Electrochemical Properties of Nitrate-Selective Electrodes: The Dependence of Resistance on the Solution Concentration

The electrochemical properties of ion-exchanger-based solvent polymeric ion-selective electrodes (ISEs)—bulk and interfacial resistance, capacitance, and polarization under a galvanostatic current step—are studied, with a nitrate ISE based on tetradecylammonium nitrate (TDANO₃) as a model system. The study is performed by chronopotentiometric and impedance measurements, and focuses on the dependence of the aforementioned properties on the concentration of NO₃⁻ anions in solution. The impacts from the bulk and the interfacial charge transfer to the overall membrane resistance are revealed. It is shown that the bulk resistance of the membranes decreases over an increase of NO₃⁻ concentration within the range of a Nernstian potentiometric response of the ISE. This fact, also reported earlier for K⁺- and Ca²⁺-selective ISEs, is not in line with current views of the mechanism of the ISE response, or of the role of ion exchange in particular. The origin of this effect is unclear. Estimates are made for the concentration of ionized species (NO₃⁻ and TDA⁺) and, respectively, for the TDANO₃ association constant, as well as for the species diffusion coefficients in the membrane.

Voltammetric determination of diffusion coefficients in polymer membranes

The diffusion-controlled transport of ions and molecules through polymer membranes utilized in chemical and biosensors is often the key factor determining the response characteristics of these sensors. A simple voltammetric method utilizing a planar electrochemical cell allows the rapid determination of diffusion coefficients in resistive polymer membranes.

Performance evaluation criteria for preparation and measurement of macro- and microfabricated ion-selective electrodes (IUPAC Technical Report)

Over the last 30 years, IUPAC published several documents with the goal of achieving standardized nomenclature and methodology for potentiometric ion-selective electrodes (ISEs). The ISE vocabulary was formulated, measurement protocols were suggested, and the selectivity coefficients were compiled. However, in light of new discoveries and experimental possibilities in the field of ISEs, some of the IUPAC recommendations have become outdated. The goal of this technical report is to direct attention to ISE practices and the striking need for updated or refined IUPAC recommendations which are consistent with the state of the art of using macro- and microfabricated planar microelectrodes. Some of these ISE practices have never been addressed by IUPAC but have gained importance with the technological and theoretical developments of recent years. In spite of its recognized importance, a generally acceptable revision of the current IUPAC recommendations is far beyond the scope of this work.