Interfering ions, potentiometry

The method does not deal with differences between the charges of the primary and interfering ions. It does not require close to the Nemstian response of the electrode to the different ionic species. The selectivity coefficient value obtained with this method has only practical significance. The values can be used for the estimation of the reliability of direct potentiometry in the case of the electrode available and samples of approximately known concentration. 

Pahnqvist, U. et al.. Competitive metal ion adsorption in goethite systems using in situ voltammetric methods and potentiometry, 7. Colloid Interf. Scz.,218, 388, 1999. 

The ISFET, developed from the fabrication techniques of semiconductor devices, is an important sensor device used in potentiometry. The main advantages are the extremely small size, solid-state structure and the ability to fabricate multi-ion sensors. More than 30 years ago, methods have been proposed to work with a differential arrangement, i.e. the integration of an ion-sensitive and an ion-insensitive structure, the later one working as the reference element (R(E)FET). The main problem is that semiconductor-modified surfaces required for R(E)FET are also not always in thermodynamical equilibrium with the test solution and can be sensitive to aggressive or interfering dissolved species or not well characterised aging phenomena. 

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