Formation of binary complexes of Pb(II), Cd(II) and Hg(II) with maleic acid in CTAB-water mixtures

Abstract

Complexation of toxic metal ions with maleic acid in (0.0–2.5% w/v) cetyltrimethylammonium bromide (CTAB)–water mixtures has been studied pH-metrically at ambient conditions and an ionic strength of 0.16 mol L-1. The existence of different binary species was established from modelling studies using the computer program MINIQUAD75. The best-fit chemical models were selected based on statistical parameters such as the crystallographic R factor and sum of the squares of residuals in mass-balance equations. The models for binary complex systems contain the chemical species ML2, ML2H and ML3 for Pb(II), Cd(II) and Hg(II) in CTAB–water mixtures. The trend in the variation of stability constants with change in the mole fraction of the medium was explained based on electrostatic and non-electrostatic forces. Distribution of the species with pH at different compositions of CTAB–water mixtures was also presented.