Determination of oxygen to uranium ratio in irradiated uranium dioxide by controlled potential coulometry

This work reports the determination of oxygen to uranium (O/U) ratio in irradiated UO_2+x fuel pellet of burnup of ca. 34 GWd/t by controlled potential coulometry. The method is based on the dissolution of the nuclear fuel in strong phosphoric acid (SPA) at 180–190 °C under an inert atmosphere. After dissolution, 8% sulphuric acid is added in order to obtain a 20% SPA in 8% sulphuric acid. A controlled potential coulometric determination of uranium(VI) is carried out at ?0.60V vs. ferri-ferrocyanide. The uranium(IV) contained in an aliquot of the fuel solution is oxidised to uranium(VI) with cerium(IV) sulphate, and the total uranium content is then determined by coulometry. Optimum experimental conditions have been established using simulated irradiated fuel solution containing various fission products which include cerium, tellurium, palladium, ruthenium, molybdenum and zirconium. Interference of the fission products and the possible removal of their interferences by preelectrolysis at +0.5 V vs. saturated calomel electrode (SCE) have been investigated. The accuracy of the coulometric method is confimed by polarographic measurement using several unirradiated UO_2+x fuel of known stoichiometry.     

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.     

Evaluation of certified reference materials for oxidation-reduction titration by precise coulometric titration and volumetric analysis

The accuracy and uncertainty of coulometric titration of Japanese certified reference materials (CRMs) for oxidation-reduction titration were examined in this study. The results for potassium dichromate, sodium oxalate, and potassium iodate are presented. Potassium dichromate was directly determined by coulometric titration, and sodium oxalate and potassium iodate were determined by volumetric analysis using potassium dichromate assigned by coulometry.The uncertainty of the method was investigated by examining the dependency on the sample size and on the electrolysis current. Changes in the titration parameters did not result in any significant effects on the titration results. The coulometric system used primarily consists of a constant current source, timer, switching circuit, indicator unit, and voltmeter. They were controlled using the coulometry software by a PC/AT compatible computer. A highly automated coulometric system achieves repeatabilities of less than one part in 30,000 (k = 2) and uncertainties of less than one part in 15,000 (k = 2). In addition, using volumetric method, SI units traceable sodium oxalate and potassium iodate (purity standards for redox reaction) CRMs were developed.Reference materials for volumetric analysis are the most basic substances used in analytical chemistry. These materials are analyzed by several analytical methods and are produced globally; however, their purities have not been compared at the international level. Therefore, the relationship between the purity and reliability of these materials has not yet been established. In this paper, we determine the relationship between these parameters by titrating each material obtained from different laboratories.     

Investigation on drying conditions and assays of amidosulfuric acid and sodium carbonate by acidimetric coulometric titration and gravimetric titration

Amidosulfuric acid and sodium carbonate as standards for acid–base titrimetry were assayed by coulometric titration and gravimetric titration. Amidosulfuric acid was directly assayed by coulometric titration with electrogenerated hydroxide ions, and sodium carbonate was assayed by gravimetric back-titration. For sodium carbonate, excess amount of sulfuric acid, whose concentration was determined by coulometric titration, was added to sodium carbonate, and then gravimetrically back-titrated using a sodium hydroxide solution whose concentration was determined by gravimetric titration using the sulfuric acid. The accuracy of the coulometric titration for amidosulfuric acid and sulfuric acid was evaluated by examining the current efficiency of pulse electrolysis, the amount of the electrolysis current used, and the time spent for a titration. In addition, the drying conditions for high purity primary standards have a significant effect on the titration results due to changes in the acid–base assay. The suitable drying conditions for amidosulfuric acid and sodium carbonate were evaluated by mass-change measurements, coulometric titration and gravimetric titration. The measurement uncertainties were estimated from the uncertainties on the titration processes. Finally, the assays of amidosulfuric acid and sodium carbonate were 99.986% ± 0.010% (k = 2) after drying at 50 °C for 2 h, and 99.970% ± 0.016% (k = 2) after drying at 280 °C for 4 h, respectively. In addition, the international consistency was confirmed by measuring certified reference materials (CRMs) available from different National Metrology Institutes, and the compatibility of values among CRMs was experimentally ascertained.     

