Fig. 8. (A) The oxidation peak current changes of PG/GCE for 5 repetitive measurements in 0.1 M PBS (pH 6.5) containing 2.0 μM Cu²⁺, Cd²⁺ and Hg²⁺. Scan rate: 0.1 V s⁻¹; (B) the changes of oxidation peak current in 0.1 M PBS (pH 6.5) containing 2.0 μM Cu²⁺, Cd²⁺ and Hg²⁺ with five different electrodes prepared in parallel. (C) The changes of oxidation peak current in 0.1 M PBS (pH 6.5) containing 2.0 μM Cu²⁺, Cd²⁺and Hg²⁺ with different soaking time of PG/GCE before initiating the measurement.