Modeling the effect of species retention on the band broadening in perfectly ordered silica monolithic column mimics with variable external porosity and intra‐skeleton diffusivity

Abstract

Computational fluid dynamics simulations of the band broadening in an idealized, and highly ordered 3-D model of silica monoliths are reported. As this high degree of order induces only a minimal eddy-dispersion, the band broadening is very sensitive to the intra-skeleton diffusivity and retention factor of the analytes. The simulations hence provide a maximal view on how the C(m)- and C(s)-contributions to the band broadening depend on the intra-skeleton diffusivity and retention factor. By comparing two model-structures with different external porosities, some interesting qualitative insights on the effect of the through-pore diameter are obtained as well. Because of the precisely known intra-skeleton diffusivity, the obtained plate height data also provide an ideal test case for the general plate height expression of chromatography. Writing out this model, identifying the geometrical parameters, and determining their value using a parameter fitting algorithm, a set of parameter values can be found which allows to accurately predict the retention factor dependency of the band broadening over a very broad range of mobile phase velocities. Remaining modeling problems are the apparent intra-skeleton diffusion dependency of the shape factor describing the intra-skeleton mass transfer, and the absence of mathematical expressions to predict the model shape factor values.