Using high-performance quantitative NMR (HP-qNMR®) for certifying traceable and highly accurate purity values of organic reference materials with uncertainties <0.1 %

Quantitative nuclear magnetic resonance (qNMR) in combination with metrological weighing is optimised to demonstrate the power of the qNMR measurement method. It is shown that with ¹H-qNMR it is possible to certify the purity of organic reference materials (expressed as mass fraction) with relative expanded uncertainties of <0.1 % for a 95 % confidence interval (k = 2). Following well-defined selection criteria, a set of twelve different chemical compounds is evaluated and certified to serve as internal references for ¹H-qNMR measurements. A series of comparison measurements is made amongst a subset of the selected compounds. The purity of maleic acid is determined by six different ¹H-qNMR measurement series, and all results show full consistency. All the six mean values are covered within the range of ±0.05 %. In two more measurement series, four different nuclei are analysed within the same sample against one calibrator. Even with non-optimised signal intensity ratios and varying signal pattern, a high consistency was obtained. Therefore, the validity and robustness of ¹H-qNMR measurement results are demonstrated. ¹H-qNMR measurement results are directly traceable to a variety of internationally accepted primary reference materials, and therefore, traceability to SI units is obtained. All experiments are performed under ISO/IEC 17025 and ISO Guide 34 accreditation.     

Synthesis of New Pyrazolo[1,5-α]quinazoline Derivatives

The reaction of various anthranilic acid derivatives or their esters with 4-oxotetrahydrothiophene-3-carbonitrile 2, 2-oxocyclopentanecarbonitrile (9, n = 1) or 2-oxocyclohexanecarbonitrile (9, n = 2) in ethanol under reflux conditions giving rise the formation of single products isolated in each case after simple filtration. The products were characterized as pyrazolo[1,5-a]quinazolin-5-ones 4 instead of the expected pyrazol-3-amines 3. These cascade condensation–intramolecular acylation processes generated in one-step reactions from simple starting materials novel heterocyclic scaffolds ready for further functionalization. The present synthetic protocol provides acceptable yields of new tetracyclic products in high purity.     

High resolution conductometry for isotopic assay of deuterium in mixtures of heavy water and light water

A PC based high resolution conductivity monitoring technique has been deployed for determination of isotopic purity of heavy water in samples containing heavy water and light water mixtures using pulsating sensor based conductivity monitoring instrument. The technique involves accurate determination of conductivities of a series of specially treated heavy water and light water mixtures of various compositions at a constant solution temperature. The shift in conductivity (Δκ), which is the difference between conductivities of composite mixture after and before the formation of a typical complex compound (boric acid–mannitol complex in this case), shows a smooth and reproducible decreasing trend with increase in percentage composition of heavy water. This relation, which is obtained by appropriate calibration, is used in the software program for direct display of isotopic purity of heavy water. The technique is examined for determination of percentage composition of heavy water in the entire range of concentration (0–100 %) with reasonable precision (relative standard deviation, RSD ≤1.5 %). About 1 mL of sample is required for each analysis and analysis is completed within a couple of minutes after pretreatment of sample. The accuracy in measurement is ≤1.75 %.     

Optimum conditions for pulse generation in diaphragm-free Karl Fischer coulometry

A flexible instrument was designed in order to investigate the influence of current magnitude, current duration and the frequency of the pulse generation on the error obtained in coulometric Karl Fischer titrations carried out in diaphragm-free cells. For a given current magnitude the lowest errors were obtained for current durations more than 60% of the total time for the pulse cycle. No significant influence of the pulse frequency (5–1000 Hz) was found independently of the pulse current duration for three different types of reagents intended for diaphragm-free coulometry. For all reagents, the errors obtained with the home-built instrument were significantly smaller than those obtained with an optimized commercial titrator based on pulsed current generation. Using optimum conditions for the former instrument, in combination with an imidazole-buffered reagent at pH 10 containing chloroform as modifier, the accuracy was close to 100%. Thus, it is now possible to achieve the same high accuracy with diaphragm-free coulometry as with the conventional diaphragm based technique. The precision of the water determinations was affected by the size of the background. Received: 16 March 2000 / Revised: 17 May 2000 / Accepted: 22 May 2000     

Selective hydrolysis of cellulose for the preparation of microcrystalline cellulose by phosphotungstic acid

