Control of Transition Between Isotachophoresis and Zone Electrophoresis by Base-Mediated De-Stacking

Key features of microchannel electrophoresis are speed and efficiency. These result from the ability to control accurately the volume of the injected sample plug with cross-channel injectors and from the short separation lengths afforded by microfabricated devices. However, narrow cross-channel injector geometries limit the total amount of sample injected into the separation channel, and therefore limit the detection sensitivity for dilute samples. Here, we present a tandem isotachophoresis-zone electrophoresis (ITP-ZE) method that allows the amount of analyte injected to be decoupled from the effective injection width. This method relies upon the use of an electrophoresis buffer system that functions initially in an ITP mode and, after a controlled amount current has passed through the system, operates in a ZE mode. The transition between the two modes of electrophoresis can be controlled by adjusting the concentration of components of the buffer. This method has been applied to separations of ACL ARA’s eTag™ reporter molecules to enable detection of concentrations up to two orders of magnitude lower than those detectable in standard ZE in microchannels. The tandem ITP-ZE mode gives separations of eTag™ reporter molecules with resolutions and analysis times equivalent to ZE alone.