Determination of Labile Iron at Low nmol L⁻¹ Levels in Estuarine and Coastal Waters by Anodic Stripping Voltammetry

Abstract

A new method is presented for the determination of electrochemically labile iron in estuarine and coastal seawater. The method is based on differential pulse anodic stripping voltammetry (DPASV) at a rotating silver-alloy disk electrode. The voltammetric parameters include a plating potential of À 1.5 V and an activation potential of À 5 V for 10s; the seawater is at the original sample pH. The main finding is the presence of a peak for low nmol L À1 levels of iron at À 0.55 V ascribed to elemental iron deposited on the bare silver alloy electrode. The peak increased linearly with the iron concentration between < 1 and 14 nmol L À1 using a 900 s plating time. At higher concentrations an additional iron peak appeared at À 0.7 V which was also found to increase linearly with the iron concentration but at a higher concentration range from ca. 15 to 90 nmol L À1 using a 300 s plating time. The second peak was ascribed to iron deposited on iron. Additions of chelating agents (EDTA and a siderophore) to seawater caused the iron peak to be masked indicating that this method is suitable for iron speciation as only the electrochemically labile fraction is determined. The detection limit was 0.3 nmol L À1 using a 900 s plating time. The method was used to determine iron in the range of 5 to 50 nmol L À1 in samples from the Mersey estuary near Liverpool and its potential use for in situ monitoring was demonstrated by using it to monitor labile iron (at 2 -3 nmol L À1) over a period of 4 days at 1 h intervals in coastal waters in the Trondheim fjord, Norway.

Modeling organic iron-binding ligands in a three-dimensional biogeochemical ocean model

“…Are external sources of ligands, e.g. from rivers (Mikkelsen et al, 2006;Rijkenberg et al, 2006) important for the open ocean? Despite this complexity, a general paradigm for ligand cycling has emerged (Hunter and Boyd, 2007;Gledhill and Buck, 2012) that contradicts how ligands are currently simulated in OGCBMs.…”

Automatic Voltammetric System for Continuous Trace Metal Monitoring in Various Environmental Samples

“…The stripping peak for iron appears around À 650 mV and origins from the reoxidation of iron deposited on the solid amalgam electrode surface; Fe 0 ! Fe 2þ þ 2e À [34], which is a typical feature of the solid dental amalgam electrode compare to mercury drop or mercury film electrode where large overpotentials are needed for depositing iron [35].…”

Electrochemical techniques and sensors for ocean research

“…Depending on the nature of the analyte different modes of stripping analysis are used. Anodic stripping voltammetry employs a mercury drop electrode, a mercury film electrode (Mikkelsen et al, 2006;Luther et al, 2008) or sometimes just a bare electrode (Bartlett et al, 2000). This technique is very sensitive and allows the detection of metal ions down to 10 −11 M (Tercier-Waeber et al, 1999).…”

“…labile Fe (Mikkelsen et al, 2006), Co (Vega and van den Berg, 1997), Ni, Sb, V, Se, Sn, U (van den Berg et al, 1991) and the list of species detected with electrochemical sensors will grow beyond H + (Reimers, 2007), dissolved oxygen, heavy metals where some of the sensors are at a technology readiness level of 7 with the detection of Cu, Pb and Cd concentrations at sub nM levels (Tercier-Waeber et al, 1999), carbonates (Choi et al, 2002), silicates (Lacombe et al, 2007), in situ speciation of Mn, Fe and in S compounds (Luther et al, 1998;Rozan et al, 1999Rozan et al, , 2000.…”