Methods and apparatus for real-time monitoring, measurement and control

Abstract

In capillary electrophoresis systems, real-time monitoring and measurement of the electroosmotic flow through a separation capillary is accomplished by coupling the outlet of the separation capillary to an electrically-conductive junction. In one embodiment, this junction is an ion-impermeable or an ion-exchange membrane unit that preferentially exchanges ions having a charge opposite to analyte ions of interest. Within a downstream region of the junction, all axial incremental voltage from the electroosmotic voltage source is terminated, which ensures that downstream electrolyte ion movement is passive, due to active flow created upstream when an incremental axial voltage existed. Upstream electrolyte ion flux is proportional to C.sub.1 .multidot.(.mu..sub.e +.mu..sub.eo), where C.sub.1 is the upstream concentration of the electrolyte ion of interest, .mu..sub.e is the electrolyte electrophoretic mobility, and .mu..sub.eo is the electroosmotic mobility. Downstream, the flux is proportional to C.sub.2 .multidot..mu..sub.eo, where C.sub.2 is the downstream concentration of the electrolyte ion of interest. The fluxes are equal, whereupon .mu..sub.eo .apprxeq.C.sub.1 .multidot..mu..sub.e /(C.sub.2 -C.sub.1). Since .mu..sub.e is known, .mu..sub.eo can be determined in real-time by measuring C.sub.2 and C.sub.1. In a second embodiment, the electrically-conductive junction preferably is a grounding capillary that converts plug-like electroosmotic flow to parabolic flow. A parabolic flow characteristic such as streaming potential, streaming current, or pressure differential is measured in real-time to ascertain electroosmotic flow rate. In each embodiment, the realtime measured flow information is feedback-coupled to preferably alter zeta-potential to regulate electrolyte solution flow in the separation capillary.