Speciation of binary complexes of Co(II), Ni(II), and Cu(II) with L-phenylalanine in anionic micellar medium

Speciation of binary complexes of Co(II), Ni(II), and Cu(II) with L-phenylalanine (Phe) in the presence of water-anionic surfactant mixtures in the concentration range of 0.0-2.5% w/v SLS has been studied pH-metrically at a temperature of 303 K and at an ionic strength of 0.16 mol L-1. The selection of best fit chemical models is based on statistical parameters and residual analysis. The predominant species detected were ML, ML2, and ML2H2 for Co(II), Ni(II), and Cu(II). The trend in the variation of stability constants with the mole fraction of SLS was explained on the basis of electrostatic and non-electrostatic forces. Distribution of the species with pH at different compositions of SLS-water media was also presented.