections of a single component led to instructive elution profiles in a preliminary investigation. The observations were found to be in qualitative agreement with predictions of the equilibrium dispersion model. Subsequently, the separation of a ternary model mixture was investigated considering a simple two-step temperature gradient. To support the quantitative analysis and to identify suitable switching and cycle times, the temperature dependencies of the Henry constants were determined by short pulse injections. A meaningful variation of the parameters of the temperature gradient is required for adjusting the cycle times, which is the time difference between two consecutive injections that needs to shorten. Decreasing this time is connected with a desirable increase in process productivity. The results achieved revealed that relatively simple to implement stepwise temperature gradients offer an option to improve and fine-tune the performance of repetitive batch chromatography.