Novel solution-free reference electrodes for potentiometric applications

Krzysztof Maksymiuk ,  Anna Kisiel ,  Agata J. Michalska 

Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland

Abstract

In recent years a considerable progress in construction of potentiometric sensors has been achieved in the area of miniaturization, disposability and internal solution free construction. However, for the reference electrodes, still classical constructions based on Ag/AgCl or Hg/Hg2Cl2 dominate. The profound stability of these highly reliable electrodes is accompanied by a serious disadvantage: presence of a liquid solution phase connected with need of refilling / maintenance and restriction of vertical working position. Moreover, these arrangements are often difficult to suit with modern miniaturized sensing devices and their production methods.

Among requirements for reliable reference electrodes, independence of recorded potentials of changes of sample activity and composition is of crucial importance from the point of view of applications in potentiometric ion sensing cells. Generally, liquid-free reference electrodes need solid conducting materials and either a reversible redox system or a membrane non-selective to ions, to assure a constant potential independent of changes in the sample medium. Recent achievements in this field will be reviewed.

The results of our recent work, connected with applications of conducting polymers (CP) for reference electrodes construction will be also presented. In this work two different arrangements have been tested: solely based on CP and those where the CP phase is covered with a poly(vinyl chloride) based outer membrane. The former system has been tailored to suppress or compensate both cation- and anion-exchange properties, by appropriate using of mobile and immobilized dopants.

The best results, profound stability of potentials and promising electrical properties have been obtained for poly(3,4-ethylenedioxytiophene) or poly(pyrrole) doped by poly(4-styrenesulphonate) anions covered by a poly(vinyl chloride) based membrane, containing both anion- and cation- exchangers as well as solid potassium chloride and silver chloride with metallic silver traces.

 

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Presentation: Tutorial lecture at SMCBS'2005 Workshop, by Krzysztof Maksymiuk
See On-line Journal of SMCBS'2005 Workshop

Submitted: 2005-07-29 10:59
Revised:   2009-06-07 00:44