Due to the complexity and elusiveness of hydrophobicity, there is no real equivalence for hydrophobic interaction (HIC) and reversed-phase chromatography (RPC) to the steric mass action model for ion-exchange chromatography. The mechanistic models used for simulation of chromatographic separation describe phenomena such as convection, mass transfer through stagnant films and diffusion well, but the actual adsorption equilibrium in HIC and RPC is often expressed as a linear or quadratic function of the modulator concentration. For the specific case study, this is often a successful strategy, but it does not enable extrapolation and predictions for other adsorbates, adsorbents and modulators.<br/><br/>Such predictability requires a model based on a theoretical framework. A number of attempts to create a thermodynamically based framework for chromatographic equilibria in HIC and RPC have been made, of which the most famous probably is the adaption of the solvophobic theory by Melander, Horváth and co-workers. There are a number of versions of adsorption and partitioning theories for RPC, e.g. by Dill et al. and by Scott and Kucera, and the preferential interaction theory and Kirkwood’s theories on macromolecules in solution have been adapted to HIC by Arakawa, Perkins and co-workers, and by Mollerup et al., respectively. There is however still a gap between well-formulated and advanced theories about HIC and RPC, and relatively user-friendly models that can be applied to real, industrial cases.<br/><br/>Our study is a step towards bridging that gap. We have evaluated two different combinations of one theory for HIC and one for RPC by applying these to experimental data for RPC of three insulin variants, using both ethanol and potassium chloride as modulators. The model terms which actually describe the observed phenomena have been distinguished from those that, at least for the studied system, have a negligible variation. This evaluation includes both linear range and high-load conditions. It is not obvious that the same simplifications can be made for other systems, but the strategy presented can be generally applied to determine the relevant terms.

Thermodynamically based modelling of effects of ethanol and potassium chloride on reversed-phase chromatography

251st National Meeting (2016)

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