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Trace metal complexation in natural waters

Trace metal complexation in natural waters. Dario Omanović, Petra Cmuk, Ivanka Pižeta Center for Marine and Environmental Research, Ruđer Bošković Institute, Croatia Yoann Louis, Rudy Nicolau Laboratoire PROTEE, Université de Toulon et du Var BP 132, 83957 La Garde, France

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Trace metal complexation in natural waters

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  1. Trace metal complexation innatural waters • Dario Omanović, Petra Cmuk, Ivanka Pižeta • Center for Marine and Environmental Research, • Ruđer Bošković Institute,Croatia • Yoann Louis, Rudy Nicolau • Laboratoire PROTEE, Université de Toulon et du Var • BP 132, 83957 La Garde, France • Cedric Garnier • LPTC, Université Bordeaux I, 351 Crs. de la Libération, F-33405 Talence CEDEX, France - Pseudopolarography - Metal complexing capacity (MCC)

  2. Distribution of trace metals Operationally defined: • Particulate - > 0.45 µm • Dissolved - < 0.45 µm • Colloidal - between 1 kD and 0.45 µm • Truly dissolved - < 1 kD

  3. Distribution of trace metals Physico-chemical classification: • Inorganic complexes • Organic complexes • Associated to particles

  4. Distribution of trace metals Methodological (electrochemical) classification: • Labile complexes • Mostly inorganic complexes (Cl-, OH-, SO42-, ...) • Fast dissociation rate • Mostly reducable • Inert complexes • Mostly organic complexes • Very stable – high stability constant • Only partly reducable

  5. Electrochemical characteristics Inert complexes Labile complexes

  6. Construction of pseudopolarogram Voltammograms Pseudopolarogram

  7. Model titrations – one ligand

  8. Model titrations – one ligand Experimental: CdCC = 0.970×10-7 M log Kapp = 8.37 Theoretical: CdCC = 1×10-7 M log Kapp = 8.44

  9. Model titrations – two ligands Stability constants @ µ = 0.1 M: Log KCdNTA = 9.76 Log KCdEDTA = 16.4 Theoretically: ΔErev = 0.059*log K / n Exp. for CdNTA: ΔE = 0.320 V log K = 10.8

  10. Model titrations – two ligands Eacc = -0.75 V CdCC = 0.973×10-7 M Eacc = -1.15 V CdCC = 0.503×10-7 M

  11. Seawater sample – addition of NTA • CADMIUM • Fast complexation with NTA • Two separate peaks of labile Cd and CdNTA

  12. Seawater sample – addition of EDTA • CADMIUM • Very slow complexation with EDTA (cca. 3 h) • Two separate peaks of labile Cd and CdEDTA

  13. Seawater sample – “not clean” (Šibenik) Copper Eacc = -0.45 V No separated well defined waves CuCC = 4.2×10-8 M Log Kapp = 9.2

  14. Seawater sample – “clean” (Zlarin) Copper Two well separated waves: - labile copper complexes @ E = -0.34 V - inert copper complexes@ E = -1.40 V

  15. Experimental setup - parameters Copper - “clean“ seawater (Zlarin) Eacc = -1.6 V, tacc = 300 s Eacc = -0.45 V, tacc = 297 s and Eacc = -1.6 V, tacc = 3 s Eacc = -0.45 V, tacc = 300 s

  16. Experimental setup - parameters Copper - “clean“ seawater (Zlarin)

  17. Seawater sample – “clean” (Zlarin) Cadmium without well separated waves

  18. Conclusion • Pseudopolarography is a tool for the characterisation of an interaction of trace metal ions in natural samples • It is the “fingerprint” of the sample • The position and the shape of the waves give us additional information about complexing ability of the particular natural sample • It is very useful in complexing capacity determination measurements • The composition of natural water samples is very complex and, unfortunatelly, it is very hard to obtain behaviours like in model solutions • Additional efforts should be done to resolve problems associated with the experimental setup as well as to interpret data regarding both pseudopolarograms and metal complexing capacity determination

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