Showing papers on "Titration published in 1987"
TL;DR: The oxygen flash yield and the kinetics of Chl a+II (P-680+) reduction have been measured under repetitive excitation as a function of pH between pH 4.0 and pH 9.0 in oxygen-evolving PS II particles from Synechococcus sp.
81 citations
01 Jun 1987
TL;DR: In this article, the surface acidity of hydrous CdS was determined by both the electrokinetic and the alkalimetric titration methods, and the potential determining role of Cd 2+ ion (PDI) was also established.
Abstract: The surface acidity of hydrous CdS was determined by both the electrokinetic and the alkalimetric titration methods. The potential determining role of Cd 2+ ion (PDI) was also established. In aqueous solution, two types of surface functional sites can be recognized, namely, Bro¨nsted sites where H + and OH − ions are PDI and Lewis sites where Cd 2+ and S 2− are PDI. In the absence of specific adsorption, both the titration and the electrokinetic methods can be used to determine the intrinsic Bro¨nsted and Lewis acidity constants. At an ionic strength of 5 × 10 −2 M , the acidity constants (p K 's) are 6.10 and 9.02 for the Bro¨nsted acid site and 4.27 for the Lewis acid site. The points of zero charge are pH zpc = 7.5 and pCd zpc = 5.6 at pH 7.5. The total number of surface sites, i.e., the sum of the Bro¨nsted and the Lewis sites, is 20 μC/cm 2 . The ratio of the Lewis to Bro¨nsted acid site depends more on the pH than on the pCd.
74 citations
TL;DR: In this paper, a high molecular weight (MW > 1000) soluble root exudate fraction (HS) was isolated from hydroponic axenic maize cultures in order to investigate its metal-binding properties.
Abstract: A high molecular weight (MW > 1000) soluble root exudate fraction (HS) was isolated from hydroponic axenic maize cultures in order to investigate its metal-binding properties. Measurements of the maximum binding ability (MBA) and the overall stability constants (log K) for cadmium-, copper-, lead- and zinc-HS associations were obtained from dialysis and ion-selective electrode titrations. All results showed the occurrence of organometallic bindings. Data fitted to linear Langmuir isotherms. The MBA, measured by dialysis titration, varied from 160 to 206 mEq/100 g HS according to the nature of the metal. log K values, following the series Pb > Cu > Cd 5 Zn, varied from 3.15 to 3.65. Due to these metal-binding properties, soluble root products could play a role in the transfer of metal into the rhizosphere.
73 citations
TL;DR: The ion exchange behavior of the exchanger Na4Ti9O20.xH2O with 0.1M [Sr/SrOH/2+SrCl2] solution yielded a strontium ion exchange capacity of 5.30 meq g−1 corresponding well with the theoretical value as discussed by the authors.
Abstract: The ion exchange behaviour of the exchanger Na4Ti9O20.xH2O was studied with particular emphasis on Sr2+ exchange. Titration of H4Ti9O20.xH2O with 0.1M [Sr/OH/2+SrCl2] solution yielded a strontium ion exchange capacity of 5.30 meq g−1 corresponding well with the theoretical value. When strontium was absorbed on Na4Ti9O20.xH2O from neutral solutions, Sr2Ti9O20.xH2O was formed. This compound decomposed to SrTiO3 and TiO2 when heated to 870 °C. From alkaline solutions strontium was absorbed both as Sr/OH/+ and Sr2+ with the proportion of the former species increasing with pH. At pH 12.8 only exchange of Sr/OH/+ was observed and the exchanged form was Na2/SrOH/2Ti9O20.xH2O. This compound decomposed to Na2Ti6O13 and an unidentified strontium titanate when heated to 870 °C. Distribution coefficients were determined for alkali and alkaline earth metal ions as a function of pH. The selectivity sequence for alkaline earth metal ions was Ba>Sr≌Ca>Mg, and that for alkali metal ions was Cs>K>Li /pH 2–6/ and Li>Cs>K /pH 7/.
69 citations
TL;DR: A method for the measurement of dissolved water in crushed and sieved volcanic glasses utilizing Karl-Fischer titration and sample pyrolysis without the addition of a flux was described in this paper.
68 citations
TL;DR: Theoretical titration curves were calculated using values for concentrations of the amphiphile in the monomer and micellar states derived from the thermodynamic model for the association of ionic amphiphiles proposed by Jonsson and Wennerstrom.
