STRUCTURAL CHARACTERISTICS OF MARINE SEDIMENTARY HUMIC ACIDS BY CP MAS C-13 NMR-SPECTROSCOPY/

Humic acids from sediments of different depositional environments have been studied by solid-state C-13 NMR and the results compared with th e traditional wet chemical analysis. Results obtained are well in agre ement with the previous literature reports that the carboxyl content m easured by NMR correlated better with the total acidity, as well as wi th the carboxyl content obtained by wet chemical analysis after correc tion for amino acid carboxyl is made (following hydrolysis of peptide bonds). There is a large discrepancy between the NMR and wet chemical measurements of phenolics. NMR spectra was also indicative of branched paraffinic structures in the humic acids from the Arabian Sea; the hu mic acids of sediments from estuarine and coastal areas of the Bay of Bengal being dominated by carbohydrates and aromatic structures and to a lesser extent by paraffinic structures. These differences are attri buted to their different biogeochemical origin. (C) Elsevier, Paris.