Chemical speciation of binary complexes of Pb(II), Cd(II) and Hg(II) with L-glutamic acid in dioxan-water mixtures

Abstract

Binary complexes of L-glutamic acid with toxic metal ions such as Pb(II), Cd(II) and Hg(II) in 0.0-60.0% v/v 1,4 dioxan-water media at 303.0 K and an ionic strength of 0.16 mol dm-3 of sodium nitrate has been studied pH-metrically. The active forms of ligand are LH3, LH2 and LH. The best fit chemical models are chosen based on statistical parameters like crystallographic R-factor, χ2, skewness and kurtosis. The predominant species detected are ML2H4 ML2H3 ML2H2 ML2 and ML. Models containing different numbers of species were refined by using the computer program MINIQUAD75. The trend in variation of complex stability constants with changes in the dielectric constant of the medium is explained on the basis of electrostatic and non-electrostatic forces. The species distribution with pH at different compositions of dioxan–water mixture and plausible equilibria for the formation of species are also presented.