Chemistry Reference
In-Depth Information
30
5
25
4
20
3
15
2
1
10
5
0
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
E
(V) vs. SCE
-5
7.8
Oxidation of sodium dithionite at a CoTSPc-modified gold
electrode in a pH
=
12 buffer solution containing (1) 9.85
¥
10
-
4
; (2)
1.46
¥
10
-
3
; (3) 1.93
¥
10
-
3
; (4) 2.39
¥
10
-
3
and (5) 2.84
¥
10
-
3
mol l
-
1
of
sodium dithionite.
T
=
298.0 K;
v
=
50 mV s
-
1
.
imately 17%. This can be explained by the fact that the dithionite oxidation
at bare gold occurs with relatively fast kinetics (well-defined, transport-
controlled peak), despite the irreversible behaviour of this reaction. There-
fore, it may be clear that it is not possible to improve significantly on the
kinetics. This partly explains the relatively mild electrocatalytic effect of
CoTSPc. Another reason is that the oxidation of dithionite is performed at
Co(III)TSPc, a species that first needs to be formed at the electrode surface.
From Fig. 7.2, it can be seen that its formation is complete around 0.1 V vs.
Ag|AgCl, the same potential where the oxidation of dithionite at CoTSPc
starts to occur.
Electrocatalysing the oxidation of sodium dithionite has advantageous
consequences for its analytical application, particularly in sensor develop-
ment to monitor the sodium dithionite concentration during processing.
Calibration curves obtained at gold electrodes and CoTSPc-modified gold
electrodes (Fig. 7.8) are shown in Fig. 7.9. The peak currents of these cali-
bration plots are the net peak currents, obtained by subtracting the back-
ground current recorded at
E
= 0V vs. SCE from the experimental peak
current. Note that this background current is dependent on the dithionite
concentration (see Fig. 7.8) for both modified and unmodified electrodes.
