Effects occurring in quantitative analyses from salt-rich solutions and of easily oxidizable analytes were studied using an Extractive Electrospray Ionization (EESI) source. A low detection limit of 100pM was achieved for the drug propanolol in the presence of 25mM TRIS salt. The oxidation of TEMPO, a stable radical, was found to be dependent on the solvent flows and could be related to a competition between two different ionization mechanisms. The addition of a source air heater was found to improve ion desolvation and increase EESI signal intensities to from 2–5% to 30–90% of the ESI intensity. These results are very encouraging for the further development of the EESI source.