Iron organic speciation determination in rainwater using cathodic stripping voltammetry.

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Geochemistry

Background:

• Iron speciation in rainwater is crucial for understanding its biogeochemical cycle.
• Existing methods lack sensitivity for typical rainwater iron concentrations.
• Rainwater pH variability presents challenges for accurate iron speciation analysis.

Purpose of the Study:

• To develop and validate a sensitive method for determining organic iron speciation in rainwater.
• To establish the conditional stability constant of a competing ligand under rainwater conditions.
• To quantify naturally occurring iron-complexing ligands in rainwater samples.

Main Methods:

• Competitive Ligand Exchange-Adsorptive Cathodic Stripping Voltammetry (CLE-ACSV) adapted for rainwater.
• Utilized 1-nitroso-2-naphthol (NN) as the competing ligand.
• Calibrated stability constants using ethylenediaminetetraacetic acid (EDTA) and validated with desferrioxamine mesylate B (DFOB).

Main Results:

• Achieved a low detection limit of 0.15 nM for labile iron, significantly lower than previous methods.
• Determined the conditional stability constant of NN for Fe(III) across a pH range of 5.52-6.20.
• Quantified organic Fe-complexing ligands in rainwater, ranging from 104.2 to 336.2 nM equivalent of Fe(III).

Conclusions:

• The developed CLE-ACSV method is highly sensitive for iron speciation in rainwater.
• This technique provides crucial data for assessing the role of wet deposition in iron biogeochemical cycling.
• The findings enhance our understanding of iron's behavior and transport in atmospheric systems.