Abstract
The interaction of the dye acid alizarin violet (AVN) with three transition metals was followed spectrophotometrically in water and in micellar solutions of the cationic cetyltrimethylammonium bromide (CTAB), the anionic sodium dode- cyl sulfate (SDS) and the nonionic triton X-100 (TX-100). The stoichiometric ratios for the complexes of AVN with each metal ion were determined by the mole ratio and the continuous variation methods. In water, the metal to dye ratios in the complexes were 1:2, 1:3 and 1:1 for Cu2+, Co2+ and Ni2+, respectively. For Ni2+ the ratio changed to 1:3 in micellar CTAB. All other ratios were unchanged in the three micellar solutions. The formation constant (βn) of the complex in water was 1.00 × 1010 for Cu2+, 4.66 × 1014 for Co2+ and 9.03 × 104 for Ni2+. βn decreased in micellar TX-100: for Cu2+ to 6.88 × 108, for Co2+ to 1.56 × 1014 and for Ni2+ to 8.65 × 104. By contrast, micellar CTAB increased βn for Cu2+ and Ni2+. For Cu2+, the increase was to 5.19 × 1010, but for Ni2+ a large jump was observed, to 1.16 × 1015. For Co2+, βn dropped to 2.16 × 1014 in CTAB. Micellar SDS decreased βn for Cu2+ and Co2+ complexes to 5.38 × 109 and 1.76 × 1014, respectively, but increased that of the Ni2+ complex to 4.40 × 105. These observations were explained in terms of structural properties.
Highlights
Chromogenic ligands have been used in quantitative determinations of heavy metals by spectrophotometric methods [1,2,3]
Cu2+-AVN Figure 1 summarizes the results of the mole ratio method for Cu2+-AVN in water and in the presence of sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX-100)
The addition of CTAB, SDS or TX-100 had no effect on Cu2+-AVN and Co2+-AVN stoichiometry
Summary
Chromogenic ligands have been used in quantitative determinations of heavy metals by spectrophotometric methods [1,2,3]. Mole ratio and continuous variation [2,7,8], have been widely used to study the composition of complexes. The former works well for weakly dissociated complexes and the latter is most useful when the dissociation constant is very large. Azo and hydrazo forms are both significant as evidenced by absorption maxima of metal complexes being somewhat close to those of the hydrazo forms of the reagent giving the highest contrast. The effect of surfactants on the absorption spectra and solubilization of azo dyes has been investigated [4,14,15,16]. This work attempts to shed light on the nature of complex formation between AVN and Cu2+, Ni2+, and Co2+ ions, in water as well as in micellar media
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