Humic substances isolation

Geochemical characterization of humic substances isolated from phosphatic pellets and their surrounding matrix, Ras-Draa, Tunisia... 

Raspor, B., Nurnberg, H.W., Valenta, P. and Branica, M., 1984. Studies in seawater and lakewater on interactions of trace metals with humic substances isolated from marine and estuarine sediments. 11. Voltammetric investigations on trace metal complex formation in the dissolved phase. Mar. Chem., 15 231-249. 

Watt, B. E., T. M. Hayes, M. H. B. Hayes, R. T. Price, R. L. Malcolm, and P. Jakeman. 1996. Sugars and amino acids in humic substances isolated from British and Irish waters. In Humic Substances and Organic Matter in Soil and Water Environments Characterization, Transformations and Interactions (C. E. Clapp, M. H. B. Hayes, N. Sensesi, and S. M. Griffith Eds.), pp. 81-91. International Humic Substances Society, St. Paul, MN. 

Figure 8.3. Fluorescence micrographs of Pinus sylvestris roots at 1mm (top) and 2 mm (bottom) behind the root tip after a treatment with LMS (low-molecular-size humic substances). Note the much smaller rate differentiation of the roots treated with LMS than the roots treated with HMS (high-molecular-size humic substances). Reprinted from Nardi, S., Pizzeghello, D., Remiero, F., and Rascio, N. (2000). Chemical and biochemical properties of humic substances isolated from forest soils and plant growth. Soil Sci. Soc. Am. J. 64,639-645, with permission from the Soil Science Society of America.

Nardi, S., Pizzeghello, D., Remiero, F., and Rascio, N. (2000). Chemical and biochemical properties of humic substances isolated from forest soils and plant growth. Soil Sci. Soc. Am. J. 64, 639-645. 

Frimmel, F. H., Immerz, A., and Niedermann, H. (1984). Complexation capacities of humic substances isolated from freshwater with respect to copper(II), mercury(II) and iron(II,III). In Complexation of Trace Metals in Natural Waters, Kramer, C. J. M., and Diunker, J. C., eds., Martinus Nijhoff/Dr. W. Junk Publishers, The Hague, pp. 329-343. 

Hejzlar, J., Szpakowska, B., and Wershaw, R. L. (1994). Comparison of humic substances isolated from peatbog water by sorption on Deae-cellulose and Amberlite XAD-2. Water Res. 28,1961-1970. 

Pettersson, C., Ephraim, J. and Allard, B. (1994) On the composition and properties of humic substances isolated from deep groundwater and surface waters. On. Geochem., 21,443-451. 

One striking result of this study was that dissolved total humic substances isolated from two sites in the mainstem (Ertel et al. 1986) exhibited A c values of +265 to +285%o (Hedges et al. 1986b). Although dissolved humic substances (isolated by hydrophobic sorption onto a resin column)... 

Only occasionally has the N content of solid phase extracts been reported. At a site in the Atlantic Ocean the carbon to nitrogen ratio (C N) of XAD 8 and XAD 2 extracts fell in the range of 40-57 (57 0.9 and 41.1 3.3, respectively DrufFel et ai, 1992). In contrast, at the same site XAD 4, when used as the second resin in series with XAD 8 or XAD 2, extracted compounds with lower C N ratios - 19—24 (21.0 2.4). These values are only slighdy higher than ratios reported for total DOM (see below). McKnight and Aiken (1998) reported a C N value of 37 for DOM extracted by XAD 8 at one site in the Pacific Ocean at other sites in the N. Pacific Ocean XAD 2 was found to extract DOM with a C N ratio between 32 and 46.5 (Druffel et al, 1992 Meyers-Schulte and Hedges, 1986). Bronk (2002, Table III) compiled various literature values and arrived at an average C N ratio of 32.8 19.5 for total humic substances isolated from a variety of aqueous environments (see McCarthy and Bronk, this volume). 

Proton and C-NMR data compare well with each other and suggest that surface ocean HMWDOM has a H C ratio of approximately 1.8—1.9 (Aluwihare, 1999 Benner et al, 1992) and an 0 C ratio between 1 and 1.1. These H C and 0 C ratios are very close to those of a pure carbohydrate with a general hexose structure (e.g., C6H12O6). In comparison, humic substances isolated from seawater have an H C ratio between 1.2 (direct elemental analyses) and 1.4 (based on NMR estimates) and are therefore, relatively C-rich (Hedges et al, 1992). The H C and 0 C composition of phytoplankton as estimated by NMR spectroscopy is approximately 1.7 and 0.3, respectively (Hedges et al, 2002). In comparison to phytoplankton... 

In the Arctic and Antarctic Ocean amino acids were also found in humic substances isolated from DOM by XAD-2 resins (Hubberten et ai, 1995). The concentration of THAA in humic substances was between 233—246 nM, with aU hydrolysable amino acids in the deep ocean and 60% of amino acids in the surface ocean residing in this fraction. Glycine was by far the most abundant amino acid detected in the humic fraction. These authors concluded that amino acids in the XAD-2 extracts represent a refractory protein background that is present throughout the ocean. The dominance of this refractory protein background in the surface and deep ocean could explain the relatively stable amino acid distribution observed by Yamashita and Tanoue (2003) at their open ocean sites. 

The isolated monosaccharides and polysaccharides represent only a small part of the total carbohydrates of soil. The soil residue after extraction, and isolated fractions of soil organic matter (for example, humic substances), might contain sugars other than those which have been detected in the polysaccharides isolated. However, hydrolysis of soils and of humic substances isolated, followed by chromatography of the freed sugars, showed that this was not the case. ... 

