Electrophoretic Behavior in Nonaqueous Capillary Zone Electrophoresis Using Tetrahydrofuran-Based Ternary Nonaqueous Solutions

Nonaqueous capillary electrophoresis has the potential to separate water-insoluble analytes. Previously, we reported the separation of water-insoluble and neutral synthetic polymers in nonaqueous capillary zone electrophoresis using tetrahydrofuran (THF)-based ternary nonaqueous solutions. In this paper, the effect of the composition of a THF-based ternary solution (THF, acetonitrile, and methanol) containing cetyltrimethylammonium chloride (CTAC) on electrophoretic behavior is investigated using small organic compounds as prove analytes. In addition to general electrophoretic parameters such as electrophoretic mobility, analytical stability was also evaluated. The electric current, electrophoretic mobility of the benzyltriethylammonium cation (ion pair formation with chloride anion), and electrophoretic mobility of coronene (solvophobic interaction with the CTA cation) were dominated mainly by the THF content, and lower THF content resulted in higher values. In contrast, electroosmotic mobility was enhanced by an increase in THF content and was affected mainly by methanol content. Interestingly, in addition to stable electropherograms, we observed instable (fluctuation of baseline or zero current) electropherograms, which were obtained irregularly. Although a notable relation between the composition and the instable behavior was not observed, it is suggested that this "discontinuous instability" is related with the composition distribution (heterogeneous composition) of the ternary solvents in a capillary. Increasing the temperature effectively suppressed the composition distribution and has the potential to decrease the risk of instable behavior.