Sephadex humic acids

Yoshimura et al. [193] carried out microdeterminations of phosphate by gel-phase colorimetry with molybdenum blue. In this method phosphate reacted with molybdate in acidic conditions to produce 12-phosphomolybdate. The blue species of phosphomolybdate were reduced by ascorbic acid in the presence of antimonyl ions and adsorbed on to Sephadex G-25 gel beads. Attenuation at 836 and 416 nm (adsorption maximum and minimum wavelengths) was measured, and the difference was used to determine trace levels of phosphate. The effect of nitrate, sulfate, silicic acid, arsenate, aluminium, titanium, iron, manganese, copper, and humic acid on the determination were examined. 

Mori, S., Hiraide, M., and Mizuike, A. (1987). Aqueous size-exclusion chromatography of humic acids on a sephadex gel column with diluted phosphate buffers as eluents. Anal. Chim. Acta 193, 231-238. 

Posner, A. M. (1963). Importance of electrolyte in the determination of molecular weights by Sephadex gel filtration, with especial reference to humic acid. Nature 196,1161-1163. 

Gel filtration chromatography on a Sephadex G 100 column has been used to fractionate humic acid. 

Gel filtration chromatography using Sephadex G100 as column packing and ultraviolet detectors, have been used in studies carried out on the elution of humic acid [8] and in characterisation studies on secondary sewage effluents [9] and in organic substances in river waters [10],... 

A. M. Posner, Nature, 198 1161 (1963). Importance of Electrolytes in the Determination of Molecular Weights by Sephadex Gel Filtration, with Especial Reference to Humic Acid. 

TABLE 4. Apparent Molecular Weight Distribution of Humic Acids and Fulvic Acids from Lake Sediments as Determined by Sephadex Gel Permeation... 

FIGURE 3. Gel permeation chromatography of humic acid on Sephadex G-lOO showing the effect of eluent on adsorption. 

Another area that must be explored is that of the NMR spectra of fractionated humic and fulvic acids. Preliminary studies in our laboratory indicate that the humic acid fractions obtained by adsorption chromatography on Sephadex gels have different NMR spectra. Fractionation of humic substances may therefore allow one to measure NMR spectra of more homogeneous samples. These spectra should be better resolved and be more readily interpretable. 

Kolesnikov, M. P. (1978). Molecular weight distribution of humic acids according to gel chromatography on Sephadexes. Sov. Soil Sci. 10, I74-I8I. 

Gel permeation chromatography has been used in studies of water-soluble melanins. Several fractions were separated from allomelanin from Aspergillus niger on Sephadex G gels (Ref. 7, p. 131). Similarly, humic acids were separated into three fractions on Sephadex G-75 (297). 

Obenaus R., Neumann H.J. and Miicke D. (1966) Determination of the humic acid content of coffee extracts by means of gel filtration on Sephadex G-25. Naturwissenschaften 53, 19-20. (Chem. Abstr. 64, 11771 h). 

Humic acids, a class of naturally occurring organic polyelectrolytes found 1n soil and natural waters, have been the subject of considerable study with Sephadex SEC (34-36). Unfortunately, both electrostatic repulsive effects and hydrophobic adsorption influence the chromatography on Sephadex of these complex polyacids. Since the first effect is diminished and the second increased by added salt, solvents that eliminate non-steric effects have apparently not been identified (36). 

LADD J.N. 1969. The extinction coefficients of soil humic acids fractionated by Sephadex gel filtration. Soil Science, 107,... 

FIGURE 5. Effect of humic acid fractions separated on G-75 Sephadex on invertase synthesis in beetroot discs (from Vaughanl )... 

MATO M.C., OLMEDO M.G. and MENDEZ J. 1972. Inhibition of indoleacetic acid oxidase by soil humic acids fractionated in Sephadex. Soil Biology and Biochemistry, 4, 469-473. 

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