Stability Constants of Iron and Zinc Chelates

An investigation was carried out to determine the stability constants of iron and zinc with chelating agents like EDTA, DTPA, CDTA, EDDHA and fulvic acid at pH 5.0 and 7.0. It was found that the log K values of the two elements decreased from pH 5.0 to 7.0. The relative efficacies of the chelating agents can beascertained from the decreasing order of thelog K values of the two elements. Fe³⁺: EDDHA > EDTA >CDTA > DTPA > FA at pH 5.0 and EDDHA > CDTA > DTPA > EDTA >FA at pH 7.0. Zn²⁺: DTPA > F >A > CDTA > EDDHA > EDTA at pH 5.0 and FA > EDDHA > CDTA > DTPA > EDTA at pH 7.0.