Potentiometric Titrimetry Research Articles

Uncertainty Estimation for Determination of Potassium Iodate Purity by Potentiometric Titrimetry

The purpose of this study was to express the uncertainty estimation for the purity determination of potassium iodate by potentiometric titrimetry method. Potassium iodate determination by using a potentiometric titrator was realized in two steps. In the first step, a factor analysis is performed using sodium thiosulfate. In the second step, the amount of potassium iodate was determined by using the factor value obtained in the first step of the measurement. Sigma Aldrich 60386 CRM (certified by BAM-with purity of 99.94%) was used for factor analysis. The documents of “Evaluation of measurement data - Guide to the expression of uncertainty in measurement” and “EA-4/02 M: 2013 Evaluation of the Uncertainty of Measurement in Calibration” were the source for the evaluation of the measurement uncertainty. The documents of “EURACHEM/CITAC Guide CG 4, JCGM 100: 2008” and “Eurolab Technical Report No.1/2007” based on the bottom-up approach were also paid regard during the uncertainty estimation study. The main factors that are forming the total uncertainty budget were repeatability of measurement results, titrant consumption, factor of sodium thiosulfate, the molar mass of potassium iodate and sample quantity. It was observed that the highest contribution to the uncertainty budget was the repeatability of measurement results. The measurement result for the purity determination of potassium iodate was found as 99.76% and the expanded uncertainty of the measurements was estimated as 0.12% which was acceptable level for the study.

An Accurate and Precise Analytical Method for Estimation of Active Sulfur Trioxide and Sulfuric acid in Triethylamine Sulfur Trioxide Complex

Triethylamine sulfur trioxide complex (TEA-SO3) is an important sulfating agent used in the synthesis of various drug substances, dyes and other chemicals. Quality of TEA-SO3 is very crucial because it provides the active sulfur trioxide (SO3) in the sulfation reaction. We developed an accurate, precise and robust analytical method for determination of quality of TEA-SO3. The potentiometric titrimetry methods are capable to estimate SO3 as well as degradation product sulfuric acid (H2SO4) present in the TEA-SO3. Estimation of SO3 involves hydrolysis of the complex using H2SO4 under reflux condition and titrating excess H2SO4 against alkali solution. H2SO4 is quantified by direct titration against alkali solution. Both assay and impurity quantification methods were validated as per the ICH guideline. Accuracy of H2SO4 determination was 102.80% with precision of 0.75% and could be detected as low as 0.01%. Method to estimate SO3 was accurate with recovery of 99.92% and precision of 0.25%. The developed methods were employed for quality check of the reagent.

Photoelectrocatalytic reduction of CO2 into formic acid using WO3–x/TiO2 film as novel photoanode

A novel WO3–x/TiO2 film as photoanode was synthesized for photoelectrocatalytic (PEC) reduction of CO2 into formic acid (HCOOH). The films prepared by doctor blade method were characterized with X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The existence of oxygen vacancies in the WO3–x was confirmed with an X-ray photoelectron spectroscopy (XPS), and the accurate oxygen index was determined by a modified potentiometric titrimetry method. After 3 h of photoelectrocatalytic reduction, the formic acid yield of the WO3–x/TiO2 film is 872 nmol/cm2, which is 1.83 times that of the WO3/TiO2 film. The results of PEC performance demonstrate that the introduction of WO3–x nanoparticles can improve the charge transfer performance so as to enhance the performance of PEC reduction of CO2 into formic acid.

