Showing papers on "Titration published in 1991"
TL;DR: In this article, surface titrations on albite indicate that the concentration of specific surface species as a function of solution pH can be correlated to previously published kinetic data for albite dissolution.
177 citations
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01 Feb 1991
TL;DR: In this paper, a classification of Potentiometry and Titrimetry is presented, including acid-base and complexometric Titrations, as well as precipitation and oxidation reduction Titrations.
Abstract: CELLS, ELECTRODES, AND BASIC PROCEDURES. Rudiments of Potentiometry. Classification of Potentiometry and Titrimetry. Classifications and Descriptions of Electrodes. Procedures of Analytical Potentiometry. Electrodes for Potentiotitrimetry. APPLICATIONS TO THE DETERMINATION OF SOLUTION EQUILIBRIUM DATA. The Determination of Ionization Constants in Aqueous Solution. Acid-Base Equilibria in Nonaqueous Solvents. The Determination of Stability Constants by Potentiometric Titration. The Basics of Titrimetry. Acid-Base Titrimetry. Complexometric Titrations. Oxidation-Reduction Titrations. Precipitation Titrations. Appendix. Index.
157 citations
TL;DR: In this article, the aqueous and surface complexation reactions between kaolinite, Pb, Cd and three organic acids were investigated, including p-hydroxybenzoic acid, o-toluic acid and 2,4-dinitrophenol.
Abstract: Potentiometric and ion-selective electrode titrations together with batch sorption/desorption experiments, were performed to explain the aqueous and surface complexation reactions between kaolinite, Pb, Cd and three organic acids. Variables included pH, ionic strength, metal concentration, kaolinite concentration and time. The organic acids used were p-hydroxybenzoic acid, o-toluic acid, and 2,4-dinitrophenol. Titrations were used to derive previously unavailable aqueous conditional stability constants for the organometallic complexes. Batch results showed that aqueous lead-organic complexation reduced sorption of Pb by kaolinite. Cadmium behavior was similar, except for 2,4-dinitrophenol, where Cd sorption was increased. Metal sorption increased with increasing pH and decreasing ionic strength. Distribution ratios (K
d
's) decreased with increasing solid/solution ratio. The subsurface transport of lead and cadmium may be enhanced via complex interactions with organic wastes or their degradation products and sorbent mineral surfaces.
120 citations
TL;DR: Flash-induced absorption changes of pH-indicating dyes were investigated in photosystem II enriched membrane fragments, in order to retrieve the individual contributions to proton release of the successive transitions of the Kok cycle, finding the stoichiometric coefficients to be noninteger and to vary as a function of pH.
Abstract: Flash-induced absorption changes of pH-indicating dyes were investigated in photosystem II enriched membrane fragments, in order to retrieve the individual contributions to proton release of the successive transitions of the Kok cycle. These stoichiometric coefficients were found to be, in general, noninteger and to vary as a function of pH. Proton release on the S0----S1 step decreases from 1.75 at pH 5.5 to 1 at pH 8, while, on S1----S2 the stoichiometry increases from 0 to 0.5 in the same pH range and remains close to 1 for S2----S3. These findings are analyzed in terms of pK shifts of neighboring amino acid residues caused by electrostatic interactions with the redox centers involved in the two first transitions. The electrochromic shift of a chlorophyll, associated with the S transitions, responding to local electrostatic effects was investigated under similar conditions. The pH dependence of this signal upon the successive transitions was found correlated with the titration of the proton release stoichiometries, expressing the electrostatic balance between the oxidation and deprotonation processes.
103 citations
01 Jan 1991
TL;DR: In this article, the authors investigated the adsorption properties of synthetic amorphous iron oxyhydroxide (Fe2O3·H2O(a)) at 25°C for initial Np(V) concentrations between 4.5 × 10−11 and 4.1 M NaNO3 electrolyte solutions undersaturated with atmospheric CO2 for pH > 7.
Abstract: Neptunium adsorption on synthetic amorphous iron oxyhydroxide (Fe2O3·H2O(a)) was investigated at 25°C for initial Np(V) concentrations between 4.5 × 10−11 and 4.5 × 10−13 M in 0.1 M NaNO3 electrolyte solutions undersaturated with atmospheric CO2 for pH > 7. The surface properties of the Fe2O3·H2O(a) were determined by CO2-free acid—base titration (pH(PZC) 8.0 ± 0.2), and surface acidity and electrolyte complexation constants were determined using the triple-layer model (TLM). The aqueous speciation of Np(V) is dominated by the neptunyl oxycation, NpO2+, in the region of the adsorption edges (5 < pH < 8). At the Np concentrations investigated, the adsorption data are consistent with the hypotheses that (1) Fe2O3·H2O(a) can be treated as an “ideal” single-site ligand, (2) no deprotonation of surface sites need be invoked to describe Np(V) adsorption, and (3) NpO2(OH)0 is the dominant Np surface species. A single surface-coordination reaction, XOH + (NpO2+)s + H2O = (XOH − NpO2(OH))0 + Hs+ (log K = −3.2), described all adsorption data and is independent of the surface-coordination model. Surface hydrolysis of NpO2+ occurs 2.4 pH units below NpO2+ hydrolysis in bulk solution (pKHY1 = 8.85).