Abstract: Differential enthalpies of dilution of 28 wt % aqueous sodium dodecyl sulphate solution have been measured using a titration microcalorimeter. In this way titration curves were determined in the concentration range 0–0.040 mol dm–3 at three different temperatures. Theoretical titration curves were calculated using values for concentrations of the amphiphile in the monomer and micellar states derived from the thermodynamic model for the association of ionic amphiphiles proposed by Jonsson and Wennerstrom. The computational procedure is described. The agreement between the calculated and experimental curves is good, which shows that the model can give quantitative predictions of the micellization process. It was observed that the decreasing monomer concentration with increasing amphiphile concentration above the c.m.c. requires the quantitative evaluation of the composition of the reaction solutions in order to derive correct values for the enthalpy of micelle formation of ionic amphiphiles from results of calorimetric measurements.
68 citations
TL;DR: In this article, a theoretical analysis of the voltammetric titration of ligand with metal, under the condition that the diffusion coefficients of the complex and the free metal are unequal, is presented.
56 citations
TL;DR: It is hypothesized that the precipitating Immobilines act as cationic detergents, and are able to cross‐link macroions with a mixed‐type, hydrophobic‐ionic interaction at the two extremities of the molecule.
Abstract: It has been impossible, up to now, to focus ferritin (a large, ca. 450 000 Da, ironstorage protein ubiquitous in mammalian systems) in immobilized pH gradients (IPG). This was not a sieving problem, as ferritin focuses readily in a 4%T polyacrylamide (or polytrisacryl) gel in conventional carrier ampholyte isoelectric focusing. A strong interaction with the IPG matrix was suspected, but an auto-buffered (pH 6.0) soluble IPG polymer failed to precipitate ferritin from solution, although it altered its visible spectrum, suggesting the formation of soluble complexes. By a Takeo plot, the dissociation constant (Kd)of the ferritin-IPG matrix complex was estimated to be 0.1 mM. However, even a 100-fold dilution of Immobilines into the IPG matrix with a concomitant addition of competing ions (up to 3 % carrier ampholytes) failed to produce good focusing patterns. An unsuspected, hitherto un-reported, precipitating power of free Immobilines in solution on the ferritin macroion was found to be the key to the riddle. The precipitating ions are (in order of aggregation power): pK 9.3 > pK 7.0 > pK 6.2. None of the acidic Immobilines (pKs 3.6, 4.4 and 4.6) and, among the basic, only the pK 8.5, exhibit any precipitation power on ferritin and other complex protein mixtures. In a new IPG pH 4–5 interval, containing only the pK 4.6 as buffering and the pK 8.5 Immobilines as titrant ions, excellent focusing patterns of ferritin were obtained. It is hypothesized that the precipitating Immobilines act as cationic detergents, and are able to cross-link macroions with a mixed-type, hydrophobic-ionic interaction at the two extremities of the molecule. Guidelines are given for handling this major problem on a short-term basis, the longterm goal being the replacement of the ‘unfavorable’ Immobilines (pKs 9.3, 7.0 and 6.2) by new chemical structures of the desirable type (the non-precipitating pK 8.5 species).
52 citations
TL;DR: The adsorptive properties of A-Mn02 for mono and divalent metal ions were investigated by pH titration and by measurements of the distribution coefficients(Kd's) of the metal ions.
Abstract: The adsorptive properties of A-Mn02for mono and divalent metal ions were investigated by pH titration and by measurements of the distribution coefficients(Kd's) of the metal ions. The pH titration curve showed an apparently monobasic acid type for a H+-Li+exchange. Those for H+-K+and H+-Cs+exchanges were nearly the same as that for blank titration. The lithium ion uptake increased with increasing solution pH and reached 5 meq/g at pH 11. X-ray diffraction analyses showed that the adsorption of lithium ions caused an increase in the lattice constant of a cubic unit cell. The potassium and cesium ion uptakes were nearly zero over a pH range between 4 and 11. A-Mn02showed a remarkably high Kd value for lithium ions, compared to a cation exchange resin. The selectivity sequences were Na+< K+< Rb+< Cs+<< Li+for alkali metal ions, Mg2+< Ca2+< Sr2+< Ba2+for alkaline earth metal ions, and Ni2+< Zn2+< Co2+< Cu2+for transition metal ions.
52 citations
TL;DR: The double-layer properties of colloidal RuO2, prepared by thermal decomposition of RuCl3 at 420°C, have been studied by potentiometric acid-base titrations in combination with electrophoretic mobility measurements as mentioned in this paper.
42 citations
TL;DR: Amperometric titrations of copper and lead with fulvic acid (FA) extracted from the River Tamar, southwest England, were carried out in 01 M NaCIO 4 at pH values in the range 64-65 as discussed by the authors.
