Proficiency testing of pH and electrolytic conductivity measurements of groundwater: a case study of the difference between consensus and metrologically traceable values

A proficiency testing (PT) scheme was designed for measurements of pH and electrolytic conductivity (EC) of groundwater in Israel. A groundwater sample was used for preparation of test items fit-for-intended-use. The interlaboratory experiment was organized taking into account changes of the test item properties which occurred after sampling due to presence of CO₂ in the groundwater. A total of 34 PT participants reported pH measurements results, while 29 of them reported results of EC measurements. The pH results were normally distributed. However, a significant bias of the pH consensus value of the PT participants from the metrologically traceable certified value (obtained by the National Physical Laboratory of Israel) was detected. This bias was caused by the drift of the measurement response due to water stirring and CO₂ degassing from the sample during the measurement process. The bias of the EC consensus value from the metrologically traceable one was negligible, in spite of an abnormal distribution of the EC results of the PT participants.     

New Japanese certified reference materials for electrolytic conductivity measurements

Accreditation and Quality Assurance - The National Metrology Institute of Japan (NMIJ) has established three certified reference materials (CRMs) in electrolytic conductivity with a primary...     

Consistency of practical salinity measurements traceable to primary conductivity standards: Euromet project 918

Measurements of practical salinity are based on conductivity measurements, which are traceable to the conductivity of a defined KCl reference solution. The conductivity of this reference solution must be traceable to the SI in order to state a reliable uncertainty for practical salinity measurements and to guarantee their comparability. Currently, the conductivity ratios from various old standard seawater batches are compared instead. However this method is inadequate on a long time-scale, which is important for oceanography studies, because it lacks a time-invariant reference. Therefore the equivalence of conductivity measurements traceable to primary conductivity standards has been investigated in Euromet project 918. Several European metrology institutes measured the conductivity of a 5 S/m KCl solution and the practical salinity of IAPSO standard seawater. The study estimates relative standard uncertainties to be of the order of 10⁻⁴ to 10⁻³ for such measurements.

Method for analysis of the composition of acid soaps by electrolytic conductivity measurements

Here, we propose a method for determining the stoichiometry of acid-soap crystallites. The method is based on dissolving the crystallites in water at an appropriate working temperature, followed by measurement of the electrolytic conductivity of the obtained solutions. The working temperature is chosen in such a way that the only precipitate in the solutions is that of carboxylic acid, whereas the carboxylate salt is dissociated, and its content in the dissolved crystals determines the solution's conductivity. In the theoretical model for data interpretation, we took into account the dependence of the molar conductance on the ionic strength. The method was applied for determining the stoichiometry of acid-soap crystals collected from solutions of potassium myristate (tetradecanoate) at 25 degrees C. The crystals were dissolved in water at working temperature of 40 degrees C, at which the conductivity was measured. The stoichiometry of all samples determined in the present study coincides with that independently obtained by another method that is based on in situ pH measurements.     

Thermal conductivity measurements on samples with low cross-sections

A simple, low-cost apparatus has been designed and constructed for measurement of the thermal conductivities of samples with low cross-sections (10^–7 m²). This apparatus has been used to determine variations in the thermal conductivity of the metallic glass Fe₈₀B₂₀ (Metglas 2605) in the crystallization process induced by thermal treatment.In spite of the simplicity, the deviations from the real values of thermal conductivities measured have been lower than 8%, which has proved to be satisfactory for establishing the glass formation, temperature, T₈, from changes in thermal conductivity.

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Zusammenfassung Eine einfache, billige Apparatur zur Messung der Wärmeleitfähigkeit von Proben mit kleinen Querschnitten (10^–7 m²) wurde entworfen und gebaut. Die Apparatur wurde zur Bestimmung von Veränderungen der Wärmeleitfähigkeit des metallischen Glases Fe₈₀B₂₀ (Mctglass 2605) während des durch thermische Behandlung ausgelösten Kristallisationsprozesses benutzt. Trotz der Einfachkeit betrug die Abweichung von den gemessenen tatsächlichen Wärmeleitfähigkeitswerten weniger als 8%, was sich als ausreichend für die Ermittlung der Glasbildungstemperatur 7₉ aus Veränderungen der Wärmeleitfähigkeit erwiesen hat.

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( 10^–7 ₄). Fe₈₀B₂₀ 2605) , . , 8%, _g .

