Speciation of L-aspartic acid complexes of Co(II), Ni(II), Cu(II) and Zn(II) in acetonitrile- and ethylene glycol-water mixtures

Chemical speciation of binary complexes of Co(II), Ni(II), Cu(II) and Zn(II) with L-aspartic acid was investigated pH-metrically in acetonitrile- and ethylene glycol-water mixtures. The stability constants were calculated using the computer program MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The models for the binary species contained ML2H2, ML2H and ML2 for Co(II) and Zn(II), ML, ML2H2 and ML2 for Ni(II) and Cu(II) in acetonitrile- and ethylene glycol-water mixtures. The trend in variation of stability constants with change in the dielectric constant of the medium was explained on the basis of electrostatic and non-electrostatic forces. Distribution of the species with pH at different variations (0.0-60.0% v/v) in acetonitrile- and ethylene glycol-water mixtures was also presented.DOI: http://dx.doi.org/10.4314/bcse.v26i2.7