Aswe know, vitamin C can be oxidized at positive potential depending
on the solution pH and type of electrode [55]. The voltammetric response
of vitamin C at a surface of CdO/NPs/ILs/CPE was obtained in
solutionswith varying pH (Fig. 3 inset). The result shows that the oxidation
peak potential of the redox couple was pH dependent with a slope
of −67.5 mV/pH unit at 25°°C which was equal to the anticipated
Nernstian value for a two-electron, two-proton electrochemical reaction.
It can be seen that the maximum oxidation peak current value
was observed at pH 7.0 (Fig. 3), so this value was selected throughout
the experiments.
The effect of scan rate (υ) on the electrochemical oxidation current
of vitamin C was also examined (Fig. 4 inset). The results showed that
the peak current increased linearly with increasing square root of scan
rate that ranged from 10 to 100 mV s−1 (Fig. 4). The result in Fig. 4
shows that the electrode process is controlled under the diffusion step.
The dependence of the oxidation peak potential (Epa) and ln(ν)
showed a linear relationship with a regression equation of: