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Interaction of cobalt(II), nickel(II) and zinc(II) with humic-like ligands studied by ESI-MS and ion-exchange method

Kostić Ivana (Faculty of Sciences and Mathematics, Niš)
Anđelković Tatjana (Faculty of Sciences and Mathematics, Niš)
Anđelković Darko (Faculty of Sciences and Mathematics, Niš)
Nikolić Ružica (Faculty of Sciences and Mathematics, Niš)
Bojić Aleksandar (Faculty of Sciences and Mathematics, Niš)
Cvetković Tatjana (Faculty of Medicine, Niš)
Nikolić Goran (Faculty of Technology, Leskovac)

An interaction of Co(II), Ni(II) and Zn(II) with humic acid and O-donor humic-like ligands was studied by ion-exchange and electrospray ionization - mass spectrometry (ESI-MS) method. Interactions were confirmed by differences between values of chromatogram peak areas for monocomponent (ligand) and binary systems (ligand with metal ion) by newly developed ESI-MS 5 μL Loop injection technique. Schubert’s ion exchange method was used for determination of stability constants of formed complexes at pH 4.0 and I = 0.01. Comparing the values of log Kmn for complexes formed by dipositive metal ions with humic, benzoic and salicylic acids, it can be concluded that the interaction strengths of transitional series metals follow the Irving-Williams order: Co(II) < Ni(II) < Cu(II) > Zn(II). The obtained values of log Kmn indicate that Pb(II) ions effect the strongest interactions with all investigated ligands. Complexation of humic acids macromolecules possessing O-donor binding sites as major binding sites can be predicted and modelled following the same order of interaction strength like Irving-Williams order.

Keywords: humic acid, humic-like ligands, heavy metals, ion exchange, ESI-MS

Projekat Ministarstva nauke Republike Srbije, br. III41018