Iron Speciation and Determination Techniques in Environmental Samples

Iron in the environment exists in multiple oxidation states and chemical forms, notably ferrous (Fe2+), ferric (Fe3+) and various organically or mineral-bound complexes. Speciation profoundly influences iron’s mobility, bioavailability, redox cycling and its role in nutrient dynamics or contaminant transport. Analytical strategies have evolved from classical wet-chemical assays—such as colourimetric ligand-complexation and atomic absorption spectroscopy—to sophisticated hyphenated and in situ techniques. High-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) enables separation and quantification of discrete iron species, while electrochemical probes and diffusive gradients in thin films (DGT) yield spatially resolved maps of labile Fe2+ and Fe3+ in waters and sediments. Synchrotron-based X-ray spectroscopies, including X-ray absorption near-edge structure (XANES), offer element-specific oxidation-state determination at micrometre resolution. Recent advances also encompass portable sensors—laser-induced breakdown spectroscopy (LIBS) and field-deployable voltammetric microsystems—that deliver rapid, on-site speciation data. Together, these approaches provide a comprehensive toolkit for understanding iron cycling in aqueous environments, soils, atmospheric aerosols and contaminated sites, with applications ranging from water-quality management to palaeoenvironmental reconstruction.

Research from Nature Portfolio

Recent studies have harnessed high-energy-resolution fluorescence-detected XANES to distinguish Fe2+ and Fe3+ in acid mine drainage with sub-millimolar detection limits, revealing redox microenvironments within biofilms. Ambient-pressure X-ray photoelectron spectroscopy has been adapted for in situ analysis of airborne particulate matter, permitting direct mapping of iron oxidation states under realistic humidity and temperature conditions. Field-portable LIBS instruments equipped with chemometric algorithms have meanwhile achieved speciation-sensitive fingerprinting of iron phases in road dust and urban soils, enabling rapid screening of anthropogenic versus geogenic iron sources.

Research from all publishers

Investigations using diffusive gradients in thin films combined with square-wave voltammetry have produced high-resolution profiles of labile Fe2+ in river sediments, uncovering redox hotspots linked to organic matter deposition. Earlier foundational work demonstrated that the ratio of Fe(II) to Fe(III) in lake and river sediments serves as a geochemical marker of depositional processes, with Fe2+ enrichment indicating anoxic decantation zones and Fe3+ dominance reflecting surface erosion pulses. Studies of rainwater composition through spectrophotometric assays with ligands such as 1,10-phenanthroline and thiocyanate have characterised spatial variability in dissolved and particulate iron inputs across industrial, rural and urban atmospheres, elucidating the role of atmospheric iron in aquatic nutrient dynamics.

Iron Speciation and Determination Techniques in Environmental Samples publication trend

The graph below shows the total number of articles in iron speciation and determination techniques in environmental samples across all publications each year (not limited to Nature Index journals).

Technical terms

Speciation: Identification and quantification of distinct chemical forms or oxidation states of an element in a sample.

X-ray absorption near-edge structure (XANES): A synchrotron-based technique that probes the electronic state and coordination environment of elements by measuring absorption features near the core-level absorption edge.

Diffusive gradients in thin films (DGT): A passive sampling method that accumulates labile ions through a defined diffusion layer onto a binding gel, allowing time-averaged concentration profiling.

Voltammetry: An electrochemical measurement in which current is monitored as a function of applied potential to identify and quantify redox-active species.

Laser-induced breakdown spectroscopy (LIBS): A field-deployable technique where a focused laser pulse generates plasma on a sample surface and the emitted light is analysed to determine elemental composition and, with chemometrics, speciation information.

References

1. Iron’s fingerprint of deposits—iron speciation as a geochemical marker. Environmental Science and Pollution Research (2017).
2. Studi Keadaan Oksidasi Besi pada Air Hujan. al-Kimiya (2019).