scholarly journals Humic acid complexation to Zn and Cd determined with the new electroanalytical technique AGNES

2007 ◽  
Vol 4 (5) ◽  
pp. 347 ◽  
Author(s):  
Encarnació Companys ◽  
Jaume Puy ◽  
Josep Galceran
Keyword(s):  
Humic Acid ◽  
Humic Acids ◽  
Metal Ion ◽  
Deposition Time ◽  
Aquatic Environments ◽  
Free Concentration ◽  
Know How ◽  
Soil Humic Acid ◽  
Free Metal

Environmental context. Humic substances are complex mixtures that play an important role in trace metal bioavailability in soils and aquatic environments. The bioavailability of a metal depends on what chemical forms, or species, it is in. We need to know how much of the metal is present as a free metal ion in solution, and how much is bound up in complexes with humic acids, for example. This work reports the complexation of Cd and Zn to humic acids by means of a simple and robust technique, AGNES (absence of gradients and Nernstian equilibrium stripping). Abstract. AGNES (absence of gradients and Nernstian equilibrium stripping), an emerging electroanalytical technique specifically designed for the determination of the free concentration of heavy metals in aqueous solutions, is here implemented to characterise the binding of CdII and ZnII to a soil humic acid. A set of metal titration experiments were performed by adding Cd or Zn to a purified humic acid (Aldrich) at pH 4, 5, 6 and 7 and measuring the free metal concentration by AGNES. The application of a program with two potential steps along the deposition stage allows for the reduction of the deposition time in the humic titration. The polyelectrolytic effects of the macromolecular ligand were taken into account through the Donnan model. Data free of electrostatic effects were reasonably described by the NICA isotherm, which accounts for heterogeneity, considering just a monomodal distribution (because of the range of pH covered). The obtained affinity parameters indicate a similar strength for Zn and Cd binding to the purified humic acid.

Ion Exchange Complexing Resins as Sensors for the Determination of Free Metal Ion Concentration at a Low Level

2008 ◽  
Vol 26 (3) ◽  
pp. 301-320 ◽  
Author(s):  
Maria Pesavento ◽  
Antonella Profumo ◽  
Raffaela Biesuz ◽  
Giancarla Alberti
Keyword(s):  
Ion Exchange ◽  
Metal Ion ◽  
Ion Concentration ◽  
Low Level ◽  
Free Metal ◽  
Free Metal Ion

A study of the Ca2+ – Arsenazo III system and its application to the spectrophotometric determination of free calcium in solution

1990 ◽  
Vol 68 (11) ◽  
pp. 1932-1936 ◽  
Author(s):  
Byron Kratochvil ◽  
Xi-Wen He
Keyword(s):  
Ionic Strength ◽  
Calcium Ion ◽  
Calcium Binding ◽  
Metal Ion ◽  
Arsenazo Iii ◽  
Free Calcium ◽  
Ionic Calcium ◽  
Free Metal ◽  
Free Metal Ion

A two-wavelength method was applied to the determination of free, ionic calcium with Arsenazo III in solutions containing calcium-binding ligands. By this procedure impurities in the indicator can be corrected for, thereby allowing the use of commercial indicator preparations with purities as low as 80%. Only a 1:1 complex with a conditional log stability constant of 4.28 ± 0.13 at pH 4.6 and ionic strength 0.1 was found under the conditions studied. Key words: free metal ion determination, calcium ion speciation, spectrophotometry, arsenazo III, ion increment method for speciation.

scholarly journals PHOTO-REDUCTION KINETICS OF MnO2 IN AQUATIC ENVIRONMENTS CONTAINING HUMIC ACIDS

2010 ◽  
Vol 8 (1) ◽  
pp. 37-41 ◽  
Author(s):  
Narsito Narsito ◽  
Sri Juari Santosa ◽  
Setya Lastuti
Keyword(s):  
Humic Acid ◽  
Aqueous Medium ◽  
Humic Acids ◽  
Radical Scavenger ◽  
Aquatic Environments ◽  
Oh Radicals ◽  
Anion Complex ◽  
Reduction Efficiency ◽  
Internal Electron ◽  
Kinetics Of

