Temperature-insensitive electrokinetic behavior in capillary zone electrophoresis

Capillary zone electrophoresis generally suffers the Joule effect at relatively high driven voltage owing to the temperature control problem. The electro-osmotic and electrophoretic velocities are greater than those predicted by the well-known Smoluchowski equation when the Joule heating is significant. It is attributed to the reduction of the solvent viscosity caused by the temperature increase. A simple analytical theory is derived to show that when the electric current is steady, the electroosmotic flow remains pluglike regardless of the temperature profile inside the capillary due to Joule heating and nonuniform surrounding convection. Moreover, the electroosmotic (or electrophoretic) velocity is always linearly proportional to the electric current. This temperature-insensitive behavior is caused by the cancellation of the temperature effects as stated in Walden's rule. A series of capillary zone electrophoresis experiments has been performed to confirm the temperature-insensitive electrokinetic behavior. Our results suggest that the Joule effect can be circumvented by controlling the electric current even under nonuniform convective cooling.