Dual-pipet techniques for probing ionic reactions

Novel dual-pipet electrodes prepared by pulling borosilicate theta-tubing are described. Three types of electrochemical experiments employing such devices include the following: (1) generation/collection experiments in which ions are ejected from one of two micropipets ("generator") into the external solution and collected at the second pipet ("collector"), (2) measurements of ohmic current-voltage curves, and (3) ion-transfer voltammetry "in the air". The first setup is used for probing ion transfers at the interface between two immiscible liquids and homogeneous reactions in solution involving ionic species. Such experiments are reported for two model processes, i.e., simple and facilitated transfers of potassium between aqueous and organic phases and complexation of potassium with dibenzo-18-crown-6 in organic solution. The second arrangement is used for characterization of theta-pipets. The last arrangement can be useful for preparation of gas sensors. The possibility of measuring the concentration of volatile substances (e.g., ammonia and nitric acid) in the gaseous phase has been demonstrated.