Fulvic acids fractionation

The humates present in soil are polyelectrolytes and bear some similarity to polyacrylic acid and polymethacrylic acid (49, 50). The molecular weight distribution for the humates is considerable fulvic acid fractions of 1,000 daltons have been isolated (51) while humic acid molecular weights obtained by gel chromatography are in the range 17,000 to 100,000 daltons according to the type of soil from which it was extracted (52). However, ultracentrifugation analysis indicates a molecular range of 2,000 to 1,500,000 daltons for humic acids (55). 

Fulvic acid fraction Fraction of soil organic matter that is soluble in both alkali and acid... 

Generic fulvic acid Pigmented material in the fulvic acid fraction... 

Step 6. Reapply fulvic acid fraction at pH 2 to XAD-8 column. Desalt fulvic acid by rinsing column with 1-void volume of distilled water to remove HC1 and inorganic salts elute fulvic acid in reverse direction with 0.1 N NaOH. 

Step 7. H-saturate fulvic acid fraction by immediately passing 0.1 N NaOH eluate through cation-exchange resin in H-form. Continue cation-exchange process until final concentration of Na+ is less than 0.1 ppm. 

Step 8. Freeze-dry humic acid and fulvic acid fractions. 

DOM is derived from autochthonous sources such as phytoplankton and photosynthetic bacteria (16) at Big Soda Lake near Fallon, Nevada. This lake is alkaline (pH 9.7) and chemically stratified. It contains DOC concentrations as high as 60 mg/L and dissolved salt concentrations as high as 88,000 mg/ L (17). The DOM in this lake is colorless. The fulvic acid fraction was isolated by adsorption chromatography (Amberlite XAD-8 resin) (18) and by zeo-trophic distillation of water from N,N-dimethylformamide (19). Average molecular model synthesis was achieved in a manner similar to that used for fulvic acid from the Suwannee River. The characterization data are presented in Table I and the structural model is presented in Structure 2. 

To maintain a focus on the use of tracers in DOM fractions, this chapter will present only brief descriptions of studies of bulk DOM properties, and will focus primarily on the use of trace moieties from the fulvic acid fraction in freshwater aquatic environments. In addition to being a major DOM fraction, fulvic acid is biogeochemically reactive in natural waters (see Maranger and Pullin, Chapter 8 Chin, Chapter 7 Moran and Covert, Chapter 10). Furthermore, current fractionation methods allow for relatively straightforward isolation of small quantities of fulvic acid from small volume filtered water samples (100-200 mL) in a reproducible manner, as well as for isolation of larger preparative quantities of material. We present examples to illustrate the use of particular trace moieties but do not present a comprehensive review of each trace moiety. 

Here we present one example to illustrate the utility of 15N for providing information about the source of dissolved organic nitrogen in a freshwater ecosystem. The 15N contents of fulvic acid fractions of different size varied slightly and were similar to the value for the 15N content of the synfulvic acid fraction in a eutrophic coastal pond in Antarctica (Table I) (Brown et al., 2002). Continuous production of mucilage by the chlorophyte population in the pond and diffusion of DOM from the sediments are the two main DOM sources these data suggest that the same source predominates for all of these fulvic acid fractions. 

Fluorophores are another type of trace moiety that is lost through photolysis (Pullin and Cabaniss, 1997 Langford and Bruccoleri, 2000). The decrease in fluorescence by photolysis is confirmed by the observation that the fluorescence intensity per mg DOC is a good indicator of the production of hydrogen peroxide from DOM photolysis in a wide range of freshwaters (Scully and Lean, 1994). As discussed above, the relative fluorescence intensity of the fulvic acid fraction is fairly simple to measure. Furthermore, measurement of FI and/or 813C may allow for differentiation between a decrease in fluorescence intensity per mg C due to mixing with fulvic acid from microbial material and a decrease due to photolysis. 

Plaza, C., Senesi, N., Brunetti, G., and Mondelli, D., (2007). Evolution of the fulvic acid fractions during co-composting of olive oil mill wastewater sludge and tree cuttings. Bioresource Technol. 98,1964-1971. 

Sposito, G., Holtzclaw, K. M., LeVesque, C. S., and Johnston, C.T. (1982). Trace metal chemistry in arid-zone field soils amended with sewage sludge II. Comparative study of the fulvic acid fraction. Soil Sci. Soc. Am. I. 46, 265-270. 

Wilson, M. A., Vassallo, A. M., Perdue, E. M., and Reuter, J. H. (1987). A compositional and solid state nuclear magnetic resonance study of humic and fulvic acid fractions of soil organic matter. Anal. Chem. 59, 551-558. 

Cheshire, M.V, Berrow, M.L., Goodman, B.A. and Mundie, C.M. (1977) Metal distribution and nature of some Cu, Mn and V complexes in humic and fulvic acid fractions of soil organic matter. Geochim. Cosmochim. Acta, 41, 1131-1138. 

Boyd, S.A. and Sommers, L.E., Humic and fulvic acid fractions from sewage sludges and sludge amended soils, in Humic Substances in Soil and Crop Sciences, Clapp, C.E., Malcolm, R.L., and Bloom, P.R., Eds., American Society of Agronomy, Inc. USA, 1990, pp. 203-220. 

Brown G. K., MacCarthy P., and Leenheer J. A. (1999) Simultaneous determination of Ca, Cu, Ni, Zn, and Cd binding strengths with fulvic acid fractions by Schubert s method. Anal. Chim. Acta 402, 169-181. 

As a first step, adsorption isotherms were determined for a commercially available humic substance and for its humic and fulvic acid fraction. Secondly the adsorption of humic substance from a river water and a marshland water was investigated. 

Secondly a solution of the fulvic acid fraction was used. For this purpose 0.1 g of ... 

The latter is explained by the fact that the fulvic acid fraction concentrates the smaller molecules present in the original humic substance solution. The lower initial concentration can be responsible for a part of tbe former findings. Since the preparations of the 2 solutions was different some unknown influences may interfere however. Moreover, throughout the investigation lumped-parameters are used TOC, U.V. 254) and since the chemical structures of the 2 adsorbates are different, we may not interpret the numerical values obtained in exactly the same way. The substances giving higher U.V. 254 absorption seem to absorb more readily than would be expected from TOC measurements. For this fraction, the ratio U.V. 

Figure 8.1 Mass spectra of a (HO lOFA) fulvic acid fraction using positive-ion and negative-ion ESI and APCl (Reprinted from [8] with permission, 2001, Elsevier Science).

At an even earlier date, Waksman (1936) isolated a separate component from the fulvic acid fraction. When the filtrate from the separation of humic acid was adjusted to pH 4.8 another precipitate was formed. This was designated as the -fraction of humus, or the neutralization fraction of Hobson and Page (1932). This material was rich in aluminum and was considered to be an Al-humate. No mention is made of the )8-fraction in the book by Kononova (1966). 

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