Lecture 312.755

Chemical Speciation cont.Note: Review paper Vraspir and Butler 2009

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Some general paper topic areas

• Specific geochemistry of element(s)• Sources/sinks (rivers, dust, hydrothermal, 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• Metalloenzyme(s) and the relationship(s) to biogeochemical function/processes• Policy of Iron Fertilization and other climate mitigation proposals• Marine Pollution• Redox processes• Toxicology• Application of Modeling Studies

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Morel, Allen, Saito, Treatise on Geochemisrty 2003

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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)• Flow Injection/Chemiluminescence/Spectrophotometry• Electrochemistry (Voltammetry)

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Types of Electrochemical Analyses

• 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• 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

• e.g. -1.4 to -0.4 V

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Bruland 1988

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Calibration of the Synthetic Ligand with EDTA

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Kinetics of Competitive Ligand Exchange

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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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From Vraspir and Butler 2009

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In culture, copper ligands are produced by cyanobacteriaMoffett 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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From Buck and Bruland 2007The physiochemical speciation of dissolved iron

in the Bering Sea, AlaskaLimnol 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.”

• FeL1 as a nutritional source?

• How do phytoplankton acquire iron and other bioactive metals?

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