Characterization of soil humic acids by 13C NMR spectroscopy and high performance size exclusion chromatography

Abstract

Humic acids (HAs), the major components of organic matter in soils, play an important role in global carbon cycling and regulation of the mobility and fate of plant nutrients and organic and inorganic pollutants. Despite intensive research on soil HAs during the past 200 years, the chemical nature of HAs is not fully understood. Studies using a variety of spectroscopic techniques have led to major advances in understanding the chemical nature of HAs, but the macromolecule structure and chemical heterogeneity of HAs is a serious hindrance. Therefore, the characterization and grouping of HAs with various chemical natures has been studied. 13C NMR analysis and high performance size exclusion chromatography (HPSEC) are the most powerful and popular tools in this study field. We here describe: (i) optimization of the HA measuring condition in both analyses, (ii) characterization of the chemical nature among HAs in various soil origins, and (iii) HA grouping by statistical analysis based on information data obtained by 13C NMR and HPSEC analyses. Thirty-three of HAs from various soil origins were analyzed and, conclusively, they were classified clearly by their chemical nature. © 2012 The Japan Society for Analytical Chemistry.