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Lecture 3
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Chemical Speciation in the Oceans
(and beyond)
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Some general paper/proposal topic areas
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Specific geochemistry of element(s)
Particular sources/sinks (rivers, dust, hydrothermal, groundwater or sedimentary)
Influences of metal(s) on primary productivity or other biological processes
Paleoclimate (Cd Zn other tracers in biominerals)
Ancient Ocean/Co-Evolution of Ocean Chemistry and Life
Analytical approaches
Specific metalloenzyme(s) and the relationship(s) to biogeochemical
function/processes
Policy of iron fertilization and other climate mitigation proposals
Aspects of marine pollution
Redox processes
Aspects of metal toxicology
Application of Modeling Studies to trace metal biogeochemistry
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Speciation is also critical to the intracellular environment
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Inorganic Analytical Approaches
• Graphite Furnace Atomic Absorption Spectroscopy (GF-AAS)
– Older technique, often coupled with solvent extraction, not used as
much anymore
• Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
– Quadrapoles, high resolution magnetic sector, multicollector
• Flow Injection/Chemiluminescence/Spectrophotometry
• Electrochemistry (Voltammetry)
• HPLC Electrospray ionization mass spectrometry (organic
molecule component of complex)
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Types of Electrochemical Analyses
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Cathodic Stripping Voltametry (Fe, Co, Ni, Zn, Cu)
– Hanging Mercury Drop Electrode (CSV-HMDE)
– Preconcentrates using adsorption of a metal-Lsynthetic complex
– Reduces the metal (and in some cases the ligand) to generate signal
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e.g. -0.6V to -1.4 V
Anodic Stripping Voltametry (Zn, Cd, Pb)
– Thin Film Mercury Rotating disk electrodes (ASV TF-RDE)
– Preconcentrates using adsorption of elemental metal holding a reduction potential
– No synthetic Ligand needed
– Oxidizes the metal to achieve signal
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e.g. -1.4 to -0.4 V
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Calibration of the Synthetic Ligand with EDTA
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Kinetics of Competitive Ligand Exchange
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A = +Fe
B = + SA
C begin analysis
L’ = unbound ligand
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To actually calculate ligand concentrations, and Kcond titration data is analyzed using
Scatchard plots or van den Berg/Ruzic plot, or non-linear fitting
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Morel, Allen, Saito, Treatise on Geochemisrty 2003
From Vraspir and Butler 2009
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Bruland 1988
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From Buck and Bruland 2007
The physiochemical speciation of dissolved iron
in the Bering Sea, Alaska
Limnol Oceanogr, 2007
“These observations suggest that the
phytoplankton community is readily able to
access dissolved Fe from the FeL1 complex,
resulting in excess L1 between dissolved Fe
and L1 ligand concentrations in samples with
intermediate dissolved Fe, and this is a
seemingly ubiquitous feature of dissolved Fe
cycling in the marine environment.”
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FeL1 as a nutritional source?
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How do phytoplankton acquire iron and
other bioactive metals?
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In culture, copper ligands are produced by cyanobacteria
Moffett and Brand, Limnol Oceanogr, 1996
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Cobalt ligands in seawater have a biological source
(Production of ligands in a Synechococcus feature in the Costa Rica Upwelling Dome
Saito et al., Limnol Oceanogr 2005)
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Competition between metals for ligands
• Nickel affinity > Cobalt
• Nickel is also much more abundant than
cobalt (from Saito and Moffett, 2001)
• How can CoL exist? Turns out it is Co(III)L
KCoL
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LC-MS Detection of siderophores in seawater (nutrient enriched incubations)
Gledhill et al., Marine Chemistry 2004
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