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Determination of the Aromaticity of Humic Substances by X-Ray Diffraction Analysis

Land Resource Centre, Research Branch, Agriculture Canada, Ottawa, Ontario, K1A 0C6

J. A. Ripmeester

Chemistry Division, National Research Council, Ottawa, Ontario, K1A 0R9, Canada

* Corresponding author.

ABSTRACT

Aromaticity is an important indicator of the origin, stability, and chemical reactivity of soil humic materials. The only method available at the present time for measuring the aromaticity of these materials is ¹³C nuclear magnetic resonance (NMR), so that there exists a need for an alternate, independent method. With this in mind, we developed a method based on the x-ray diffraction (XRD) analysis of humic materials. Total areas in XRD patterns are subdivided into areas due to G (aromatic) and (aliphatic) bands. The G-band area, expressed as a percent of the total area, is assumed to be a measure of the aromaticity. The method was tested on 14 natural humic acids, one natural fulvic acid, and one synthetic humic acid. Aromaticities so measured were then compared with aromaticities computed from ¹³C-NMR spectra. The agreement between the two methods was acceptable. This establishes the XRD method as a valid alternative to the ¹³C-NMR method.

Contribution no. 90-43. LRRC.

Received for publication June 25, 1990.