Voltammetric determination of dissolved iron and its speciation

Analytical methods were developed to determine the concentration of total dissolved iron and its chemical speciation in freshwater using cathodic stripping voltam- metry (CSV) with 1-nitroso-2-naphthol (NN) at pH 8.1. The concentrations of total dissolved iron in river water that iron concentration was certified and in natural water samples from Lake Kasumigaura were determined success- fully. The natural iron ligand concentration and the condi- tional stability constant were determined by ligand competition between NN and the natural ligands present in the sample. In the water samples from Lake Kasumigaura, the concentrations of total dissolved iron and natural ligand were 47.8 � 4.4 nM and 80.0 � 19.6 nM and the conditional stability constant (K�) was 10 25.9� 0.4 M � 1 (n � 3). The value of KFeL was greater than any reported KFeL for seawater. More than 99.9% of the dissolved iron existed as organic species due to the very high value of the conditional stabil- ity constant. The inorganic iron concentration calculated from these results was 10 � 13.4 M, indicating that the inor- ganic iron level in Lake Kasumigaura was similar to that in the open ocean and therefore that iron can be a limiting factor for algal growth in Lake Kasumigaura. This is the first report of the complexation of iron(III) and inorganic iron levels in lake water determined by CSV.