Adsorption-based approach to determine the size and mass of humic acids molecules

Abstract

The state of sodium humate in aqueous solution and on a solid surface is studied using various methods. It is shown that in aqueous solution at neutral pH and low ionic strength this substance exists in an associated state. The values of molecular mass of the molecules in the preparation studied (Aldrich) are determined to be 1, 3-6 and 15 kDa. A new adsorption-based approach for initial estimation of the molecular mass and size of humic acid molecules is proposed, which can be used instead of any specific sophisticated equipment. The size of the molecules of the studied preparation estimated in this way (in the range of 2.3 to 9.0 nm), agree well with data obtained by chromatographic and electron microscopic measurements, which confirm the reliability of the proposed method.

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

“…A similar approach used by Esfahani et al ( 2015 ) detected three populations in SRHA, SRFA and Aldrich humic acids (10–100, 100–1,000 nm, and >1 μm) on the basis of volume based distributions. Volume distributions were also preferred by Tarasevich et al ( 2016 ) who analyzed the sodium salt of Aldrich humic acids and divided it into three fractions called nanoparticles (30–150 nm), submicroparticles (200–700 nm), and microparticles (1.6–5.6 μm).…”

“…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.…”

“…Angelico et al ( 2014 ) showed that particle size, charge, and colloidal stability were strictly dependent on surface functional groups. Tarasevich et al ( 2016 ) divided humate particles into three fractions: nanoparticles, submicroparticles and microparticles. The characteristic diameter and zeta potential of the fractions were strongly dependent on concentration.…”

Characterization of coal-based fulvic acid and the construction of a fulvic acid molecular model

“…The results of titration experiments with acidic functional groups showed that the carboxyl group content in FA was approximately three times the phenolic hydroxyl group content. Combined with the spectral data for oxygen-containing functional groups in the range of 1000-1800 cm À1 and the relative content of oxygen, the molecular 3,21,[23][24][25][26][27][29][30][31] with the ndings of past research on HA and FA, the numbers and positions of functional groups were continuously adjusted to approximate the experimental test parameters. The resulting two-dimensional planar molecular structure model of FA is shown in Fig.…”

Determination of Organic Compounds, Fulvic Acid, Humic Acid, and Humin in Peat and Sapropel Alkaline Extracts

“…Research carried out in various countries suggests that the efficacy of humic acid depends on its extremely complex chemical structure, which makes biochemical investigations elaborate, costly, and difficult to reproduce [ 7 ]. Many fundamental questions relating, in particular, to the physicochemical characteristics of humic and fulvic molecules are yet to be answered [ 21 , 22 ]. Differences in the obtained values have been attributed to either the variability of humic substances or the intrinsic limitations of methods when applied to poly-disperse humic systems [ 23 , 24 ].…”