84 citations
TL;DR: In this paper, a pH-dependent continuous multiligand distribution model was used to determine the stability constant between Cu(II) and dissolved humic material, and the spectral titration curves were then fit to the calculated values produced by the model.
Abstract: We report the use of a pH-dependent continuous multiligand distribution model to determine the stability constant between Cu(II) and dissolved humic material. Fluorescence quenching of the humic material by Cu(II) is used to produce spectral titration curves. The values from the titration curves are then fit, by use of a leastsquares fitting routine, to the calculated values produced by the model. Three titrations at pH 2.5, 3.5, and 4.5 were conducted using this method, and the observed and calculated values are compared
79 citations
TL;DR: In this paper, the reactions of proton consumption in the organic O i and O a+e horizons of strongly acid forest soils (Dystrochrepts) on granite, phyllite and basalt in NE Bavaria, where spruce shows various degrees of decline.
61 citations
TL;DR: In this article, a novel technique is described for the investigation of polyanions by direct polyelectrolyte titration, which enables both the determination of charge densities for polymer characterization as well as the detection of polymers in aqueous solution down to trace concentrations of 10 μg/L.
Abstract: A novel technique is described for the investigation of polyanions by direct polyelectrolyte titration. In connection with a specially developed phototitrator, an extremely high sensitivity can be reached using 3,6-ionene bromide as cationic titrant and eriochrome black T as metachromatic indicator for end-point detection. This enables both the determination of charge densities for polymer characterization as well as the detection of polymers in aqueous solution down to trace concentrations of 10 μg/L. Monovalent salt ions do not interfere with the titration up to concentrations of about 0,1 mol/L. Potential interference of divalent metal ions can be prevented by adding ethylenediaminetetraacetic acid (EDTA) as chelating agent. The applicability of the method was proved by measuring charge densities of poly(sodium acrylate) (NaPAA) in the concentration range of 0,01 to 10 mg/L and of poly(potassium vinyl sulfate) (KPVS). As expected, the charge density of NaPAA decreases with a pH decrease from 11 to 7, whereas the charge density of KPVS is independent of pH.
61 citations
TL;DR: Turbidimetric titration is used for the examination of pectin-casein interactions and is shown to be a simple and reliable method as discussed by the authors. But it is not shown that the addition of Pectin to casein solutions lowers the pH-value at which the casein precipitates.
61 citations
TL;DR: In this article, the main aluminum species have been identified and quantified: unreacted hydrolyzed, complexed monomers, and the Al{sub 13} tridecamer.
Abstract: Aluminum (III) hydrolysis and precipitation in the presence of acetic acid and oxalic acid have been studied by combining potentiometric titration and liquid-state {sup 27}Al NMR. The main aluminum species have thus been identified and quantified: unreacted hydrolyzed, complexed monomers, and the Al{sub 13} tridecamer. A solid species appeared when precipitation occurred and was quantified by difference with the other species. The quantitative evolution of these species was followed for pH values up to 5. Acetate forms weak complexes with aluminum. The precipitated phase was hypothesized to be aggregated Al{sub 13}. Oxalate forms strong multiligand complexes to form Al{sub 13} requires higher hydroxyl content. High oxalate contents (L/M > 1) inhibit tridecamer formation and precipitation occurs only at high pH values. With oxalate the precipitated phase seems to be devoid of Al{sub 13} and of a more condensed nature than it is with acetate.
60 citations
TL;DR: A method is described for simultaneous measurements of heat production rate, oxygen activity and pH, using a 3-ml stirred microcalorimetric titration/perfusion vessel fitted with a polarographic oxygen sensor and a combination pH-electrode.
TL;DR: A sensitive and quick assay for redox proteins based on electrochemical titrations in a thin-layer electrochemical cell is described, using a combination of modified-electrode and "mediator-enhanced" electrochemistry to equilibration of the cell volume with the applied potential.
TL;DR: In this article, a solid titration technique has been developed to avoid a number of the difficulties inherent in solubility studies of calcium phosphates; this employed a graphical method based on pH and calcium-ion electrode potential to identify breakpoints.
