A sheath-flow interface for producing electrospray from a capillary, the interface comprising: (a) a silica capillary configured to separate analytes contained by an analyte liquid, the capillary having an injection end configured to receive the analyte liquid and a distal end configured to expel analyte effluent, wherein the outer diameter of a segment of the distal end tapers to a reduced outer diameter within the range of 20 μm to 200 μm, and wherein the inner diameter of the capillary remains unchanged; (b) a non-conductive electrospray emitter coaxially disposed surrounding at least the distal end of the capillary, the electrospray emitter having a distal end that is tapered to terminate at an opening, the opening being coaxially disposed in relation to the distal end of the capillary, wherein the distal end of the capillary resides from 750 μm from the emitter opening within the distal end of the emitter to 100 μm beyond the emitter opening of the electrospray emitter; (c) a sheath liquid reservoir in liquid communication, through a connecting fixture about the capillary, with an interior of the electrospray emitter, the connecting fixture being capable of directing flow of the sheath liquid into the interior of the electrospray emitter, such that an electrically conductive sheath liquid can flow from the sheath liquid reservoir, through the interior of the electrospray emitter to the distal end of the capillary where it can ensheath the analyte effluent, and through the opening at the distal end of the electrospray emitter; and (d) a target surface disposed in use adjacent, but not in physical contact with, the opening of the emitter wherein an electrokinetic flow is generatable in use by an electric potential between the electrospray emitter and the target surface. (a) a silica capillary configured to separate analytes contained by an analyte liquid, the capillary having an injection end configured to receive the analyte liquid and a distal end configured to expel analyte effluent, wherein the outer diameter of a segment of the distal end tapers to a reduced outer diameter within the range of 20 μm to 200 μm, and wherein the inner diameter of the capillary remains unchanged; (b) a non-conductive electrospray emitter coaxially disposed surrounding at least the distal end of the capillary, the electrospray emitter having a distal end that is tapered to terminate at an opening, the opening being coaxially disposed in relation to the distal end of the capillary, wherein the distal end of the capillary resides from 750 μm from the emitter opening within the distal end of the emitter to 100 μm beyond the emitter opening of the electrospray emitter; (c) a sheath liquid reservoir in liquid communication, through a connecting fixture about the capillary, with an interior of the electrospray emitter, the connecting fixture being capable of directing flow of the sheath liquid into the interior of the electrospray emitter, such that an electrically conductive sheath liquid can flow from the sheath liquid reservoir, through the interior of the electrospray emitter to the distal end of the capillary where it can ensheath the analyte effluent, and through the opening at the distal end of the electrospray emitter; and (d) a target surface disposed in use adjacent, but not in physical contact with, the opening of the emitter wherein an electrokinetic flow is generatable in use by an electric potential between the electrospray emitter and the target surface.