Effect of physico-chemical heterogeneity of natural complexants

Buffle, Jacques; Altmann, Robert Scott; Filella, Montserrat

doi:10.1016/s0003-2670(00)81237-4

Cited by 57 publications

(14 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Modeling such interactions requires, among other parameters, accurate determination of acid-base properties (concentrations and equilibrium constants). [1][2][3][4][5][6][7][8][9] A major fraction of dissolved OM in natural ecosystems is in fact formed by humic substances (HS), which are characterized by the presence of several functional groups with labile protons such as carboxylic acids, phenols and amines. These moieties are able to bind protons and metal cations that not only affect the geochemistry of natural systems, but also regulate the buffer capacity of waters, soils and sediments, and metal speciation and transport.…”

Section: Introductionmentioning

confidence: 99%

“…These moieties are able to bind protons and metal cations that not only affect the geochemistry of natural systems, but also regulate the buffer capacity of waters, soils and sediments, and metal speciation and transport. [1][2][3][4][5] The assessment of concentrations and equilibrium constants of carboxylic and phenolic groups is, therefore, a key step in the characterization of acidity, ion exchange capacity, and charge development properties of HS systems. 3,[6][7][8][9] Within this context, two main approaches have been employed in the determination of acid contents of fulvic acid (FA) and humic acid (HA) systems: indirect and direct titrations.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Potentiometric acidity determination in humic substances influenced by different analytical procedures

Fernandes¹,

Giacomelli²,

Giovanela³

et al. 2009

J. Braz. Chem. Soc.

View full text Add to dashboard Cite

Os valores de acidez carboxílica (CA), fenólica (PhA) e total (TA) de um conjunto de cinco amostras padrão da Sociedade Internacional de Substâncias Húmicas (IHSS) e de quatro compostos modelo foram determinados pelo método de titulação potenciométrica. Os dados das curvas de titulação foram tratados pelo programa BEST7 assim como pela equação de Henderson-Hasselbalch modificada (MHHM) e os parâmetros obtidos mostraram-se extremamente dependentes do modelo matemático aplicado. Para as amostras de substâncias húmicas (SH), a aplicação da MHHM resultou em uma alta CA e uma baixa PhA, sendo o resultado praticamente oposto quando o programa BEST7 foi empregado. No caso dos compostos modelo entretanto, os valores de acidez convergiram aos valores esperados (teóricos) independente do modelo aplicado. Para investigar as razões das discrepâncias, variações na condução das titulações (p.e., titulação rápida ou lenta) também foram consideradas. O conjunto de informações mostrou que a determinação da acidez de SH por titulação potenciométrica é extremamente dependente do modelo matemático, assim como das condições experimentais aplicadas.Carboxylic (CA), phenolic (PhA) and total (TA) acidity contents of five International Humic Substances Society (IHSS) standards and four model compounds were determined via the potentiometric titration method. Titration curves were scrutinized both by the BEST7 algorithm and the modified Henderson-Hasselbalch model (MHHM). In the case of IHSS samples, the fitting data depended on the analytical procedure undertaken. Whilst high CA and low PhA were usually recorded using the MHHM, the opposite trend was observed employing the BEST7 algorithm. In contrast, in the case of model compounds the acidity values matched well with theoretical data regardless of the procedure. In order to better understand the reasons for such discrepancies changes in the titrations procedure (e.g.: fast or slow) were also considered. General data strongly suggest that acidity determination of humic substances (HS) by potentiometric methods is extremely dependent on both the choice of mathematical model to fit experimental data points as well as the experimental conditions employed.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Potentiometric acidity determination in humic substances influenced by different analytical procedures

Fernandes¹,

Giacomelli²,

Giovanela³

et al. 2009

J. Braz. Chem. Soc.

View full text Add to dashboard Cite

show abstract

“…It is important to emphasize the contribution of the most humified fractions, especially F5 where log K i increased from 4.6 to 6.6 for Al, from 5.9 to 6.5 for Cu, and from 5.7 to 6.6 for Fe. These increments significantly influenced the final value of log K. According to Buffle et al, 4 the buffering behavior of natural heterogeneous complexants plays an important role in controlling free metal ion concentrations. This suggests that the overall effect of organic fractions of differing molecular size is more important than individual site properties, and indicates that the most humified fractions exert a large influence on the complexation of metals in the aquatic environment, and therefore on transport processes, accumulation and bioavailability of metals in natural waters.…”

Section: Resultsmentioning

confidence: 99%

“…Natural OM presents a polyelectrolyte structure, with a large number of polyfunctional groups that are ionized in solution, and different binding sites including carboxylic and phenolic groups, or combinations of these groups. 3 According to Buffle et al, 4 complexation sites of natural complexants exert a buffering action over many orders of magnitude of log[M], which is essential for maintenance of life in natural systems.…”

Section: Introductionmentioning

confidence: 99%

Characterization of interactions between natural organic matter and metals by tangential-flow ultrafiltration and ICP OES