TL;DR: In this paper, the ion exchange/atomic absorption (IEX) method was used to measure free copper(II) species (Cu/sup 2 +/) in the presence of various concentrations of the ligands citrate, glycinate, phthalate, salicylate, chloride and fulvate.
Abstract: Concentrations of the free copper(II) species (Cu/sup 2 +/) measured by the ion exchange/atomic absorption (IEX) method in the presence of various concentrations of the ligands citrate, glycinate, phthalate, salicylate, chloride, and fulvate are compared to concentrations measured with a cupric ion selective electrode (ISE) and/or to concentrations calculated from known metal-ligand formation constants. The IEX method is considerably more sensitive for Cu/sup 2 +/ than the ISE method but is subject to interference from cationic and neutral copper complexes as well as from filterable colloids copper-hydroxo species at higher pH values. Accurate values of Cu/sup 2 +/ concentration are obtained by both methods in the presence of anionic copper-ligand complexes. Since fulvate, which is the principal ligand present in natural freshwaters, forms anionic copper complexes, the IEX method possesses adequate selectivity for measuring Cu/sup 2 +/ at trace levels in such waters. The complexing capacity of an acidic lake water with a very low dissolved organic carbon content was measured as 3.0 x 10/sup -8/ M by monitoring Cu/sup 2 +/ concentration by the IEX method during titration with copper nitrate.
TL;DR: In this article, the effect of pH on the binding of Ni(II) to phytate has been determined spectrophotometrically and compared with results obtained for the Binding of Co(II, Cu(II), and Ca(II).
TL;DR: In this paper, the voltammetric measurement of the labile metal ion concentration as a function of pH (from an acidimetric titration of a natural sample) may provide useful information on the pH-dependent distribution of soluble and particulate concentrations and on the stability of (surface and solute) complexes formed.
Abstract: In natural waters the form of occurrence of heavy metal ions needs to be known to understand the factors that control their concentrations, their reactivity and bioavailability. In natural samples, it is difficult to identify the species present and to distinguish between dissolved and particulate concentrations, because of the lack of sufficiently sensitive and specific analytical detectors. It is suggested that the voltammetric measurement of the labile metal ion concentration as a function of pH (from an acidimetric titration of a natural sample) may provide useful information on the pH-dependent distribution of soluble and particulate concentrations and on the stability of (surface and solute) complexes formed. (Abstract retrieved from CAB Abstracts by CABI’s permission)
TL;DR: The earlier conclusion that the acylation of papain depends on two protonic dissociations each with pKa approx.
Abstract: The characteristics of actinidin (EC 3.4.22.14) and papain (EC 3.4.22.2), two cysteine proteinases whose catalytic-site regions appear to superimpose to a degree that approaches atomic co-ordinate accuracy of both crystal structures, were evaluated by determining (a) the pH-dependence in acid media of the acylation process of the catalytic act (k+2/Ks) using N alpha-benzoyl-L-arginine p-nitroanilide (L-Bz-Arg-Nan) as substrate and (b) the sensitivity of the reactivity of the catalytic-site thiol group and its pH-dependence to structural change in small, thiol-specific, two-protonic-state reactivity probes (2,2'-dipyridyl disulphide and methyl 2-pyridyl disulphide) where enzyme-probe contacts should be restricted to areas close to the catalytic site. Distortion of the catalytic sites of the two enzymes at pH less than 4 was evaluated over time-scales appropriate for both stopped-flow reactivity probe kinetics (less than or equal to 1-2 s) and steady-state substrate catalysis kinetics (3-5 min) by using the 2,2'-dipyridyl disulphide monocation as a titrant for non-distorted catalytic sites. This permitted a lower pH limit to be defined for valid kinetic analysis of both types. The behaviour of the enzymes at pH less than 4 requires a kinetic model in which the apparently biomolecular reaction of enzyme with probe reagent is separated from the process leading to loss of conformational integrity by a potentially reversible step. The acylation of actinidin with L-Bz-Arg-Nan in acidic media occurs in two protonic states, one produced by raising the pH across pKa less than 4 which probably characterizes the formation of -S-/-ImH+ ion pair (pKa approx. 3) and the other, of higher reactivity, produced by raising the pH across pKa 5.5, which may characterize rearrangement of catalytic-site geometry. The pH-dependence of the acylation of papain by L-Bz-Arg-Nan is quite different and is not influenced by protonic dissociation with pKa values in the range 5-6. The earlier conclusion that the acylation of papain depends on two protonic dissociations each with pKa approx. 4 was confirmed. This argument is now more firmly based because titration with 2,2'-dipyridyl disulphide permits the loss of conformational integrity to be taken into account in the analysis of the kinetic data at very low pH. Methyl 2-pyridyl disulphide was synthesized by reaction of pyridine-2-thione with methyl methanethiolsulphonate and its pKa at I = 0.1 was determined by spectral analysis at 307 nm to be 2.8.(ABSTRACT TRUNCATED AT 400 WORDS)
TL;DR: In this paper, the copper-binding in the soluble fraction of a digested sewage sludge was determined using ion-selective electrodes and showed that ion exchange with protons is a principal component in copper binding and that the soluble organic matter has a cation exchange capacity of 8.86 m-equiv g−1 at pH 6.5.
