On-line fractionation and characterization of aquatic humic substances by means of sequential-stage ultrafiltration

Burba, P.; Shkinev, V. M.; Spivakov, B. Ya.

doi:10.1007/bf00324294

Cited by 72 publications

(44 citation statements)

References 4 publications

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“…As bandas nas regiões de 1630 e 1720 cm -1 são devidas a vibrações de carbonílas de grupos carboxilatos e/ ou carboxílicos e/ou cetonas. Picos em torno de 1385 cm -1 e bandas na região de 1035 -1100 cm -1 estão associados ao estiramento do grupo carboxilato e estiramento CO de álcoois, respectivamente 20,22 . Comparando-se os espectros das frações de diferentes tamanhos moleculares, verificam-se praticamente as mesmas bandas de absorção, indicando grande similaridade entre os grupos funcionais presentes nas estruturas das frações.…”

Section: Resultados E Discussão Fracionamento E Caracterização Das Frunclassified

Distribuição de metais e caracterização das constantes de troca entre espécies metálicas e frações húmicas aquáticas de diferentes tamanhos moleculares

et al. 2002

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100 - <5 kDa) and characterized by several techniques. Molar ratios H/C suggested higher aromaticity for fractions F1 and F6 whereas molar ratios C/N didn´t show any differences regarding the humification degree between the fractions. The UV-Vis absorbance a254/a436 ratio showed higher results for F4 and F5, probably by less condensed features. FTIR studies showed high similarity in the functional groups in the fractions. The highest percentage of traces of Co, Al, Fe, Mn, Cu, Zn and Ni (determined by ICP-AES) was preferably complexed by fractions F3 and F4 with a greater amount of dissolved organic carbon (DOC). In addition, the exchange constants, determined by ultrafiltration method, showed complexes AHS-Fe and AHS-Al with higher stability than complexes AHS-Co in all fractions.]]>

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Section: Resultados E Discussão Fracionamento E Caracterização Das Frunclassified

Distribuição de metais e caracterização das constantes de troca entre espécies metálicas e frações húmicas aquáticas de diferentes tamanhos moleculares

et al. 2002

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“…All of the methods mentioned above may only be applied to aqueous solutions, giving rise to erroneous molecular mass distribution data due to aggregation phenomena (see Reference 8) depending on the pH value and salt concentration. 9 It has been suggested that increasing electrolyte concentrations cause changes to the size of the HA macromolecule as the intramolecular charge repulsion power decreases. In this case it is not the actual molecular mass of the HA molecules which is changed, but their tertiary structure.…”

Section: Resultsmentioning

confidence: 99%

Evaluation of matrix-assisted laser desorption/ionization (MALDI) time- of-flight (TOF) mass spectrometry as a method for the determination of the molecular mass distributions of humic acids

Remmler¹,

Georgi²,

Kopinke³

1995

Eur. J. Mass Spectrom.

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Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was investigated for the characterization of natural polymers of environmental interest. The results suggest that the method can be used only with limitations, because of cluster formation and fragmentation phenomena, for the determination of the molecular mass distribution of humic acids. Evidence for existing basic groups in this materials was found. However, a quantification or estimation of the proportion of these basic units to the intact humic acid structure is not yet possible.

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“…The percentages of these fractions in TOC were as follows: >200 kDa ({(TOC<0.45 µm -TOC<200 kDa)/TOC<0.45 µm} × 100) = 35.5%, 10 k -20 kDa ({(TOC<20 kDa -TOC<10 kDa)/TOC<0.45 µm} × 100) = 17.4%, <1 kDa ((TOC<1 kDa/TOC<0.45 µm) × 100) = 33.3%. In contrast, the E350/E450 values, which roughly depend on the humification degree of humic substances, 13 gradually increased as the molecular weight decreased. This tendency implies that the molecular weight of the humic acid became small by humification.…”

Section: Methodsmentioning

confidence: 93%

Evaluation of the Copper(II) Complexing Ability of Ultrafiltered Humic Acid by the Solvent Extraction Method

et al. 2003

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A commercial humic acid dissolved in water was fractionated to nine samples by means of ultrafiltration (UF); the nominal molecular weight used for UF membranes was 1 k -200 kDa. Concerning the nine samples, copper(II) complexing capacities (CuCC) and conditional stability constants (β) of the formed copper(II) complexes were measured by a solvent extraction method. A total organic carbon (TOC) and the UV-VIS absorption ratio (E350 nm/E450 nm) were also measured. From a comparison of these data, it was found that a) humic acids in each fraction formed two kinds of copper(II) complexes with different stability; b) the β values obtained from each fraction were almost the same; c) large CuCC values were observed in the molecular weight range from 10 kDa to 20 kDa and below 1 kDa; d) molecules with molecular weight higher than 50 kDa scarcely had any copper(II) complexing ability; e) the values of CuCC/TOC of each fraction were in the range from 1.7 to 3.4 × 10 -7 mol mg -1 .

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On-line fractionation and characterization of aquatic humic substances by means of sequential-stage ultrafiltration

Cited by 72 publications

References 4 publications

Distribuição de metais e caracterização das constantes de troca entre espécies metálicas e frações húmicas aquáticas de diferentes tamanhos moleculares

Distribuição de metais e caracterização das constantes de troca entre espécies metálicas e frações húmicas aquáticas de diferentes tamanhos moleculares

Evaluation of matrix-assisted laser desorption/ionization (MALDI) time- of-flight (TOF) mass spectrometry as a method for the determination of the molecular mass distributions of humic acids

Evaluation of the Copper(II) Complexing Ability of Ultrafiltered Humic Acid by the Solvent Extraction Method

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