A method of forming a capillary tube for electrospray ionization (ESI) having at least one tip with a desired tip profile. The method includes providing a pre-finished capillary tube of substantially homogenous material. The capillary tube has a first end and an internal bore. The first end of the pre-finished capillary tube is wet-etched in an etchant for an etch duration. A protective fluid flows through the internal bore of the capillary tube at a flow rate during the etch duration and the flow rate and the etch duration are determined to obtain the desired tip profile below a liquid level of the etchant.