Chemistry Reference
In-Depth Information
PVC
mantle
Epoxy
resin
Electrode
material
Copper
piece
1.7
Scheme of the construction of micro electrodes starting from a
rod of the electrode material, a copper base, a PVC moulding and
epoxy resin.
where
N
is the collection efficiency,
I
R
is the ring current (density), and
I
D
is the disc current (density). The collection efficiency is dependent on the
geometry of the ring-disc electrode (radius of the disc, gap between disc
and ring and the thickness of the ring) and can be determined by using a
reversible system such as [Fe(CN)
6
]
4-
|
[Fe(CN)
6
]
3-
.Typical values of
N
for a
well-constructed ring-disc electrode vary around 0.25.
Flow electrodes
45
Alternatively, the solution can be moved, rather than the electrode, by a
solution flow passing a stationary electrode. Flow electrodes are described
in different setups and shapes. The main reasons for using these electrodes
are that, depending on the flow rate, a steady state will be obtained (time-
independent current signal), and that these electrodes are very useful for
analysis of continuous flow of solution. A typical scheme for such an elec-
trode setup is shown in Fig. 1.8. A very important condition that needs to
be fulfilled in flow electrodes is that there is no turbulent behaviour because
this would seriously disturb the measured signal.
Wall-jet disc electrode
46
Electrodes can also be positioned in a wall-jet disc electrode configuration,
a home prepared construction, schematically shown in Fig. 1.9. From a small
bath (1) with a capacity of about 3 l, solution is taken by an EHEIM pump
