Chemistry Reference
In-Depth Information
2
Electrochemical methods
P. WESTBROEK
2.1
Introduction
Electrochemical methods include potentiometry, cyclic voltammetry and
chronoamperometry. These methods as well as other voltammetric methods
and the impedance of electrochemical systems are discussed in this chapter.
2.2
Potentiometry
2.2.1
Introduction
A galvanic cell produces a potential which is in relation with the concen-
tration of an electroactive species, given by the Nernst equation. This equa-
tion provides a quantitative relationship between potential and the ratio of
activities (
a
O
/
a
R
) or, in a simplified form, the ratio of the concentrations for
a redox couple ([O]/[R]), and is the basis for potentiometry and potentio-
metric titrations
1-3
. Despite the comparatively late development of poten-
tiometry, the application of potentiometric measurements for analytical
purposes was established with the development of the glass electrode in
1909 for a selective potentiometric response to hydronium ion concentra-
tions. A second milestone in the development of potentiometric measure-
ments was the introduction of the hydrogen electrode for the measurement
of hydronium ion concentrations, which was also of significant use for other
electrochemical methods. The potential of the H
2
/H
+
equilibrium at pla-
tinised platinum electrodes became the reference point of the potential
scale. Subsequent development of special glass formulations has made it
possible to have electrodes that are selective to different monovalent
cations. This also led to the development of electrodes that are selective for
many cations and anions, as well as several gas- and bioselective electrodes
4
.
The use of these electrodes and the potentiometric measurement of pH
continue to be among the most important applications of electrochemistry.
The pH electrode is discussed in more detail in Chapter 3.
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