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.     

Primary methods of measurement in chemical analysis

 Primary methods of measurement have a central function in metrology. They are an essential component in the realisation of the SI units and therefore are indispensable for establishing traceability of measurements of all kinds of physical quantities to the corresponding SI units. This is also true for chemical analysis. Gravimetry, titrimetry, coulometry, and isotope dilution mass spectrometry (IDMS) are evaluated with regard to their potential to be primary methods according to a general definition of primary methods recently given by the Comité Consultatif pour la Quantité de Matière (CCQM). Optical absorption spectrometry and methods based on colligative properties are also considered. A general scheme for establishing traceability of chemical measurements to the SI units using primary methods is discussed. Received: 17 April 1997 · Accepted: 9 August 1997     

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...     

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.     

Competency evaluation on electrolytic conductivity measurement in Indonesia by an unofficial bilateral comparison between RCChem-LIPI and NIMT

Accreditation and Quality Assurance - The Research Centre for Chemistry—Indonesian Institute of Sciences (RCChem-LIPI) organized an unofficial bilateral comparison on electrolytic...     

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.     

New membrane-based electrolytic suppressor device for suppressed conductivity detection in ion chromatography

This paper discusses the newest advancement in chemical suppression preceding conductivity detection. The new suppressor uses electrolysis of deionized water to generate the required acid or base for the suppression neutralization reaction and utilizes the electrical field to enhance, through electrodialysis, the suppressor's capacity for neutralization. The suppressor is able to accommodate eluents as high as 150 mM NaOH, without the need for a separate regenerant solution, by recycling the conductivity detector cell waste to the regenerant and electrolysing the water in the waste stream to the required acid or base. The device is able to use deionized water as regenerant and neutralize the eluent stream to deionized water without the expected increase in resistance by employing ion exchange material in intimate contact with the electrodes and the membranes. The current is carried with low resistance through the ion-exchange material via ion transport from one ion-exchange site to another.     

pH and electrolytic conductivity as parameters to characterize bioethanol

To guarantee the quality of bioethanol and avoid damage to the fuel system in a car, the determination of acidity, water content, as well as chloride, sulfate, alkali metal and alkaline earth metal content are important. Electrochemical quantities like pH and electrolytic conductivity are frequently used in biofuel analysis as sum parameters mainly to indicate the risk of corrosion. Many standards and measurement methods used today in the analysis of biofuel are adopted from specifications and test methods originally developed for fossil-based fuels and commercial alcohol. This results from the rapid expansion of the biofuel production. There are efforts to solve remaining metrological and regulatory issues on a regional and international basis on a short term. In the following an overview on the fundamentals for the measurement of pH in bioethanol blends is given. It will be discussed if the electrolytic conductivity of the bioethanol could be a reliable measure of corrosion causing ionic contaminations in biofuel. State of the art, limitations and future tasks for metrology will be discussed.     

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 microgram amounts of carbon in the for of carbamate by non-aqueous electrolytic conductivity detection

An absorption/detection system is described for the determination of carbon at and below microgram detection level. The carbon dioxide formed by combustion of an organic substances (solid or in solution) is led into a simple absorption/detection system containing 2.00 cm³ of an ethanolic 2 M solution of 3-methoxypropylamine. The conductivity of the carbamate solution formed is measured by means of platinum electrodes built in the absorption tube, and the integrated d.c. voltage signal obtained is fed to a precision digital voltmeter. Detector response is linear up to 6.6 μg of carbon, and the detection limit is 2 × 10^?2 μg. A single determination takes 5 min. Precision was found to be better than +? 1.0% (P-=95%) for 1–6 μg or carbon.     

Certification of a low value electrolytic conductivity solution using traceable measurements

Reliable measurement results of electrolytic conductivity (EC), in particular for low values, must be metrologically traceable and be based on a realistic measurement uncertainty budget. The use of certified reference materials (CRMs) can help to achieve this goal. This paper presents results from all stages of the certification of an EC CRM with a conductivity of 1.5 μS cm^?1, including the preparation of the batch solution and the evaluation of the homogeneity and stability of the bottled CRM. An uncertainty budget is presented for the CRM, including the main contributions from each of these sources. The CRM batch remained stable within its certified uncertainty for more than 1 year.     

Development of a thermal conductivity cell with nanolayer coating for thermal conductivity measurement of fluids

Various techniques and methodologies of thermal conductivity measurement have been based on the determination of the rate of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy of the rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude of transient thermal diffusivity along these directions. The transient hot-wire technique is broadly used for absolute measurements of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous measurement of both thermal conductivity and thermal diffusivity together with the determination of the specific heat. However, these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. Recently developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. A thermal conductivity cell for measurement of the thermal properties of electrically conducting fluids has been developed and discussed.     