Abstract: Despite the well documented importance of carbon dioxide dissolved in physiological media, consideration of its effect on calcium phosphate solubilities has been neglected, an omission now shown to be serious. A solid titration technique has been developed to avoid a number of the difficulties inherent in solubility studies of calcium phosphates; this employed a graphical method based on pH and calcium-ion electrode potential to identify breakpoints. The solubility isotherm at 37.0 °C for hydroxyapatite has thus been determined for the chosen saliva-like medium. A numerical model of the system provided corroboration for the results obtained. An approximately 10-fold increase in the calcium-carrying capacity of that medium was then demonstrated with CO2 present at a fixed partial pressure of 0.035 bar, a result not explicable in terms of known equilibria. Two new complexes, CaH2PO4H2CO+3(β= 54) and CaH2PO4HCO3(β= 43), are postulated to account for the data.
TL;DR: Under certain conditions, a decrease in electroosmotic flow can be observed when the pH is increased at constant buffer concentration, which is related to changes in the ionic strength caused by the titrant.
TL;DR: In this paper, the authors discuss reactions, side reactions, reagent composition, and experimental mechanics as well as the issues involved in assay development for the Karl Fischer titration, including reactions and side reactions.
Abstract: This REPORT includes discussions of the reaction chemistry, side reactions, reagent composition, and experimental mechanics as well as the issues involved in assay development for the Karl Fischer titration
TL;DR: In this article, the Gibbs free energy and the acid equilibrium constant for S2−aq,K2 were determined for aqueous metal sulphides in unusually concentrated media, and the authors made use of the anomalously high equivalent conductance of hydroxide compared with other anions.
TL;DR: In this paper, the enthalpies associated with proton adsorption and desorption in aqueous alumina (γ-Al 2 O 3 ) suspensions were investigated.
TL;DR: In this paper, the adsorption/desorption of oxalic acid and Cd on goethite has been characterized in function of pH in KNO3 medium.
Abstract: The adsorption/desorption of oxalic acid and Cd on goethite has been characterized in function of pH in KNO3 medium. Electrophoretic mobilities and pH titrations show that while anion desorbs, cation adsorbs, the maxima of adsorption being in significantly different pH ranges. Adsorption-desorption phenomena of oxalic acid in function of pH are identical in absence or presence of Cd. Contrarily, not only adsorption, but also desorption of Cd is enhanced in presence of oxalic acid. Surface sites are shown to never be saturated even in presence of excess of ligand and cation. So, competition between anions and cations for surface sites is minor. Ligand in solution does not compete with surface sites for the Cd, probably due to the low tendency of oxalic acid to form complexes with Cd. Behavior of Cd in presence of oxalate is discussed and results suggest a surface-binding of Cd via an oxalate-bridge between the surface and the metallic cation.
TL;DR: In this article, two fluorescence techniques to study metal-humic interactions are presented, namely, Lanthanide Ion Probe Spectroscopy (LIPS) and quenching of the humic material by Cu2+ ions.
Abstract: Two fluorescence techniques to study metal-humic interactions are presented. In the first technique, Lanthanide Ion Probe Spectroscopy (LIPS), the humic samples are titrated by Eu3+ ions. The ratio of the intensities of two emission lines of Eu3+, R=I592/I616, is used to estimate the amount of bound and free species of the probe ions. The titration plot is presented as R versus the logarithm of total added Eu3+. In the second technique, fluorescence quenching of the humic material by Cu2+ is used to produce titration curves of intensity versus the logarithm of total added Cu2+. The two techniques are used in conjunction with a model that treats the various ligands in humic substances as continuous distributions of binding sites in which individual ligand concentrations are normally distributed with respect to the individual stability constants for metal binding. The model includes the effects of pH, ionic strength, and competing metal ions. The parameters of the model are estimated by fitting the spectral titration data to the calculated titration plot. Some simulation and experimental data are presented and discussed.
TL;DR: In this paper, enthalpy decreases with decreasing pH are most likely due to the presence of two or three distinct proton binding sites on the alumina surface, and the authors discussed possible explanations for these effects including inherent heterogeneous site distributions, steric interactions, counterion association with the charged surface and electrostatic contributions.
TL;DR: In this paper, the surface charge of two illitic clays (Fithian and Muloorina illite) was analyzed and it was shown that these clays have similar surface chemistries.
TL;DR: The observed rate constants at 25 degrees C are greater than or equal to 100-fold larger than kcat for this enzyme and indicate that intramolecular electron transfer is not intrinsically rate-limiting in overall catalysis.
