Characterization of pH-fractionated humic acids with respect to their dissociation behaviour

Klučáková, Martina

doi:10.1007/s11356-015-5932-2

Cited by 22 publications

(17 citation statements)

References 36 publications

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“…The concentration, pH, ionic strength, and nature of the counter-ion influence the size and shape of the dissolved organic species (Durce et al, 2016 ). However, many fundamental questions relating, in particular, to the physicochemical characteristics of humic and fulvic molecules are yet to be answered (Klučáková, 2016 ; Tarasevich et al, 2016 ). The data on the molecular mass and size of humic molecules reported in literature are rather confusing and are strongly influenced by differences in experimental conditions.…”

Section: Introductionmentioning

confidence: 99%

Size and Charge Evaluation of Standard Humic and Fulvic Acids as Crucial Factors to Determine Their Environmental Behavior and Impact

Klučáková

2018

Front. Chem.

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In this work, the size and charge of humic and fulvic standards purchased from the International Humic Substances Society are presented and discussed. The secondary structure of humic substances in water environment as well as the size and shape of the dissolved humic species and their changes are ill-defined, very dynamic and can be strongly affected by environmental conditions as the concentration, pH, and ionic strength. They have a strong propensity to aggregate which control their interactions with other components, mobility, and functioning in the environment. Particle size distributions were determined by means of dynamic light scattering, zeta potential by Doppler electrophoresis. The intensity, volume, and number particle size distribution were obtained. Two or three different size fractions were detected in the studied systems. Large macroparticles (>1 μm) were observed in the majority of them, mainly in the case of more concentrated solutions. Medium fractions of fulvic submicroparticles had higher average diameters (500–1,200 nm) than those in humic acids (300–600 nm). Small nanoparticles (<100 nm) were detected mainly in alkaline solutions. Fulvic acids with more functional groups (active sites) can form more easily bigger particles mainly in medium concentration region. Alkaline conditions supported the expansion of humic and fulvic coils and liberation of small particles from them. The colloidal stability, indicated by more negative zeta potentials, was higher for humic acids. In the case of fulvic acids, the colloidal stability increased with increasing pH as a result of the dissociation of their functional groups. The increase of particle size corresponded usually with higher stability.

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Section: Introductionmentioning

confidence: 99%

Size and Charge Evaluation of Standard Humic and Fulvic Acids as Crucial Factors to Determine Their Environmental Behavior and Impact

Klučáková

2018

Front. Chem.

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“…Amounts of acidic functional groups determined on the basis of flow-through coulometry involved both protonated (undissociated) and dissociated groups in studied systems. It is very useful mainly in the case of humic acids which are only partially soluble in water and the determination of their concentration in leachates is accompanied with several problems [29][30][31]36]. Amounts of dissociated acidic groups were determined on the basis of pH-measurements.…”

Section: Resultsmentioning

confidence: 99%

“…It is the most important medium of organic carbon transport from terrestrial to aquatic ecosystems. This fraction can be rich in acidic functional groups and its size can be the result of equilibrium between dissolved and undissolved humic acids [31,32,36].…”

Section: Introductionmentioning

confidence: 99%

New possibility for characterization of dissociation behaviour of supramolecular electrolytes: results obtained for the International Humic Substances Society standard and reference samples by coulometry

Klučáková

2021

Chem. Biol. Technol. Agric.

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Background Humic substances can be considered as polyelectrolytes with supramolecular character and complicated behaviour in water environment. The fractions of humic substances dissolved in water are the most active ones and determinative for their functioning in nature, where the proton-binding and dissociation ability play a crucial role. The dissociation behaviour of humic and fulvic acids can be affected by different circumstances including their concentration which is directly connected with the molecular organization of humic particles in solution and the accessibility of their ionizable functional groups. This study is focused just on these active fractions and their dissociation behaviour in the dependence on their content in studied system. Results Standards and reference samples of International Humic Substances Society were used. Flow-through coulometry was used to determine the total content of acidic functional groups in fulvic solutions and humic leachates. The amount of dissociated acidic groups was determined on the basis of potentiometry. Several differences between the behaviour of humic and fulvic acids were found. While whole samples of fulvic acids including the weakest functional groups were analysed, only the active dissolved humic fractions containing stronger acidic functional groups were characterized. The fractions containing higher amounts of the weakest functional groups remained insoluble. The dissociation degree of fulvic acids decreased with their increasing content, but a maximum on its concentration dependence obtained for humic acids was observed. Conclusions Two different values of dissociation constants were determined for each sample. The first was determined on the basis of the extrapolation of infinite dilution, second was determined as their average value in the region of high concentrations in which it was constant. Obtained values characterize the functioning of dissolved humic substances from point of view of their dissociation ability. The results obtained by this approach can help to predict the acid–base behaviour of dissolved organic carbon in soil and generally in nature. The acid–base behaviour of dissolved organic carbon depends on its ratio to water. It behaves differently in soil which is dry and in soil which is wet or saturated by water.

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“…As reported previously by others [24,25], we also observed unusual solubility behavior of this HA sample, which enabled us to isolate four fractions by sequential dissolution under near-neutral pH conditionstwo water-soluble products (S1 and S2) and two water-insoluble residues (I1 and I2). Although not carried out here, it is possible that a more exhaustive separation scheme, perhaps including pH and ionic strength variation, would lead to a greater number of narrower class fractions as are being studied by Klučáková and her coworkers [78][79][80][81].…”

Section: Discussionmentioning

confidence: 99%

Water-based fractionation of a commercial humic acid. Solid-state and colloidal characterization of the solubility fractions

Swiech

Hamerton

Zeng³

et al. 2017

Journal of Colloid and Interface Science

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Using this simple approach, the HA has been shown to contain non-covalently bonded species with different polarity and water solubility. The soluble and insoluble fractions have very different chemical structures, as revealed particularly by their solid-state properties (C NMR and IR spectroscopy, and TGA); in particular, S1 and S2 are characterized by higher carbonyl and aromatic contents, compared with I1 and I2. As shown by solution SAXS measurements and AFM, the soluble fractions behave as hydrophilic colloidal aggregates of at least 50nm diameter.

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Characterization of pH-fractionated humic acids with respect to their dissociation behaviour

Cited by 22 publications

References 36 publications

Size and Charge Evaluation of Standard Humic and Fulvic Acids as Crucial Factors to Determine Their Environmental Behavior and Impact

Size and Charge Evaluation of Standard Humic and Fulvic Acids as Crucial Factors to Determine Their Environmental Behavior and Impact

New possibility for characterization of dissociation behaviour of supramolecular electrolytes: results obtained for the International Humic Substances Society standard and reference samples by coulometry

Water-based fractionation of a commercial humic acid. Solid-state and colloidal characterization of the solubility fractions

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