Resolution optimisation in micellar electrokinetic chromatography using empirical models

Theoretical and empirical models can be used to model the migration or separation characteristics in micellar electrokinetic chromatography in order to optimise the resolution. In this paper only empirical models were used, because it is easier and more straightforward to obtain these models. Several empirical approaches for the optimisation of the resolution were compared in order to determine which response should be modelled preferably. The use of models of the effective mobility in combination with average plate numbers proved to be the most suitable approach to optimisation of the resolution, because the relative prediction errors of the models of the effective mobility were a factor of 2-4 smaller than the relative prediction errors of the models of the apparent mobility. Moreover for the least separated peak pair the resolutions based on the models of the apparent and effective mobility showed relative prediction errors that were approximately a factor of 2 smaller than the relative prediction errors of the resolutions based on the models of the resolution and separation factor. The predictions of the separation factor based on the different models generally showed lower prediction errors than the predictions of the corresponding resolutions. Although the relative prediction errors were large, particularly for closely migrating compounds, the empirical approach will probably lead to the optimum separation buffer composition.