Coulometric Titration Method Research Articles

Oxygen-vacancy concentration in A2MgMoO 6−δ double-perovskite oxides

Accurate oxygen-content analysis by means of a coulometric redox titration method specially devised for the purpose shows that as-synthesized (in 5% H 2/Ar) samples of the recently reported novel solid oxide fuel cells anode material Sr 2MgMoO 6− δ contain oxygen vacancies with a concentration of δ≈0.05. Oxygen contents and the resultant Mo-valence values are also analyzed for various A 2MgMoO 6− δ samples in order to reveal both the isovalent and aliovalent A-site cation substitution effects.

Validation of a gas chromatography/thermal conductivity detection method for the determination of the water content of oxygenated solvents

A gas chromatographic (GC) method for the determination of the water content of acetone solutions containing methyl isobutyl ketone (MIBK) and other by-products of MIBK synthesis was developed and validated. Linearity is demonstrated ( R 2 = 0.9999) over a broad range of water concentrations in acetone ranging from 0.04 to 15.2% (w/w). The quantitation limit (QL) of this technique was found to be 0.346% (w/w) and the detection limit (DL) was estimated to be 13 ppm. Validation of this analytical method's accuracy against a coulometric Karl Fischer titration (KFT) method showed excellent agreement between these two techniques. The GC/TCD method is accurate to within a relative error of 3.49% with respect to the KFT method for water concentration above the QL. However, the analysis of six samples below the QL showed an average relative error of 10.96%. Consequently, the KFT method is recommended for the moisture analysis of samples for water concentrations below 0.35% (w/w). Excellent precision is realized for water concentration above the QL (RSD ≪ 0.8%). Good precision (RSD = 1.1%) was obtained for the sample with the lowest water concentration investigated (0.04%, w/w). Repeatability, robustness and excellent specificity of this technique are demonstrated.

Vaporisation coulometric Karl Fischer titration: A perfect tool for water content determination of difficult matrix reference materials

Volumetric Karl Fischer titration (V-KFT) is the reference method to determine the water content in a whole range of organic and inorganic matrices. The method has several important drawbacks e.g. a high solvent consumption and a rather large measurement uncertainty when determining the water content in reference and candidate reference materials containing starch (e.g. maize, toasted bread, etc.). It is also labour intensive for routine measurements. In order to overcome these disadvantages, a relatively new method of coulometric Karl Fischer titration, equipped with a fully automated oven system, has been established and optimised. The objective of this study was to establish the robustness of the vaporisation coulometric Karl Fischer titration method (vap-C-KFT) and to compare measurement uncertainties with those obtained by V-KFT. The overall results obtained with the proposed vap-C-KFT methods correlate well with the results obtained by V-KFT ( R 2 = 0.998). Due to the good repeatability and intermediate precision of the vap-C-KFT methods compared to V-KFT, significant lower measurement uncertainties were obtained from vap-C-KFT measurements.

Employing sulfide-conductive solid electrolytes for the production of semiconducting sulfides with controlled composition and properties

Nonstoichiometry of sulfides of cadmium and lead is studied by the method of coulometric titration in electrochemical cells with sulfide-conductive solid electrolytes on the basis of MLn2S4. The range of the homogeneity region is estimated at temperatures 300 to 400°C. A feasible model for the formation of defects in nonstoichiometric sulfides of cadmium and lead is proposed.

Use of solid electrolyte GeSe-GeI2 for electrochemical doping with germanium

Lead tellurite is study to show that solid electrolyte GeSe-GeI2, which has the optimum composition and contains 5 mol % of GeI2, can in principle be used for electrochemical doping of semiconducting materials with germanium by the coulometric titration method. Some parameters of the coulometric titration are considered. The doping efficiency is monitored by determining variations in the concentration of charge carriers using the Hall method and by measuring the EMF of corresponding galvanic cells.

