reference electrode (REF) potential by means a “voltage clamp”, an electronic feedback circuit
that compensates for polarization effects at the electrodes.
At the WE, which is kept at virtual ground, the electrochemical reaction takes place (electrons are
transferred at the WE). This results in an electrical current to the I/E converter, which is a special
type of operational amplifier. The output voltage can be measured by an integrator or recorder.
Figure 15–2: Schematic representation of an electrochemical cell with a three-electrode
configuration
Essentially, for the oxidation or reduction reaction, it would be sufficient to use only two
electrodes. However, the three-electrode configuration has several advantages over a two-
electrode configuration. If the working potential would be applied only over an AUX versus the
WE (without REF), the working potential would continuously change due to polarization effects at
the electrodes, resulting in highly unstable working conditions.
If the working potential would be applied only over the REF versus the WE (without AUX), the
working potential would be very well defined. However, the potential of a REF is well defined only
if the current drawn is extremely low (pico-amperes), resulting in a very limited dynamic range.
A three-electrode configuration combines the best of both electrodes. The REF stabilizes the
working potential and the AUX can supply high currents. This results in the tremendous dynamic
range of a three-electrode system.
15.1.3 Working electrode
Electrochemical detection puts high demands on the WE material. The WE should be made of an
electrochemically inert material. Furthermore, to avoid an irregular flow profile over the electrode,
it should have a very well defined surface. Finally, it is important that the analyte of interest can
be oxidized (or reduced) with favorable I/E characteristics. This means that a high signal must be
obtained at a low working potential. For most applications, glassy carbon is the WE material of
December 16, 2021, 715007395 Ver. 00
Page 124
