PRE-COATED MERCURY FILM ON GLASSY-CARBON ELECTRODE FOR THE SIMULTANEOUS DETERMINATION OF Cu²⁺, Zn²⁺, Cd²⁺, AND Pb²⁺ IN WATER

Abstract

A mercury film was pre-coated on glassy-carbon electrodes to improve the precision and detection limit of the electrodes in anodic stripping voltammetry. A mixed solution containing 0.1 mg/l Zn^²⁺, 0.01 mg/l Pb^²⁺, 0.01 mg/l Cd^²⁺, and 0.5 mg/l Cu^²⁺ was used to investigate the simultaneous detection of these ions by the electrode. The influence of the base solution pH and the accumulation time on the electrochemical reactions of Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺ were investigated, as well as the effect of the concentration of the film coating solution and the number of mercury coating step on the stripping signals of the four ions. Optimizing the parameters of the pre-coated mercury film improved the precision of the glassy-carbon electrode in evidence. When the base solution pH was 4.68, and the accumulation time was 300 s, the positions of the stripping peaks were optimal, and the peak signals were at a maximum. When the concentration of the film coating solution was 0.03 mol/l HgCl_2, and the mercury coating step was repeated three times, the prepared electrode showed a moderately high elution peak with little noise. The optimized electrode demonstrated superior precision and detection limits in the simultaneous detection of Zn²⁺, Cd²⁺, Pb²⁺, and Cu²⁺, compared with the uncoated electrode. The calibration curves were highly linear with determination coefficients (R²) of 0.9913 (Cu²⁺), 0.9939 (Pb²⁺), 0.9933 (Cd²⁺), and 0.9962 (Zn²⁺); the detection limits (µg/l) were 5 for Cu²⁺, 1 for Pb²⁺, 0.1 for Cd²⁺, and 10 for Zn²⁺, and the relative standard deviations obtained from five replicate experiments were 4.1% (Cu²⁺), 2.1% (Pb²⁺), 2.7% (Cd²⁺), and 3.4% (Zn²⁺). It is reasonable to suppose that the precision and detection limits of this mercury film electrode may meet the requirements for the simultaneous detection of multiple heavy metal ions in water in the natural environment.