Santos¹,

Romão²,

Oliveira³

et al. 2011

J. Braz. Chem. Soc.

View full text Add to dashboard Cite

O fracionamento por tamanho molecular da matéria orgânica natural (MON) de amostras de água do Parque Nacional Serra de Itabaiana (Brasil) foi utilizado para caracterização temporal da complexação de íons metálicos. Um sistema de ultrafiltração em cinco estágios foi usado para separar a MON em seis frações (F1: > 100; F2: 100-50; F3: 50-30; F4: 30-10; F5: 10-5; F6: < 5 kDa). A distribuição obtida, inicialmente para amostra in natura, mostrou que metais (Al, Ba, Cr, Cu, Fe, Mn, Ni, Pb e Sr) foram complexados, preferencialmente, pela fração F1, a qual continha maior concentração de carbono orgânico dissolvido (COD). A seguinte ordem decrescente de distribuição de carbono foi obtida: F1 >> F3 > F2 = F4 > F6 > F5. As frações F2 e F5 foram as mais humificadas e F6 a menos humificada. Após 30 dias com adição de elevadas concentrações de metais nas amostras filtradas novas distribuições de COD e metais foram observadas. Maior COD ainda foi encontrado na F1 com teores de carbono decrescendo na seguinte ordem: F1 > F2 > F3 > F4 > F5 > F6. Os metais apresentaram distribuições similares e homogêneas em todas as frações. Valores de log K foram similares para as amostras in natura e para aquelas de 30 dias após a adição dos metais (7,1 e 7,0; 6,6 e 6,9; e 7,2 e 7,0 para Al, Cu e Fe-MON, respectivamente), indicando uma nova condição de equilíbrio na distribuição dos metais após 30 dias. As espécies formadas entre MON e os metais adicionados mostraram um modelo de distribuição que mudou em função do tempo de complexação, indicando uma transformação dos sítios de ligação da MON, sugerindo que o efeito coletivo das frações é mais importante que as propriedades individuais e confirmando que as frações mais humificadas exercem grande influência na complexação de metais em ambientes aquáticos.Molecular size fractionation of the natural organic matter (NOM) in water samples from the Serra de Itabaiana National Park (Brazil) was used to characterize the temporal behavior of metal ion complexation. A special five-stage tangential-flow ultrafiltration device was used to separate NOM in six size fractions (F1: > 100; F2: 100-50; F3: 50-30; F4: 30-10; F5: 10-5; F6: < 5 kDa). The distribution patterns obtained for one in natura sample showed that metals (Al, Ba, Cr, Cu, Fe, Mn, Ni, Pb and Sr) were preferentially complexed by the F1 fraction, which contained higher concentration of dissolved organic carbon (DOC). The following decreasing order of carbon distribution in the different fractions was obtained: F1 >> F3 > F2 = F4 > F6 > F5. Fractions F2 and F5 were the most humified, and F6 the least. New distributions of DOC and metals were observed after 30 days when high concentrations of metals were added to filtered samples. Highest DOC was still found in F1, with carbon contents decreasing in the following order: F1 > F2 > F3 > F4 > F5 > F6. The studied metals presented similar and homogeneous distributions in all fractions. Values of log K were similar for samples in natura and 30 days after addition of metals (7.1 and 7.0, 6.6 and 6.9, ...

show abstract

“…In the first one, an expression for the heterogeneous polarographic wave is developed assuming a Langmuir-Freundlich isotherm for the complexation [5,6]. The parameters of the isotherm are fitted using the half-wave potentials [7,8,9].…”

Section: Introductionmentioning

confidence: 99%

Binding Curve from Normalized Limiting Currents of Labile Heterogeneous Metal‐Macromolecular Systems. The Case of Cd/Humic Acid

et al. 2003

View full text Add to dashboard Cite

A set of titrations of different amounts of humic acid with cadmium are performed at pH 6.0 and fixed ionic strength (0.1 M KNO 3 ). Both reverse pulse polarograms, which minimize the electrodic adsorption effects on the limiting current, and potentiometric measurements with an ion selective electrode are recorded along the titrations. The free metal concentration is determined from the polarographic measurement by means of an iterative numerical method recently developed. The resulting binding curve is found to agree very well with the one obtained through the potentiometric data obtained along the same titration. After application of the Donnan model to correct for polyelectrolytic effects, different complexation isotherms have been used to fit the specific binding. Complexation parameters for the Cd/HA system obtained with a Langmuir-Freundlich and Gaussian isotherms are briefly discussed.

show abstract

Effect of physico-chemical heterogeneity of natural complexants

Cited by 57 publications

References 10 publications

Potentiometric acidity determination in humic substances influenced by different analytical procedures

Potentiometric acidity determination in humic substances influenced by different analytical procedures

Characterization of interactions between natural organic matter and metals by tangential-flow ultrafiltration and ICP OES

Binding Curve from Normalized Limiting Currents of Labile Heterogeneous Metal‐Macromolecular Systems. The Case of Cd/Humic Acid

Contact Info

Product

Resources

About