Enhancement of Separation Efficiency in Capillary Electrophoresis by Electrostacking without Liquid Contact

Quantitative reproducibility and separation efficiency in high-performance capillary electrophoresis is often limited by the reproducibility and the nature of the sample introduction procedure. This is particularly true where electrostacking is involved, whether such is deliberately carried out or happens automatically with the choice of ionic strength of the running electrolyte. Extraneous dispersion frequently originates in the act of sample introduction, for example, from the shock of the capillary entering a sample vial or a sample-filled capillary entering the carrier electrolyte source vial. A method based on the stacking of the sample constituents, before the capillary actually contacts the liquid in a vial, can reduce this problem. This technique can be utilized for the preconcentration of sample constituents and to improve separation efficiency by reducing dispersion. In favorable cases, plate counts can increase by as much as 160%, approaching theoretical diffusion-limited efficiencies.