Abstract A new electrospray ionization source (emitter) has been developed which allows the effective utilization of very small sample volumes at much lower flow rates than previously demonstrated. A small diameter etcched‐tip capillary has been incorporated into a pressure‐infusion electrospray ionization source. The ability to electro‐spray aqueous solutions without the use of an ancillary sheath flow is demonstrated with several biopolymers. High signal intensities and stable signals are observed for this source in a comparison with a standard methanol‐sheath source.