Kinetic Approach to Calculating the Peak Shape in Thermochromatography of Ultra Small Amounts of Substances

A model is suggested for calculating the shape of a thermochromatographic peak. The model is based on the adsorption–desorption kinetic equation for ultramicroscopic amounts of substances. An analytical solution of the kinetic equation was obtained by using a number of assumptions about the nature of the process, with these assumptions being valid in a certain range of experimental parameters. The resulting theoretical expressions describe different variants of thermochromatography: with fast introduction of the adsorbate into the column, at a permanent introduction of the adsorbate (frontal thermochromatography), and in exponential introduction. It was shown that the peak shape depends on various experimental parameters: enthalpy of adsorption, time of performing the thermochromatography, temperature gradient, etc. The results of theoretical calculations are compared with experimental data on separation of radionuclides and with the results of calculations by the Monte Carlo method with another existing model.