Colorimetric Detection of Co²⁺, Cu²⁺, and Zn²⁺ by a Multifunctional Chemosensor in Aqueous Solution

A novel multifunctional colorimetric sensor HMBC ((E)-3-((2-hydroxy-3-methoxybenzylidene)amino)benzofuran-2-carboxamide), based on 3-aminobenzofuran-2-carboxamide and 2-hydroxyl-3-methoxylbenzaldehyde, was designed and synthesized. The chemosensor HMBC could sense Co²⁺, Cu²⁺, and Zn²⁺ by color changes from colorless to yellow. Limits of detection (0.38, 0.41, and 1.02 μM) of HMBC for Co²⁺, Cu²⁺, and Zn²⁺ were much lower than the New Jersey Department of Environmental Protection (NJDEP) standard (1.70 μM) for Co²⁺ and the WHO guidelines (31.5 μM and 76 μM) for Cu²⁺ and Zn²⁺. Significantly, HMBC could be applied for the quantification of Co²⁺, Cu²⁺, and Zn²⁺ in real samples. The sensing process of HMBC for Co²⁺, Cu²⁺, and Zn²⁺ was well demonstrated by ¹H NMR and UV–Visible titrations, Job plots, theoretical calculations, and ESI-mass spectroscopy.