Potentiometric analysis of humic substances and other colloids

1983 ◽  
Vol 61 (7) ◽  
pp. 1671-1682 ◽  
Author(s):  
Paul A. Arp
Keyword(s):  
Humic Substances ◽  
Functional Groups ◽  
Surface Potential ◽  
Goodness Of Fit ◽  
Dissociation Constants ◽  
High Surface ◽  
Colloidal Suspensions ◽  
Acid Base ◽  
Titration Curves ◽  
Consistent Information

The acid–base behaviour of colloidal suspensions of γ-Al2O3, TiO2 (rutile), high surface-charge latex, and humic substances in water is reexamined by using a Nernst-like model and two electrostatic models to simulate the proton-affecting surface potential. The Nernst-like model is based on the assumption that the proton-affecting surface potential is proportional to the Nernst potential. The other models are based on conventional double-layer assumptions. All models yield numerically consistent information about (i) number of chemically discernible functional groups (or collections of functional groups), (ii) their dissociation constants and concentrations, (iii) the free H+- (or OH−-) concentrations in the suspending medium, (iv) surface area of colloidal substance, and (v) surface potential (and charge) as function of ph. Potentiometric analyses are performed on documented titration curves by employing a modified version of the ACBA (acid–base) program developed by Arena etal. The goodness-of-fit information provided by this program suggests that the Nernst-like model is particularly useful for generating and verifying estimates for surface capacities as function of ph.

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

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Martina Klučáková
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Humic Substances ◽  
Functional Groups ◽  
Dissociation Constants ◽  
Fulvic Acids ◽  
Molecular Organization ◽  
Humic And Fulvic Acids ◽  
Acid Base ◽  
Reference Samples

Abstract 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.

scholarly journals Acid dissociation constants of glycopeptides

1977 ◽  
Vol 163 (1) ◽  
pp. 31-38 ◽  
Author(s):  
B M Austen ◽  
R D Marshall
Keyword(s):  
Amino Acid ◽  
Dissociation Constants ◽  
Acid Dissociation ◽  
Hydroxyl Group ◽  
Amino Acid Residues ◽  
Acid Base ◽  
Titration Curves ◽  
Pka Value ◽  
Hen’S Egg ◽  
Additional Amino Acid

Glycopeptides containing mainly four amino acid residues in the sequence Asn-Leu-Thr-Ser, with small amounts of additional amino acid residues, were isolated from enzymic hydrolysates of hen's-egg albumin. Heterogeneity of the carbohydrate moiety was confirmed. Acid-base titrations showed that the alpha-amino group has a pKa value of 6.43 at 25 degrees C. The standard free engery and entropy changes associated with the ionization at 25 degrees C were 37.2kJ-mol-1 and -0.014kJ-mol-1- K-1 respectively. The complications arising in the interpretation of titration curves of the glycopeptides, which are heterogeneous with respect to the peptide chain, were considered and discussed in the light of the earlier suggestion that the titration curve of the glycopeptide might be interpreted as being due in part to a structure in which the hydroxyl group of the threonine residue is hydrogen-bonded to the beta-aspartamido oxygen atom [Neuberger & Marshall (1968) in Symposium on Foods - Carbohydrates and their Roles (Schultz, H.W., Cain, R.F. & Wrolstad, R.W., eds.), pp. 115-132, Avi Publishing Co., Westport, CT]. It is concluded that either the glycopeptides do not contain a hydrogen bond of that type, or, if they do, that it cannot be recognized by acid-base-titration studies.

Nuclear magnetic resonance studies of the acid–base chemistry of amino acids and peptides. III. Determination of the microscopic and macroscopic acid dissociation constants of α,ω-diaminocarboxylic acids

1976 ◽  
Vol 54 (21) ◽  
pp. 3392-3400 ◽  
Author(s):  
Thomas L. Sayer ◽  
Dallas L. Rabenstein
Keyword(s):  
Chemical Shift ◽  
Dissociation Constants ◽  
Nonlinear Least Squares ◽  
Acid Dissociation ◽  
Acid Base ◽  
Acid Dissociation Constants ◽  
Ammonium Group ◽  
Titration Curves ◽  
Chemical Shift Titration ◽  
The Difference

The acid–base chemistry of 2,3-diaminopropionic acid (dap), 2,4-diaminobutyric acid (dab), ornithine (orn), and lysine (lys) has been studied by 13C and proton nmr spectroscopy. Macroscopic acid dissociation constants for titration of the two ammonium groups of each molecule have been calculated from the 13C chemical shift titration curves for the alkyl carbon atoms by nonlinear least squares curve fitting methods. Microscopic acid dissociation constants for the simultaneous titration of the two ammonium groups of protonated orn and lys have been obtained from their proton chemical shift titration curves and from the 13C titration curves for orn and dap. The results indicate that the α-ammonium group of each of these α,ω-diaminocarboxylic acids is more acidic than its ω-ammonium group, but that the difference decreases as the number of carbons separating the ammonium groups decreases so that the acidities of the two ammonium groups of dap are almost identical. Results of pmr studies of the acid–base chemistry of glycyl-L-lysine and L-lysylglycine also are reported.

Acid-base properties of 1,3-diphenyl-5-(1H-tetrazol-2-yl)formazan and 1,3-diphenyl-5-(2H-1,2,4-triazol-3-yl)formazan

1982 ◽  
Vol 47 (11) ◽  
pp. 2882-2889
Author(s):  
Nadezhda Likhareva ◽  
Ladislav Šůcha ◽  
Miloslav Suchánek
Keyword(s):  
Computer Program ◽  
Dissociation Constants ◽  
Acid Base ◽  
New Compounds ◽  
Base Properties

Two new compounds from the formazan series, viz. 1,3-diphenyl-5-(1H-tetrazol-2-yl)formazan and 1,3-diphenyl-5-(2H-1,2,4-triazol-3-yl)formazan, were prepared, and the dissociation constants and molar absorptivities of all of their acid-base species were determined spectrophotometrically employing the SPEKTFOT computer program.

scholarly journals Bifunctional acid–base mesoporous silica@aqueous miscible organic-layered double hydroxides

RSC Advances ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 3749-3754 ◽  
Author(s):  
Hongri Suo ◽  
Haohong Duan ◽  
Chunping Chen ◽  
Jean-Charles Buffet ◽  
Dermot O'Hare
Keyword(s):  
Mesoporous Silica ◽  
Pore Size ◽  
Layered Double Hydroxides ◽  
High Surface ◽  
High Surface Area ◽  
Core Shell ◽  
Acid Base ◽  
Double Hydroxides ◽  
Hierarchical Morphology ◽  
Size And Structure

Core@shell materials which exhibit hierarchical morphology with ultra high surface area and controllable pore size and structure have been synthesised.

Analytical constraints on acidic functional groups in humic substances

2008 ◽  
Vol 39 (6) ◽  
pp. 783-799 ◽  
Author(s):  
Jason D. Ritchie ◽  
E. Michael Perdue
Keyword(s):  
Humic Substances ◽  
Functional Groups

Acid-Base Titration Curves in Disproportionating Redox Systems

1994 ◽  
Vol 71 (8) ◽  
pp. 632 ◽  
Author(s):  
Tadeusz Michalowski ◽  
Andrzej Lesiak
Keyword(s):  
Redox Systems ◽  
Acid Base ◽  
Titration Curves ◽  
Acid Base Titration
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