TL;DR: In this paper, the kinetics of desorption from a contaminated Malaysian padi soil, English Supreme kaolinite and Wyoming bentonite are studied using a constant potential titration method.
Abstract: SUMMARY
The kinetics of Cu2+ desorption from a contaminated Malaysian padi soil, English Supreme kaolinite and Wyoming bentonite are studied using a constant potential titration method. This technique involves maintaining a constant Cu2+-sensitive electrode potential corresponding to a Cu2+ ion activity below that which would naturally be supported by the soil in suspension. This is achieved by the controlled addition of complexing agent. Desorption occurs in response to the artificially reduced solution activity and the rate of the desorption reaction is revealed by the rate of addition of the complexing agent.
The desorption results were fitted to three established kinetic equations, all of which showed reasonable agreement with the data. In particular, a two-constant rate equation demonstrated some consistency between different materials. Both first-order and ‘diffusion’ kinetic equations appeared to apply within specific titration conditions. Each equation is discussed in terms of its implied desorption mechanism and the inconclusive nature of such mechanisms for short term (< 1 hour) desorption reactions is illustrated.
TL;DR: A method for the simultaneous determination of calcium and magnesium (hardness) in water by flow injection analysis (FIA) is suggested and the chemical systems used are conventional.
Abstract: A method for the simultaneous determination of calcium and magnesium (hardness) in water by flow injection analysis (FIA) is suggested. The method is applied to the determination of these parameters in natural, drinking, urban and bottled waters. The determinations are performed by an FIA titration with spectrophotometric detection. The chemical systems used are conventional, i.e., murexide-EDTA for calcium and eriochrome black T-EDTA for the sum of calcium and magnesium, the concentration of the latter being obtained by difference.
Journal Article•
TL;DR: In this article, the copper-zinc catalysts used in methanol synthesis from CO and H/sub 2/ have been studied in order to determine their behavior in presence of hydrogen.
Abstract: Copper-zinc catalysts used in methanol synthesis from CO and H/sub 2/ have been studied in order to determine their behavior in presence of hydrogen. All the samples prepared by the coprecipitation process are hydrogen reservoirs. The titration method based on the hydrogenation of isoprene without gaseous hydrogen show that the catalytic performances are directly correlated with the amount of occluded hydrogen in the solids. On the other hand, oxygen chemisorption results obtained at low temperature using a dynamic method lead to correct values of the copper area if the surface hydrogen is taken into account. 31 refs.
TL;DR: In this article, the pH values are obtained on the seawater pH scale, and the instruments used for the determinations are very simple and the standard deviation of the alkalinity determination of seawater is − 0.10%.
TL;DR: In this paper, a peristaltic pump with a precisely adjustable rotation rate was used to add titrant to a flowing sample stream for continuous flow titration of weak acids and weak bases.
Abstract: Continuous flow titrations of weak acids or weak bases can be carried out with a simple apparatus if the pH and titrant flow-rate data are treated using a linear titration plot method. Titrant is added to a flowing sample stream by a peristaltic pump with a precisely adjustable rotation rate. The results obtained for a variety of weak acids and weak bases are similar in accuracy to those given by corresponding burette titrations of discrete portions of sample.
Book•
15 Jan 1987
TL;DR: In this article, the authors present a method for determining molecular masses of compounds of solvents based on acid-base theory and base strength in Nonaqueous Solvents.
Abstract: 1. Acid-Base Theories. 2. Solvents. 3. Acid and Base Strength in Nonaqueous Solvents. 4. Choice and Purification of Solvents. 5. Titrants and Primary Standards. 6. Indication of Titration End-Point. 7. Methodology of Titrations. 8. Acid-Base Titrations. 9. Oxidation-Reduction Titrations. 10. Determinations of Molecular Masses of Compounds. Index.
