Three dimensional excitation-emission matrix fluorescence spectroscopy of typical Japanese soil powders

Abstract

Front face fluorescence spectroscopy of typical Japanese soil powders (soil A: Typic Hapludand; soil H: Typic Hydraquent; soil Y: Typic Paleudult) has been conducted. Three dimensional excitation-emission matrix fluorescence spectra of the 100 wt% soils showed similar fluorescence patterns to each other. The fluorescence patterns were similar between the soil samples and their residues after extraction by NaOH solution for 60 min. In order to examine fluorescence extinction from a view point of whiteness of the soils, the soil powders were mixed with white and black diluents (Al₂O₃ and Fe₃O₄) and fluorescence spectra of the mixtures were measured at 450 nm excitation. At low levels of dilution with Al₂O₃ (2-100 wt% of A; 50-100 wt% of H and Y), the fluorescence intensities increased with dilution. At high levels of dilution with Al₂O₃, the fluorescence intensities decreased with dilution. On the other hand, fluorescent intensities decreased by dilution with Fe₃O₄. These results suggested inner filter effect-like fluorescence extinction by (1) large amount of blackish organic compounds giving high total carbon value and (2) blackish non-fluorescent mineral compounds. In order to correct the fluorescence intensities of the mixtures containing the sample soils and the diluents, we preliminary applied a correction method based on the Kubelka-Munk theory using diffuse reflectance. The corrected fluorescence intensities of samples with white diluents (Al₂O₃) were described by a simple fluorescence response model having saturation values.

Keywords: Fluorescence extinction; Front face fluorescence spectroscopy; Humic substances; Soil organic matter; Solid state.