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.     

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.

     

Application of the Hall™ electrolytic conductivity detector for the analysis of chloroanilines and chloronitroanilines in POTW sludges

Simultaneous detection with a 700-A Hall? and an NPD detector is an effective technique for characterizing chloro-and chloronitroanilines in highly complex Publicly Owned Water Treatment Works (POTW) sludges. The utilization of a modified Varian effluent splitter and a SE-54 fused silica capillary column permitted the detection of mid-picogram quantities of the polar chloroanilines without sacrificing peak shape. The response of the Hall? detector in the halogen mode was roughly proportional to the number of chlorine atoms present, while the response of the Hall? in the nitrogen mode and the NPD was less predictably influenced by the presence of one or more nitro groups. When combined with retention time data, the ratio of the NPD response to the Hall? response has been found to substantiate the presence of chloro- and chloronitroanilines in sludge extracts.     

Absolute determination of electrolytic conductivity for primary standard KCl solutions from 0 to 50°C

An absolute determination of aqueous electrolytic conductivity has been made for primary standards 0.01D and 0.1D (demal) potassium chloride solutions over the temperature range of 0 to 50°C in 5 degree intervals. A cell with a removable center section of accurately known length and area was used for the measurements. Values were adjusted to be in conformity with the ITS-90 temperature scale. The overall uncertainty over the entire temperature range is estimated to be 0.03%. Values at 25°C for 0.01D and 0.1D KCl solutions are 0.0014086 and 0.012852 S-cm^–1, respectively.     

Intercomparison of thermal conductivity and thermal diffusivity methods for plastics

An intercomparison of measurements of the thermal conductivity and thermal diffusivity of two poly(methyl methacrylates) is reported. A wide variety of methods were used: temperature wave analysis, laser flash, transient plane source (Hot Disk^®), transient line-source probe, and heat flux meter methods. Very good agreement of thermal conductivity results and, separately, of thermal diffusivity results was obtained. Similarly, good agreement between thermal conductivity and thermal diffusivity results, when converted using specific heat capacity and density values, was also obtained. Typically, the values were within a range of approximately ±10%. Considering the significant differences between the methods and the requirements on specimen dimensions, the level of agreement between results was considered to be good.     

A multi point conductivity measurement system for characterisation of protein foams

Protein foams play an important role in both food and biotechnological processes. A sound understanding of foaming properties of proteins relevant to such processes is useful e.g. to allow adequate control of unwanted foams and appropriate choice of protein-physical system when foams of certain characteristics are required. In general, measurements of changes in foam volume (volumetric method) are used for foam characterisation. However, recently there has been increased interest in the use of measurement methods based on conductivity and capacitance. Simple relative techniques based on electrical conductivity measurements provide information on both foamability and foam stability. A multi point conductivity measurement system has been designed and used for characterisation of model protein foams (0.1 and 1.0 mg ml⁻¹ Bovine serum albumin, BSA). The solution of BSA was sparged with nitrogen or carbon dioxide gas at constant flow rate (90 cm³ min⁻¹) via a stainless steel sinter (0.5 or 2.0 μm in pore size). A comparison of foaming properties determined by volumetric and conductimetric techniques is provided. Both methods show that more stable foams are obtained for solutions at higher BSA concentrations. At all BSA concentrations, higher foamability and stability are achieved with a smaller sinter pore size. When nitrogen rather than carbon dioxide is used as a dispersed phase, higher foamability and foam stability are obtained. The conductivity measurements indicate that foamability is dependent on gas type, whereas, volumetric measurements do not show such differences.     

Comparison of three methods for the determination of the electrical conductivity of ion-exchange polymers

The development of ion-exchange membranes techniques using an electrical potential gradient incite often to define the electrical conductivity of this category of functional polymers. The investigation methods of this conductivity did not stop to vary, to such a point that some results can be contradictory. So we have determined this dynamic characteristic in comparing three recent methods. This has been done with three ion-exchange membranes often used in industrial applications: CM1 and CM2, made from sulfonated and crosslinked polystyrene, and Nafion^® 117 made from sulfonated uncrosslinked polytetrafluoroethylene. Measurements were achieved in sodium chloride solutions, at concentrations from 0.1 to 2 mol l⁻¹. The results show, whatever the polymer microstructure, non-negligible disparities between the three methods.