Scanning electrochemical microscopy (SECM) of facilitated ion transfer at the liquid|liquid interface

Abstract

A new mode of the scanning electrochemical microscope (SECM) operation is presented. A micropipette-based electrode is used as an amperometric microprobe (tip). The tip current is produced by facilitated transfer of ions from the aqueous solution inside the pipette into the organic solvent, e.g., the transfer of K+ into 1,2-dichloroethane (DCE) assisted by dibenzo-18-crown-6 (DB18C6). A positive feedback current is observed when the tip approaches the water|DCE interface due to the transfer of potassium into the aqueous layer and regeneration of DB18C6 species. Good agreement with the SECM theory can be demonstrated. Negative feedback is observed when the tip approaches a glass insulator. The dependence of the SECM response on the shape of the liquid meniscus formed at the micropipette tip is discussed. The technique developed can be used for studies of ion transfer processes at the liquid|liquid and liquid|membrane interfaces and for high resolution electrochemical imaging.