System selectivity cube: a 3D visualization tool for comparing the selectivity of gas chromatography, supercritical-fluid chromatography, high-pressure liquid chromatography, and micellar electrokinetic capillary chromatography systems.

A three-dimensional visualization tool termed the system selectivity cube (SSC) has been developed to aid in the selection of chromatography systems. The most effective way to change the resolution of a complex mixture is to change the selectivity of the separation. The SSC allows efficient identification of systems of differing selectivity. Our approach is based on comparisons of the energetics of two systems and in this way is somewhat akin to the kappa-kappa plots of Horvath et al. Our comparisons, however, are based on linear solvation energy relationships (LSERs) or other multiparameter models of retention. Our approach unifies LSERs, kappa-kappa plots, and the "effective selectivity" concept introduced by Zhao and Carr. The utility and versatility of the SSC is demonstrated with LSERs for 74 micellar electrokinetic chromatography (MEKC) systems taken from the literature. The SSC groups those systems which provide little or no difference in selectivity and those systems which do differ in their selectivities. We anticipate that this approach will be useful for selecting replacement columns, systems that may offer better results for difficult separations, and orthogonal phases for 2D gas chromatography (GC) and reversed phase liquid chromatography (RPLC) separations.