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Organic Copper Speciation by Anodic Stripping Voltammetry in Estuarine Waters With High Dissolved Organic Matter

Pađan, Jasmin; Marcinek, Saša; Cindrić, Ana- Marija; Santinelli, Chiara; Retelletti Brogi, Simona; Radakovitch, Olivier; Garnier, Cédric; Omanović, Dario (2021) Organic Copper Speciation by Anodic Stripping Voltammetry in Estuarine Waters With High Dissolved Organic Matter. Frontiers in chemistry, 8 . ISSN 2296-2646

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The determination of copper (Cu) speciation and its bioavailability in natural waters is an important issue due to its specific role as an essential micronutrient but also a toxic element at elevated concentrations. Here, we report an improved anodic stripping voltammetry (ASV) method for organic Cu speciation, intended to eliminate the important problem of surface-active substances (SAS) interference on the voltammetric signal, hindering measurements in samples with high organic matter concentration. The method relies on the addition of nonionic surfactant Triton-X-100 (T-X-100) at a concentration of 1 mg L−1. T-X-100 competitively inhibits the adsorption of SAS on the Hg electrode, consequently 1) diminishing SAS influence during the deposition step and 2) strongly improving the shape of the stripping Cu peak by eliminating the high background current due to the adsorbed SAS, making the extraction of Cu peak intensities much more convenient. Performed tests revealed that the addition of T-X- 100, in the concentration used here, does not have any influence on the determination of Cu complexation parameters and thus is considered "interference-free." The method was tested using fulvic acid as a model of natural organic matter and applied for the determination of Cu speciation in samples collected in the Arno River estuary (Italy) (in spring and summer), characterized by a high dissolved organic carbon (DOC) concentration (up to 5.2 mgC L−1) and anthropogenic Cu input during the tourist season (up to 48 nM of total dissolved Cu). In all the samples, two classes of ligands (denoted as L1 and L2) were determined in concentrations ranging from 3.5 ± 2.9 to 63 ± 4 nM eq Cu for L1 and 17 ± 4 to 104 ± 7 nM eq Cu for L2, with stability constants logKCu, 1 = 9.6 ± 0.2– 10.8 ± 0.6 and logKCu, 2 = 8.2 ± 0.3–9.0 ± 0.3. Different linear relationships between DOC and total ligand concentrations between the two seasons suggest a higher abundance of organic ligands in the DOM pool in spring, which is linked to a higher input of terrestrial humic substances into the estuary. This implies that terrestrial humic substances represent a significant pool of Cu-binding ligands in the Arno River estuary.

Item Type: Article
Uncontrolled Keywords: Copper speciation ; Anodic stripping voltammetry (ASV) ; Organic ligands ; Estuary
Subjects: NATURAL SCIENCES > Interdisciplinary Natural Sciences
Divisions: Division for Marine and Enviromental Research
Project titleProject leaderProject codeProject type
Novi metodološki pristupbiogeokemijskim istraživanjima specijacije metala u tragovima u obalnim vodenim ekosustavimaOmanović, DarioIP-2014-09-7530HRZZ
Depositing User: Dario Omanović
Date Deposited: 01 Apr 2021 11:39
DOI: 10.3389/fchem.2020.628749

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