A novel colorimetric chemosensor for multiple target metal ions Fe²⁺, Co²⁺, and Cu²⁺ in a near-perfect aqueous solution: Experimental and theoretical studies

A selective and multifunctional chemosensor 1 for Fe²⁺, Co²⁺ and Cu²⁺ was designed and synthesized. 1 could simultaneously detect Fe²⁺, Co²⁺ and Cu²⁺ by changing its color from colorless to pink (Fe²⁺) and to yellow (Co²⁺ and Cu²⁺), respectively, in a near-perfect aqueous solution. The binding modes of 1 to Fe²⁺, Co²⁺ and Cu²⁺ were determined to be a 1:1, 2:1, and 1:1, respectively, through Job plot and ESI-mass spectrometry analysis. The detection limits (0.43 μM, 0.11 μM and 0.28 μM) of 1 for Fe²⁺, Co²⁺ and Cu²⁺ were much lower than the US Environmental Protection Agency (EPA) guidelines (5.36 μM for Fe²⁺ and 1.7 μM for Co²⁺) and the WHO guideline (31.5 μM for Cu²⁺) for the drinking water. Moreover, the chemosensor 1 could be used to quantify Fe²⁺, Co²⁺ and Cu²⁺ in water samples, and applied to test kits for detecting Fe²⁺, Co²⁺ and Cu²⁺. The sensing mechanisms of Co²⁺ and Cu²⁺ by 1 were supported by theoretical calculations.