Precise coulometric titration of sodium thiosulfate and development of potassium iodate as a redox standard

In this paper, we determine the effective purity of potassium iodate as a redox standard with a certified value linked to the international system of units (SI units). Concentration measurement of sodium thiosulfate solution was performed by precise coulometric titration with electrogenerated iodine, and an assay of potassium iodate was carried out by gravimetric titration based on the reductometric factor of sodium thiosulfate assigned by coulometry. The accuracy of the coulometric titration method was evaluated by examining the current efficiency of iodine electrogeneration, stability of sodium thiosulfate solutions and dependence on the amount of sodium thiosulfate solution used. The measurement procedure for gravimetric titration of potassium iodate with sodium thiosulfate was validated based on determination of a reference material of known purity (potassium dichromate determined by coulometry with electrogenerated ferrous ions) using the same gravimetric method. Solutions of 0.2 and 0.5 mol/L sodium thiosulfate were stable over 17 days without stabilizer. Investigation of the dependency of titration results on the amount of sodium thiosulfate solution used showed no significant effects, no evidence of diffusion of the sample, and no effect of contamination appearing during the experiment. Precise coulometric titration of sodium thiosulfate achieved a relative standard deviation of less than 0.005% under repeating conditions (six measurements). For gravimetric titration, the results obtained for the effective purity of potassium dichromate were sufficiently close to its certified value to allow confirmation of the validity of the gravimetric titration was confirmed. The relative standard deviation of gravimetric titration for potassium iodate was less than 0.011% (nine measurements), and a redox standard with a certified value linked to SI units was developed.

希釈法による超高強度コンクリートの塩化物イオン濃度試験に関する研究

Using bleeding water gathered by pressurized and filtered of diluted concrete sample with purified water, some methods were suitable to test for chloride concentration in water of fresh concrete with low-water binder ratio and with few bleeding water. As a result, the following conclusions were obtained. 1) In case of high-strength concrete, which W/B is 16% and 18%, using diluted concrete sample by purified water 50cc against fresh concrete 3kg, it is possible to test in about 1 5 minutes for chloride concentration in water of fresh concrete with low-water binder ratio. 2) It is preferable to gather a quantity of filtered water necessary for examine within 4 hours, while the change of density is small. 3) Among the methods by JASS5T-502, Coulometric titration and Mohr's method may have applicability to test for chloride concentration in water of fresh concrete with low water binder ratio, with dilution method. It is possible to examine for chloride concentration in water of fresh concrete with low water binder ratio at the construction site.

Coulometric determination of total sulfur and reduced inorganic sulfur fractions in environmental samples

Evaluation of the solid-phase partitioning of sulfur is frequently an important analytical component of risk assessments at hazardous waste sites because minerals containing reduced-sulfur can significantly affect the transport and fate of organic and inorganic contaminants in natural environments. We applied selected methods for the determination of total sulfur, acid-volatile sulfide (AVS), chromium-reducible sulfur (CRS), and extractable-sulfate in standard reference materials and sediment samples from a contaminated site. A coulometric titration method is presented and evaluated for total sulfur, AVS, and CRS. This method is especially advantageous for AVS and CRS determinations because hydrogen sulfide gas evolved during chemical extraction is detected and quantitated in-line; consequently, measurement endpoints can be precisely determined without need for setting arbitrary time limits. The coulometric method allows for improved data quality and increased laboratory throughput of samples. Data on sulfur partitioning are presented for four standard reference materials (NIST 1646a, NIST 2780, CCRMP LKSD-1, CCRMP RTS-3) for the purpose of supporting quality control in environmental studies involving the geochemical and biochemical cycling of sulfur.

