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

Abstract

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 ionisation – 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. Schuberts 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 K_mn 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 K_mn 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.