الفهرس 
ACKNOWLEDGMENTS
Environmental Pollution and Environmental AnalysisOnly 14 pages are availabe for public view
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Abstract
CHAPTER THREE
3. RESULTS AND DISCUSSION
3.1 Spectrophotometric Determination of Copper (II), Zinc (II) or Manganese (II):
A simple spectrophotometric method has been developed for the determination of copper (II), zinc (II) or manganese in solution. The method is based on the ternary metal complexes formed with Alizarin Complexon (Alizarin–3–methylamine–N, N–diacetic acid, AC) and Fluoride ion. The molar absorptivity at the max for each analyte is given. The ternary complexes formed have the same stoichiometric ratio 1:1:1 (M–AC–F). The ternary complexes formed at pH 5.0 allow precise and accurate determination of Cu(II), Zn(II) and Mn(II) in the ranges of 1.30–15.8, 1.25–13.2 and 1.2–13.7 g ml–1 respectively.
3.1.1 Acid–base properties of AC:
In ethanol water mixtures containing 40% (/) ethanol and at pH 3.2–10.5, AC exists in five different forms (LH4, LH–3, LH22–, LH3– and L4–), exhibiting the absorbance maxima at 270, 335, 423, 525 and 580nm, respectively. The mean pKa values of the reagent are pKa1 (LH4/LH–3) = 4.5, pKa2 (LH–3/ LH22–) = 5.0, pKa3 (LH22–/LH3–) = 5.4, and pKa4 (LH3–, L4–) = 8.5, I = 0.1, 25 ºC [182].
3.1.2 Absorption spectra and optimum pH:
The visible spectra of Alizarin complexone (AC, 2×10–4M) show an absorption band at 423 nm within the pH
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range 4.8–5.2 The spectrum of fluoride (2×10–4 M) exhibits no measurable absorbance in the visible region and there are no significant changes in colour or absorbance in the presence of Cu(II),Zn(II) or Mn(II) ions. However, the solution containing AC and F– undergoes an observable change in colour from yellowish brown to violet when mixed with Cu (II), Zn (II) or Mn (II) ions. The spectrum of the reaction mixture against a blank solution containing the same concentration of the two ligands exhibits a new band at 507, 504, or 520 nm for solutions containing Cu(II), Zn(II) or Mn(II) respectively. The latter bands are unambiguously due to the formation of mixed–ligand complexes of the metal ion studied with Alizarin Complexone and Fluoride ion, with maximum colour development at pH = 5.0 (Fig. 1).
3.1.3 Stoichiometry of the complexes:
Job’s method of continuous variation [181] was applied to establish the molar composition of Cu (II)–AC–F, Zn (II)–AC–F or Mn (II)–AC–F mixed ligand complexes. The molar fractions of two of the components were varied continuously, keeping their combined concentration constant, while keeping the third component in a large excess for all solutions in the series. Under such conditions, the ternary system was modified to a quasi–binary system. The results shown, in
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Figs. (2–5) for copper, Figs. (6–9) for zinc, and Figs. (10–13) for manganese complexes, indicate that the overall composition of (M–AC–F) complexes is (1:1:1) at the pH studied.
Taking into the account the pKa values of Alizarin Complexone, and the stoichiometric composition of the ternary complexes, the complexation equilibria will proceed according to the following reaction.
M2+ + H2L2– + F– = MLF3– + 2H+
where M2+ = Cu2+ , Zn2+ , Mn2+
3.1.4 Spectrophotometric determination of Cu(II), Zn(II) or Mn(II):
A standard solution containing 30–375 g of copper, zinc or manganese was introduced into a 25 mL calibrated flask, then 5 ml of 2.5×10–3 M AC and 5 ml of F– ion (2.5×10–3 M) were added. Dilute perchloric acid or sodium hydroxide was added to adjust the pH at 5.0 , 2.5 ml of 0.1 NaClO4 were added, then the solution was diluted to the volume with doubly distilled water and the request amount of ethanol (40% /). After thoroughly mixing the reaction mixture, the absorption spectra are recorded from 400–700,
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against a reagent blank similarly prepared but containing no metal ions (Figs. 14–16). Measure the absorbance at max 507, 504 or 520 nm to determine Cu(II), Zn(II) or Mn(II) respectively.