02590 IUPAC Gold Book - gas sensing electrode 10.1351/goldbook.G02590 G02590 current 1 A sensor composed of an indicator and a reference electrode in contact with a thin film of solution which is separated from the bulk of the sample solution by a gas-permeable membrane or an air gap. This intermediate solution interacts with the gaseous species (penetrated through the membrane or an air gap) in such a way as to produce a change in a measured constituent (e.g. the $\ce{H^{+}}$ activity) of the intermediate solution. This change is then sensed by the ion-selective electrode and is related to the partial pressure of the gaseous species in the sample. [Note: In electrochemical literature the term gas electrode is used for the classical, redox-equilibrium-based gas electrodes as well, such as the hydrogen or the chlorine gas electrodes ($\ce{Pt(s)}$|$\ce{H2(g)}$|$\ce{H^{+}(aq)}$ or $\ce{Pt(s)}$|$\ce{Cl2(g)}$|$\ce{Cl^{-}(aq)}$]. These electrodes respond both to the partial pressure of the gas ($\ce{H2}$ or $\ce{Cl2}$) and to the ionic activities ($\ce{H^{+}}$ or $\ce{Cl^{-}}$). The Clark oxygen electrode fits under this classification although, in contrast to other gas sensors, it is an amperometric and not a potentiometric device. constituent https://goldbook.iupac.org//terms/view/C01281 ion-selective electrode https://goldbook.iupac.org//terms/view/I03244 membrane https://goldbook.iupac.org//terms/view/MT06878 partial pressure https://goldbook.iupac.org//terms/view/P04420 reference electrode https://goldbook.iupac.org//terms/view/R05229 thin film https://goldbook.iupac.org//terms/view/T06345 PAC, 1994, 66, 2527. 'Recommendations for nomenclature of ionselective electrodes (IUPAC Recommendations 1994)' on page 2534 (https://doi.org/10.1351/pac199466122527) https://goldbook.iupac.org/terms/view/G02590/html https://goldbook.iupac.org/terms/view/G02590/json https://goldbook.iupac.org/terms/view/G02590/plain Citation: 'gas sensing electrode' 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.G02590 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. 2026-07-21T16:15:38+00:00