Microcrystalline cellulose (MCC), prepared from natural cellulose through acid hydrolysis, has been widely used in the food, chemical and pharmaceutical industries because of its high degree of crystallinity, small particle size and other characteristics. Being different from conventional mineral acids, phosphotungstic acid (H₃PW₁₂O₄₀, HPW) was explored for hydrolyzing cellulose selectively for the preparation of MCC in this study. Various reaction parameters, such as the acid concentration, reaction time, temperature and solid-liquid ratio, were optimized. Rod-like MCC was obtained with a high yield of 93.62 % and also exhibited higher crystallinity and narrower particle diameter distribution (76.37 %, 13.77–26.17 μm) compared with the raw material (56.47 %, 32.41–49.74 μm) at 90 °C for 2 h with 58 % (w/w) HPW catalyst and a solid-liquid radio of 1:40. Furthermore, HPW can easily be extracted and recycled with diethyl ether for four runs without affecting the quality of the MCC products. The technology of protecting the crystalline region while selectively hydrolyzing the amorphous region of cellulose as much as possible by using HPW is of great significance. Due to the strong Brønsted acid sites and highest activity in solid heteropoly acid, the use of effective homogeneous HPW may offer an eco-friendly and sustainable way to selectively convert fiber resources into chemicals in the future.     

Optimum conditions for pulse generation in diaphragm-free Karl Fischer coulometry

A flexible instrument was designed in order to investigate the influence of current magnitude, current duration and the frequency of the pulse generation on the error obtained in coulometric Karl Fischer titrations carried out in diaphragm-free cells. For a given current magnitude the lowest errors were obtained for current durations more than 60% of the total time for the pulse cycle. No significant influence of the pulse frequency (5–1000 Hz) was found independently of the pulse current duration for three different types of reagents intended for diaphragm-free coulometry. For all reagents, the errors obtained with the home-built instrument were significantly smaller than those obtained with an optimized commercial titrator based on pulsed current generation. Using optimum conditions for the former instrument, in combination with an imidazole-buffered reagent at pH 10 containing chloroform as modifier, the accuracy was close to 100%. Thus, it is now possible to achieve the same high accuracy with diaphragm-free coulometry as with the conventional diaphragm based technique. The precision of the water determinations was affected by the size of the background. Received: 16 March 2000 / Revised: 17 May 2000 / Accepted: 22 May 2000     

Enzymatic Reaction Coupled with Flow-Injection Analysis with Charged Aerosol,Coulometric, or Amperometric Detection for Estimation of Contamination of the Environment by Pesticides

Because excessive using of pesticides poses a threat to the environment and to human health, development of low-cost and sensitive methods for analysis of pesticides in the environment is needed. Several bacteria can release halide ions from the molecules of halogenated hydrocarbons. This can be used in a device for analysis of halogenated hydrocarbons in the environment by quantification of the halide anions. Here we directed our attention to selecting an instrument for detection of chloride anions. We tested three different detectors, amperometric, and coulometric, both coupled with flow-injection analysis and charged aerosol, coupled with high performance liquid chromatography. Detection limits (3 × S/N) for measurement of chloride anions by use of these detectors was 30 μM (charged aerosol), 100 nM (coulometric), and 1 nM (amperometric). Because of its lowest detection limit for chloride anions and the many technical possibilities of miniaturization, the amperometric detector was used to test of effect of different cations on the chloride signal under the optimized experimental conditions (working electrode potential −365 mV; “Current R” 5 μA; mobile phase 0.2 M phosphate buffer, pH 6; flow rate 0.5 mL min⁻¹). NaCl, SrCl₂, NH₄Cl, and CsCl were tested as sources of chloride anions. We then used the detector to detect chloride anions catalytically cleaved from 1-chlorohexane by the enzyme haloalkane dehalogenase LinB from the bacterium Sphingobium japonicum UT26. The activity of the enzyme increased with increasing reaction temperature until the maximum was observed at 39°C. The results obtained were in good agreement with data obtained by colorimetric detection.

     

Development of a new certified reference material of high-purity chrysin for the quality control of traditional Chinese medicine

Chrysin, a naturally occurring flavone, extracted from traditional Chinese herbs and abundantly found in propolis has been known to exhibit a wide range of biological activities, such as antioxidant, anti-inflammatory, hypolipidemic, anti-hypertensive, anti-diabetic, and anti-tumour activities. Among this, its anticancer effects make chrysin promising to be a candidate drug. The objective of this study was to develop a new certified reference material (CRM) for the quality control of traditional Chinese medicine, chrysin, and the related pharmaceuticals. The studies of sample preparation, homogeneity, stability, value assignment, and uncertainty evaluation were accomplished in this paper. Two different methods, namely differential scanning calorimetry and coulometric titration, were utilized for the first time to determine the purity of chrysin. The purity of the high-purity chrysin CRM, after validation and evaluation, was certified to be (0.996 ± 0.015) g/g (k = 2).     

