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The alkaline extracts of an andic soil, a Bhir horizon of a spodic soil and leonardite which, after electrofocusing, displayed bands in the neutral region of the pH gradient, were fractionated by electrophoresis in phosphate buffer at pH 6.5. The non-migrated fraction gave an electrofocusing profile containing only bands focused at pH values above that of the electrophoretic separation. Electrophoresis in sodium acetate buffer pH 4.8 of humic substances extracted from peat permitted isolation of bands focusing above pH4.8. The distribution of metals after electrophoresis suggests that a great part of humic substances which originate bands above pH 6.5 consists of negatively charged Fe and Al complexes. Addition of EDTA to solutions of humic substances extracted from the samples resulted in the disappearance of bands in the neutral region of the pH gradient in the electrofocusing profile of the Bhir sample, while a consistent lessening of these bands was observed in the leonardite and andic soil samples. 相似文献
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Humic substances (HS) extracted from 14 Sphagnum peats of various geographical origin were submitted tocapillary electrophoresis (CE) in free solution and in entangled polymer solutions (25 gl-1 and 50 gl?1) of polyethylene glycol (PEG). Electrophoretic runs were made in uncoated capillaries (75 μm internal diameter) using a tris-hydroxymethylaminomethane (TRIS)-phosphate buffer (pH 8.3) eventually containing PEG and applying a voltage of 10 kV. The HS extract of a Lithuanian peat was fractionated by ultrafiltration into five fractions with a nominal mean relative molecular mass (M) of 3000, 7500, 20 000, 75 000 and 200 000 Da. Without PEG, migration times were not correlated with the logarithm of M, but linear relations were obtained with 25gl?1 and 50gl?1 PEG solutions. Both solutions separated the different fractions by size; the best regression and the largest interval of linearity, M from 3000 to 200 000 Da, was obtained with the 25gl?1 PEG solution. At 10kV and without PEG, migration times ranged from 6.5 to 8.1 min and did not differentiate the peats, whereas at 25gl?1 PEG, migration times ranged from 3.3 to 6.5 min and, when plotted as a function of either the r value or the von Post index (H), which are used to evaluate the degree of decomposition of horticultural peats, they separated samples on the basis of their geographical origin and probable type of mire complex. At 25gl?1 PEG, migration times also showed a well-defined linear decreasing trend with the increase of mean annual temperatures. These relations suggest the hypothesis that humification in mires goes along with an increase in the average size of humic molecules. 相似文献
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The basic principles of the electrophoretic behaviour of humic substances (HS) still need to be systematically investigated. HS extracted from a Cryorthod (HS–1) and from an Haplumbrept (HS–2) were first fractionated by ultrafiltration to obtain two series of fractions of reduced polydispersity with a nominal mean relative molecular mass (M) of 7500, 20000, 40000, 75000 and 200 000 Da. Fractions extracted from the same soil behaved like an homologous series when tested by size exclusion chromatography, showing a linear relation of M with molecular size. When plotted against their mean M, the elution volumes of HS fractions extracted from the two different soils originated lines of different slope. Absolute electrophoretic mobilities of the fractions were determined in polyacrylamide gel slabs of increasing polyacrylamide concentration using a single buffer system; in all gels there was a close linear relation between the electrophoretic mobility and the logarithm of the mean M of HS fractions. Extrapolation of mobilities of HS–1 at zero gel concentration gave intercepts that did not differ significantly, showing that there was a constant mobility for all fractions in free solution. These results mean that charge differences have little effect on the electrophoretic mobilities of HS extracted from the same soil and imply the theoretical possibility of determining M distributions of HS by polyacrylamide gel electrophoresis in a single buffer system. Mobilities of HS–2 fractions were compared with those of HS–1: the latter fitted the regression equations of mobility against logarithm of the molecular weight obtained from HS–1 humic substances only in gels of small acrylamide concentration. Deviations were larger at small M, probably because of the increasing fulvic character of the fractions, and increased in gels of greater acrylamide concentration, indicating that charge differences may not be negligible when comparing humic substances extracted from different soils. 相似文献
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