Development of chemosensor for determination of Hg2+ and Cu2+ ions

In this study, it was aimed to synthesise a new chemosensor for the determination of metal ions in water samples. Especially for the determination of Hg2+ ions, which show toxic effects even at low concentrations, synthesis of a thiourea-based ligand was envisaged since sulfur-containing ligands behave selectively. For this purpose, 1,5-dicinnamylidene-thio carbonohydrazide Schiff base (L), which is expected to form coloured complexes with metal ions as a result of the reaction of thiocarbohydrazide and cinnamaldehyde, was synthesised. FT-IR, 1H-NMR, mass spectra and elemental analysis results were evaluated for the characterization of the ligand. It was observed that the synthesized ligand was selective towards Cu2+ ions as well as Hg2+ ions and gave a distinct colour change from colourless to yellow in the presence of these ions. The sensing properties of L as a chemosensor for the determination of mercury and copper were investigated by UV-Vis absorption spectroscopy. The chemosensor showed a highly selective absorption enhancement response towards mercury and copper ions among all anions and cations examined. The binding stoichiometry of the ligand with Hg2+ and Cu2+ was determined as 2:1 by Job's method. In addition, the binding stoichiometry was supported by 1H-NMR titration and mass spectra. Binding constant (Ka) values were calculated as 2.6x105 M-1 and 2.6x104 M-1 for Hg2+ and Cu2+, respectively, from the Benesi-Hildebrand equation. The detection limits for Hg2+ and Cu2+ ions were found to be 1,1x10-7 M (0,11 μM, 22,1 ppb) and 1,8x10-7 M (0,18 μM, 11,4 ppb), respectively. L-Hg2+ and L-Cu2+ complexes formed by L with these ions exhibit different shades of yellow colour. Therefore, the colour differences were analysed with the CIE Lab standard. For the characterisation of the colours, two different colour spaces (CIELab and CIELuv) were used to calculate and verify that the colour shades for Hg2+ and Cu2+ were distinguishable. In addition, the determination of Hg2+ and Cu2+ concentrations was integrated into a smartphone application for real-time chemosensor applications. Finally, chemosensor has been successfully applied for the determination of Hg2+ and Cu2+ ions in various water samples.