Speciation of iron in rain water by size fractionation, acid decomposition, acid extraction and catalytic determination

For the speciation of trace iron in rain water, the concentration (C-L) of labile iron was determined by a catalytic spectrophotometric method based o n the oxidation of o-phenylenediamine with hydrogen peroxide. The total con centration (C-T) of iron was determined by the same method after acid decom position to obtain the concentration (C-T-C-L) of non-labile iron. For the particle fraction (particle size greater than or equal to 0.45 mu m), 0.1 M HCl-soluble iron was determined by atomic absorption spectrometry. Coexist ing humic substances were spectrofluorometrically determined as humic acid. Labile iron was found in the fraction of molecular weight (MW) <10(3) and estimated as FeOH2+ and Fe(OH)(2)(+) from the chemical equilibria of hydrox o iron(III) ions. Non-labile iron was found in the particle fraction and ch aracterized as acid-soluble iron hydroxide and humic iron aggregates as wel l as acid-insoluble compounds, like oxides and silicates. Labile iron was a lso found in the particle fraction of initial rainfall samples and characte rized as iron complexed on humic iron aggregates. The above speciation resu lts were confirmed by the analysis of synthetic samples.