Trace metal complexation in natural waters - Pseudopolarography - Metal complexing capacity (MCC) 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, La Garde, France Cedric Garnier LPTC, Université Bordeaux I, 351 Crs. de la Libération, F Talence CEDEX, France

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

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

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

Electrochemical characteristics Labile complexes Inert complexes

Construction of pseudopolarogram VoltammogramsPseudopolarogram

Model titrations – one ligand

Experimental: CdCC = 0.970×10 -7 M log K app = 8.37 Theoretical: CdCC = 1×10-7 M log K app = 8.44

Model titrations – two ligands Stability µ = 0.1 M: Log K CdNTA = 9.76 Log K CdEDTA = 16.4 Theoretically: ΔE rev = 0.059*log K / n Exp. for CdNTA: ΔE = V log K = 10.8

Model titrations – two ligands E acc = V CdCC = 0.973×10 -7 M E acc = V CdCC = 0.503×10 -7 M

Seawater sample – addition of NTA CADMIUM Fast complexation with NTAFast complexation with NTA Two separate peaks of labile Cd and CdNTATwo separate peaks of labile Cd and CdNTA

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

Seawater sample – “not clean” (Šibenik) E acc = V No separated well defined waves CuCC = 4.2×10 -8 M Log K app = 9.2 Copper

Seawater sample – “clean” (Zlarin) Copper Two well separated waves: - labile copper E = V - labile copper E = V - inert copper E = V - inert copper E = V

Experimental setup - parameters E acc = -1.6 V, t acc = 300 s E acc = V, t acc = 300 s E acc = V, t acc = 297 s and E acc = -1.6 V, t acc = 3 s Copper - “clean“ seawater (Zlarin)

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

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

Conclusion Pseudopolarography is a tool for the characterisation of an interaction of trace metal ions in natural samples Pseudopolarography is a tool for the characterisation of an interaction of trace metal ions in natural samples It is the “fingerprint” of the sample 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 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 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 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 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