Structural Studies of Humic Substances. Solid-state C NMR has played a major role in past studies of the chemical structure of humic substances isolated from soil as mentioned above. Recent studies have focused on the examination of humic substances from various environments to establish variabihties which might be indicative of structure and structural evolution.(29-34) Also, combined use of NMR with other analytical methods such as analytical pyrolysis, chemical degradative methods, and solution NMR studies has proved vduable in elucidating structural components. However, the complexity of humic substances has precluded all but inferred structures based on these combined studies. 

Sample Preparation of Foam and Water Samples and Humic Substances Isolation. All foam and water samples were filtered through 0.45- Lim silver filter using stainless-steel filtration units. Silver filtration of Como Creek and Suwannee River foam samples resulted in build up of a brown extract on the filter paper, which was readily solubilized in 0.1 N sodium hydroxide. This extract was refiltered through silver filters as a sodium hydroxide solution. This fraction was believed to be colloidal in nature and was treated as a separate humic fraction, called the "foam-extract" fraction. A part of the filtered foam was freeze dried directly and considered "raw" foam. Fulvic and humic acids were isolated from foam and stream-water samples via the XAD-8 adsorption technique developed by Thurman and Malcolm (77), freeze dried, and weighed. To obtain a sufficient mass of humic substances, each entire sample was used for one extraction. As multiple samples were not extracted, calculation of the error associated with humic substances isolation cannot be made, and the contributions of humic substances to the DOC content must be regarded as estimates. 

Humic substances isolated from stream samples from each site fell within these common ranges, with Como Creek humic substances accounting for 55% of the DOC whereas the Suwannee River humic substances accounted for 81 % of the DOC. In contrast, foam humic substances accounted for 93% of the DOC from Como Creek foam and for 89% of the DOC from the Suwannee River foam. Organic carbon determinations were not made on the foam-extract fraction, and the percentage contribution by weight of humic substances to this material could not be determined. 

Table III. Elemental data (reported as percentage contribution by weight) for raw foams and humic substances isolated from stream, foam, and foam-extract samples from Como Creek and the Suwannee River.

Based on comparison of data from UV, fluorescence, and NMR spectroscopy, and from carbon isotope determination for humic substances isolated from coastal and open ocean environments, the authors have concluded the following (1) other than its metal complexation and redox functions, the only resemblance between humic substances from open ocean (marine) and terrestrial environments is that they are both colored organic acids soluble in water, and (2) marine humic substances are formed in situ and only in the coastal zone is there an admixture of terrestrially derived humic substances from rivers. However, this second conclusion has not yet been reconciled with the observations discussed by Mayer in Chapter 8 that riverine humic... 

Except for extracts with anhydrous EDA, data in Table 4 were obtained for humic substances isolated from an air-dried H+-exchanged humic histosol soil. For extractions with pyridine, A,A-dimethylformamide (DMF), di-methylsulfoxide (DMSO), and sulfolane, soils (60 g) were thoroughly mixed with the appropriate solvent (250 cm ). After centrifugation the residues were repeatedly extracted with water until the supernatants were only faintly colored. Supernatants for each of the solvent systems were combined and the pH values of the solutions were adjusted to 1.0 using 5M hydrochloric acid. Humic and fulvic acids were separated by centrifugation. 

Raspor, B., and P. Valenta, (1988), Adsorption of Humic Substances Isolated from Marine and Estuarine Sediments, Mar. Chem. 25, 211-226. 

Figure 20. NEXAFS spectra of N in sediments collected from different locations and their isolated humic substances (a), and humic substances isolated by the International Humic Substance Society (b). The spectra are collected in electron yield mode and are sensitive to surface coordination (especially for the sediment samples). [Used with permission from Vairavamurthy and Wang 2002, American Chemical Society],...

The NEXAFS spectroscopic studies conducted on Cl functional groups of humic substances isolated from soils, sediments and river waters showed an intense feature at... 

Figure 46. Is NEXAFS spectra of Cl in humic substances isolated from river water, soils, peat and lignite (taken from Myneni 2002). HA humic acid HA, FA fulvic acid. Different spectra represent (A) Suwannee River FA, (B) Suwannee River HA, (C) soil FA, (D) soil HA, (E) Lake Fryxell FA, (F) peat HA, (G) peat FA, and (H) Leonardite HA.

Clapp, C. E., and M. H. B. Hayes. 1999. Characterization of humic substances isolated from clay- and silt-sized fractions of a com residue-amended agriculture soil. Soil Science 164, no. 12 899-913. 

Table 2. Distribution of amino acid - and nucleic acid-N in 6M HCl hydrolysates of the fractions of alkali-soluble humic substances, isolated from a brown forest soil, and separated by "salt-boundary" gel chromatography.

Oxidized quinones are relatively poor fluorophores however, the reduced forms, hyd-roquinones, are highly fluorescent, a property that has been utilized in developing photochemical-reaction fluorescence detectors for liquid chromatography (Poulson and Bitks, 1989). Klapper et al. (2002) used the differences in fluorescence properties between oxidized and reduced samples of humic substances isolated from a range of environments to infer the presence of quinone-like moieties. These authors proposed that quinone moieties contribute significantly to the fluorescence of humic substances and that fluorescence analyses could be used to assess the redox status of humic substances. 

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