Voltammetry at Micropipet Electrodes

Abstract

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 can 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.

Chronoamperometric response at nanoscale liquid–liquid interface arrays

“…has been reported by various researchers [18,25,31,32]. Nirmaier and Henze reported that the cell time constant for establishing the electrode potential at the electrode surface varies linearly with the electrode surface radius for disk-shaped electrodes.…”

“…PSCA experiments by Yuan et al [18], Beattie et al [31] and Shao and Mirkin [32] reported that the lower time scale (or charging time) for carrying out potential step experiments at a microITIES is crucially restricted by the large resistance at the narrow microhole of polymer membranes or glass micropipettes used to form such microITIES. Comparison of the charging time of a water | 1,2-dichloroethane (DCE) microinterface with a metal | water microinterface of the same size showed that the charging time of the former was nearly three orders of magnitude greater than that of the latter [18].…”

Scanning Electrochemical Cell Microscopy: A Versatile Technique for Nanoscale Electrochemistry and Functional Imaging

“…Hitherto, the overwhelming majority of SECCM studies have employed aqueous electrolyte solutions. Therefore, after the pipette is pulled, the outer wall is usually silanized with dimethyldichlorosilane [Si(CH 3 ) 2 Cl 2 ], rendering it hydrophobic, which helps to confine the aqueous meniscus to the very end of the tip (57). Both barrels are then filled with an electrolyte solution and, if desired, a redox mediator of interest.…”

Interface Between Two Immiscible Liquid Electrolytes: A Review

“…To make the ion more oil soluble, complexation with large, usually neutral species, is performed. Besides the already mentioned analytical applications 32 many other determinations with facilitated transport were reported, of which only selected few can be mentioned 16,[41][42][43][44][45][46][47][48][49] .…”