     

Thermal conductivity measurements using the flash method

Thermal diffusivity is the speed with which heat propagates through a material. It has a multitude of direct applications, such as determining heat transfer through brake pads at the moment of contact, etc., but more often it is used to derive thermal conductivity from the fundamental relationship tying it with specific heat capacity and density. Using a new multi-sample configuration system, and testing a reference sample adjacent to the unknown, specific heat capacity can be obtained parallel with thermal diffusivity. Thus, a single test yields thermal diffusivity and thermal conductivity with prior knowledge of density. The method is fast and produces results with high accuracy and very good repeatability. The sample size, 12 to 30 mm diameter and 2 to 5 mm thickness, is easy to handle and is well suited for a broad range of materials, even for composites, often a problem for other methods. Typical data on two polymers, Pyrex glass and Pyroceram 9606 are presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Newer methods of determining electrolytic conductivity

This paper describes, in outline, the theory, construction and use of a three-terminal transformer ratio-arm bridge. The effect of strong impedance and capacitance are minimized without the use of a Wagner earth. By using special cells the use of contacting metal electrodes can be eliminated. The use of the bridge for measuring dielectric constants is also described.     

Intensification of proton conductivity through polymer electrolytic membrane using novel electrode pattern

The performance of a polymer electrolyte membrane fuel cell is contingent on the focal property of the protonic conductivity to accelerate the electrochemical reaction based on the membrane activity or on the uniform and even distribution of the reactants. For the even distribution, novel Flow Fields (FF) of the electrode pattern are obligatory to maintain the distribution for a long period for the conversion of protons from the anode reactant. In this study, a novel X Flow Field (XFF) electrode pattern is developed and compared with the conventional serpentine Flow Field (SFF) electrode pattern numerically and experimentally. The performance of the cell through the XFF electrode pattern has shown an improvement of 14.89% numerically and 14.61% experimentally as it distributes the reactants evenly to accelerate the electrochemical reaction, and induce a lower pressure drop and lower water saturation. The effect of pressure and Mass Flow Rate (MFR) of the reactants on the cell performance is discussed and it is found that the increment in Power Density (PD) of the cell is proportional to the increment of the MFR and the pressure because of the even distribution of the reactants, better membrane protonic conductivity, enhancement of the electrode kinetics and improvement in the mass transfer.     

Development of an in-line calibration system for flow-through cells for low electrolytic conductivity values

This paper describes a comparison calibration system applicable to meters for low electrolytic conductivity values. In this system, measurements are performed in a closed circuit with a flowing solution. This circuit contains a flow-through reference cell and a flow-through cell under calibration. Results of calibrations by substitution and by comparison at 3 mS/m (KCl aqueous solution) are compared. The result of a calibration by comparison at 0.3 mS/m is also reported.     

Electrochemical characterization of a primary electrolytic conductivity cell at CENAM

Linear voltammetry and electrochemical impedance spectroscopy experiments were performed in order to obtain basic information about the electrochemical behavior of the primary cell of electrolytic conductivity at Centro Nacional de Metrología. Linear voltammetry shows that the amplitude of the sinusoidal perturbation must be smaller than 300 mV. Electrochemical impedance results indicate that optimal frequency interval extends from 5 to 0.6 kHz. Regarding sinusoidal signal amplitude, a lower bias with respect to electrolytic conductivity of an independent reference solution is obtained at 10 mV than at larger amplitudes; in addition, electrode integrity is improved.     

Determination of electrolytic conductivity of a 0.01D aqueous potassium chloride solution at various temperatures by an absolute method

A critical study of the conductance calibration standard, 0.01D aqueous potassium chloride solution, at 0°C, 18°C, and 25°C has been made using a highly precise thermostat and temperature program, a conductance measuring assembly of comparable precision, and a new type of absolute conductance cell. In spite of the high precision with which cell constants can be determined at any one temperature, the values at differents temperatures are only compatible with a linear temperature dependence within much larger limits.     

Primary methods for the measurement of electrolytic conductivity

This paper surveys the state of the art for primary methods for the evaluation of electrolytic conductivity in aqueous solutions as they are currently carried out in several national metrological institutes (NMIs). The theoretical and practical basic knowledge of this measurement is described. Analysis of and comments on the different approaches are offered to give emphasis to technical difficulties and possible solutions. Further development is foreseeable, ensuring a common effort for the sharing of expertise that has been undertaken at the NMIs. In particular, improvements are expected towards traceable measurements of solutions with conductivity values lower than those actually standardized, down to the level of ultrapure water.     

Electrochemical behaviour of a snake-cage cation-exchange membrane electrolytic sorption and ionic conductivity

Summary The uptake of electrolyte by a snake-cage cation-exchange membrane has been measured by different methods. The experimental data are interpretable by local application of theDonnan law and consequently result from the heterogeneous structure of the membrane. The ionic conductivity measurements confirm these results. No ion-exchange polymer is imprisoned in the superficial layers of the membrane, but it is concentrated in a central zone of maximum capacity. Moreover, the development of continuous and poorly charged pores enhances the structural heterogeneity and lowers the permselectivity. If the snake-cage technique is very versatile to insolubilise many different groups, the structure of the resulting systems must be controlled by an adequate choice of matrix porosity and imprisoned chain length.

