Voltage-induced Variation of Capacity Factors for Neutral Solutes by Using Hexa-6-bromo-hexa-6-deoxy-β-cyclodextrin Modified Column in Electrochromatography

The capillary electrochromatography (CEC) takes an important position in the separation sciences [1-8], and its further development will contribute to the analytical chemistry field. Therefore the study of the electrochromatographic behavior is very important. The key factor of CEC is the electric field applied along a capillary column. In general, the role of the applied electric field in CEC is to provide two kinds of the flow, i.e . electroosmotic flow and electrophoresis of the charged solute. The mechanisms and roles of these two flows are well known [1, 10]. In addition, the applied electric field induces some interesting phenomena [2-9]. One of the phenomena is voltage-induced variation of the capacity factor [5-8]. The voltage-induced variation of the capacity factors in the electrochromatography using the column packed with ion-exchange supports were described in our former reports [6, 7]. The unique point of this phenomenon is that the variation of the capacity factor recognized the direction of the electric field. When the application of a negative voltage decreases the capacity factor of the solute, the positive-voltage application increases its capacity factor. Tsuda reported that the elution time was depended on the period from the beginning of the application of the voltage [2], and Unger and Eimer also reported that the period to obtain the stable retention time after the release of the voltage was more than 4 hours [3]. These phenomena might also reflect the voltage-induced retention variation. Other phenomenon is the dependence of the electric resistance of the capillary column on the applied electric field [5, 9]. The electric resistance of the capillary column varies with the application of the voltage. This phenomenon also recognizes the direction of electric field, and the variation pattern of the column resistance was governed by the surface charges of the packing materials. The variation of the column electric resistance might suggest that the variation of the ion concentrations around the surface of the packing materials. Namely applied electric field might change the condition around the packing materials. These phenomena might suggest that application of the electric field along the column changes the condition of the stationary phase. The investigation of this phenomenon is necessary to the Original