Determination of Stoichiometric Dissociation Constants of Acetic Acid in Aqueous Solutions Containing Acetic Acid, Sodium Acetate, and Sodium Chloride at (0 to 60) °C

Equations were determined for calculation of stoichiometric (molality scale) dissociation constants Km of acetic acid in buffer solutions containing acetic acid, sodium acetate, and sodium chloride from determined thermodynamic dissociation constants Ka of this acid at temperatures from (0 to 60) °C, and molalities of components in solution. These equations were based on single-ion activity coefficients obtained by Hückel-type equations. The thermodynamic dissociation constants and acetate parameters required were determined from the Harned cell data of Harned and Ehlers. The interaction parameter between neutral acetic acid molecules and acetate ions was determined from Harned cell data for unbuffered aqueous mixtures of acetic acid and NaCl at 25 °C, and the resulting value applied to all temperatures. The interaction parameters between hydrogen ions and chloride ions were taken from the recent data reassessment by Partanen and Covington. The parameters resulted from interactions between hydrogen ions and sodium ions and between sodium and chloride ions were determined from the Harned cell data measured by Harned for aqueous mixtures of HCl and NaCl. The resulting equations were tested with literature data for cells both with and without a liquid junction at various temperatures. The new equations predict well the literature data used in the tests. The new parametric equations were used to check the pH values of 0.01 molal acetate and 0.1 molal acetate buffers recommended by IUPAC for temperatures from (0 to 60) °C, and agreement was usually found to be within ±0.005. Calculated p(mH) values are also tabulated for buffer solutions containing NaCl as the major component and acetate species as minor components for calibration glass electrode cells for direct measurement, particularly in potentiometric titrimetry, of hydrogen ion molality.

Metal ion complexation properties of fulvic acids extracted from composted sewage sludge as compared to a soil fulvic acid

Complexation properties of an anthropogenic fulvic acid (FA) extracted from a composted sewage sludge (csFA) for Cu(II), Pb(II) and Cd(II) were studied at pH=6 and at a concentration of 25 mg L −1. For the case of Cu(II), a particular analysis of the complexation phenomena was done at pH values of 3, 4, 5 and 6 and at aqueous FA concentrations of 25, 50 and 100 mg L −1 by synchronous excitation molecular fluorescence spectroscopy (SyF). Potentiometric titrimetry with Cu(II), Pb(II), Cd(II) and H + ion-selective electrodes and acid–base conductimetric titrations were used to obtain experimental information about the acid properties and complexation phenomena. A comparison of the results obtained for csFA with a natural soil FA (sFA) was made. Differences have been detected in the structural composition of the two samples and in the structure of the binding sites. In the csFA, binding site structures containing nitrogen probably play an important role in the complexation, besides oxygen containing structures. Complexation by sFA is mainly due to carboxylic and phenolic structures. Nevertheless, this work shows that csFA have macroscopic complexation properties (magnitude of the conditional stability constant and binding sites concentration) somewhat similar to the natural sFA samples.

Acid-base properties of fulvic acids extracted from an untreated sewage sludge and from composted sludge

The acid-base properties of two samples of anthropogenic fulvic acids (FA) extracted from the untreated sewage sludge (rsFA) of a municipal wastewater treatment plant and from the compost (csFA) obtained in the aerobical digestion of this sludge were studied. Potentiometric titrimetry, infrared spectroscopy and synchronous molecular fluorescence (SyF) spectroscopy were used to obtain experimental information about the acid-base properties of the samples. Moreover, the SyF spectral data which were collected as function of the pH were analysed by a self-modelling curve resolution technique, evolving factor analysis with a gradient concentration window (EFA-GCW), to calculate the number of acid-base systems, their SyF spectra and the corresponding distribution diagrams, from which the p K a values were estimated. Two acid-base systems with p K a values about 6.2 and 8.9 were detected for rsFA and three systems with p K a values about 3.8, 6.6 and 9.4 for csFA. The amounts of acid groups directly titrated in water were (standard deviations in brackets) about 6.8(1) for rsFA and 6.73(3) for csFA. This information for rsFA and csFA was compared with similar information for natural soil FA samples extracted from a pinewood soil. Beyond different structural composition, this comparison showed that the anthropogenic samples have a higher amount of acid structures, but the structures of natural samples have stronger acid properties.

