High sensitivity electrospray interface

A sheath-flow interface for producing electrospray from a capillary comprising:

• (a) a capillary configured to contain 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 about 20 μm to about 200 μm;
• (b) an 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;
• and
• (c) a sheath liquid reservoir in liquid communication with an interior of the electrospray emitter, such that an electrically conductive sheath liquid can flow from the sheath liquid reservoir, through a connecting fixture intermediate the capillary and the electrospray emitter, across the distal end of the capillary, and through the opening at the distal end of the electrospray emitter;
• wherein the sheath liquid provides electrical contact between the capillary and the electrospray emitter, the sheath-flow interface is configured to produce a nanospray generated by electrokinetic flow of the sheath liquid mixed with the analyte effluent, and the electrokinetic flow is generated by an electric potential between the electrospray emitter and a target surface disposed adjacent, but not in physical contact with, the opening of the emitter.