Speciation of trace metals in seawater by anodic stripping voltammetry: Critical analytical steps

Capodaglio, Gabriele; Scarponi, Giuseppe; Toscano, Giuseppa; Barbante, Carlo; Cescon, Paolo

doi:10.1007/bf00322907

Cited by 48 publications

(26 citation statements)

References 25 publications

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“…The results from this limited shipboard intercomparison indicate that freezing at -20°C is not an ideal form of storage for Cu speciation samples. However, as freezing at -20°C was found to be suitable for Fe speciation sample storage here and suitable for Cu in a previous study (Capodaglio et al 1995), we suggest that this storage technique merits further evaluation for Cu speciation measurements over a broader oceanographic context. Freezing samples to -80°C caused problems and unpredictable trends in Cu speciation measurements, much as it did for Fe.…”

Section: Buck Et Al Geotraces Speciation Intercomparisonmentioning

confidence: 59%

“…Given the time-intensive nature of analyses, however, this is simply not possible in all cases. Alternatively, seawater samples for speciation are stored frozen at -20°C until analysis in the lab; it remains unknown what effect the freezing of seawater samples has on ambient speciation, although other studies reported no difference in Cu speciation results between fresh and frozen (-20°C) samples (Capodaglio et al 1995;Bruland et al 2000).…”

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confidence: 99%

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The organic complexation of iron and copper: an intercomparison of competitive ligand exchange‐adsorptive cathodic stripping voltammetry (CLE‐ACSV) techniques

Buck

Moffett

Barbeau

et al. 2012

Limnology & Ocean Methods

107

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Competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) is used in chemical oceanography to measure the organic complexation of metal ions in seawater. The bioactive trace metals iron, copper, cobalt, nickel, and zinc are all complexed (up to > 99% of iron and copper) by organic ligands in seawater (van den Berg and Nimmo 1987;Coale and Bruland 1988;Bruland 1989;Gledhill and van den Berg 1994;Rue and Bruland 1995;Wu and Luther 1995;Ellwood and van den Berg 2001), which can control solubility and bioavailability of these elements. Measuring the organic complexation of trace metals is, thus, an exceedingly important component of their biogeochemistry. To date, CLE-ACSV is the only widely accepted technique employed for measuring dissolved metalbinding ligand concentrations ([L i ]) in seawater and the conditional stability constants ( ) for their complexes with the metal of interest (M).To accomplish this, CLE-ACSV employs a well-characterized added ligand (AL) to compete against ambient ligands for M over a complete titration of a buffered seawater sample with additions of inorganic metal (M¢; typically from + 0 to + 10 ¥ [M]). Following equilibrium first with the metal additions (typically several hours) and then with the added ligand (minutes to hours), the resulting M(AL) x complex for each titration point is adsorbed to the surface of a hanging mercury drop electrode (HMDE) at a set voltage potential over a deposition time prede- AbstractCharacterization of the speciation of iron and copper is an important objective of the GEOTRACES Science Plan. To incorporate speciation measurements into such a multinational program, standard practices must be adopted that allow data from multiple labs to be synthesized. Competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) is the primary technique employed for measuring metal-binding ligands and determining metal speciation in seawater. The determination of concentrations and conditional stability constants of metal-binding ligands is particularly challenging, as results can be influenced both by experimental conditions and interpretation of titration data. Here, we report an investigation between four laboratories to study the speciation of iron and copper using CLE-ACSV. Samples were collected on the GEOTRACES II intercomparison cruise in the North Pacific Ocean in May 2009 at 30° N, 140° W. This intercomparison was carried out shipboard and included an assessment of the viability of sample preservation by freezing. Results showed that consensus values could be obtained between different labs, but that some existing practices were problematic and require further attention in future work. A series of recommendations emerged from this study that will be useful in implementing multi-investigator programs like GEOTRACES.

