An effective phthalazine-imidazole-based chemosensor for detecting Cu2+, Co2+ and S2- via the color change

A novel and effective phthalazine-imidazole-based colorimetric chemosensor (E)-1-(2-((1H-imidazol-2-yl)me-thylene)hydrazinyl)phthalazine NNI was synthesized and tested to detect Cu2+ or Co2+ ions in buffer solution. NNI could probe Cu2+ and Co2+ by the color change from colorless to yellow. The complexation stoichiometries of NNI toward Cu2+ and Co2+ were, respectively, confirmed to be as 1:1 ratio and 2:1 by results of Job plot and ESI-mass. Detection limits of NNI for each metal showed 0.12 mu M and 65 nM which are lower than WHO guideline (31.5 mu M for Cu2+) and US Environmental Protection Agency (EPA) guideline (1.7 mu M for Co2+). Quantification of NNI for each metal was successful in real water samples. The Cu2+-NNI complex could detect S2- by demetallation with color change from yellow to colorless, and detection limit for S2- was determined as 0.80 mu M, which is lower than WHO guideline (14.8 mu M). Cu2+-NNI could detect S2- without interference when other anions coexisted. Detection of Cu2+, Co2+ and S2- among various metal ions and anions was successfully confirmed using test papers stained with NNI and Cu2+-NNI. Sensing processes of Cu2+, Co2+ and S2- by NNI were elucidated by UV-vis titration, ESI-mass, FT-IR, H-1 NMR titration and DFT calculations.