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An interesting point in quantitative capillary zone electrophoresis, when applying conductivity detection or indirect UV detection with non-UV absorbing components, is the existence of a relationship between effective mobilities and peak area, independent of the kind of ionic species. This relationship is theoretically considered for fully ionized monovalent ions resulting in a linear relationship, passing through the origin, between temporal peak area and the product of a correction factor (dependent only on the effective mobilities of the ionic species) and migration time for an equimolar sample composition. A good correlation between theory and practice could be established by applying experimental measured data.

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Nonaqueous (NA) solutions are often used as background electrolytes (BGEs) and NA solvents are added to aqueous BGEs as organic modifiers in capillary zone electrophoresis (CZE), in order to optimize the separations. This can be tricky, however, because the pH* and pK* concepts may be totally different in NA solvents, whereas often less knowledge is available concerning phenomena, such as system zones, applying NA solvents. In this paper, the concepts of pH* and pK* are considered for methanol as a solvent and pK* values are determined for several components in mixtures of water and methanol. With a mathematical model, adapted for calculations in methanol, parameters are calculated describing the fronting or tailing character of peaks and the question of peaks or dips, and the existence of system zones is discussed for pure methanol as a solvent. These aspects are experimentally verified, applying BGEs useful for the separation of cationic species in the indirect UV mode. It can be concluded that the mathematical model developed for aqueous BGEs is applicable to BGEs in methanol, too, and that the behavior of BGEs in methanol is comparable with that in water concerning the fronting or tailing character of peaks and the question of peaks and dips, although the mobilities and pK values can change significantly.