The kinetics of photo-reduction of manganese(IV) oxide, MnO2 in aqueous medium, in the presence of humic acid has been investigated, including the possibility for the involvement of such radicals in the reduction. Results showed that in aqueous medium, the efficiency of the photo-reduction of MnO2 producing a soluble ionic Mn(II) was governed strongly by an internal electron transfer within an intermediate of HA-MnO2 anion complex, resulted in the chemical adsorption of humic acid on MnO2 surface. It was observed that under solar radiation and atmosphere containing oxygen, the rate of MnO2 reduction increased considerably, by factors of about 46 and 2 respectively. Moreover, there was evidence that some radicals certainly played a role in the photo-reduction of MnO2, since radical scavenger addition significantly decreased the reduction efficiency of MnO2. In the present of an excess of propanol-2, however, which was expected to remove all OH radicals present, only about 60 % decrease in reduction efficiency were observed, suggesting that radicals other than OH radical are involved in the reduction of MnO2. It was observed further that the presence of iron(III) in MnO2 up to 1 % (w/w) did not alter the reduction efficiency of MnO2.   Keywords: MnO2 kinetics, photo-reduction, aquatic, humic acids

scholarly journals Determination of free metal ion concentrations with AGNES in low ionic strength media

2013 ◽  
Vol 689 ◽  
pp. 276-283 ◽  
Author(s):  
D. Aguilar ◽  
C. Parat ◽  
J. Galceran ◽  
E. Companys ◽  
J. Puy ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Metal Ion ◽  
Ion Concentrations ◽  
Low Ionic Strength ◽  
Free Metal ◽  
Free Metal Ion

scholarly journals HUMIC ACID CRACKING BY ACTIVATED CLAY CATALYSTS AND IDENTIFICATION OF ITS PRODUCTS

2015 ◽  
Vol 1 (1) ◽  
pp. 9-17
Author(s):  
Abdullah Abdullah ◽  
Rina Twinasty ◽  
Taufiqur Rohman
Keyword(s):  
Humic Acid ◽  
Surface Area ◽  
Functional Groups ◽  
Humic Acids ◽  
Pore Radius ◽  
Ash Content ◽  
Fixed Bed Reactor ◽  
Liquid Smoke

Humic acid is a compound of colloidal,amorphous, and complex aromatic polymerwith functional groups of -COOH (carboxyl), -OH (phenol), and C = O (carbonyl). The presence of these functional groups provides a rationale for assuming that humic acids have a potential to produce phenolic, carboxylic and carbonylic compounds through cracking process. In this study the cracking was done by isolating humic acids from peat soil, and facilitated by a clay catalyst which had been activated. Humic acids were isolated by extracting the acids from the peat with NaOH and HCl. The characterization of humic acids included the determination of the ash content by gravimetric method and the analysis of the functional groups of humic acids by Infrared spectrometer (FTIR). The clay to be activated was shaped into two forms, pellets and 20-40 mesh granules. The clay was activated by immersing it in HCl and NH4NO3, and then calcined. The characterization of catalysts included the determination of acidity and the Si/Al ratio gravimetrically, as well as the analysis of the pore volume, maximum pore radius, surface area and average pore radius by Surface Area Analyzer NOVA-1000. Humic acid cracking was performed by a fixed-bed reactor system at a temperature of 400°C. The Liquid smoke, the product of cracking, was analyzed by GC and GC-MS to determine the number of compounds and major compounds contained in the liquid smoke. The results show that the isolated humic acid had ash content of 9.10%. Activated clay had acidity and Si/Al ratio higher than the clay before actifated. Based on the analyses of GC and GC-MS it can be found out that the major compounds contained in liquid smoke, the product of humic acid cracking with 20-40 mesh catalyst at a temperature of 400°C were phenolic compounds (74.56%), and no carboxylic and carbonylic compounds as the major compounds. The activated clay can be used as the catalyst for humic acid cracking.

scholarly journals Cu and Pb accumulation by the marine diatom Thalassiosira weissflogii in the presence of humic acids

2010 ◽  
Vol 7 (3) ◽  
pp. 309 ◽  
Author(s):  
Paula Sánchez-Marín ◽  
Vera I. Slaveykova ◽  
Ricardo Beiras
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Humic Acids ◽  
Metal Ion ◽  
Cell Membranes ◽  
Marine Diatom ◽  
Membrane Properties ◽  
Thalassiosira Weissflogii ◽  
Cell Surfaces ◽  
Free Metal

