Methodological study on simultaneous determination of lead and cadmium in water by reduced graphene oxide-electrodeposition mercury film modified glassy carbon electrode

Background The pollution of heavy metals such as lead and cadmium in water is receiving increasing attention. Strengthened monitoring and early warning of heavy metals in water is an important part of environmental monitoring in China, so it is necessary to establish a sensitive and rapid detection method.

Objective This study is conducted to establish a new method for simultaneous determination of Pb²⁺ and Cd²⁺ concentrations in water using reduced graphene oxide (rGO)-electrodeposition mercury film modified glassy carbon electrodes (GCE).

Methods Linear cyclic voltammetry was used to reduce graphene oxide on the surface of glassy carbon electrode (GCE) to obtain rGO modified glassy carbon electrode (rGO/GCE). Then rGO/GCE was placed in a 10 mg·L^-1 Hg²⁺ solution, and Hg²⁺ was deposited on the surface of rGO/GCE by electrochemical deposition method to obtain rGO-electrodeposition mercury film modified glassy carbon electrode (rGO-Hg/GCE). Pb²⁺ and Cd²⁺ were detected by a method combining electrochemical deposition and differential pulse voltammetry. The deposition potential, deposition time, and buffer pH of the proposed method were optimized. The linear range and detection limit of Pb²⁺ and Cd²⁺ were determined under the optimal experimental conditions. The accuracy and precision of the method were evaluated, and coexisting ion interference was tested at the same time. The method was applied to the simultaneous detection of lead and cadmium in water samples.

Results When the deposition potential was -1.2 V, the deposition time was 360 s, and the buffer pH was 4.5, the response currents of Pb²⁺ and Cd²⁺ were optimal. The Pb²⁺ concentration within the range of 1.0-50.0 μg·L^-1 showed a good linear relationship with the peak current, the correlation coefficient was 0.997, the detection limit was 0.73 μg·L^-1, the standard recovery was 95.8%-105.6%, and the relative standard deviation was 1.98%-5.01%; the Cd²⁺ concentration within the range of 1.0-50.0 μg·L^-1 showed a good linear relationship with the peak current, the correlation coefficient was 0.998, the detection limit was 0.99 μg·L^-1, the standard recovery was 90.9%-100.7%, and the relative standard deviation was 3.33%-5.71%. Other common cations in water did not interfere with the peak shape and current value of the Pb²⁺ and Cd²⁺ dissolution peaks. In actual waste water samples, the test results by the established method were compared with those by graphite furnace atomic absorption spectrophotometry by paired t test, and there was no significant difference in the results by the two methods (P>0.05).

Conclusion rGO-Hg/GCE has the advantages of simple operation and high sensitivity, and is suitable for simultaneous determination of Pb²⁺ and Cd²⁺ in water samples.