The fully protonated PDMA has a charge of +2 (H5PDMA 2+ ), while fully deprotonated PDMA has a charge of -3 (PDMA 3-) and is able to complex divalent ions. Both PDMA and monoprotonated PDMA are able to chelate Zn II or other divalent ions yielding complexes with a net charge of -1, i.e. [Zn(PDMA)] -for the former and a neutral complexes for the latter. In this study, only three of possible five protonation constants of PDMA were determined by potentiometric titrations because the last two protonation steps (H4PDMA + and H5PDMA 2+ ) happen at pH < 2, too low to be accurately determined by potentiometric titrations. The protonation constant values of H3PDMA, H2PDMA -, HPDMA 2-(Table ) are in agreement with those determined by Suzuki et al. . These three protonation steps occur on the two amine and one of the carboxylate groups. . They are also commonly found in the formulation of mineral fertilizers used in agriculture increasing their concentration in soil and hence the possible competition with Zn II for PDMA.