Complex-forming properties of natural organic acids Fulvic acid complexes with cobalt, zinc and europium

The complex-forming properties of a fulvic acid sample have been studied by an ion-exchange distribution method. The results have been analysed by a novel physicochemical approach which attempts to take into account complications introduced by the polyelectrolyte nature and functional heterogeneity of the fulvic acid molecule. These studies with trace level concentrations of cobalt, zinc and europium show that these metal ions are selectively complexed by the weakly acidic enol grouping of the fulvic acid molecule. The logarithms of the stability constants (β 1 ) for the cobalt, zinc and europium chelates are 6.5, 6.4 and 10.3 respectively.