Multilayer adsorption in liquid chromatography - The surface heterogeneity below an adsorbed multilayer

A numerical method was introduced for the estimation of the surface heterogeneity below an adsorbed multilayer of the analyte. The calculation procedure is based on the raw adsorption isotherm data points obtained by frontal analysis experiments. To permit the mapping of the nature of the analyte-surface interaction, a numerical procedure was used to pre-estimate the adsorbate-adsorbate interactions occurring during the adsorption process. The surface heterogeneity estimation was carried out using the affinity-energy distribution calculations with assuming local BET isotherm. In the local BET isotherm the pre-estimated adsorbate-adsorbate interaction constant was used, and the surface heterogeneity was described. After the test of the numerical method with benchmark isotherms, the algorithm was tested on several experimental isotherms. The isotherms were measured using phenol as test molecule on reversed phase adsorbents, with different surface coverage of the octadecyl ligands. The surface of the non-end-capped stationary phases showed detectable heterogeneity, while the surface end-capped phases were found to be homogeneous.