Development of absorption spectrophotometry of iron(III) in environmental water and sediments using NEDA and its application to the field

In this study, we developed a simple method that enables iron(III) in environmental water to be directly determined via spectrophotometry. In water samples, iron(III) formed a yellowish complex with N-1-Naphthylethylenediamine dihydrochloride (NEDA) at pH 2.0–2.8, the maximum absorption wavelength of which was 462 nm. Detection sensitivity increased in the presence of chloride ions and remained constant for 2–24 h with 0.05–0.57 mol L−1 chloride. Therefore, NEDA solution containing chloride ions was used as a chromogenic reagent for the determination of iron(III). The determination range for this method was 0.1–20 mgFe(III) L−1 in a 5 cm glass cell. The developed method is highly selective for iron(III) and has been successfully applied to freshwater, brackish water, seawater, turbid water in rivers, as well as to riverbed and freshwater lake sediments. In addition, a combination of the proposed NEDA method and the 1,10-phenanthroline method enabled simultaneous determination of iron(III) and iron(II).