03304 IUPAC Gold Book - isopotential point 10.1351/goldbook.I03304 I03304 current 1 For an ion-selective electrode cell, there is often a particular activity of the measured ion for which the emf of the cell is independent of temperature. That activity, and the corresponding potential difference, defines the isopotential point. The specification of the ion-selective electrode and outer reference electrode must be described. Comment: When an isothermal cell is used with identical reference electrodes, the isopotential point is the activity of sensed species that gives zero net membrane potential, e.g. sensed activity is the same in the inner and outer (test) solution. Calibration lines for different cell temperatures have different slopes, but intersect at a common activity point. Cells with temperature gradients are not recommended. ion-selective electrode https://goldbook.iupac.org//terms/view/I03244 ion-selective electrode cell https://goldbook.iupac.org//terms/view/I03245 membrane potential https://goldbook.iupac.org//terms/view/M03825 reference electrode https://goldbook.iupac.org//terms/view/R05229 PAC, 1994, 66, 2527. 'Recommendations for nomenclature of ionselective electrodes (IUPAC Recommendations 1994)' on page 2531 (https://doi.org/10.1351/pac199466122527) https://goldbook.iupac.org/terms/view/I03304/html https://goldbook.iupac.org/terms/view/I03304/json https://goldbook.iupac.org/terms/view/I03304/plain Citation: 'isopotential point' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.I03304 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-06-29T04:27:59+00:00