Chemistry Reference
In-Depth Information
1200
1000
800
600
400
200
0
0
0.2
0.4
0.6
0.8
1
Concentration (mol l
-1
)
4.4
Calibration curve of the hydrogen peroxide oxidation with a
glassy-carbon electrode at
E
=
0.45 V vs. SCE. pH
=
11.45 and
T
=
298.0 K.
relation is not linear, and the deviation of the linear behaviour increases as
the hydrogen peroxide concentration increases. Moreover, it was estab-
lished that the voltammetric signal is strongly pH-dependent and that the
relation between the current and the hydrogen peroxide concentration is
also dependent on the pH. Although the possible causes for such behaviour
are not obvious, the prewave in the anodic voltammetric curve of hydrogen
peroxide with glassy carbon also offers perspectives to serve as a basis of a
hydrogen peroxide sensor. Therefore, a detailed study was necessary,
described in the next sections.
4.5.2
Electrode behaviour at high hydrogen
peroxide concentrations
From the preliminary research described in the previous section, it appears
that the small oxidation wave with half-value potential (
E
1/2
) of ca. 0.21 V
vs. SCE offers favourable perspectives for the amperometric determination
of relatively high hydrogen peroxide concentrations. In contrast to the
second oxidation wave with
E
1/2
= 0.76 V vs. SCE, the pseudo-limiting cur-
rents obtained in the prewave do not satisfy the relation of Levich (Chapter
1, Equation 1.15). However, they are almost completely independent of the
rotation rate of the electrode, revealing that these limiting currents are
not controlled by transport of electroactive species but by (an)other
process(es). This is illustrated in Fig. 4.5.
