Direct evidence of ionic fluxes across ion-selective membranes: a scanning electrochemical microscopic and potentiometric study.

Scanning electrochemical microscopy (SECM) supplemented with potentiometric measurements was used to follow the time-dependent buildup of a steady-state diffusion layer at the aqueous-phase boundary of lead ion-selective electrodes (ISEs). Differential pulse voltammetry is adapted to SECM for probing the local concentration profiles at the sample side of solvent polymeric membranes. Major factors affecting the membrane transport-related surface concentrations were identified from SECM data and the potentiometric transients obtained under different experimental conditions (inner filling solution composition, membrane thickness, surface pretreatment). The amperometrically determined surface concentrations correlated well with the lower detection limits of the lead ion-selective electrodes.

Scanning electrochemical microscopy. 32. Gallium ultramicroelectrodes and their application in ion-selective probes.

Gallium ultramicroelectrodes for amperometric measurements in scanning electrochemical microscopy were fabricated by introduction of liquid Ga into drawn glass micropipets. Cyclic voltammetry of Ru(NH(3))(6)(3+) and the use of this species for SECM imaging is described. Double-barrel micropipet tips with a Ga amperometric electrode and an ion-selective (K(+)) potentiometric probe can also be constructed. This probe was used to image the K(+) activity near a 20-µm-diameter lumen of a glass capillary.