Determination of Iron Speciation by Cathodic Stripping Voltammetry in Seawater Using the Competing Ligand 2-(2-Thiazolylazo)-p-cresol (TAC)

Abstract

A new sensitive competitive ligand exchange‐adsorptive cathodic stripping voltammetric (CLE‐ACSV) method for the determination of iron speciation in seawater has been developed using the iron binding ligand TAC 2‐(2‐thiazolylazo)‐p‐cresol. An earlier method for determining iron using TAC [1] was reexamined and optimized for measurements in seawater at pH 8.0. The sensitivity was improved by employing a fast (10.12 V/s) linear sweep scan waveform. The detection limit (3σ of blank) is 0.10 nM after an adsorption time of 300 s; the detection limit can be lowered, however, by using a longer deposition time or for the determination of total iron, by increasing the pH to 8.5. This method was applied to samples from Swedish coastal waters and the results indicate the possible efflux of iron binding ligands from sediments in coastal waters.

An Intercomparison of Dissolved Iron Speciation at the Bermuda Atlantic Time-series Study (BATS) Site: Results from GEOTRACES Crossover Station A

“…The competing ligand "TAC" was used with a final concentration of 10 µM, resulting in α Fe(TAC) 2 of 251 as the center of the analytical window. The Fe(TAC) 2 complex was measured after equilibration (> 6 h) by adsorptive cathodic stripping voltammetry (AdCSV) (Croot and Johansson, 2000). Each of the 14 sub-samples was measured twice, resulting in a total of 28 titration data points.…”

“…Fe-binding ligand concentrations and their conditional stability constants in seawater are typically determined using competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV) techniques (Gledhill and van den Berg, 1994;Rue and Bruland, 1995;Croot and Johansson, 2000). These techniques involve equilibrating filtered and buffered seawater samples with a range of inorganic DFe additions and a single concentration addition of a well-characterized competing (or "added") ligand before analysis of each titration point by AdCSV on a hanging mercury drop electrode.…”

Distribution and Speciation of Dissolved Iron in Jiaozhou Bay (Yellow Sea, China)

“…The concentrations of L t vary widely in marine environment: for open oceans, L t concentration is low, e.g., 0.44 nM was observed in Indian Sector of the Southern Ocean (Gerringa et al, 2008), 17.6 nM was observed in the Atlantic Sector of the Southern Ocean (Croot and Johansson, 2000), and range from 0.09 to 0.77 nM in Central N Pacific (Rue and Bruland, 1995). In coastal waters, the L t is higher than in the open ocean, whereas the highest concentrations of L t were observed in the estuary areas and river plumes [e.g., 526 nM in the Scheldt Estuary; 4.3-64.1 nM in the Mississippi River plume (Powell and WilsonFinelli, 2003;Gerringa et al, 2007)].…”

Organic Matter Controls of Iron Incorporation in Growing Sea Ice

“…A significant amount of DFe (30 µM) was added to these 2 solutions, without addition of organic ligands (e.g., EDTA) to balance the addition of DFe and keep it in solution. Organic ligands can be produced in situ by sea-ice algae and bacteria (Lannuzel et al, 2015) or supplied externally from e.g., sediment resuspension (Croot and Johansson, 2000;Buck et al, 2007). EDTA is synthetically produced and is therefore not an adequate model ligand of the natural environment.…”

“…EPS are a good candidate for metallic anion binding (Croot and Johansson, 2000;Verdugo et al, 2004) given their high stickiness and negatively charged surfaces (Decho, 1990;Underwood et al, 2010). EPS exist in a continuum of sizes from dissolved and colloidal to particulate fractions (Verdugo et al, 2004), and therefore may control the enrichment of all Fe size fractions in sea ice.…”