Figure 5A: Cyclic voltammograms of 50 μM EN at the TX-100/CPE in different pH: (a) 5.5; (b) 6.0; (c) 6.5; (d) 7.0; (e) 7.5; (f) 8.0; (g) 8.5. Inset shows the graph of peak potential versus pH.