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Zusammenfassung Die Elektrolytkonzentration in einer Snake-Cage-Kationenaustauschermembran wird mit verschiedenen Methoden gemessen. Die experimentellen Ergebnisse lassen sich durch lokale Anwendung desDonnan-Gesetzes erklären und folgen demgemäß aus der heterogenen Membranstruktur. Die Leitfähigkeitsmessungen bestätigen die früheren Ergebnisse. Kein Ionenaustauscherpolymeres wird in den oberflächlichen Membranschichten festgehalten, es wird vielmehr in einer zentralen Zone mit der Maximalaustauschkapazität konzentriert. Darüber hinaus vergrößert die Anwesenheit von durchgehenden und schwach geladenen Poren die strukturelle Heterogenität und verkleinert die Permselektivität. Wenn viele verschiedene Gruppen durch die Snake-Cage-Technik unlöslich gemacht werden, was möglich ist, so muß die Struktur der entsprechenden Systeme durch eine angemessene Wahl der Matrix-Porosität und der Längen der festgelegten Ketten kontrolliert werden.

     

Rapid and selective determination of free barbiturates by gas chromatography using the electrolytic conductivity detector.

A rapid and specific gas chromatographic method for the analysis of free barbiturates in serum and urine at all levels of clinical interest is described. The method employs an improved electrolytic conductivity detector, and can be used for the determination of barbiturate levels of 0.01 mg/dl without sample clean-up. The preparation of columns for the analysis of nanogram quantities of free barbiturates is also discussed.     

Peculiarities of metal electrodeposition inside a flow-through porous electrode with low initial conductivity in oxidant containing solution

The earlier developed dynamic model of a flow-through electrode is used for studying how the variations in initial conductivity of a porous matrix κ_s,ini and a metal deposit affect the rate of metal deposition from an oxidant-containing solution for the direct-flow operation mode of the porous electrode. It is found that in contrast to an oxidant-free solution in which the decrease of κ_s,ini improves the uniformity of deposit distribution inside the porous cathode and increases the deposit final mass m _f, the opposite situation is observed in the presence of an oxidant, namely, a decrease in κ_s,ini, under otherwise similar conditions reduces the deposit mass and leads to its specific spatial distribution. The final metal deposit is divided into two separate fragments (rear and front) with a region of low conductivity of the initial porous matrix in between. Dynamics of the current and metal redistribution within the porous electrode, the reasons for the formation and stabilization of the rear fragment of coating, the correlation between the metal deposition rate and changes in the anodic zone position and intensity are discussed. It is shown that with the appearance of a specific profile of deposit distribution, the dependence of m _f on the metal conductivity develops a limit that differs considerably from the deposit final mass for an equipotential porous electrode.     

A look at surfactant partitioning in polymeric latexes using conductivity measurements

An attempt was made to analyse the partitioning of anionic surfactants in a mixed surfactant system using surface tension and conductivity measures. This last technique gives us access to the quantity of free ions in solution, and thus a measure of the amount of anionic surfactant available in the aqueous phase. The range of surfactant concentrations studied here is such that the global surface coverage (assuming that the totality of the emulsifier is at the particle surface) varies around 100%.     

Dosimetry for low temperature measurements using single and poly-crystals

The aim of this work was to study the behavior of a single and poly crystalline homemade solid state dosimeters (a) LiF co-doped with Mg, Cu and P, and (b) CaSO₄ doped with Dy. We analyzed the response of these dosimeters using thermoluminiscence. The dose-response at liquid nitrogen temperature was followed to observe the nature of the response.     

Conformation of a chain polyelectrolyte in solution with low molecular weight salt: small angle neutron scattering measurements

Small angle neutron scattering measurements have been carried out on the tetramethylammonium salt of the polystyrenesulfonic acid withDP _w =310 and 1060 in water solution with tetramethylammonium chloride with ionic strength between 0.02 M and 1.0 M. The scattering curves in the scattering vector range 0.05 nm^–1Q1.8nm^–1 have been fitted using the form factor of a worm-like chain of finite thickness. The conformational parameters mean square radius of gyration, statistic chain element, mass per unit length and mean square radius of the cross-section have been determined experimentally and used for describing the conformation of the coils. By these molecular weights and ionic strengths, excluded volume is not necessary to explain the conformation changes depending on the salt content of the solutions; relatively short coil molecules can be described in their unperturbed dimensions even in a thermodynamically good solvent: a change in the stiffness of the chain according to Odijk's theory succeeds in describing the conformation of the polyions. Together with a slow decrease of the coil dimension by increasing salt content, a transition at ionic strength 0.1–0.5 M between two different conformations has been observed. The conformation at lower ionic strength is characterized by higher stiffness of the chain and lower mass per unit length than the form at higher salt concentration.