{"term":{"id":"09120","title":"Nikolsky–Eisenman equation","longtitle":"IUPAC Gold Book - Nikolsky–Eisenman equation","doi":"10.1351\/goldbook.09120","code":"09120","status":"current","definitions":[{"id":1,"text":"Equation describing the contribution of interfering ions, \\(i\\), to the electrode potential of an ion-selective electrode that is mainly dominated by the primary ion \\(\\ce{X}\\). \\[E = {\\rm{const}} + \\frac{RT}{z_{\\rm{X}}F} \\ln \\left(a_{\\ce{X}} + \\sum\\limits_i K_{{\\ce{X}},i}^{\\rm{pot}}a_{i}^{(z_{\\ce{X}}\/z_i)} \\right)\\] where \\(E\\) is the measured electrode potential of an ISE when the only variables are activities in the test solution. \\(R\\) is the gas constant, \\(T\\) the thermodynamic temperature, \\(z_{\\rm{X}}\\) and \\(z_{\\rm{i}}\\) are the numbers of electrons transferred by the analyte ion \\(\\ce{X}\\) and \\(i\\), respectively, \\(F\\) is the Faraday constant, \\(a_{\\rm{X}}\\) and \\(a_{\\rm{i}}\\) the activity of \\(\\ce{X}\\) and \\(i\\), respectively, and \\(K_{\\ce{X},i}^{\\rm{pot}}\\) is the potentiometric selectivity coefficient for interfering ion \\(i\\) with respect to the primary ion \\(\\ce{X}\\).","notes":{"1":"The Nikolsky–Eisenman equation is an extension of the Nernst equation."},"links":[{"term":"Nernst equation","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/09068"},{"term":"the numbers of electrons transferred","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/09063"}],"sources":["PAC, 2020, 92, 641. 'Terminology of Electrochemical Methods of Analysis (IUPAC Recommendations 2019)' on page 666 (https:\/\/doi.org\/10.1515\/pac-2018-0109)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/09120\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/09120\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/09120\/plain"},"citation":"Citation: 'Nikolsky–Eisenman equation' 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.09120","license":"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.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"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.","accessed":"2026-05-22T16:56:27+00:00"}}