https://doi.org/10.1351/goldbook.16254
Response of an ion-selective electrode according to a local thermodynamic equilibrium, over a given range of activity (or concentration) that follows the Nernst equation.
Notes:
- For the Nernstian response, the potential difference of the ion-selective electrode cell is proportional to the decadic logarithm of the ionic activity of a given species (\(a_{\rm{A}}\)) with coefficient \((RT/z_{\rm{A}}F)/\log_{10}(\rm{e})\) (about \(0.0592/z_{\rm{A}}\,\pu{V}\) at \(\pu{298.15 K}\)), where \(R\) is the gas constant, \(T\) the thermodynamic temperature, \(F\) the Faraday constant, and \(z_{\rm{A}}\) the electron number of an electrochemical reaction of species \(\ce{A}\).
- Nernstian response implies ideal sensitivity, but not necessarily ideal selectivity, since interfering ions may also give a Nernstian response when they are present as the sole potential determining species.