Cosolvent Effect on Goethite Surface Protonation

Extensive research has been conducted on the surface acidity of hydrous metal oxides in aqueous solutions. However, little information is available on mineral surface acidities in mixed solvent solutions. The present study examined goethite surface protonation in acetone−water and methanol−water mixtures with potentiometric titrimetry. Surface acidity constants, K+int = [XOH2+]eFΨ/RT/[XOH][H+] and K-int = [H+][XO-]e-FΨ/RT/[XOH], were calculated using constant capacitance and diffuse-layer models. The number of apparent surface sites increased with increasing cosolvent content. Linear log K+int vs 1/(dielectric constant ε) was observed. Simple electrostatic correction using a modified Born equation adequately predicted changes of K+int from water to mixed solvents. Changes in K-int were less tractable, however, showing nonlinearity with 1/ε.

Proton Affinity Distributions of TiO 2-SiO 2 and ZrO 2-SiO 2 Mixed Oxides and Their Relationship to Catalyst Activities for 1-Butene Isomerization

Proton-releasing properties at the oxide/aqueous solution interface were examined as a function of pH for two series of mixed oxide aerogels and their pure oxide components using potentiometric titrimetry. Reports of synthesis, surface characterization, and catalytic activity (1-butene isomerization) have appeared recently for similar preparation batches of titania-silica and zirconia-silica. After deconvolution of potentiometric titration data, the pK spectra of the oxide surfaces were obtained; they reveal the number and strength of various proton donor sites present under "wet" conditions. The activity in 1-butene isomerization measures weak Brønsted sites of the "pseudo-dry" catalyst (reaction at 423 K after drying at 473 K). We find that the activity for 1-butene isomerization is linearly related to the density of a particular type of proton donor site determined from pK spectra. This shows that only a limited number of the total Brønsted sites accessed by potentiometric titrimetry is specifically active for 1-butene isomerization under the conditions used here. The pK range of active sites and the corresponding TOF numbers are 6.3 < pK < 8.7, (8.2 ± 2.1) × 10(-3) s(-1) for titania-silica and 6.4 < pK < 6.5, (93 ± 24) x 10 −3 s −1 for zirconia-silica. In the two catalysts series the catalytic performance varied with either composition (titania-silica) or preparation parameters (zirconia-silica) at constant composition.

Determination of the p Ka values of sparingly soluble substances in water revisited: application to some benzodiazepines

The acid-base behaviour of four benzodiazepines sparingly soluble in water (diazepam, medazepam, chlordiazepoxide and prazepam) was studied by potentiometric and spectrophotometric titrimetry in water. A method was devised to obtain the p K a values of these substances by potentiometric titrimetry in water-rich water-methanol media [up to 50% (v/v) methanol] by extrapolation to pure water, thus obviating the solubility problems associated with them. The method was found to be accurate and easily applicable, and the results obtained for the p K a values are identical, within experimental error, with those obtained in water. The operational criteria for applying this methodology are indicated.

Simultaneous determination of amoxycillin and dicloxacillin in capsules by potentiometric titrimetry and high-performance liquid chromatography

Direct potentiometric titration and two HPLC conditions for the simultaneous determination of amoxycillin and dicloxacillin in their capsules have been developed. One-run titration utilizing 0.05 M acet. HClO 4 enables the quantification of both antibiotics. The HPLC-separation could be undertaken on reversed phase, LiChrosorb RP-18 (10 μm), and LiChrospher 100 RP-18 (5 μm), columns by using mobile phases containing acetonitrile + 1% aq, acetic acid, in proportions of 47:53 or 39:61 (v/v), respectively, at a flow rate of 1.5 ml/min with UV-detection at 240 nm. Recoveries of the individual drugs by the application of each described method were found to be fairly satisfactory.

