The problem of electrochemical decomposition due to extraction of single polarity ions from a novel ionic liquid ion source (ILIS) is solved by periodically alternating the voltage Source so that the potential difference that appears across the double layer formed between the emitter conductive material and the liquid is maintained below the electrochemical window limit, thus eliminating electronic reactions. The ionic liquid EMI-BF4 is used to externally wet a solid tungsten emitter, establishing a physical boundary with a certain liquid-metal contact area. Theoretical and experimental evidence suggests that this area is close to the effective surface involved in the double layer charging dynamics. The extent of this surface is relatively large, thus increasing the net capacitance and consequently the double layer charging time, demonstrating that low frequency voltage alternation of the order of 1 Hz is enough to obtain clean and reliable ion emission. (C) 2004 Elsevier Inc. All rights reserved.