Electrolytic modification of a buffer during a capillary electrophoresis run

The electrolyte composition and pH changes in the electrode reservoirs caused by the electric current in a capillary electrophoresis system are analyzed. Parameters determining the pH, electric conductivity and the ionic strength variations are the initial electrolyte composition, applied voltage, the capillary dimensions, volume of the reservoirs, and the electroosmotic flow. Equations for the pH and molarities of the electrolyte components as functions of time are derived. Experimentally measured pH shifts in the electrode reservoirs are in good agreement with the predicted values. The time interval after which the electrode buffer needs to be replenished is determined as a function of the electric field strength, mobilities of the buffer ions, capillary cross-section and volume of the buffer in the reservoir.