Environmental context.Dissolved organic matter protects aquatic microorganisms from toxic metals by complexing and decreasing the concentration of the biologically reactive species such as free metal ions. However, there are some cases of enhancement of toxic effects when humic acids are present, which is thought to be due to effects of adsorbed humic acids on cell membranes. For a marine diatom, humic acids adsorbed to cell surfaces enhanced metal adsorption, whereas intracellular metal contents decreased as a result of metal binding by humic acids. These findings suggest that the diatom wall, the frustule, presents a barrier against direct effects of adsorbed humic acids on the plasma membrane. Abstract.Metal complexation by dissolved organic matter, as humic acids, is considered to decrease metal bioavailability by lowering the free metal ion concentration. However, dissolved organic matter adsorption on cell surfaces can modify cell membrane properties, which can also influence metal uptake. Copper and lead accumulation and internalisation by the marine diatom Thalassiosira weissflogii were studied in the absence and presence of humic acids, and adsorption of humic acids to cell surfaces was evaluated. Both Pb and Cu intracellular concentrations decreased in the presence of humic acids according to labile metal concentrations measured by anodic stripping voltammetry, whereas total (intracellular plus adsorbed) metal content was enhanced in the presence of humic acids, probably owing to enhanced metal plus humics adsorption to cell surfaces. The results of the present work stress the importance of differentiating between intracellular and total cellular metal in bioavailability studies, and suggest that the silica frustule of diatoms represents a barrier against humic acids effects on cell membranes.

Inhibition and simulation of proteolytic enzyme activities by soil humic acids

Soil Research ◽  
1969 ◽  
Vol 7 (3) ◽  
pp. 253 ◽  
Author(s):  
JN Ladd ◽  
JHA Butler
Keyword(s):  
Humic Acid ◽  
Humic Acids ◽  
Metal Ion ◽  
Proteolytic Enzymes ◽  
Relative Effectiveness ◽  
Trypsin Activity ◽  
Carboxypeptidase A ◽  
Molecular Weights ◽  
Soil Humic Acids ◽  
Stimulation Of

The effects of neutralized solutions of soil humic acids on the activities of a range of proteolytic enzymes and of tyrosinase have been measured. Humic acids inhibit carboxypeptidase A, chymotrypsin A, pronase, and trypsin activities, stimulate papain, ficin, subtilopeptidase A, and thermolysin activities, and had no effect on phaseolain and tyrosinase activities. Stimulation of papain and ficin activities is not due to formation of metal ion-humic acid complexes. Inhibition of trypsin activity and stimulation of papain activity increased with increasing molecular weight of the humic acid. However, humic acid fractions of varying molecular weights had similar effects on the magnitude of inhibition of pronase and carboxypeptidase A activities. Polycondensates derived from p-benzoquinone and catechol influenced enzyme activity in the same way as humic acids, although the order of their relative effectiveness changed with different enzymes. Polyacrylate preparations were the most effective inhibitors of trypsin activity but had no effect on papain and ficin activities.

Spectrophotometric determination of free, ionized, metal ion concentrations in solution by an indicator increment method. Application to the determination of free Mg2+ with calmagite

1995 ◽  
Vol 73 (2) ◽  
pp. 296-302
Author(s):  
Hongji Ren ◽  
Byron Kratochvil ◽  
Xiwen He
Keyword(s):  
Metal Ion ◽  
Ion Concentration ◽  
Multiple Equilibrium ◽  
Conditional Stability ◽  
Ligand Complex ◽  
Conditional Stability Constant ◽  
Visible Spectra ◽  
Free Magnesium ◽  
Free Metal

A spectrophotometric method, called the Indicator Increment Method, is described in which varying amounts of a complexing indicator are added to a sample and the visible spectra recorded after each addition. Through multiple equilibrium calculations the free metal ion concentration, as well as total metal and total ligand concentrations, can be estimated in systems that contain a single metal ion and one ligand. The technique was tested successfully for the determination of free magnesium in the presence of NTA, phosphate, or oxalate using calmagite as indicator. The method requires the approximate conditional stability constant of the metal–ligand complex to be known beforehand. Keywords: ionized magnesium, indicator increment method, spectrophotometry.

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