AI Article Synopsis

  • Increasing evidence shows stabilized Fe(II) linked to organic matter in aquatic environments, but reliable methods to determine its speciation have been lacking, hindering research in Fe biogeochemistry.
  • A new technique involving competitive ligand reverse titration and spectrophotometry was developed to measure Fe(II) organic complexation in natural waters, achieving high sensitivity and precision using a liquid waveguide capillary cell (LWCC).
  • Tests conducted in the Itchen River revealed that Fe(II) is organically complexed at salinities of 0 to 21, with a conditional stability constant value around 8, while no complexation was found at a salinity of 31, showcasing the method’s effectiveness for studying metal speciation in natural

Article Abstract

Whilst there is increasing evidence for the presence of stabilized Fe(II) associated with organic matter in aquatic environments, the absence of a reliable method for determining Fe(II) speciation in solution has inhibited the study of this aspect of Fe biogeochemistry. A technique is described here for the determination of Fe(II) organic complexation in natural waters that is based on competitive ligand reverse titration and a model fit to experimental results, from which ligand concentration and a conditional stability constant can be obtained. Spectrophotometry was used to detect the Ferrozine (FZ) complex with reactive Fe(II), which in combination with a liquid waveguide capillary cell (LWCC) enabled high sensitivity and precision measurements of Fe(II) to be made. A series of samples was collected in the Itchen River in Southampton, UK to test the method at a wide range of salinities including river water. Levels of Fe(II) and total dissolved Fe were within previously reported values for this system. Fe(II) was found to occur organically complexed with values for K'(Fe(II)L) (conditional stability constant for Fe(II)-natural ligand complexes) of ≈8 at salinities between 0 and 21, whilst no measurable complexation was detected at a salinity of 31. This work demonstrates that spectrophotometry can be used in combination with ligand competition to investigate metal speciation in natural waters.

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http://dx.doi.org/10.1016/j.aca.2012.07.014DOI Listing

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