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Determining Manganese Oxidation State in Soils Using X‐ray Absorption Near‐Edge Structure (XANES) Spectroscopy
Author(s) -
Schulze D. G.,
Sutton S. R.,
Bajt S.
Publication year - 1995
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1995.03615995005900060005x
Subject(s) - manganese , analytical chemistry (journal) , chemistry , xanes , oxidation state , soil water , corundum , spectroscopy , absorption (acoustics) , mineralogy , materials science , environmental chemistry , catalysis , physics , environmental science , organic chemistry , quantum mechanics , soil science , composite material , biochemistry
The redox chemistry of soil Mn is important in Mn uptake by plants, the movement of trace elements absorbed on or occluded in Mn‐oxides, and the etiology of some soil‐borne plant fungal diseases. The objectives of this study were to develop calibration curves for determining Mn oxidation states in moist soil samples using micro‐x‐ray absorption near‐edge structure spectroscopy and to test the method on selected soils. Oxidation‐state standards were prepared by mixing dry powders of MnSO 4 ·H 2 O (Mn 2+ ) and a synthetic Na‐birnessite, Na 4 Mn 14 O 27 ·9H 2 O (Mn 4+ ) to obtain various Mn 2+ mole fractions, f (Mn 2+ ), where f (Mn 2+ ) = Mn 2+ /(Mn 2+ + Mn 4+ ). Corundum (α‐Al 2 O 3 ) was used as a diluent to prepare mixtures containing 50, 1000, and 100 000 mg Mn kg −1 . Quantitative analysis of Mn oxidation state is possible using either the energy of the pre‐edge peak at 6540 eV or a ratio based on the intensity of the Mn 2+ white line peak at 6552.6 eV divided by the intensity of the Mn 4+ white line peak at 6560.9 eV. The white line intensity ratio is more sensitive, with an estimated lower detection limit of 20 mg Mn kg −1 using a 300 by 300 µm spot, and predicts f (Mn 2+ ) with an accuracy of ±0.1 mole fraction (95% confidence interval) through most of its range. The f (Mn 2+ ) for four air‐dried Indiana surface soils ranged from 0.26 to 0.44 ± 0.1. Saturation and reduction for 5 d resulted in complete reduction of Mn in the soil matrix.