Composition of humic acids extracted under air and nitrogen atmosphere

Abstract

Differences in nature and composition of humic matter, attributed to NaOH extraction under air or a N₂ gas atmosphere, were investigated. Samples from the Ap horizons of a Cecil and Onaway soil, and lignite were shaken with 0.1 M NaOH in the presence of air or under N₂ gas. The humic (HA) and fulvic acid (FA) separated were weighed, and analyzed for C, H, O, N, and S contents. Total acidity, carboxyl and phenolic‐OH group contents were determined by chemical analysis. Characterization was performed by ¹³C nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. The results indicated that differences in amounts of HA and FA, attributed to NaOH extraction under air and N₂ gas, were small and no definite trend was noted for more HA and FA extracted under air. No differences in C, H, O, N, and S contents of HA and FA were also noticed as a result of the influence of air or N₂ gas during extraction. However, HA and FA exhibited larger values for total acidities when extracted under a N₂ gas atmosphere than under air. The lower amounts of carboxyl and phenolic‐OH group contents in HA and FA as a result of NaOH extraction under air, however, do not support the idea of increased oxidation by NaOH. No differences were noticed in NMR and IR spectra of HA and FA attributable to the two extraction methods. The differences in NMR and IR features obtained were more the result of differences in origin than in methods of extraction.