TL;DR: The reaction of the glutathione transferase from human placenta with a maleimide spin label derivative with a thiol group which plays a crucial role for the maintenance of the catalytic activity and is characterized by a low pK.
TL;DR: Yields and equilibrium water contents of complex coacervates from these polymers were measured, and microcapsule forming systems based on this effect were developed as potential prostheses for organ transplantation.
TL;DR: In this article, simple ion-selective electrodes of the coated wire type were prepared using an ordinary aluminum wire conductor, coating the central wire with the membrane formed by plasticized poly vinyl chloride.
Abstract: Simple ion-selective electrodes of the coated wire type were prepared using an ordinary aluminum wire conductor, coating the central wire with the membrane formed by plasticized poly vinyl chloride. These simple and inexpensive electrodes can be used advantageously as sensors in ion pair formation-based titrations of surfactants of various types. Cationic surfactants are titrated using sodium tetraphenylborate titrant yielding titration curves with sharp potential breaks. For the determination of nonionic surfactants containing poly oxyalkylene chains, the method used was based on the precipitation of ternary compounds with sodium tetraphenylborate in the presence of bivalent metal ion with an ionic radius higher than 100 pm. Also ampholytic surfactants can be titrated directly with tetraphenylborate in acidic solutions, in which they are cationic; but for the determination of some of them, back-titration is more convenient. Anionic surfactants are titrated using lipophilic cationic titrants such as quaternary ammonium or pyridinium salts. Some mixed systems can also be analyzed. Several examples are given.
TL;DR: In this article, an aerated open-aqueous system where a continuous influx of mixed Mn 2+ and Cd 2+ solution was supplied and pH was maintained with an automated pH-stat adding dilute NaOH X-ray diffraction and electron diffraction identified the solids produced as mixtures of cd 2 Mn 3 4+ O 8 and MnO 2.
TL;DR: In this article, the acid dissociation constants of diclofenac in ethanol-water mixtures, in connection with percutaneous absorption, were determined using the titration method.
TL;DR: In this article, a new all-iridium oxide sensor-actuator device is presented, of which the titrant is generated by a reversible redox reaction occurring in the electroactive iridium oxide actuator electrode, and the equivalence point in the titration curve is detected by the pH-sensitive iridium sensor.
Abstract: Acid or base concentrations can be determined by coulometric titration. A new all-iridium oxide sensor-actuator device is presented, of which the titrant is generated by a reversible redox reaction occurring in the electroactive iridium oxide actuator electrode, and the equivalence point in the titration curve is detected by the pH-sensitive iridium oxide sensor. The advantage with respect to the formerly used noble metal actuator electrode/ISFET sensor device is twofold: on the one hand, interference of Cl− ions, which oxidize at the noble metal actuator electrode during titration, is avoided and on the other hand, the preparation of the all-iridium oxide device is easier than of the ISFET-based devices. In addition to the conventional potential sweep method of oxide growth, a new current-pulse method is proposed, of which the parameters for optimal growth depend less on the pH of the solution.
01 Apr 1991
TL;DR: In this paper, the surface electrochemical properties of capillary pore inorganic microfiltration membranes have been characterized by means of computerized measurements of rates of electroosmosis as a function of pH (reported as ζ potentials) and computerized surface pH titration.
Abstract: The surface electrochemical properties of capillary pore inorganic microfiltration membranes have been characterized by means of computerized measurements of rates of electroosmosis as a function of pH (reported as ζ potentials) and computerized surface pH titration. The membranes have modest values of ζ potential and high titratable surface charge. The incorporation of anions during the membrane manufacturing process has a substantial effect on their surface electrochemical properties. The electrokinetic and titration data have been quantitatively analyzed for a range of pH in 0.01M NaCl solution using models based on electrical double-layer theory and accounting for the nature of the charge-determining groups. Membranes produced in phosphoric acid and membranes produced in oxalic acid have been studied. A description of the membrane surface in terms of a two-dimensional array of aluminum oxide and phosphate or oxalate groups, a site dissociation—site binding model, gave estimates of the ratio (q) of aluminum oxide/incorporated anion groups at the membrane surface and of the pK values of these groups. However, such a model gave a reasonable match of calculated and experimental surfae charge density/pH profiles only if physically unreasonable values for the thickness or dielectric constant of the inner part of the double layer were used. A much more satisfactory approach was to describe the membrane surface as a three-dimensional array (gel) of charged groups and consider that both protons and counterions could penetrate this gel region. Such a gel model allowed the a priori prediction of both surface charge density/pH and ζ potential/pH profiles and gave a good description of the membrane surface for both types of membrane. The model allowed estimation of the thickness of the gel layer, the specific adsorption energy of the counterions, the ratioq, and the pK values of charge-determining groups.