Assessment and assurance of quality in water measurement by coulometric Karl Fischer titration of petroleum products

The precise and accurate determination of water in petroleum products—gasoline, diesel oil and aromatic hydrocarbons—is of significant importance for their normal functional and operational characteristics for economics as well as in meeting international requirements. The standard method ISO 12937 for the measurement of water by the coulometric Karl Fischer titration method was subject to within-laboratory assessment. Thereby it was established that the analytical procedure could not always be relied upon, especially when low levels of water were determined. The aim of this work is to assess each stage of the test procedure depending on the particular problems defined by the samples, using high-reactive Karl Fischer reagents and coulometric cells with and without a diaphragm, and to indicate the major factors causing the uncertainty. A reduced combined uncertainty was achieved by modifying the sample preparation step, the administration of the moisture in the coulometric cell, and sample injection manipulation. Experiments showed that the cell without the diaphragm ensures lower and uniform uncertainty of the measurements in the range of 0.01 to 10 mg H2O in comparison to the cell with a diaphragm and therefore is more appropriate for the determination of low water levels in the petroleum products. A procedure that utilized a mixture of the reagent and toluene (10:6) was able to resolve the problem of two phases of formation and reduced conductivity of the reagent in direct titration of diesel oils. The results suggest that the modified procedure ensures relative expanded uncertainty equal to or less than 2.0% (n=5, confidence interval close to 95%) and 99.4% recovery for petroleum products investigated in repeatability conditions.

Thermodynamics of Binary and Ternary Copper-, Cadmium, and Indium-Containing Semiconducting Phases: An Electrochemical Study

Optimum compositions of ion-selective membranes in quasi-binary systems CuCl-CdCl2, LiCl-CdCl2, and In2S3-InCl3 are selected by a method of coulometric titration in cells with solid electrolytes. Transport numbers for ions are close to unity for the optimum compositions; transport numbers for electrons are vanishingly small (\(\bar t_e\) ≺10−3 to 10−4); the electroconductivity is equal to ≈ 10−3 S cm−1 at 200°C; the diffusion coefficients for the current-producing component are on the order of 10−6 to 10−7 cm2 s−1. When using a solid electrolyte of the composition CuCl-CdCl2, which contains 30 mol % CdCl2, methods of emf and electroconduction reveal that the region of homogeneity of copper(I) selenide falls in the region of compositions Cu1.33Se-Cu2.67Se.

Coulometric titration at low temperatures—nonstoichiometric silver selenide

A modified coulometric titration technique is described for the investigation of nonstoichiometric phases at low temperatures. It allows to obtain titration curves at temperatures where the conventional coulometric titration technique fails because of too small chemical diffusion coefficients of the mobile component. This method for indirect coulometric titration is applied to silver selenide between −100 and 100 °C. The titration curves are analyzed on the basis of a defect chemical model and provide thermodynamic data of the α-silver selenide phase. The boundaries of the homogeneous phase field are determined.

Electronic transport in Ce 0.8Sm 0.2O 1.9− δ ceramics under reducing conditions

Ce 0.8Sm 0.2O 1.9− δ powders were prepared by a freeze drying method and used to obtain ceramic disks. These samples were used to study the electronic transport properties of this material. A Hebb–Wagner method was used to obtain the electronic conductivity under ion blocking conditions. Typical values of electronic conductivity measured for this material at 800 °C were about 0.37 S m −1 at Po 2=10 −16 atm and 0.58 S m −1 at P O 2 =10 −18 atm. These values are significantly lower than results reported for ceria-based materials with different trivalent additives. A coulometric titration method was used to estimate the charge carrier concentrations, and the mobility of carriers was obtained on combining the results of conductivity and concentration. Typical values of mobility show weak temperature dependence and decrease with increasing oxygen deficiency, suggesting a limiting value of about 0.5×10 −7 m 2. V −1 s −1 for relatively high δ.

Electrooxidation of iodide in the presence of 4-hydroxycoumarin: application to a simple coulometric titration of 4-hydroxycoumarin.

The electrochemical oxidation of iodide ion in the presence of 4-hydroxycoumarin (1) was studied using cyclic voltammetry and controlled-potential coulometry. The result indicates that the resulting iodine takes part in a halogenation reaction and reacts with 4-hydroxycoumarin (1). According to the obtained results, a new and simple coulometric titration method with potentiometric end-point detection for the determination of 4-hydroxycoumarin (1) is presented. In the presented method, 2-200 micromol of 4-hydroxycoumarin (1) was successfully determined.