Preparation and characterization of anode materials using expanded graphite/pitch composite for high-power Li-ion secondary batteries

Expanded graphite was prepared by the intercalation of natural graphite using ammonium peroxodisulfate as an oxidizing agent and a high purity of sulfuric acid as an intercalate. The amounts of oxidizing agent and intercalate were changed to determine the preparation conditions of expanded graphite as the anode material for high-power Li-ion batteries. The expanded graphite was tested as the anode material and further composited with the different amounts of petroleum pitch to improve the electrochemical properties. Although the expanded graphite anode showed the improved electrochemical properties such as initial reversible capacities of around 400 mAh/g and a charge capacity at 5 C-rate of 83 mAh/g as compared with those for the natural graphite anode of 378 and 19.4 mAh/g, respectively, it still had some weak points for a high-power anode material such as low initial efficiency and potential plateaus with the stage characteristic. The anode composites with high performance could be obtained by compositing the expanded graphite and the petroleum pitch at the ratio of 1:2, showing an improved initial efficiency of 78 % and decreased potential plateaus with 389 mAh/g of the initial reversible capacity.     

A candidate reference measurement procedure for Cyclosporine A in whole blood

Monitoring of Cyclosporine A (CsA) concentrations in whole blood is widely performed due to the narrow therapeutic index of the drug. Required standardisation for routine analysis of CsA is still missing. The candidate reference measurement procedure presented here is designated for the assignment of CsA values in hemolysed blood associated with expanded measurement uncertainty. Separate stock solutions for calibration and control materials were prepared by spiking hemolysed blood with CsA under gravimetric control. The essential sample pretreatment step was protein precipitation. Analysis was performed using isotope dilution LC-MS/MS with online solid phase extraction. Interference by matrix components was investigated. Using [²H₄]-CsA as the internal standard, no interference from the investigated matrices were detected. Measurement repeatability using three pools of whole blood as samples revealed coefficients of variation (CV) ranging from 1.0 % to 1.6 %. Intermediate measurement precision was determined by repeated analysis of self-prepared control materials taken from different stock solutions of pooled whole blood. CVs were between 0.8 % and 2.4 %. Measurement accuracy was checked using three control materials prepared from three different stock solutions. The recoveries of the mean of mean values obtained on four measurement days ranged from 99.4 % to 101.3 %. The combined expanded uncertainty of measurement based on 5 days of measurement and was evaluated according to the GUM as U = 2.0 % (k = 2).     

Controlled potential coulometry: the application of a secondary reaction to the determination of plutonium and uranium at a solid electrode

A method is described for the simultaneous determination of plutonium and uranium in mixed oxides by controlled potential coulometry at a gold working electrode in two stages: first a coulometric oxidation, at 0.73 V vs. a silver/silver chloride electrode, of Pu(III) and U(IV) to Pu(IV) and U(VI) by a combination of a direct electrode reaction and a secondary chemical reaction proceeding concurrently, and secondly, a coulometric reduction at 0.33 V of Pu(IV) to Pu(III), leaving uranium as U(VI). The determination is carried out in a mixture of sulphuric and nitric acids, and Ti(III) is used to reduce plutonium and uranium to Pu(III) and U(IV) before electrolysis. The precision (3sigma) of Pu:U ratio results obtained from mixtures containing about 30% and 2% plutonium was 0.5% and 1-5% respectively. The effect of experimental variables on the time taken to complete the coulometric determination is discussed.     

Precipitation and purification of uranium from rock phosphate

This study was carried-out to leach uranium from rock phosphate using sulphuric acid in the presence of potassium chlorate as an oxidant and to investigate the relative purity of different forms of yellow cakes produced with ammonia, magnesia and sodium hydroxide as precipitants, as well as purification of the products with TBP and matching its impurity levels with specifications of the commercial products. Alpha-particle spectrometry was used for determination of activity concentration of uranium isotopes in rock phosphate, resulting phosphoric acid, and in different forms of the yellow cake. Likewise, atomic absorption spectroscopy was used for determination of impurities. On the average, the equivalent mass concentration of uranium was 119.38 ± 79.66 ppm (rock phosphate) and 57.85 ± 20.46 ppm (phosphoric acid) with corresponding low percent of dissolution (48 %) which is considered low. The isotopic ratio (²³⁴U:²³⁸U) in all stages of hydrometallurgical process was not much different from unity indicating lack of fractionation. Upon comparing the levels of impurities in different form of crude yellow cakes, it was found that the lowest levels were measured in hydrated trioxide (UO₃·xH₂O). This implies that saturated magnesia is least aggressive relative to other precipitants and gives relatively pure crude cake. Therefore, it was used as an index to judge the relative purity of other forms of yellow cakes by taking the respective elemental ratios. The levels of impurities (Fe, Zn, Mn, Cu, Ni, Cd and Pb) in the purified yellow cake were found comparable with those specified for commercial products.     

