Use of soil color meter for aqueous iron and ammonium measurements

Abstract

In this paper, we proposed a new approach for on-site colorimetric analysis of ferrous ions (Fe2+) and ammonium-nitrogen (NH4 +-N) using a soil color meter as an alternative method to conventional spectrophotometry. The soil color meter we used can express solution color numerically on the basis of L*a*b* color space. After coloring of water by the 1, 10 phenanthroline method and the Indophenol blue method, the color of solution was measured by the soil color meter. A linear relationship between Fe2+ and a* or b* values, and systematic change of NH4 +-N with L* value, enable us to make a calibration curve. The Fe2+ and NH4 +-N concentrations in groundwater samples (Fe2+: 0.3–1.3 mg L−1; NH4 +-N: 0.02–0.62 mg L−1) determined by the proposed method agreed well with those determined by conventional spectrophotometry with the difference being ± 0.05 mg L−1 and ± 0.02 mg L−1, respectively. Since a similar apparatus is widely used in the soil science field, this technique would facilitate field surveys.