Metrohm 2.946.0010, Manual

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7.4 Some voltammetric troubles in detail
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current at positive potentials is due to the oxidation of the electrode mate-
rial, in this case gold. Oxidation of the electrode material means dissolu-
tion of the working electrode and as a consequence reduced lifetime of
the electrode. The presence of chloride facilitates the oxidation of gold
due to the formation of AuCl and AuCl
3
. These complexes can form easier
the more chloride is present in the measuring solution. Therefore, less pos-
itive potentials are necessary to oxidize the gold when the concentration
of chloride is high.
Figure 17 Influence of chloride concentration on the background cur-
rent of the scTRACE Gold electrode. (Measuring solution
c(H
2
SO
4
) = 1 mmol/L with 5, 50 and 500 mmol/L KCl)
c(KCl) = 5 mmol/L c(KCl) = 50 mmol/L
c(KCl) = 500 mmol/L
For a determination this means care has to be taken about the chloride
concentration of the sample. In the voltammetric parameters of the
method rather positive potentials can be found in the cyclovoltammetric
and potentiostatic pretreatment, which are used for cleaning purposes.
These potentials are chosen with respect to the chloride concentration
given by the electrolyte solution. If additional chloride, which exceeds the
amount added by the electrolyte, is introduced by the sample matrix,
either the concentration of chloride in the electrolyte has to be reduced or
the potentials in the voltammetric parameters have to be adapted in order
to avoid damage to the working electrode.