Humic functional groups, characterizing

Two minor points worthy of note are (a) formation of carbon dioxide and water at temperatures below ca. 300°C. appears, from the evidence of this study, to be caused mainly by Reaction 1—i.e., at such relatively low temperatures, Reaction 2 does not proceed significantly towards its ultimate conclusion (b) abstraction of humic acids by stripping of functional groups— i.e., by reactions characterized by fa, is likewise minimal at T < 300°C. (The fact that no observable decay of humic acids occurs during extended oxidation unless reaction temperatures approach 300°C. is, perhaps, a direct consequence of (a) and (b).)... 

Perdue, E. M. 1985. Acidic functional groups of humic substances. In Humic Substances in Soil, Sediment and Water Geochemistry, Isolation, and Characterization, (G. R. Aiken,... 

Both of these methods have been used for DOM isolation from major rivers and the surface ocean, and the general characteristics of these fractions of DOM are presented in Table I. The major C functional groups of humic substances and ultrafiltered DOM (UDOM) have been characterized by solid-state, cross-polarization magic angle spinning 13C nuclear magnetic resonance (NMR) spectroscopy. The samples of humic substances that were characterized by NMR spectroscopy were collected from the Amazon River... 

Vairavamurthy, A., Maletic, D., Wang, S., Manowitz, B., Eglinton, T., and Lyons, T. (1997). Characterization of sulfur-containing functional groups in sedimentary humic substances by X-ray absorption near-edge spectroscopy. Energy Fuels 11,546-553. 

Because of the considerable potential of titration calorimetry as an analytical technique for characterization of the acidic functional groups of humic substances, our studies have been extended to river water humic substances. In this paper, results are presented for the thermochemical characterization of the acidic functional groups of river water humic substances from two quite different river systems 1) the Satilla River in southeastern Georgia, and 2) the Williamson River in southern Oregon. 

A variety of spectroscopic methods have been employed to characterize the functional groups within the humic molecule. Traditionally, the method of choice for studying fimctional groups of organic molecules would be infrared spectroscopy. An... 

Vibrational spectroscopy is the method of choice for the characterizing functional groups in complex organic molecules. Infrared transmission spectroscopy has been used on dried humics pressed into KBr pellets to determine the relative carboxylate content of humic materials (14-16). However, interferences arise from the presence of water bands and possible alterations of the samples under the high pressures used to form the pellets. Diffuse-reflectance techniques can avoid some of the difficulties associated with the KBr pressed-pellet method (9,17-18). To obtain a spectrum analogous to an absorption spectrum, the data are transformed from reflectance units to Kebulka-Munk (K-M) units. However, K-M units are related to... 

Foams form where surface-active chemicals or "surfactants" are present. Surfactants also are called amphipathic agents and are characterized by the presence of both hydrophilic and hydrophobic functional groups (7). Surface-active agents that may be present in natural waters include fulvic and humic acids, collectively termed humic substances, (2,3), fatty acids and lipids (4), and proteins (5), and all have been identified as contributing surfactants in the few characterization studies that have been conducted on natural foams in freshwater environments (5-70) and marine surface layers (77-76). 

Steroids are hydrophobic molecules and sparingly soluble with only one hydroxyl functional group. Normally steroids are found concentrated in the sediment phase via partitioning onto organic matter on sediments (25). Their concentration in the foam and humic-acid fraction is indicative of the hydrophobic nature of these fractions. The increasing compositional complexity from stream, to foam, to foam-extract samples is also consistent with other characterization trends of increasing compositional complexity and hydrophobicity. 

Elemental composition, functional group analyses, spectral properties, and characterization of acid hydrolysates have shown that peat humic acids tend to be similar to those from mineral soils. NMR spectroscopy has revealed that peat fulvic acids are largely carbohydrate in nature while the residue of alkali extraction is not all humin. 

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