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.

Electrodeposition of actinides from saline groundwaters for alpha-spectrometric determination

An establishéd electrodeposition method for separating americium and plutonium from highly saline used-fuel-leaching solutions has been extended to the determination of Np and U in saline groundwaters. The interference of major ionic species in groundwater on the yield was investigated using three groundwaters of varying salinity (ionic strength I=1.37, 0.0748 and 0.0253 mol/l). High average yields (>92%), and good reproducibility were obtained for Np and U electroplated from solutions with ionic strength less than 0.1. The greatest interferences from individual ions were caused by Mg²⁺ and HCO ₃ ^– .     

A general treatment for the conductivity of electrolytes in the whole concentration range in aqueous and nonaqueous solutions

Despite the great importance of ion transport, most of the widely accepted models and theories are valid only in the not very practical limit of low concentrations. Aiming to extend the range of applicability to moderate concentrations, a number of modified models and equations (some approximate, some fundamented on different assumptions, and some just empirical) have been reported. In this work, a general treatment for the electrical conductivity of ionic solutions has been developed, considering the electrical conductivity as a transport phenomenon governed by dissipation and feedback. A general expression for the dependence of the specific conductivity on the solution viscosity (and indirectly on concentration), from which the whole conductivity curve can be obtained, has been derived. The validity of this general approach is demonstrated with experimental results taken from the literature for aqueous and nonaqueous solutions of electrolytes.     

Electrolytic conductivity and molar heat capacity of two aqueous solutions of ionic liquids at room-temperature: Measurements and correlations

As part of our systematic study on physicochemical characterization of ionic liquids, in this work, we report new measurements of electrolytic conductivity and molar heat capacity for aqueous solutions of two 1-ethyl-3-methylimidazolium-based ionic liquids, namely: 1-ethyl-3-methylimidazolium dicyanamide and 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate, at normal atmospheric condition and for temperatures up to 353.2 K. The electrolytic conductivity and molar heat capacity were measured by a commercial conductivity meter and a differential scanning calorimeter (DSC), respectively. The estimated experimental uncertainties for the electrolytic conductivity and molar heat capacity measurements were ±1% and ±2%, respectively. The property data are reported as functions of temperature and composition. A modified empirical equation from another researcher [1] was used to correlate the temperature and composition dependence of the our electrolytic conductivity results. An excess molar heat capacity expression derived using a Redlich–Kister type equation was used to represent the temperature and composition dependence of the measured molar heat capacity and calculated excess molar heat capacity of the solvent systems considered. The correlations applied represent the our measurements satisfactorily as shown by an acceptable overall average deviation of 6.4% and 0.1%, respectively, for electrolytic conductivity and molar heat capacity.     

Protonation and complex formation of 5-sulfosalicylate in NaCl,CaCl2 and MgCl2 aqueous media. Speciation in synthetic seawater

The binding capacity of 5-sulfosalicylic acid (ssa) towards cationic macro-components of natural waters has been investigated in different ionic media (NaCl, MgCl2 and CaCl2 aqueous solutions) and in the ionic strength range 0 < or = I < or = 1 mol dm-3. In order to contribute to the speciation of this multi-sites ligand, measurements have been carried out also in a synthetic seawater (SSWE) containing the major components of seawater (Na+, K+, Ca2+, Mg2+, Cl- and SO4(2-)). Measurements have been performed by potentiometry ([H+]-glass electrode), at t = 25 degrees C. A critical analysis on the experimental and literature data is also given.     

Interactions of diethylenetriaminepentaacetic acid (dtpa) and triethylenetetraaminehexaacetic acid (ttha) with major components of natural waters

The binding ability of diethylene triamine pentaacetate (dtpa(5-)) and triethylene tetraamine hexaacetate (ttha(6-)) ligands towards major components, H(+), Na(+), Mg(2+) and Ca(2+), of natural waters was studied in both single and mixed ionic media at different ionic strengths and at T=25 degrees C. Some measurements, performed in Mg(2+)-Ca(2+) mixtures, allowed us to find the formation of new mixed species MgCa(dtpa), MgCa(ttha) and MgCaH(ttha), here reported for the first time. All the complexes formed in the various systems were characterized in terms of both stoichiometry and stability, and an attempt was made to find general rules for the stability of mixed metal complexes in comparison with that of simple species. To obtain quantitative information on the complexing ability of dtpa and ttha in seawater, measurements have been carried out in artificial seawater ionic medium (Na(+), K(+), Ca(2+), Mg(2+), Cl(-) and SO(4)(2-)). Calculations, performed by considering the salt mixture as single salt BA, allowed us to find some quite stable B(i)H(j)L species. Under the natural seawater conditions [S(salinity)=35], we found for the most important species logbeta( B(dtpa))=9.64 and. Literature data comparison is also reported.     