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Section: Buck Et Al Geotraces Speciation Intercomparisonmentioning

confidence: 59%

mentioning

confidence: 99%

The organic complexation of iron and copper: an intercomparison of competitive ligand exchange‐adsorptive cathodic stripping voltammetry (CLE‐ACSV) techniques

Buck

Moffett

Barbeau

et al. 2012

Limnology & Ocean Methods

107

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“…It is shown that discrete models of one to three classes of natural ligands are often sufficient to fit experimental data [3,5,13]. Among many, voltammetric techniques such as anodic stripping voltammetry (ASV) and competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV) are widely used because of their excellent sensitivity and selectivity in natural water samples [3,5,6,[8][9][10][11][12][13][14][15]. Both techniques are based on sample titration by metal of interest (usually copper), followed by the mathematical treatment of measured data to obtain one or more conditional stability constants of formed metal complexes and concentrations of corresponding ligands.…”

Section: Introductionmentioning

confidence: 99%

“…Equilibration time during titration is a critical part for the ASV, as well. Very large differences in equilibration time are reported in the literature, ranging from only few minutes to overnight equilibration [3,6,8,9,[12][13][14]23,24]. Checking of signal stability during larger period of time (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Significance of data treatment and experimental setup on the determination of copper complexing parameters by anodic stripping voltammetry

Omanović

Garnier

Louis

et al. 2010

Analytica Chimica Acta

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Different procedures of voltammetric peak intensities determination, as well as various experimental setups were systematically tested on simulated and real experimental data in order to identify critical points in the determination of copper complexation parameters (ligand concentration and conditional stability constant) by anodic stripping voltammetry (ASV). Varieties of titration data sets (Cu(measured)vs. Cu(total)) were fitted by models encompassing discrete sites distribution of one-class and two-class of binding ligands (by PROSECE software). Examination of different procedures for peak intensities determination applied on voltammograms with known preset values revealed that tangent fit (TF) routine should be avoided, as for both simulated and experimental titration data it produced an additional class of strong ligand (actually not present). Peak intensities determination by fitting of the whole voltammogram was found to be the most appropriate, as it provided most reliable complexation parameters. Tests performed on real seawater samples under different experimental conditions revealed that in addition to importance of proper peak intensities determination, an accumulation time (control of the sensitivity) and an equilibration time needed for complete complexation of added copper during titration (control of complexation kinetics) are the keypoints to obtain reliable results free of artefacts. The consequence of overestimation and underestimation of complexing parameters is supported and illustrated by the example of free copper concentrations (the most bioavailable/toxic specie) calculated for all studied cases. Errors up to 80% of underestimation of free copper concentration and almost two orders of magnitude overestimation of conditional stability constant were registered for the simulated case with two ligands.

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Sample Preparation Techniques for Elemental Analysis in Aqueous Matrices

Marin

2000

Encyclopedia of Analytical Chemistry

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The reliability of results obtained from chemical analysis of environmental samples is related to the sample collection and preparation techniques. A succession of stages is required to obtain a result that is both accurate and representative of the initial material. The task begins by taking the appropriate precautions during collection of the liquid and solid samples, and during their later shipment to the laboratory. The environmental conditions in the laboratory where the sample will be prepared are important, as is the quality of the apparatus, containers, glassware, and reagents that are usually used. The preparation of solid waste samples requires the selection of appropriate digestion procedures, apparatus that is of high enough quality to resist the aggressiveness of some inorganic acids, and convenient systems of security for the procedures that are carried out. The information produced by the laboratory should have a high degree of reliability. For this reason, the procedures used usually permit the results obtained to be guaranteed. The more important procedures include the use of certified reference materials (CRM) and participation in interlaboratory programs. Some organizations, for example the United States Environmental Protection Agency (USEPA), have developed and distributed procedures for environmental sample preparation, which are used by many laboratories as normalized methods of reference.

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Speciation of trace metals in seawater by anodic stripping voltammetry: Critical analytical steps

Cited by 48 publications

References 25 publications

The organic complexation of iron and copper: an intercomparison of competitive ligand exchange‐adsorptive cathodic stripping voltammetry (CLE‐ACSV) techniques

The organic complexation of iron and copper: an intercomparison of competitive ligand exchange‐adsorptive cathodic stripping voltammetry (CLE‐ACSV) techniques

Significance of data treatment and experimental setup on the determination of copper complexing parameters by anodic stripping voltammetry

Sample Preparation Techniques for Elemental Analysis in Aqueous Matrices

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