Simultaneous Detection of Cu²⁺ and Co²⁺ by a Water-Soluble Carboxamide-Based Colorimetric Chemosensor

A novel carboxamide-based colorimetric chemosensor ATA-Msal ((E)-3-((2-hydroxy-3-methoxybenzylidene)amino)thiophene-2-carboxamide) for detecting Cu²⁺ and Co²⁺ in aqueous solution was synthesized. Sensor ATA-Msal could probe Cu²⁺ and Co²⁺ by color change from colorless to pale yellow. According to results of Job plot and ESI-mass, the binding modes of ATA-Msal to Cu²⁺ and Co²⁺ were determined to be a 1 : 1 ratio. The detection limits (0.14 μM and 0.88 μM) of ATA-Msal for Cu²⁺ and Co²⁺ were much lower than WHO standard (31.5 μM for Cu²⁺) and US Environmental Protection Agency (EPA) standard (1.70 μM for Co²⁺). ATA-Msal can be applicable to real samples and test strips, and F⁻ could be used to distinguish between ATA-Msal -Cu²⁺ and ATA-Msal -Co²⁺. The sensing process of Cu²⁺ and Co²⁺ by ATA-Msal was demonstrated by UV-vis titration, ESI-mass, EPR, ¹H NMR titration, and DFT.