Coaxial flow-gating interface for capillary electrophoresis.

A coaxial flow-gating interface is described in which the separation capillary passes through the sampling capillary. Continuous flow of the sample solution flowing out of the sampling capillary is directed away from the injection end of the separation capillary by counter-current flow of the gating solution. During the injection, the flow of the gating solution is interrupted, so that a plug of solution is formed at the inlet into the separation capillary, from which the sample is hydrodynamically injected. Flow-gating interfaces are originally designed for on-line connection of capillary electrophoresis with analytical flow-through methods. The basic properties of the described coaxial flow-gating interface were obtained in a simplified arrangement in which a syringe pump with sample solution has substituted analytical flow-through method. Under the optimized conditions, the properties of the tested interface were determined by separation of K+ , Ba2+ , Na+ , Mg2+ and Li+ ions in aqueous solution at equimolar concentrations of 50 μM. The repeatability of the migration times and peak areas evaluated for K+ , Ba2+ and Li+ ions and expressed as relative standard deviation did not exceed 1.4%. The interface was used to determine lithium in mineral water and taurine in an energy drink.