Synergism of capillary isotachophoresis and capillary zone electrophoresis

The combination of capillary isotachophoresis and capillary zone electrophoresis may enhance greatly the performance of analytical capillary electrophoresis with respect to both separation power and the concentration sensitivity. The concentrating effects and the separation power of isotachophoresis allow the analysis of diluted samples and the elimination of interferences due to bulk components. The separation process of zone electrophoresis enables one to resolve the stack of trace analytes and detect the resulting individual zones with high sensitivity. The transition of isotachophoresis into zone electrophoresis plays the key role in the overall performance of this hyphenated technique. This article describes the dynamics of the conversion of isotachophoresis into zone electrophoretic mode and shows that the key role is played by the segments of the leading and terminating zones from the isotachophoretic stage. The magnitude of these segments directly effects the detection time as well as the separation width of the peaks of analytes. It is shown that these effects are also important in the analyses by capillary zone electrophoresis where isotachophoresis is induced by the sample itself. Finally, the paper presents a list of recommended, user-friendly, electrolyte systems which enable one to simply predict the performance of the combination isotachophoresis-zone electrophoresis.