DETERMINATION OF THE AROMATICITY OF HUMIC SUBSTANCES BY X-RAY-DIFFRACTION ANALYSIS

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 C-13 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 gamma (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 C-13-NMR spectra. The agreement between the two methods was acceptable. This establishes the XRD method as a valid alternative to the C-13-NMR method.