Emersion peaks in capillary electrophoresis

Abstract An anomalous phenomenon in capillary electrophoresis (CE), referred to as the ‘emersion peak’, has been observed. The emersion peak is generated at the inlet end of the capillary whenever this end is temporarily removed from the solution prior to application of the electrophoretic field. This phenomenon, which is believed to have physical origins at the capillary inlet, is transported along the capillary at the rate of electroosmotic flow and is detected by on-column UV absorbance. Emersion peaks have been observed in a CE system with a uniform sodium benzoate electrolyte without sample injection or deliberately-formed concentration boundaries, and are attributed to the adsorption of benzoate at the air-solution interface formed upon emersion of the capillary inlet. Emersion peak size has been found to depend on the number of emersions, the duration of each emersion, the height to which the inlet is raised above the supply electrolyte reservoir during an emersion, the delay between completion of the emersion and application of the electric field, and the cut of the capillary forming the inlet end.