An air-assisted flow-gating interface for capillary electrophoresis.

A new kind of flow gating interface (FGI) has been designed for online connection of CE with flow-through analytical techniques. The sample is injected into the separation capillary from a space from which the BGE was forced out by compressed air. A drop of sample solution with a volume of 75 nL is formed between the outlet of the delivery capillary supplying the solution from the flow-through apparatus and the entrance to the CE capillary; the sample is hydrodynamically injected into the CE capillary from this drop. The sample is not mixed with the surrounding BGE solution during injection. The functioning of the proposed FGI is fully automated and the individual steps of the injection process are controlled by a computer. The injection sequence lasts several seconds and thus permits performance of rapid sequential analyses of the collected sample. FGI was tested for the separation of equimolar 50 μM mixture of the inorganic cations K+ , Ba2+ , Na+ , Mg2+ , and Li+ in 50 mM acetic acid/20 mM Tris (pH 4.5) as BGE. The obtained RSD values for the migration times varied in the range 0.7-1.0% and the values for the peak area were 0.7-1.4%; RSD were determined for ten repeated measurements.