Alkylated Lariat Ethers as Solvent Extraction Reagents: Surveying the Extraction of Alkali Metals by Bis-t-octylbenzo-14-crown-4-acetic Acid by Use of Potentiometric Two-Phase Titration

Abstract Two-phase potentiometric titrimetry was used to survey the extraction of alkali metal cations from aqueous chloride solution by the lipophilic, ionizable lariat ether bis-(t-octylbenzo)-14-crown-4-acetic acid (BOB14C4AA) in o-xylene. Analysis of the data indicates that ion-exchange extraction by the crown-carboxylic acid at low loading (i.e., low conversion of BOB14C4AA to its salt form) is stronger for lithium ion than for the other alkali metals. Little or no selectivity occurs at high loadings. In comparison with the long-chain carboxylic acid 2-methyl-2-heptylnonanoic acid (HMHN), BOB14C4AA extracts lithium and sodium at significantly lower pH; in the loading range of 0.1 to 0.7, the pH shift is 1.4–1.8 pH units for sodium ion and 1.7–2.3 pH units for lithium ion. The titration data are interpreted in terms of aggregated organic-phase species. In the case of lithium extraction, clear evidence was found for a species in which neutral BOB14C4AA participates in the organic-phase complexation of ...

An investigation into the nature of the electrochemical and surface properties of polyacrylamides and a study of their adsorption onto the surface of papermaking woodpulps using alternating‐current polarography

AbstractA cationic polyacrylamide was examined using polarography, constant potential coulometry, photon correlation spectroscopy, electrocapillarity and potentiometric titrimetry. A polarographic response was found in differential‐pulse polarography (DPP), direct‐current and Kalousek modes at −1,7 V versus a silver/silver chloride electrode. In each case the magnitude of the response was a function of polymer concentration. However, it is thought that the response is not due to the polymer itself but impurities found with it. These were found to have a pK of 4,75. The polymer appears to develop a more open structure in LiCl solution (&lt;0,0013 mol/L). The unwashed polymer was found to greatly increase the interfacial tension at the mercury drop, but this effect was considerably reduced on washing the polymer in 70% acetone solution. Hydrolysis of the polymer seems to occur at pH 10. The suppression of the negative tensammetric peak of poly(ethylene glycol) (PEG200) by a range of cationic polyacrylamides was used for their analysis in the determination of their adsorption onto the surface of woodpulp. The adsorption was found to be a function of both their cationicity and mean molar mass. The rate of hemicellulose desorption from the woodpulp appears to be pH dependent. The impurity is thought to be mainly adipamic acidSystematic name: 5‐carbamoylpentanoic acid. .

Thermodynamic and kinetic implications involved in the titration of polyfunctional acids by catalytic thermometric titrimetry

The influence of the concentration of reactants on the results of titrations of salicylic acid in acetone with potassium and tetramethylammonium hydroxides in propan-2-ol were investigated. The titrations were performed by catalytic thermometric titrimetry using acetone as the end-point indicator and by potentiometric titrimetry. These and other results are discussed in terms of the equilibrium and kinetic aspects involved in the titrations of polyfunctional acids capable of forming intramolecular hydrogen bonds.

Titration of proteins in dimethyl sulphoxide–water mixtures

The acid–base behaviour of arginine, lysozyme and ovalbumin has been studied by potentiometric and catalytic thermometric titrimetry in a mixture of dimethyl sulphoxide–water, with acrylonitrile as the end-point indicator in the latter technique. It was observed that, with the exception of the SH groups, all the protonated groups, including the guanidine groups of lysozyme and ovalbumin, were titrated by catalytic thermometric titrimetry. By using potentiometric titrimetry, all the titratable groups of ovalbumin were determined, whereas the guanidine groups of lysozyme were not determined by this technique.

Potentiometric titrimetry for the simultaneous quantification of ticarcillin and clavulanic acid in bulk and injectable dosage forms

A direct potentiometric procedure for the simultaneous determination of ticarcillin and clavulanic acid in binary mixtures and injectable dosage formulations has been developed. Adoption of non-aqueous potentiometry, using 0.1 mol/l acetic HClO4, enables the simultaneous quantification of the two named drugs in a single sample run. Recovery of each individual drug was found fairly satisfactory on the application to clavulanate-potentiated ticarcillin (100.86% for ticarcillin and 101.47% for clavulanic acid).

