Charge detector for the measurement of ionic solutes

We describe a flow-through ionic charge detector in the form of a three-compartmented system. A central water channel is separated from two outer channels bearing water (or a dilute electrolyte) by a cation-exchange membrane (CEM) and an anion-exchange membrane (AEM). Independent fluid input/output ports address all channels. One platinum electrode is put in each outer channel. When the AEM-side electrode is positive with respect to the CEM-side electrode and voltage (∼1−10 V) is applied, the observed background current is from the transport of H+/OH− through the CEM/AEM to the negative/positive electrodes, respectively. The H+ and OH− are generated by the ionization of water, in part aided by the electric field. If an electrolyte (X+Y−) is injected in to the central channel, X+ and Y− migrate through the CEM and AEM to the negative and positive electrodes, respectively, and generate a current pulse. The integrated area of the current signal (coulombs) elicited by this electrolyte injection is dependent o...