Tandem isotachophoresis/zone electrophoresis method and system

A method of separating components having a given negative or positive charge and contained in a sample, comprising

• (a) loading a separation microchannel having, in an upstream to downstream direction, an upstream end, an upstream channel region, a sample-volume channel region, a downstream separation channel region, and a downstream end, so as to fill
• (i) the upstream channel region with a trailing-edge electrolyte containing a trailing edge ion having an electrophoretic mobility lower than that of any of the sample components, and containing a selected concentration of a titratable species,
• (ii) the sample-volume channel region with the dilute sample, and
• (iii) the separation channel region with a leading-edge electrolyte, containing a leading edge ion having an electrophoretic mobility greater than that of any of the sample components;
• and
• (b) creating an electrical field potential across said microchannel, by applying a voltage potential across electrodes in contact with said upstream and downstream channel ends,
• thereby causing charged components in said sample to stack by isotachophoresis, and subsequently causing hydroxyl or hydrogen ions to migrate into the trailing-edge electrolyte, titrating said titratable species therein, under conditions that permit the sample to stack into a relatively small sample volume before hydroxyl- or hydrogen-ion migration into and through the sample-volume region is effective to overtake the charged sample components,
• wherein continued application of an electric potential across the channel ends causes charged sample components in the stacked sample volume to separate by zone electrophoresis.