The Quantitative Assay of Minerals for Fe2+ and Fe3+ Using 1,10-Phenanthroline: II. A Photochemical Method
1981
Stucki, J. W.
A photochemical method for measuring Fe³⁺ and total Fe in minerals is described. The method determines Fe²⁺ concentration by measuring the Fe(phen)₃²⁺ (phen = 1,10-phenanthroline) complex formed during HF-H₂SO₄ digestion of the mineral. To measure Fe²⁺ accurately in the presence of Fe³⁺ from the mineral, the sample digestion and analysis are performed under red light to prevent photochemical reduction of the ferric-phen species. Total iron is measured by converting any Fe³⁺ in the digestate to Fe(phen)₃²⁺ by photochemical reduction using a fluorescent lamp. This procedure avoids the problems associated with adding chemical reducing agents to iron-phen solutions. The calibration curves were linear up to 8-µg Fe/ml with a lower detection limit of 0.011 µg/ml. The absorptivities of the calibration curves were 0.1852 ± 0.0017 and 0.1960 ± 0.0018 ml/cm-µg for Fe²⁺ and total Fe, respectively. Ferric iron in the mineral samples was calculated by difference.
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