A new colorimetric chemosensors for Cu2+ and Cd2+ ions detection: Application in environmental water samples and analytical method validation

- Detection of Cu2+ and Cd2+ ions has gained significance by virtue of its key role in biological and environmental science.
- The R3 and R4 showed instantaneous color change from colorless to yellow in the presence of Cu2+ and Cd2+ ions respectively.
- The proposed detection methods were validated and successfully applied to the different environmental water samples.
- R3 and R4 showed high selectivity of towards Cu2+ and Cd2+ ions in the presence of other tested cations and anions.
- Detection limit of 2.8 μM for Cu2+ ions and 0.20 μM for Cd2+ ions with good linear range is obtained for R3 and R4.

A new heterocyclic thiophene-2-caboxylic acid hydrazide based chemosensor R1 to R4 were designed, synthesized and characterized by various spectroscopic techniques like FT-IR, UV-Vis, 1H NMR, 13C NMR, Mass and SC-XRD. The chemosensor R3 showed a significant color change from colorless to yellow in the presence of Cu2+ ions and chemosensor R4 showed a significant color change from colorless to yellow in the presence of Cd2+ ions over the other tested cations such as Cr3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Zn2+, Ag2+, Al3+, Pb2+, Hg2+, K+, Ca2+ and Mg2+. The high selective and sensitivity of R3 towards Cu2+ and R4 towards Cd2+ ions was confirmed by UV-Vis spectroscopic study. The R3 showed a red shift in the presence of Cu2+ ions by Δλmax 67 nm and R4 showed a red shift in the presence of Cd2+ ions by Δλmax 105 nm in the absorption spectrum. The binding stoichiometric ratio of the complex between R3 - Cu2+ and R4 - Cd2+ ions have been found to be 1:1 using the B-H plot. Under optimized experimental conditions, the R3 and R4 exhibits a dynamic linear absorption response range, from 0 to 50 μM for Cu2+ ions and 0 to 30 μM for Cd2+ ions, with the detection limit of 2.8 × 10−6 M for Cu2+ and 2.0 × 10−7 M for Cd2+ ions. The proposed analytical method for the quantitative determination of Cu2+ and Cd2+ ions was validated and successfully applied for the environmental samples with good precision and accuracy.

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