Structural Characterization of a Fulvic Acid and a Humic Acid Using Solid-State Ramp-CP-MAS ¹³C Nuclear Magnetic Resonance

Abstract

This study uses the analysis of 13 C nuclear magnetic resonance (NMR) spectra and NMR relaxation parameters to study the structure and functional group distribution of a fulvic acid and a humic acid. The spectra and relaxation parameters are obtained with a new cross polarization magic angle spinning (CP-MAS) 13 C NMR technique that gives qualitatively and quantitatively accurate results at higher fields. The analysis of the spectra and relaxation parameters indicates that carbohydrate moieties play a major structural role in the fulvic acid studied and contain the major chemical functionality. This analysis also suggested that the majority of the weakly acid protons may be aliphatic/carbohydrate -OH and not phenolic alcohols, as assigned earlier. Models for the fulvic acid and the humic acid are proposed based on spectra and relaxation parameters obtained. The fulvic acid model consists of three units: (i) large relatively immobile units that are mainly aliphatic in nature and largely unfunctionalized; (ii) relatively unfunctionalized more mobile units that are mainly aromatic in nature; and (iii) and more mobile functionalized units that are mainly carbohydrate in nature. The humic acid model consists of one major immobile unit associated with slightly more mobile functionalized units that are mainly aromatic in nature.

Sorption of radioactive cesium and barium ions onto solid humic acid

“…4 of HA and sodium form of insolubilized humic acid (INaA) include the following peaks: (a) alkyl carbons and O-alkyl carbons (aminoacids/carbons adjacent to ester/ether/hydroxyl) (0-60 ppm). Because that peak was not well resolved we observe those two groups in a broad band; (110-145) ppm is assigned to aromatic carbon, that at (150-190) ppm include phenolic and carboxylic carbons [15][16][17].…”

A stochastic model for the synthesis and degradation of natural organic matter part II: molecular property distributions

“…Like MW, Ar is readily calculated from structural information; unlike MW, a single analytical method ( 13 C NMR) is generally accepted as the standard experimental technique for estimating Ar. However, quantitative measurements of Ar depend both on the specific pulse sequence used and the method of integration, so that more recent results are considered more reliable (Cook and Langford 1998;Perdue and Ritchie, 2004).…”

Chemical Speciation of Organics and of Metals at Biological Interphases

“…FA and HA are polymeric ligands with molecular weights typically in the range 500-2000 g mol À1 for FA and 2000-5000 g mol À1 for HA. Recent spectroscopic work has started to reveal more clearly the structures of these polymeric molecules [40][41][42][43]. FA and HA comprise both hydrophobic and hydrophilic domains.…”