TL;DR: Optosensing flow injection analysis (FIA) is a technique that utilizes immobilized selective indicators for determining a selected species and some problems with indicator sorption encountered when using soluble indicator and buffer carriers are discussed.
Abstract: Optosensing flow injection analysis (FIA) is a technique that utilizes immobilized selective indicators for determining a selected species. The indicator color change is monitored spectrophotometrically. This technique is investigated as a method for performing rapid sequential acid and base FIA titrations. Dilute acid, gas, and buffer are investigated as carriers, to determine dilute acids and bases over a wide concentration range. With a buffer as carrier, dilute acids and bases can be determined in the same single-line system at the rate of approximately 120 samples per hour using a 30-..mu..L injected sample volume. Peak height and peak width measurements are both used to extend the working range of the system for acids and bases in the range of 0.001 to 0.11 M. Standard deviations range from 1% to 8%. Some problems with indicator sorption encountered when using soluble indicator and buffer carriers are discussed.
TL;DR: Electron-transferring flavoprotein from the anaerobic bacterium Megasphaera elsdenii exhibited reversible, two-electron transfer during electrochemical reduction in the presence of mediator dyes, and thermodynamic stabilization of the radical form of the FAD cofactor during Electrochemical reduction at pH 5.4 was reported.
TL;DR: By depositing PVC membranes containing surfactant ion pairs as ion exchangers on a graphite support, ion-selective electrodes have been constructed that are responsive to ionic surfactants at concentrations between 10−2 and 10−6M.
Abstract: By depositing PVC membranes containing surfactant ion pairs as ion exchangers on a graphite support, ion-selective electrodes have been constructed that are responsive to ionic surfactants at concentrations between 10–2 and 10–6M. The operating characteristics of the electrodes have been evaluated, particularly with respect to their use in mixed solvent systems. Successful quantification of alkyl sulphates, alkylbenzenesulphonates and quaternary salts has been achieved by ion-pair titration. The electrodes have also been applied successfully in the analysis of commercially formulated detergent products after their surface-active components had been recovered and fractionated.
Patent•
10 Mar 1987
TL;DR: In this paper, a controlled valve is provided in the supply line for the reagent, and the opening and closing times of this valve and the frequency and duration of the pulses of liquid, are chosen such that the ratio of the average sample flow to the average reagent flow is sufficient to achieve the ratio in the equivalence point.
Abstract: The sample and the reagent required for titration are fed into a titration vessel (1), the reagent and/or sample being supplied intermittently in the form of pulses of liquid. Toward this end, a controlled valve (9) is provided in the supply line (4) for the reagent. The opening and closing times of this valve (9) and, hence, the frequency and duration of the pulses of liquid, are chosen such that the ratio of the average sample flow to the average reagent flow is sufficient to achieve the ratio of sample to the reagent at the equivalence point. This renders continuous titration possible, for which only one pump (7) is needed, which does not require any complex servo system and, therefore, has a low energy consumption.
TL;DR: In this paper, a photometric method is developed for the determination of the molar mass of 2,4-ionene by attaching a chromophoric moiety to its end-groups.
TL;DR: In this paper, a flow-injection single-point titration of acids is based on biamperometric measurement of iodine formed quantitatively in the reaction of iodide with iodate, and results are presented for determination of sulphuric, hydrofluoric, monochloroacetic, formic and acetic acids.
TL;DR: The characteristics of the anion transport system in human erythrocyte, which can be modified by eosin 5-isothiocyanate (EITC), were studied using the pH titration method and by measuring the sulfate efflux to characterize the EITC-binding site and the inhibitory effect of E ITC was dependent on pH.
TL;DR: In this article, a multi-parametric curve-fitting method for the determination of basic impurities present in solutions of hydrolysable salts is proposed, which consists in pH titration in isomolar titrand-titrant systems characterised by a high ionic strength.
Abstract: A multi-parametric curve-fitting method for the determination of basic impurities present in solutions of hydrolysable salts is proposed. It consists in pH titration in isomolar titrand-titrant systems characterised by a high ionic strength. A suitably defined regression function of the Pade type enables the concentrations of the strong and weak acids present in solution to be found by an iterative procedure. The basicity, Δca=ca*–ca, of the salt in solutions is defined as the difference between the concentration of the strong acid added (ca*) and that calculated (ca) from titration data (Vj, pHj). A linear correlation between Δca and the relative error in the determination of a weak acid concentration (cL) was observed (a standard solution of the weak acid was added as a buffering agent in the system). The method proposed has been applied successfully to the determination of basic contaminants in mixtures of concentrated solutions of cadmium and magnesium chlorides.