Antec Scientific VT-03, User Manual, Page: 6 / 36

6 VT03 flow cell user manual, ed. 8
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 only well defined 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 stabilises the working potential and the AUX can supply high currents.
This results in the tremendous dynamic range of a three-electrode system.
Working electrode
Electrochemical detection puts high demands on the WE material. The WE
should be made of a (electro-)chemically 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 oxidised (or
reduced) with favourable I/E characteristics. This in fact means that a high
signal must be obtained at a low working potential. For most applications
glassy carbon will be the WE material of choice. Under certain circumstances
other materials are favourable.
For example, for the analysis of iodide a silver WE can be used. At the silver
WE the following oxidation reaction occurs for iodide:
Ag + I
-
→
AgI + e
-
This reaction already takes place at a very low working potential (1 mV !),
which results in an extremely high selectivity. This allows the determination of
iodide in urine samples to take place almost without any sample pre-
treatment.