Ion‐Selective Adsorption/Desorption Processes at Inorganic Materials/Solution Interfaces as a Novel Mode for Ion Sensing

Abstract

Several studies on response mechanisms of solid membrane ion‐selective electrodes (ISEs) and developments of ion sensors mainly from the authors' laboratory were reviewed. Face‐specific responses of CdS single crystals showed that ion‐selective response of solid membrane ISEs based on scarcely soluble salts is due to adsorption of component ions, and resultant charge separation at the membrane/solution interfaces. Potentiometric response mechanisms of CuS‐based ISEs in metal buffer solutions were discussed. Crystal surfaces of scarcely soluble inorganic salts were formed to provide remarkably selective molecular recognition sites at which adsorbed component ions were detected by an underlying quartz crystal microbalance (QCM). Not only single layer adsorption of component ions on the respective inorganic salt, but also multilayer crystal formations at QCM surface also showed ion‐selective response to the respective component ions. Ion selectivities of ion sensors based on scarcely soluble salts, which include ISE and QCM, are basically limited by solubility products. Several studies on ISEs based on inorganic materials having a three‐dimensional (3D) network structure with interstitial ions demonstrated that the formation of vacant sites by dissolution of the interstitial ions from the membrane surfaces is prerequisite for ion‐selective responses. For these ISEs, potentiometric selectivities are essentially governed by size and dehydration energies of analyte ions. Taken these together, approaches for ion‐sensor developments based on inorganic materials were critically evaluated and updated.

^†In memory of Professor Harry B. Mark Jr., who greatly contributed to the progress of modern electrochemistry and electroanalytical chemistry.

Keywords:

• ISE
• Adsorption/desorption processes
• QCM
• Size
• Dehydration energies
• Solid membranes

Acknowledgments

This work was supported by grants from the Ministry of Education, Science and Culture, Japan. Also acknowledged is the Hungarian Academy of Sciences and Japan Society for the Promotion of Science for support part of the presented works.

Notes

^†In memory of Professor Harry B. Mark Jr., who greatly contributed to the progress of modern electrochemistry and electroanalytical chemistry.