Electrochemical sensing of Cr(VI): Leveraging the copper electrode by copper chromium interaction

This work reports the detection of Cr(VI) using a copper electrode without electrode modification, pre-concentration, and the reagent. The electrochemical detection of Cr(VI) was achieved by the interaction between Cr(VI) and the Cu electrode. On exposure chromium adsorbed onto the surface of the copper electrode. The adsorbed chromium passivates the Cu electrode and, in turn, suppresses the original anodic peak current of copper. The electrode coverage by the adsorbed layer varied and resulted in a proportional decrease in the current over the tested range, 10 to 50 µg L^-1, of Cr(VI). The calibration graph was obtained using the linear regression equation y=-0.012x+0.708 and an R² value of 0.998. The tested heavy metal ions Hg²⁺, Co²⁺, Ni²⁺, and Zn²⁺ did not interfere at 10-fold excess than Cr(VI). The analytical figures of merit LOD and LOQ were 0.981 µg L^-1 and 2.974 µg L^-1 respectively. The applicability of the method to quantify Cr(VI) in water samples was examined and validated using a standard AAS method. The relative difference in sample analysis was less than 4%. In the proposed method, the characteristic interaction between the copper electrode and Cr(VI) is manifested to demonstrate that a pristine copper electrode can selectively sense toxic Cr(VI) down to µg L^-1. The electrodes were characterized by XRD, SEM, EDS, and XPS after the Cr(VI) interaction. The detailed characterization confirmed the changes in the surface morphology and facile adsorption of chromium on the copper electrode.

Graphical Abstract