Voltammetry at micropipet electrodes

The use of micropipet electrodes for quantitative voltammetric measurements of ion-transfer (IT) and electron-transfer (ET) reactions at the interface between two immiscible electrolyte solutions (ITIES) requires knowledge of geometry of the liquid interface. The shape of the meniscus formed at the pipet:tip was studied in situ by video microscopy under controlled pressure. The shape of the interface: dan be changed from a complete sphere to: a concave spherical cap by varying the pressure applied to the pipet, and the diffusion current to the pipet changes accordingly. With no external pressure applied, the water/organic interface turned out to be flat, and the voltammetric response of a pipet must follow the well known theory for a microdisk electrode. The large deviations from this theory observed previously can: be attributed to a small amount of the filling aqueous solution which escapes from the pipet and forms a thin layer on its outer wall. This effect can be eliminated by making the outer pipet:wall hydrophobic. Procedures have been developed for independent silanization of the inner and outer walls of the pipet. Pipets with a silanized inner wall can be filled with an organic solvent (e.g., 1,2-dichloroethane) and be used for voltammetric measurements in aqueous solutions. Another mode of voltammetry is based on trapping of a thin layer of organic solvent in the narrow shaft of a pipet between the filling solution and the aqueous outer phase. This arrangement is potentially useful for. electrochemical catalysis and sensor applications.