A novel carboxamide-based colorimetric chemosensor ATA-Msal ((E)-3-((2-hydroxy-3-methoxybenzylidene)amino) thiophene-2-carboxamide) for detecting Cu 2 + and Co 2 + in aqueous solution was synthesized. Sensor ATA-Msal could probe Cu 2 + and Co 2 + by color change from colorless to pale yellow. According to results of Job plot and ESI-mass, the binding modes of ATA-Msal to Cu 2 + and Co 2 + were determined to be a 1 : 1 ratio. The detection limits (0.14 μM and 0.88 μM) of ATA-Msal for Cu 2 + and Co 2 + were much lower than WHO standard (31.5 μM for Cu 2 + ) and US Environmental Protection Agency (EPA) standard (1.70 μM for Co 2 + ). ATA-Msal can be applicable to real samples and test strips, and F À could be used to distinguish between ATA-Msal -Cu 2 + and ATA-Msal -Co 2 + . The sensing process of Cu 2 + and Co 2 + by ATA-Msal was demonstrated by UV-vis titration, ESI-mass, EPR, 1 H NMR titration, and DFT. Results and DiscussionATA-Msal was gained by the combination of 3-aminothiophene-2-carboxamide and 2-hydroxy-3-methoxybenzaldehyde with 29 % yield in ethanol (Scheme 1). It was characterized by 1 H NMR ( Figure S1), 13 C NMR ( Figure S2) and ESI-mass analysis.

A water‐applicable hexamethylbenzene (HMB) chemosensor, (E)‐2‐((2‐hydroxy‐3‐methoxybenzylidene)amino)benzamide, displayed a selective colour change from colourless to yellow in the existence of copper ions. The detection limit was computed as 1.57 μmol/L, which is substantially lower than the World Health Organisation guideline (31.5 μmol/L) for copper ions. Probe HMB could also sense and quantify copper ions in real water samples. The coordination mode of HMB to copper ions was demonstrated through Job plot, electrospray ionisation mass spectroscopy and proton nuclear magnetic resonance titration, and was also supported by theoretical studies.

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