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ARS Home » Northeast Area » Orono, Maine » New England Plant, Soil and Water Research Laboratory » Research » Publications at this Location » Publication #199920

Title: Phosphorus Features in FT-IR Spectra of Natural Organic Matter

item He, Zhongqi
item Honeycutt, Charles

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/3/2006
Publication Date: 9/24/2006
Citation: He, Z., Honeycutt, C.W., Ohno, T., Hunt, J.F., Cade-Menun, B.J. 2006. Phosphorus Features in FT-IR Spectra of Natural Organic Matter. [abstract].Chinese Journal of Geochemistry 2006. 25(suppl):259-260.

Interpretive Summary:

Technical Abstract: Fourier-Transform Infrared (FT-IR) spectroscopy has been used extensively to characterize natural organic matter (NOM). Absorption bands at 1100-1000 cm-1 in FT-IR spectra of NOM have been frequently assigned to alcoholic and polysaccharide C-O stretching or to vibrations of SiO2-related impurities. However, these interpretations do not consider that a strong band associated with P-O bonds of phosphate also appears in the same region. We evaluated the correlation between absorbance in this region and P content of 19 NOM samples from terrestrial, aquatic and plant shoot sources. In the spectra of 10 humic and fulvic acid samples, shoulder to minor bands appeared around 1050 cm-1. Absorbance intensity at 1050 cm-1 (Y) was linearly related to P content (X) by the following: Y=4.38X+0.31, with R2=0.90. We did not observe such a close correlation between absorbance and P content in two aquatic NOM samples. In FT-IR spectra of seven dissolved organic matter (DOM) samples obtained from dried plant shoots, broad and/or multiple bands around 1075 cm-1 were observed with a shoulder at 977 cm-1. These characteristics were more like those of organic P compounds (such as inositol phosphate). However, solution 31P NMR spectroscopic analysis showed no significant amounts of organic P present in these samples. Thus, the FT-IR bands around 1100-1000 cm-1 in FT-IR spectra of these DOM samples were contributed not only by phosphate, but also by alcoholic and polysaccharide compounds present in plant shoots. From this work, we concluded that the characteristic absorbance at 1100-1000 cm-1 can provide a simple and rapid diagnostic for P present in humic substances, but not for unprocessed/isolated (i.e.unpurified) NOM.