Accurate oxygen-content determination method for decreased sample amounts of superconductive and other functional oxides

In a conventional wet-chemical redox analysis applied to the determination of oxygen contents of nonstoichiometric functional oxides such as superconductive copper oxides, the sample amount required for a single experiment is typically 50–100 mg. Here we demonstrate that an improved coulometric titration method works to precisely analyze oxygen contents of decreased amounts of various complex oxides containing, e.g., copper, cobalt, or iron at mixed valence values. The improved titration method is found to yield the oxygen content of the YBa2Cu3O7−δ reference sample with high reproducibility, i.e., |Δδ|<0.01, for samples with a mass of only ∼10 mg.

Simultaneous coulometric determination of iodide, bromide and chloride in a mixture by automated coupling of constant current chronopotentiometry and square wave voltammetry

A novel method for simultaneous coulometric titration and determination of iodide, bromide and chloride is described. An electronic circuit is used for automatic switching of three-electrode constant current chronopotentiometric operation to the three-electrode square wave voltammetric (SWV) operation using the same electrochemical device. A four-electrode cell is used in common for both methods. A pure Ag wire (99.999% purity) as the anode for chronopotentiometry, SMDE as the working electrode for the SWV method, auxiliary Pt wire, and triple junction Ag/AgCl reference electrodes are used in common for both sequential methods. Each experimental run contains two alternating steps with a total time of about 9 s. The first step is a constant current coulometric titration with a 1 s run time. After the coulometric titration is automatically switched off, and the second step consisting of SWV (about 8 s) is started up by computer. The voltammetric peak current is monitored for end point-detection of each halide titration. The proposed method can determine 7×10 −8 mol of Br − and I − and also 2×10 −7 mol of Cl − in a sample solution. The current efficiency of the method is estimated to be ≥99.5%. The method is applied to the analysis of halides in a sample of mineral water.

Electrochemical study of iodide in the presence of barbituric acid. Application to coulometric titration of barbituric acid

Electrochemical oxidation of iodide in the presence of barbituric acid has been studied using cyclic voltammetry and controlled-potential coulometry. The results indicate that the resulting iodine takes part in halogenation reaction and reacts with barbituric acid. According to obtained results, a new coulometric titration method with potentiometric end-point detection for the determination of barbituric acid is presented. In the presented method, 1–200 μmol of barbituric acid was successfully determined.

Peak effect in critical current density induced by oxygen non-stoichiometry in cation-stoichiometric SmBa 2Cu 3O 7− δ superconductor

Cation-stoichiometric SmBa 2Cu 3O 7− δ superconductor (Sm-123) samples were synthesized by a conventional (without any liquid phases involved) solid-state-reaction technique, followed by annealing in flowing O 2 gas at 350°C for 40–200 h. A “peak effect” was observed in the critical current density ( J c) vs. applied magnetic field ( H) characteristics measured at 77 K. Pronounced peak effect was observed in a sample annealed at 350°C for 40 h, while the peak was suppressed in a sample annealed at 350°C for 200 h. Since the average oxygen content determined by a coulometric titration method increased with decreasing J c value at the peak, certain oxygen-deficient regions induced by oxygen non-stoichiometry might have formed. They could work as the magnetic fluxon pinning centers, since transmission electron microscopy (TEM) observations revealed the presence of both the tetragonal phase and a twin-free orthorhombic phase with width of ca. 200 nm in the sample annealed in O 2 gas at 350°C for 40 h which would have contained a significant amount of oxygen deficiency. The presence of the oxygen-deficient Sm-123 phase especially close to the boundary between either or both of the orthorhombic and tetragonal phases and an ordinary orthorhombic phase containing twins could be working for magnetic flux pinning to yield the peak effect in the J c vs. H characteristics.