Coulometrie und das coulomb als universelle urtitersubstanz

The theoretical bases of coulometry are described as Well as the newly developed coulometric methods, such as the indirect coulometric method, coulometric iodometry, coulometric perman-ganatometry, and coulometric metallometry. Furthermore the application of coulometric methods to the determination and preparative separation of various isomers, to the study of chemical kinetics and for coulometric buffering is dicussed; the respective results obtained are presented and the potential further development is indicated.Based on the results mentioned, the possibility and usefulness is pointed out of the introduction in analytical chemistry of the electron or the coulomb, as a universal standard, instead of the -numerous cliemical substances, more or less suitable for this purpose, and the general use of the universal coulomb is proposed.     

Spatial and vertical distributions of natural and anthropogenic radionuclides and cesium fractionation in sediments of the Var river and its tributaries (southeast France)

This paper reports results on the natural and anthropogenic radionuclides activity concentrations in sediments of the Var river and its tributaries. Natural (²³⁸U, ²³²Th and ⁴⁰K) and artificial (¹³⁷Cs) radionuclides activities were measured using high purity germanium detector. Measured activity concentrations differ widely; they depend on the pertinent environmental situation such as the presence of dams, and sediments type. Other factors controlling the distribution of the studied radioisotopes have been discussed. A sequential extraction method consisting of six operationally-defined fractions has been used for determining the geochemical partitioning of anthropogenic radionuclide ¹³⁷Cs in a 405–410 cm deep sediments collected in the lower valley of the Var river. This method corresponds to a modification of the three-stage sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR, now Standards, Measurements and Testing Program). Two steps with weak reagents, (fraction A: water; fraction B: nitric acid 0.001 M), were added before the first step of BCR (carbonate fraction) in order to better detect anthropogenic components. A total acid digestion of solid residues by microwave assisted was also added. The 6-steps extraction method was tested and validated by certified reference materials. ¹³⁷Cs was found mostly in the hydrosoluble fraction (20–24 %), oxide and hydroxide fraction (22–25 %) and in the residue (51–58 %), while ¹³³Cs was mostly found in the residual fraction (>97 %).     

Synthesis and Properties of a Sulfonic Acid-Containing Gemini Surfactant

A novel sulfonic acid-containing gemini surfactant, 6,6′-(butane-1,4-diylbis(oxy)) bis(3-nonylbenzenesulfonic acid), 9BA-4-9BA, was synthesized in high purity and high yield using a facile preparation pathway, and characterized by FTIR, ¹H NMR, and elemental analysis. The content of two sulfonic acid groups was measured by the acid-base titration. DSC and TGA were used to reveal the thermal properties and the product purity. The surface properties of 9BA-4-9BA were evaluated by equilibrium surface tension measurement. It shows that its CMC was 0.65 mmol/L, while the C₂₀ of 0.018 mmol/L was above two orders of magnitude lower than that of traditional monomeric surfactants such as SDS and SDBS, indicating excellent efficiency of micelle formation and reduced surface tension.     

Stability-Indicating HPLC and RP-TLC Determination of Cefpirome Sulfate with Kinetic Study

Two sensitive and selective stability-indicating methods were developed for the determination of the antibiotic cefpirome sulfate in bulk powder, pharmaceutical formulation and in presence of its acid, alkaline, photo- and oxidative degradation products. Method A was based on HPLC separation of cefpirome sulfate in the presence of its degradation products on a reversed phase column C18, 250 × 4.6 mm, 5-μm particle size and mobile phase consisting of 0.1 M disodium hydrogen phosphate dihydrate pH 3.9 adjusted with phosphoric acid–acetonitrile (85:15, v/v). Quantitation was achieved with UV detection at 270 nm. The linear calibration curve was in the range 5.0–50.0 μg mL^?1. Method B was based on reversed phase TLC separation of the cited drug in the presence of its degradation products followed by densitometric measurement of the intact drug at 270 nm. The separation was carried out using disodium hydrogen phosphate dihydrate 2.0 g %w/v, at pH 3.5 adjusted with phosphoric acid–acetone (15:10, v/v) as a developing system. The calibration curve was in the range of 1.0–10.0 μg/spot. The HPLC method was used to study the kinetic of cefpirome sulfate acid degradation. The results obtained were statistically analyzed and compared with those obtained by applying the official Japanese method.