Thermal, rheological, and ion-transport properties of phosphonium-based ionic liquids

Phosphonium-based ionic liquids with varying counteranions from commercially available ionic liquid precursors enabled tunable viscosity, ionic conductivity, and thermal stability. Thermogravimetric analysis revealed a relationship between thermal stability and anion composition where anions with lower basicity remained stable to higher temperatures. Determination of glass transition temperatures and melting temperatures using differential scanning calorimetry revealed supercooling, crystallization, and dependence on anion composition. Rheological and ionic conductivity measurements determined the temperature-dependence of the viscosity and ionic conductivity of the phosphonium-based ionic liquids. Arrhenius analyses of conductivity and viscosity provided activation energies, which showed a decrease toward larger, more delocalized anions. An assessment according to the Walden plot displayed their efficacy relative to other ionic liquids.     

Ion chromatographic system with a novel switching suppression device

Ion chromatography (IC) has been a powerful tool for measuring ionic species in environmental samples such as tap, river and drain waters. Suppressor modules (membrane and disposable column types) have been used for reducing the background of a baseline. A new type of suppressor device, which has a suppressor resin and switching valve was developed. Fresh ionic resin is introduced into a groove for each analysis to perform the suppression of the working eluent. The eluent composition for obtaining higher sensitivity and better resolutions among ionic species and carbonate ion was also investigated. Although carbonate buffers are used for ion separation in general, the separation of carbonate ion from other ions was not achieved. A borate eluent resulted in good resolutions and higher sensitivity. A new column was also developed for obtaining higher column efficiency and resolution. The optimization of anion separation using a new IC system (IC-2001) that consists of a new suppressor device, an anion-exchange column (TSKgel SuperIC-Anion, 150x4.6 mm), an autosampler, a conductivity cell and a pump in a compact module is described.     

Mixed micelle formation between amino acid-based surfactants and phospholipids

The mixed micelle formation in aqueous solutions between an anionic gemini surfactant derived from the amino acid cystine (C(8)Cys)(2), and the phospholipids 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC, a micelle-forming phospholipid) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC, a vesicle-forming phospholipid) has been studied by conductivity and the results compared with the ones obtained for the mixed systems with the single-chain surfactant derived from cysteine, C(8)Cys. Phospholipid-surfactant interactions were found to be synergistic in nature and dependent on the type of phospholipid and on surfactant hydrophobicity. Regular solution theory was used to analyse the gemini surfactant-DHPC binary mixtures and the interaction parameter, β(12), has been evaluated, as well as mixed micelle composition. The results have been interpreted in terms of the interplay between reduction of the electrostatic repulsions among the ionic head groups of the surfactants and steric hindrances arising from incorporation of the zwitterionic phospholipids in the mixed micelles.     

Inorganic constituents in aerosols, cloud water and precipitation collected at the high alpine measurement station Sonnblick: Sampling, analysis and exemplary results

Background measurements at the high alpine station of the Sonnblick (altitude 3106 m) are reported. For a period of 13 months samples have been collected during 4 campaigns of 1–2 weeks duration each and analysed for their ionic and elemental composition, pH and conductivity. These samples were aerosols collected with filters, cloud water and precipitation. The samples were mainly analysed with ion chromatography (IC) and atomic absorption spectrometry (AAS). Analysis proved to be difficult due to the low amounts of aerosols collected and the low concentrations of components in cloud water and wet precipitation. Also major problems arose in sampling due to the extreme climatic conditions. The analytical techniques, particularly those for sampling the materials, are critically evaluated and results on pollutant levels, their variation with time and the distribution of the components between the gaseous and liquid phases are presented.Abbreviations ET-AAS Electrothermal Atomic Absorption Spectrometry - F-AAS Flame Atomic Absorption Spectrometry - FIA Flow Injection Analysis - IC Ion Chromatography Dedicated to Prof. Dr. Dieter Klockow on the occasion of his 60th birthday     

