Heterogeneity of surface energies in reversed-phase perfusive packings

The surface energetic heterogeneity of the packing media used in perfusion chromatography was investigated based on the liquid-solid adsorption information of phenol. The adsorption isotherms on two perfusive packings, POROS R1 and POROS R2, were measured by stepwise frontal experiments at varying mobile-phase concentrations and temperatures. The isosteric heat of adsorption was calculated from the isotherm data and the adsorption energy distributions (AEDs) were obtained numerically by the expectation maximization (EM) method. The adsorption isotherms corroborated the Langmuir-Freundlich (LF) isotherm well, suggesting the heterogeneity of surface energies of the perfusive medium. The analysis of the isosteric heat of adsorption indicated that this surface heterogeneity might have arisen from the differences in the pore size distributions of the perfusive particles. This observation was further confirmed by the numerically obtained adsorption energy distribution functions. Bimodal energy distribution functions were obtained for the perfusive packings, which is a reflection of the bimodal pore size distributions of the materials. In addition, it has also been found that the temperature dependence of the surface energetic heterogeneity is insignificant for such polymer-based support used in perfusion chromatography, whereas its dependence on the acetonitrile concentration in the mobile phase is rather pronounced. (C) 2001 Academic Press.