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 second solution or gas phase composition can be changed as a step function or as a gradient to run pH or conductivity scans in the first solution to optimize or modify Electrospray performance in Electrospray mass spectrometry applications. The first or sample solution forms a charged droplet spray by Electrospray or pneumatic nebulization in the presence of an electric field from the first solution flow channel exit. Evaporating charged liquid droplets form ions from species in solution that are transferred into vacuum and mass to charge analyzed. The second solution or composition can be modified to selectively change pH, conductivity and/or composition of the sample solution during Electrospray ionization to enhance or extend analytical performance for given ES/MS analytical applications. 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.