Individual equivalent conductances of the major ions in seawater

A radioactive tracer method has been used to determine the trnasference numbers of eight major ions in seawater of salinity 38.4 g-kg ^–1 at 25°C. Data are presented for Na⁺, K⁺, Ca ²⁺ , and Mg ²⁺ cations and Cl^–, Br^–, SO ₄ ^2– , and HCO ₃ ^– anions, which contribute to the overall electrical conductance by more than 99%. The results have been checked by electrophoretic migrations on esters of cellulose strips providing independent values of the ratios of ionic mobilities to be compared to previous estimations. Through the individual ionic contributions to the electrical conductance, a method for calculating seawater density is proposed; this method is based on a nine-constitutents seawater model in which relative ionic concentrations can deviate from that of standard seawater.     

Determination of perchlorate at parts-per-billion levels in plants by ion chromatography

A method for the analysis of perchlorate in plants was developed, based on dry weight, and applied to the analysis of plant organs, foodstuffs, and plant products. The method reduced greatly the ionic interferences in water extracts of plant materials. The high background conductivity, due to the plant matrix, was reduced sufficiently to allow quantitation of perchlorate with little or no matrix interference. Ion chromatography (IC) on a microbore AS16 anion-exchange column and a conductivity detector was used for separation and detection of perchlorate from the ionic plant extract. The extract was heated to precipitate proteins, centrifuged, exposed to alumina, and filtered through a cartridge filled with divinylbenzene to yield a water clear extract for IC analysis, even from highly colored solutions. Heating the extract and treatment with alumina reduced substantially the ionic content of the extracts without loss of perchlorate.     

Modified McKay–Perring Equation and Its Two Particular Solutions

Zdanovskii’s rule is the simplest isopiestic molality relation of mixed electrolyte aqueous solutions and the McKay–Perring equation is a differentio-integral equation particularly suitable for calculating solute activity coefficients from isopiestic measurements. However, they have two unsolved problems, which have puzzled solution chemists for several decades: (1) Zdanovskii’s rule has been verified by precise isopiestic measurements. But, several scientists suggested that the rule contradicts the Debye–Hückel limiting law for extremely dilute unsymmetrical mixtures. (2) In the McKay–Perring equation, a solute activity coefficient is multiplied by a solute composition variable. Different scientists have suggested that the composition variable may be the total ionic strength, common ion concentration, total ionic concentration, or an additive function with arbitrary proportionality constants. But, the different choices of the composition variable may lead to different activity coefficient results. Here, I derive a modified McKay–Perring equation in which the composition variable has the exclusive physical meaning of total ionic concentration for mixed electrolyte solutions (or of total solute particle concentration for the mixed solutions containing nonelectrolyte solutes). I also demonstrate that Zdanovskii’s rule is consistent with the Debye–Hückel limiting law for extremely dilute unsymmetrical mixtures. I derive two particular solutions of the modified McKay–Perring equation: one for the systems obeying Zdanovskii’s rule and another for the systems obeying a limiting linear concentration rule. These theoretical results have been verified with literature experiments and model calculations.     

Enhanced ionic conductivity in an otherwise poorly conducting Ce0.90Ca0.10O(2-δ) system

A poorly conducting ionic material Ce(0.90)Ca(0.10)O(2-δ) was converted to a highly conducting composition by a codoping strategy with Sm(3+) and Gd(3+). A 50% replacement of Ca with either Sm or Gd has increased the conductivity at 550 °C of Ce(0.90)Ca(0.10)O(2-δ) from 0.0040 to 0.0169 S/cm for the Ce(0.90)Ca(0.05)Sm(0.05)O(2-δ) composition and to 0.0184 S/cm for the Ce(0.90)Ca(0.05)Gd(0.05)O(2-δ) composition. The enhancement in the oxide ion conductivity of these codoped samples has been related to the low ionic radii mismatch and the elastic strain. The extended X-ray absorption fine structure measurements on these systems confirmed that Gd, when coupled with Ca, introduced more disorder in the system, leading to lower activation energy and higher conductivity. In addition, a reduction in the Ce-O bond distance and coordination number has also been observed with codoping.     

