Practical Strategy for Arsenic(III) Electroanalysis without Modifier in Natural Water: Triggered by Iron Group Ions in Solution.

Significant progress has been made in nanomaterial-modified electrodes for highly efficient electroanalysis of arsenic(III) (As(III)). However, the modifiers prepared using some physical methods may easily fall off, and active sites are not uniform, causing the potential instability of the modified electrode. This work first reports a promising practical strategy without any modifiers via utilizing only soluble Fe as a trigger to detect trace-level As(III) in natural water. This method reaches an actual detection limit of 1 ppb on bare glassy carbon electrodes and a sensitivity of 0.296 μA ppb with excellent stability. Kinetic simulations and experimental evidence confirm the codeposition mechanism that Fe is preferentially deposited as Fe, which are active sites to adsorb As(III) and H on the electrode surface. This facilitates the formation of AsH, which could further react with Fe to produce more As and Fe. Meanwhile, the produced Fe can also accelerate the efficient enrichment of As. Remarkably, the proposed sensing mechanism is a general rule for the electroanalysis of As(III) that is triggered by iron group ions (Fe, Fe, Co, and Ni). The interference analysis of coexisting ions (Cu, Zn, Al, Hg, Cd, Pb, SO, NO, Cl, and F) indicates that only Cu, Pb, and F showed inhibitory effects on As(III) due to the competition of active sites. Surprisingly, adding iron power effectively eliminates the interference of Cu in natural water, achieving a higher sensitivity for 1-15 ppb As(III) (0.487 μA ppb). This study provides effective solutions to overcome the potential instability of modified electrodes and offers a practical sensing platform for analyzing other heavy-metal anions.