Overview
ABSTRACT
Potentiometry allows two main types of measurement: pH and ion or molecule concentration. This article describes the electrodes that allow these measurements. The hydrogen electrode, quinhydrone electrode, antimony electrode, glass electrode, and pH ISFET are described for pH measurements. In the case of ion concentration measurement, the operation of ion indicator electrodes is based either on the exploitation of a redox potential or a membrane potential. The problem of selectivity and the impact on the measurement of the presence of other ions is also addressed. Dissolved gas indicator electrodes have also been described.
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Read the articleAUTHORS
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Nicole JAFFREZIC : Emeritus Research Director, Université Marie et Louis Pasteur, Besançon
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Gérard DURAND : Honorary Professor at École Centrale de Paris - Author of the version published in 2010
INTRODUCTION
The article
Presented in this way, it might appear that the field of application of potentiometry is quite limited. This is clearly not the case.
The measurement of pH, at the origin of the development of potentiometry, still constitutes a privileged field of action (in aqueous media and solvents) (§ 1 ). First, we review the general principles of this measurement, in addition to its very definition, and the means of measuring it.
In most cases, the glass electrode is the ideal measurement medium. However, this is not always the case, especially for complex or corrosive media which do not allow the use of glass. This is why, in addition to the hydrogen electrode, we also mention so-called second type electrodes (quinhydrone, antimony), which can be used as alternatives, as well as the pH ISFET.
The operating characteristics of glass electrodes are described, as they determine the reliability of pH measurement. While the use of a glass electrode combined with a device for automatic delivery of acid or base on either side of a set point can provide a means of continuously controlling the pH of a liquid medium, acidity buffers are more commonly used. The first case is more a matter of industrial processes (where the use of buffers is hardly conceivable), while the second is implemented in analysis and control laboratories. The operating characteristics of buffers and their composition according to the media concerned are described.
Measuring the concentration of ions or molecules greatly extends the possibilities of potentiometry. The principle of measurement is described, along with the general characteristics of ion indicator electrodes (§
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KEYWORDS
pH electrodes | buffer solutions | ion-selective electrodes | dissolved gas indicator electrodes
EDITIONS
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Potentiometry - PH or concentration measurement
pH measurement
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