Combined optimisation of mobile phase pH and organic modifier content in the separation of some aromatic acids by reversed-phase HPLC.

Using the separation of some closely related aromatic acids as an example, a mixture design approach is applied to the optimization of pH as a single parameter in aqueous mobile phases and also to the combined optimization of pH and modifier content in aqueous‚ÄövÑvÆorganic mobile phases. The approach used has an advantage over factorial design experiments in that it requires substantially fewer retention data in order to locate the optimal mobile phase composition. A simple optimization criterion which considers both the separation characteristics and duration of a chromatogram is described and its use is illustrated.