title: Intercalation Compounds as Inner Reference Electrodes for Reproducible and Robust Solid-Contact Ion-Selective Electrodes.
abstract: With billions of assays performed every year, ion-selective electrodes (ISEs) provide a simple and fast technique for clinical analysis of blood electrolytes. The development of cheap, miniaturized solid-contact (SC-)ISEs for integrated systems, however, remains a difficult balancing act between size, robustness, and reproducibility, because the defined interface potentials between the ion-selective membrane and the inner reference electrode (iRE) are often compromised. We demonstrate that target cation-sensitive intercalation compounds, such as partially charged lithium iron phosphate (LFP), can be applied as iREs of the quasi-first kind for ISEs. The symmetrical response of the interface potentials towards target cations ultimately results in ISEs with high robustness towards the inner filling (ca. 5 mV dec(-1) conc.) as well as robust and miniaturized SC-ISEs. They have a predictable and stable potential derived from the LiFePO4/FePO4 redox couple (97.0±1.5 mV after 42 days).
authors.affiliation: Center for Technology Innovation, Healthcare, Research & Development Group, Hitachi Ltd., Higashi-Koigakubo 1-280, Kokubunji-shi, Tokyo, 185-8601, Japan.
authors.forename: Yu
authors.initials: Y
authors.lastname: Ishige
authors.affiliation: Analytical Chemistry, Center for Electrochemical Sciences, Ruhr-University Bochum, Universitätsstrasse 150, 44780, Bochum, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Klink
authors.affiliation: Analytical Chemistry, Center for Electrochemical Sciences, Ruhr-University Bochum, Universitätsstrasse 150, 44780, Bochum, Germany. wolfgang.schuhmann@rub.de.
authors.forename: Wolfgang
authors.identifier: http://orcid.org/0000-0003-2916-5223
authors.initials: W
authors.lastname: Schuhmann
keywords: cation intercalation compounds; inner reference electrode; ion-selective electrodes; lithium iron phosphate; solid contact