Fig. 5. Nyquist plots of MBICl/NiO/NPs/CPE (a), MBICl/CPE (b), NiO/NPs/CPE (c), and CPE (d) in the presence of 500 μmol L− 1 of l-DOPA. Conditions: pH, 6.0; Edc, + 0.5 V vs. Ag/AgCl; Eac, 5 mV; frequency range, 0.1–100000 Hz. The equivalent circuit compatible with the Nyquist diagram in the absence and presence of L-DOPA.Figure optionsDownload full-size imageDownload as PowerPoint slide
The value of m = 0.046 is calculated from Eq. (3). Therefore, the MG262 transfer coefficient (α) is approximately 0.72 for the quasi-reversible electrode process.
Chronoamperometric measurements of l-DOPA at MBICl/NiO/NPs/CPE were carried out by setting the working electrode potential at 600 mV vs. Ag/AgCl/KClsat for the various concentrations of l-DOPA in buffered aqueous solutions (pH 6.0) (Fig. 6A). For an electroactive material (l-DOPA in this case) with a diffusion coefficient of D, the current observed for the electrochemical reaction at the mass transport limited condition is described by the Cottrell equation. Experimental plots of I vs. t−/12 were employed, with the best fits for different concentrations of l-DOPA (Fig. 6B). The slopes of the resulting straight lines were then plotted vs. l-DOPA concentration. From the resulting slope and Cottrell equation the mean value of the D was found to be 1.76 × 10− 6 cm2/s.