Objective: Influence of ionic strength on the proton-ligand stability constants and metal-stability constants of Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) with 3-(((2-hydroxyquinolin-3-yl) methylene) hydrazono) indolin-2-one (HQMHI). Material and methods: The interaction of Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) metal ions with 3-(((2-hydroxyquinolin-3-yl) methylene) hydrazono) indolin-2-one (HQMHI). has been investigated in aqueous, ethanol-water (25% v/v) and dioxane-water (25% v/v) mixtures at different ionic strengths (0.1 M and 0.2 M) of NaNO3 at temperature 30 ± 1 oC by potentiometric titration. Findings and conclusion: The data obtained is used to calculate the values of proton-ligand stability constants and metal-ligand stability constants. The pKa and stability constants values decreased with increase in ionic strength and the polarity of the media, which indicated the opposite charges on reacting species.
