<p>Charged droplet spray is formed from a solution with all or a portion of the charged droplet spray current generated from reduction or oxidation (redox) reactions occurring on surfaces removed from the first or sample solution flow path. In one embodiment of the invention, two solution flow channels are separated by a semipermeable membrane. A first or sample solution flowing through the first solution flow channel exchanges cation or anion charged species through the semipermeable membrane with a second solution or gas flowing through the second flow channel. Charge exchange is driven by the electric field applied at the charged droplet sprayer sample solution outlet. Redox reactions occur at an electrode surface in contact with the second solution. The invention increases the control and range of the Electrospray ionization process during ES/MS operation. Alternative embodiments of the invention provide for conducting redox reactions on conductive surfaces removed from the first or sample solution flow path but not separated by semipermeable membranes.</p>
