Binary complexes of Mg(II) and Ca(II) in water–surfactant mixtures

Abstract

Chemical speciation of Mg(II) and Ca(II) complexes of L-histidine in the presence of water–surfactant mixtures in the concentration range 0.0–2.5% w/v CTAB and SDS, 0.0–5.0% v/v TX-100 maintaining an ionic strength of 0.16 mol dm^?3 at 303 K has been studied pH metrically. The active forms of the ligand are LH₃²⁺, LH₂⁺, LH and L^?. The models containing different numbers of species were refined by using the computer program, MINIQUAD75. The predominant species detected were ML₂H₄⁴⁺, ML₂H₃³⁺, ML₂H₂²⁺, and ML₂. The best fit chemical models were arrived at based on statistical parameters. The trend in variation of complex stability constants with change in the composition of the medium is explained on the basis of electrostatic and non-electrostatic forces. The effect of errors in the stability constants was also studied. Chemical speciation was also discussed based on the distribution diagrams.