Humic acid fractions

Characterization of Aquatic Humic Acid Fractions by Fluorescence Depolarization Spectroscopy... 

In this chapter, we present the theory and results of measurements on humic acid fractions using fluorescence techniques. The fluorescence techniques are attractive for this application because of the natural fluorescence of humic materials, the hi sensitivity of fluorescence detection, and the ability to directly observe the morphology of the molecule in aqueous solutions without the need for drying or applying harsh chemical conditions. Several interesting types of information are obtained from fluorescence measurements ... 

GOLDBERG AND NEGOMIR Aquatic Humic Acid Fractions... 

This chapter presents new information about the physical properties of humic acid fractions from the Okefenokee Swamp, Georgia. Specialized techniques of fluorescence depolarization spectroscopy and phase-shift fluorometry allow the nondestructive determination of molar volume and shape in aqueous solutions. The techniques also provide sufficient data to make a reliable estimate of the number of different fluorophores in the molecule their respective excitation and emission spectra, and their phase-resolved emission spectra. These measurements are possible even in instances where two fluorophores have nearly identical emission specta. The general theoretical background of each method is presented first, followed by the specific results of our measurements. Parts of the theoretical treatment of depolarization and phase-shift fluorometry given here are more fully expanded upon in (5,9-ll). Recent work and reviews of these techniques are given by Warner and McGown (72). 

Malcolm RE, Vaughan D (1979) Effects of humic acid fraction on invertase activities in plant tissues. Soil Biol Biochem 11 65-72 Malcolm RL (1989) Application of solid-state 13C NMR spectroscopy to geochemical studies of humic substances. In Hayes MHB, MacCarthy P, Malcolm RL, Swift RS (eds) Humic substances II. In search of structure. Wiley, Chichester, UK, pp 339-372... 

Beller and Simoneit [20] studied the occurrence of hexachlorophene in extracts of estuarine sediments taken from the Hudson River. Hexachlorophene was detected only in the humic acid fractions of the samples, indicating that it could bind strongly to organic matter and was highly resistant to degradation in that form. 

Mahieu N, Oik DC, Randall EW. 2000b. Analysis of phosphorus in two humic acid fractions of intensively cropped lowland rice soils by P-31-NMR. European Journal of Soil Science 51 391-402. 

Oik DC, Cassman KG, Mahieu N, Randall EW. 1998. Conserved chemical properties of young humic acid fractions in tropical lowland soil under intensive irrigated rice cropping. European Journal of Soil Science 49 337-349. 

Fig. 5.1. Scheme of separating the soil fulvic and humic acid fractions. 

Step 5. Adjust pH to 1.0 with HC1 to precipitate humic acid. Separate humic and fulvic acids by centrifugation. Rinse humic-acid fraction with distilled water until AgN03 test shows no Cl . Dissolve humic acid in 0.1 N NaOH and hydrogen saturate by passing solution through cation-exchange resin in H-form. 

The Temi River samples had the largest aromatic carbon content because of inclusion of the humic acid fraction. Tropical blackwater rivers are known to contain large percentages (as much as 30%) of humic acid DOM because of the low-conductivity waters and lack of solubility controls associated with the sandy podzols in the tropical rain forest (24, 25). 

Figure 1.2. Differential thermal analysis for the humic acid fraction isolated in NaOH from a sapric histosol (1), from the acid precipitate isolated from products of the reaction of meth-ylglyoxal with glycine (2), and from the acid precipitate formed from the reaction of glucose with glycine (3), alkali lignin (4), casein (5), lignin-casein 3 1 complex (6), and lignin-casein 6 1 complex (7).

Figure 1.5. Relationship between the frictional ratio (/// ,m) and the molecular weight for different humic acid fractions isolated from a sapric histosol. The line is the theoretically derived relationship between frictional ratio and molecular weight for a randomly coiled polymer. After Cameron et al. (1972).

Gonzalez-Vila, F. J., and Martin, F. (1987). Modifications of the humic acid fraction in a soil treated with composted municipal refuse. Sci. Total Environ. 62,459 466. 

Senesi, N., Sposito, G., Holtzclaw, K. M., and Bradford G. R. (1989). Chemical properties of metal-humic acid fractions of a sewage sludge-amended aridisol. I. Environ. Qual. 18, 186-194. 

Golchin, A., Clarke, P., Baldock, J. A., Higashi, T., Skjemstad, J. O., and Oades, J. M. (1997). The effects of vegetation and burning on the chemical composition of soil organic matter in a volcanic ash soil shown by 13C NMR spectroscopy. I. Whole soil and humic acid fraction. Geoderma 76,155-174. 

Malcolm, R. E., and Vaughan, D. (1978). Effects of humic acid fractions on invertase activities in plant tissues. Soil Biol. Biochem. 11, 65-72. 

Trubetskoj, O. A., Trubetskaya, O. E., Afanaseva, G. V., Reznikova, O. I., and Saiz-Jimenez, C. (1997). Polyacrylamide gel electrophoresis of soil humic acid fractionated by size-exclusion chromatography and ultrafiltration. J. Chromatogr. A 767, 285-292. 

Francioso, O., Sanchez-Cortes, S, Casarini, D., Garcia-Ramos, J. V., Ciavatta, C., and Gessa, C. (2002). Spectroscopy study of humic acids fractionated by means of tangential ultrafiltration./. Mol. Struct. 609,137-147. 

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