Effect of the flow profile on separation efficiency in pressure-assisted reversed-polarity capillary zone electrophoresis of anions: Simulation and experimental evaluation.

Capillary electrophoresis connected to electrospray ionization mass spectrometry is a promising combination to analyze complex biological samples. The use of sheathless electrospray ionization interfaces, such as a porous nanoelectrospray capillary emitter, requires the application of forward flow (either by pressure or electroosmosis) to maintain the electrospray process. The analysis of solute molecules with strong negative charges (e.g., aminopyrenetrisulfonate labeled glycans) necessitates a reversed-polarity capillary electrophoresis separation mode, in which case the electroosmotic flow is counter current, thus pressure assistance is necessary. In this study, we compared the effect of forced convection with and without counter electroosmotic flow on the resulting separation efficiency in capillary electrophoresis based on flow profile simulations by computational fluid dynamics technique and by actual experiments. The efficiencies of the detected peaks were calculated from the resulting electropherograms and found approximately 950 000 plates/m for electrophoresis with counter electroosmotic flow, 20 000 plates/m with pressure only (such as would be in open tubular liquid chromatography), and 480 000 plates/m for electrophoresis with simultaneous counter electroosmotic flow and forward pressure assistance, which validates the simulation data.