Determination of the cyclodextrin inclusion constant with the constant current coulometric titration method

With fluorometry this paper has proved that α-cyclodextrin (CD) and γ-CD do not form inclusion complexes with procaine, while β-CD and HP-β-CD do. Their molar ratios are demonstrated both 1:1 with the equimolar variation method. The constant current coulometric titration method (CCCT) is first proposed and applied in the determination of the CD inclusion constant. To compare with this method, the fluorescence experiment has been done with the satisfactory results.

High-pressure synthesis of CuBa 2Ca n−1 Cu nO x ( n=3, 4) superconductors without external oxidizing agents

We have successfully synthesized non-stoichiometric BaCuO 2+ δ as a precursor for the high-pressure synthesis of CuBa 2Ca n−1 Cu n O x [Cu-12( n−1) n] superconductors. The oxygen content of BaCuO 2+ δ was determined by a coulometric titration method. Using this precursor but no external oxidizing agents, samples which were superconducting with T c=116 K have been obtained by sintering at 1100°C under 5 GPa. The T c=116 K phase was identified to be the CuBa 2Ca 3Cu 4O x (Cu-1234) phase. The Meissner volume fraction of the sample was estimated at ca. 30% at 5 K. A sample which contained a superconducting phase with T c at 80 K was also obtained at a temperature as low as 950°C. The 80 K phase was identified to be the CuBa 2Ca 2Cu 3O x (Cu-1223) phase. Thus, the Cu-1234 and Cu-1223 phases were successfully synthesized without the presence of any external oxidizing agents.

Establishment of strongly overdoped states in theHgBa2Ca2Cu3O8+δsuperconductor

Strongly overdoped ${\mathrm{HgBa}}_{2}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ (Hg-1223) samples with superconducting transitions as low as 97 K were successfully obtained by using HgO, ${\mathrm{Ca}}_{2}{\mathrm{CuO}}_{3},$ CuO, and mixtures of highly oxidized ${\mathrm{BaCuO}}_{2+\mathrm{\ensuremath{\epsilon}}}$ $(\ensuremath{\epsilon}\ensuremath{\approx}0.13)$ and/or ${\mathrm{BaO}}_{2}$ powders as starting materials for the high-pressure synthesis at 5 GPa and 950 \ifmmode^\circ\else\textdegree\fi{}C. The overdoped state was confirmed by observing negative values for the Seebeck coefficient throughout the temperature range from ${T}_{c}$ to 320 K in a thermoelectric power measurement. Also, both of the cell parameters $a$ and $c$ were found to decrease with decreasing ${T}_{c},$ reflecting, respectively, an increase in hole concentration in the ${\mathrm{CuO}}_{2}$ planes and the incorporation of oxygen into the ${\mathrm{HgO}}_{\mathrm{\ensuremath{\delta}}}$ layer. The oxygen excess \ensuremath{\delta} as determined by the $\mathrm{Cu}(+\mathrm{I})/\mathrm{C}\mathrm{u}(+\mathrm{I}\mathrm{I})$ coulometric titration method, was $\ensuremath{\sim}0.19$ in the overdoped sample with ${T}_{c}=107\mathrm{K}.$ Subsequent reducing annealing in an Ar atmosphere at 280 \ifmmode^\circ\else\textdegree\fi{}C increased the ${T}_{c}$ to 131 K. Consistently, only positive Seebeck coefficient values were observed up to 320 K for the Ar-annealed sample. A clearly underdoped material with ${T}_{c}=118\mathrm{K}$ was obtained by annealing the same sample in Ar at a higher temperature $(\ensuremath{\sim}400\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}).$ Finally, high-pressure synthesis starting from less-oxidized ${\mathrm{BaCuO}}_{2+\mathrm{\ensuremath{\epsilon}}}$ $(\ensuremath{\epsilon}\ensuremath{\approx}0.06)$ yielded a Hg-1223 material with $\ensuremath{\delta}\ensuremath{\approx}0.10$ and ${T}_{c}=132\mathrm{K}.$