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Carbon‐13 Nuclear Magnetic Resonance Spectra of Soil Humic Substances Extracted by Different Mechanisms
Author(s) -
Piccolo A.,
Campanella L.,
Petronio B. M.
Publication year - 1990
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1990.03615995005400030021x
Subject(s) - chemistry , acetone , humic acid , nmr spectra database , nuclear magnetic resonance spectroscopy , spectral line , nuclear chemistry , organic chemistry , fertilizer , physics , astronomy
Humic substances were extracted from an organic soil of Tuscany, Italy, with solutions operating by three different mechanisms: charge repulsion (NaOH under N 2 ), ligand exchange (Na 4 P 2 O 7 at pH = 7), and H‐bond disruption (dipolar aprotic solvents in mixture with dilute HCl). Solution‐state 13 C‐nuclear magnetic resonance (NMR) spectra were obtained for the unpurified and purified (HCl‐HF treatment) extracts, revealing that humic matter obtained through the H‐bond‐disruption mechanism was different from materials extracted using the two other mechanisms. Extracts obtained using dipolar aprotic solvents (DMF, DMSO, acetone) showed better resolved spectra than those using NaOH and Na 4 P 2 O 7 . This was due to a lower content of coextracted silicate materials and lower molecular weights. Spectra of humic substances extracted with acetone and DMF had a higher percentage of aliphatic C than did the spectrum of the extract with DMSO. The latter was, in general, more similar to the spectra of stronger extractants. The H‐bond‐disruption mechanism of dipolar aprotic solvents appeared to have extracted more unsubstituted aromatic rings than NaOH and Na 4 P 2 O 7 , although percent of aromatic C was generally equivalent in the spectra of all extractants. Purification with a HCl‐HF treatment decreased mainly the content of aliphatic, carbohydrate, and amino acid components of all extracts. Poor agreement between values for total acidity of extracts calculated by NMR and those given by chemical methods was also observed in this study.