Kinetics of polyesterification and models, 3. Kinetics and mechanism of pentaerythritol esterification by long‐chain carboxylic acids at technological conditions

AbstractKinetics of the esterification of pentaerythritol by long‐chain carboxylic acids (C7 – C18) has been followed by potentiometric titrimetry. A simplified approach for the estimation of the rate constant values and the rate constants of the consecutive processes was developed according to the previous established kinetic law for similar systems.A computer simulation of the component concentrations variation has been carried out in order to prove the selected kinetic model.

Kinetics of polyesterification and models, 2. Kinetics and mechanism of 1,1,1‐trimethylolpropane esterification by long‐chain carboxylic acids at technological conditions

AbstractKinetics of 1,1,1‐trimethylolpropane esterification by long‐chain (C4 —C18) carboxylic acids has been followed by GLC, HPLC, 1H‐NMR, and potentiometric titrimetry. The system composition evolution was established at technological conditions, i.e. molar ratio between 1/1 and 1/3 and temperatures between 160 and 205°C. The rate constants of the three involved consecutive reactions were determined according to the kinetic law which assumes a partial order of 1.5 with respect to the acid and 1.5 with respect to the alcohol.Once the three rate constants k1, k2, and k3 are known by direct determination, a computer simulation for the esterification process has been carried out. The experimental variation of the component concentrations and the calculated values show a proper agreement, thus proving the selected kinetic model.

Factors affecting the precisions of analyses, by potentiometric titrimetry, of solutions containing two weak acids

This paper deals with potentiometric titrations in which mixtures of two monobasic weak acids are titrated with a strong base, and in which weighted non-linear regression analysis is used to find the concentrations and values of p K a for both acids. The precisions of the resulting values of the concentrations depend on the difference between the values of pka, the ratio of the initial concentrations, and on the standard errors of measurement of both the pH and the volume of base. For any given values of the ratio of concentrations and the standard errors of measurement, the precision with which the concentration of the stronger acid can be evaluated is, in general, poorest when the difference between the p K a values (Δ) is approximately 1.5, and improve if Δ is either larger or smaller than that value. Even if Δ is as small as 0.1, the precision that is attainable is very much better than it is generally believed to be. Surprisingly, there are conditions under which the concentrations of both acids can be determined with fair precision even though titrimetric data will not reveal that two acids are present in the sample.

Procedure for the simultaneous determination of tartaric and citric acids and total carbonate by potentiometric titrimetry and its application to antacid analysis.

The application of a linear algebraic method to the potentiometric titration of a mixture of tartaric and citric acids and sodium carbonate and sodium hydrogen carbonate (previously treated with strong acid), permits the determination of the concentration of each individual acid and the total equivalent of carbonate in antacids. It is also possible to determine individual concentrations of sodium carbonate and sodium hydrogen carbonate by combining the results of the described titration with the acidimetric titration of a sample previously treated with an excess of strong base.

Diamine/Silane-Modified controlled pore glass: The covalent attachment reaction from aqueous solution and the mechanism of reaction of bound diamine with copper(II)

The reaction of N-2-aminoethyl-3-aminopropyltrimethyoxysilane (en-silane) with the surface of controlled pore glass (CPG) in aqueous solution was examined. The reaction appears to involve the rapid (ca. l min) formation of a covalently bound monolayer of en-silane at room temperature. Multilayers of bound polymeric en-silane can be obtained by reaction at elevated temperature. The latter reaction is slower, presumably because of the more stringent steric requirements of polymer formation in chain growth away from the CPG surface. For en-silane coverages ranging from 1.7 to 8.5 μ mol m -2, the mechanism for the complexation of copper(II) by ethylenediamine (en) bound to a CPG surface by reaction of en-silane with CPG was also investigated by thermometric and potentiometric titrimetry. A two-step mechanism is proposed. The data indicate that the first step of the surface reaction involves formation of a Cu(en) 4 complex as opposed to the Cu(en) complex formed in the first step of the solution reaction. The second step results in a complex similar to the Cu(en) 2; species formed in solution.