Microchip-Based Electrophoretic Separations with a Pressure-Driven Backflow.

It is well known that the resolving power of capillary zone electrophoretic separations may be improved with an increase in the applied electric field strength and separation time. While large electric fields may be realized in short analysis channels commonly employed in microfluidic systems, this experimental design is not suitable for achieving long separation times. In this chapter, we describe the use of a steady and/or a periodic pressure-driven backflow to increase the separation time in short microchannels thereby enabling the analysis of closely related species on microchip devices. The reported backflow was realized in our assays using an on-chip pressure-generation capability that relied on the partial blockage of electroosmotic flow around a junction of two glass channel segments having different depths. Although the noted strategy led to additional band broadening in the system, the resolving power of our device was observed to substantially improve upon introduction of the reported steady/periodic pressure-driven backflow for analysis channels shallower than 5 μm.