Standard Potential of Ion-Sensors

Monday, May 12, 2014: 14:00
Floridian Ballroom L, Lobby Level (Hilton Orlando Bonnet Creek)
A. Lewenstam (Åbo Akademi University, AGH - University of Science and Technology)
The potentiometric measurement of ions belongs to the most frequently applied electroanalytical methods. It is owing to the need of routine determinations of the main blood electrolytes (Na+, K+, Cl-, and HCO3-), pH and PCO2.  Growing demand for improved reliability of the sensors response and manageable response time is associated with their fundamental properties characterized by sensitivity, selectivity, detection limit and standard potential [1].  The latter should be preferably stable over certain time, and in this way not to be a source of analytical error.

The interpretation of the standard (resp. formal) potential is often ignored owing to the application of internal electrode solution, i.e. symmetric ion-sensor systems. However, the present wave in ion-sensor technology typically utilizes all-solid-state sensor architecture, in which the internal liquid contact is substituted by a solid contact, with resulting assymetricion-sensors. This type of contact was first used for ion-selective electrodes with a solid-state (crystalline) membrane, and made by platinum, silver, carbon. More recently, conducting polymer as a solid-contact material for the ion-selective electrodes with plastic membranes was proposed [2]. Very recently the application of nanostructured materials was offered [3]. Beyond any doubt, the understanding of the reason(s) of standard potential stability of the asymmetric solid-contact ion-sensors is of a primary importance, but rarely undertaken. 

Thermodynamic interpretation the standard potential of the asymmetric all-solid-state ion-selective sensors will be presented. This interpretation is related to the fundamental concepts metallic electrodes and all-solid-state electrodes presented by Trasatti [4] and Buck & Koebel [5], and extended by Lewenstam [6] for the solid contacts made of conducting polymers. The applicability of the interpretation for the whole family of all-solid-state ion-selective sensors will be discussed.


[1]  A. Lewenstam, Clinical analysis of blood gases and electrolytes by ion-sensitive sensors, in: S. Alegret, A. Merkoci (eds.), Electrochemical Sensor Analysis (Comprehensive Analytical Chemistry vol. 49), Chapter 1, Elsevier, Amsterdam 2007.

[2] A.Cadogan, Z.Gao, A.Lewenstam, A.Ivaska and D.Diamond; Analytical Chemistry, 64 (1992) 2496; A. Lewenstam, in: G. Inzelt, A. Lewenstam, F. Scholz (Eds.), Handbook of Reference Electrodes, Springer, Heidelberg New York Dordrecht London, 2013, pp. 279-288.

[3]  G.A. Crespo, S. Macho, F.X Ruis, Anal. Chem.  50 (2008) 1316-1322.

[4] R.P. Buck, V.R. Shepard, Anal. Chem.  46 (1974) 2097-2109;  M. Koebel, Anal. Chem.,46 (1974) 1559–1563.

[5] A. De Battisi, S. Trasatti, 79 (1977) 251-258.

[6] A. Lewenstam, J. Bobacka, A. Ivaska, J. Electroanal. Chem., 368 (1994) 23-31.