Viscometric and conductometric study of polyelectrolytes of low charge density in salt free aqueous solutions

Viscometric and conductometric measurements have been performed on dilute, salt free solutions of poly(vinyl alcohol) (PVA) and poly(vinyl alcohol, vinyl sulphate ester) copolymer salts in order to get information on transition from a neutral to charged macromolecules. With increasing linear charge density from a very low value to a moderate one a non linear dependence of polyelectrolyte effect on copolymer composition was observed. A comparison has shown that there is a close analogy between the expansion of polyanions and swelling of polyelectrolyte networks at comparable linear charge density range. Due to the intra- and inter-molecular mobile ionic bridges a considerable contraction was pointed out by viscometry for barium, magnesium and copper salts. However, the differences in properties of counterions of higher charge number indicates that in addition to the valency, there is a definite chemical effect, too. It has been revealed by the electric conductance measurements that the transition from a neutral to charged macromolecules could be a very complex one calling for a new and more detailed theoretical consideration of polyelectrolyte solutions.     

Chromatographic studies of corrosion sites in metallic materials

Many types of corrosion phenomena are controlled by the ionic composition of a small volume of solution at the surface. Localized corrosion and atmospheric corrosion are two examples in which < 1 μl of solution can cause dramatic damage. Ion chromatographic (IC) techniques have been used to analyze these solutions in order to gain a better understanding of the mechanisms which govern them. Two examples are presented. The presence of minor alloying elements at localized corrosion sites in two aluminum alloys has been demonstrated, indicating non-stoichiometric dissolution of the alloy during localized corrosion. In addition, IC analysis allowed the determination of the species responsible for the atmospheric corrosion failure of electrical connectors, including their likely origin.     

Speciation of polyelectrolytes in natural fluids Protonation and interaction of polymethacrylates with major components of seawater

Acid-base properties of two sodium polymethacrylates (W=4000 and 5400 Da) were studied potentiometrically in aqueous solution at 25 degrees C. Measurements were made in different salt solutions: LiCl 0.1-1.5, NaCl 0.1-2, KCl 0.1-2, Et(4)NI 0.1-0.75 mol l(-1), and in artificial seawater in the salinity range 10相似文献   

Optical sensor for seawater salinity

An optical sensor for the measurement of salinity in seawater has been developed. It is based on a chloride-quenchable fluorescent probe (lucigenin) immobilized on a Nafion film. Two approaches for measuring salinity via chloride concentration are presented. In the first, a change in salinity corresponds to a change in the fluorescence intensity of lucigenin. In the second, the fluorescence intensity information is converted into a phase angle information by adding an inert phosphorescent reference luminophore (a ruthenium complex entrapped in poly(acrylonitrile) beads). Under these conditions, the chloride-dependent fluorescence intensity of lucigenin can be converted into a chloride-dependent fluorescence phase shift which serves as the analytical information. This scheme is referred to as dual lifetime referencing (DLR). The sensor was used to determine the salinity in seawater and brackish water of the North Sea.     

Recent advances of transient isotachophoresis-capillary electrophoresis in the analysis of small ions from high-conductivity matrices

Since its invasion into the field of small ion analysis, quantitation of trace ionic analytes has always been a challenging task for CE, especially when dealing with highly saline samples. This review summarizes the method's progress and significant developments in the area due to its combination with on-line preconcentration by transient ITP (tITP). Principles of tITP stacking in high-conductivity solutions and operational preconcentration modes are considered. The most important application areas covered in this review include the analysis of seawater and biological fluids (urine, serum, etc.). Examples cited in this review demonstrate that tITP-CE is now on a certain way of becoming a recognized technique when the determination of trace ionic species in loaded matrices is the aim.     

Uncertainty Budget for Simultaneous Determination of Minor and Major Ions in Seawater with Ion Chromatography Confronted with Uncertainties in Concentrations of Calibration Standards

This work deals with the development and application of the detailed uncertainty budget for simultaneous determination of minor and major ions in seawater and derived saline solutions. Combination and sequence of gravimetric or/and volumetric steps involved in introducing each particular ion into stock and final combined calibration standards; cross contamination of chemicals and dilution of samples were critically assessed and their significance to the combined uncertainty was evaluated. The main uncertainty components were identified and quantified for all anions and cations determined with ion chromatography in seawater and estuary water and confronted with uncertainties associated with concentrations of ions in combined calibration standards. Similar uncertainty components reflect very differently upon different ions.