Analysis and Stability of the Electroosmotic Flow in Capillary Zone Electrophoresis

PIAGGIO, MARÍA VIRGINIA; DEIBER, JULIO ALCIDES

Buenos Aires

Simposio; International Symposium on Electrohydrodynamics (2006 ISEHD); 2006

The non isothermal electroosmotic flow in a vertical capillary tube is studied through basic equations describing electrokinetic phenomena of suspended charged particles. Simple analytical expressions for the velocity, temperature and electrical potential fields are provided by placing emphasis on the thermal coupling between these fields with Joule heating and natural convection. These buoyant effects are introduced in the model through the Boussinesq approximation. It is thus found that the Grashof number is controlling the stability of the electroosmotic flow. Calculations show that the capillary radius affects significantly the critical Grashof number (proportional to radius raised to the fourth power) at which a mixing backflow is enhanced destabilizing the plug EOF required for optimal separation of analytes. It is also observed that the parabolic shape of the upward velocity profile around the capillary centerline increases with the applied electric field. This effect may decrease the resolution of electropherograms because the near plug electroosmotic flow expected is not achieved. The interplay between protocol variables to avoid undesirable effects is readily visualized through dimensionless numbers provided.