Fig. 4. (A) SWASV of 20 μg L⁻¹ Cd(ii) and Pb(ii) in 20 mL of acetate buffer solution (0.1 M, pH 4.5) at the Bi/GCE using a single deposition and stripping step (deposition time: 140 s; deposition potential: −1.2 V; Bi(iii) concentration: 600 μg L⁻¹). (B) SWASV of 20 μg L⁻¹ Cd(ii) and Pb(ii) in 1 mL of acetate buffer solution (0.1 M, pH 5.0) at the Bi/GCE using double deposition and stripping steps (the first electrode is the GCPE, and the second electrode is the GCE). (C) SWASV of 20 μg L⁻¹ Cd(ii) and Pb(ii) in 1 mL of acetate buffer solution (0.1 M, pH 5.0) at the Bi/MWCNT–Nafion/GCE using double deposition and stripping steps (the first electrode is the Bi/GCPE, and the second electrode is the Bi/MWCNT–Nafion/GCE). First deposition step: deposition time: 700 s; deposition potential: −1.2 V; Bi(iii) concentration: 600 μg L⁻¹. Second deposition step: deposition time: 140 s; deposition potential: −1.2 V.