Calcium ion selective membrane electrode

The calcium salts of the mono- and diesters of [4-(1,1,3,3-tetramethylbutyl)phenyl phosphoric acid] have been prepared, and the individual esters as well as mixtures of the esters have been used with several varieties of polyvinyl chloride to construct macro membrane electrodes selective to calcium ions. These electrodes have been calibrated by using solutions of CaCl₂ and Ca ion buffers. The mixed ester electrodes showed Nernstian response in the concentration range 10^-1 to 10^-7M; the diester electrodes showed Nernstian response down to 7.9 x 10^-8M. The detection limit of the mixed ester electrode was 10^-8M, whereas that of the diester electrode was 7.9 x 10^-9M. Contrary to these results, the monoester electrodes showed unsatisfactory behavior. The responses of both the mixed ester and diester electrodes to calcium ions were not affected by the presence of sodium, potassium, or other divalent ions. Only ferric and lanthanum ions showed interferences with the electrode response to calcium ions. p]The electrode response was independent of pH in the approximate range 5–8 at a CaCl₂ concentration of 10^-4M. As the Ca ion concentration was increased, the range of pH independence widened to approximately 4–8. The dynamic response time constant of the mixed ester electrode was in the range 0.7–1.5 sec, whereas that of the diester electrode was in the range 0.5–0.75 sec.     

Trace fluoride determination with specific ion electrode

A method is described for determining 10^-5–10^-4M fluoride in a variety of solutions potentiometrically with a fluoridc-specific electrode, by a standard addition method. Any change of ionic strength or the nature of the solution that might alter activity coefficients or junction potentials is minimized. The relationship between potential and fluoride concentration thus follows the Nernst equation, and the unknown concentration can be calculated. Experimental data are given for solutions of sodium choride, sodium nitrate, acidified sodium silicate and sodium hydroxide, lithium chloride, and phosphoric acid. Metal ions (e.g., Al³⁺, UO₂²⁺, Fe³⁺, Th⁴⁺) that interfere by forming complexes with fluoride can be precomplexed with phosphoric acid. The relative error is estimated at 10%, and the relative standard deviation is less than 5% over the concentration range 10^-5–10^-4M fluoride.     

Analytical study of a cadmium ion-selective ceramic membrane electrode

Summary A cadmium ion-selective membrane electrode has been developed by applying a hot-pressing method. The membrane contains cadmium sulphide, silver sulphide, and copper(I)-sulphide.The best response was obtained with a membrane containing less than 30% of copper(I) sulphide and more than 5% of cadmium sulphide. The Nernstian slope was secured over an activity range of 10^–1 to 10^–6 M, and potentiometric analysis could be carried out over a concentration range of 10^–1-10^–7 M. The potentials were maintained at constant values over more than 6 months. Also, the potentials satisfied the Nernst's factor 2.303 RT/2F at the temperature range between 0 and 95°C. Among the common ions, silver, copper(II), iron(III), mercury(II), sulphide, and iodide ions interfered seriously. However, about 10–100 times of lead and bromide ions and more than 1000 times of alkali metal, alkaline earth metal, zinc, aluminium, nickel, cobalt, manganese(II), perchlorate, and nitrate ions did not interfere at all.

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Analytische Untersuchung einer cadmiumionenselektiven keramischen Membranelektrode

Zusammenfassung Die Membran wurde durch Pressen von Cd-, Ag und Cu(I)-sulfid bei 200–500°C und 3–7 t/cm² hergestellt. Die beste Ansprechempfindlichkeit ergab sich bei einem Gehalt von <30% Cu₂S und >5% CdS. Die Nernstsche Gleichung war gültig im Bereich von 10^–1–10^–6 M, der analytische Bereich war 10^–1–10^–7 M. Die Potentiale konnten mehr als 6 Monate auf einem konstanten Wert gehalten werden. Sie entsprachen dem Nernstschen Faktor, 2,303·R·T/2 F, im Temperaturbereich von 0–95°C. Erhebliche Störungen werden durch Ag⁺-, Cu²⁺-, Fe³⁺-, Hg²⁺-, S^2– und J^–-Ionen verursacht. Jedoch verursachen etwa 10–100fache Mengen von Pb²⁺- und Br^–-Ionen sowie mehr als 1000fache Mengen von Alkali-, Erdalkali-, Zn²⁺-, Al³⁺-, Ni²⁺-, Co²⁺-, Mn²⁺-, ClO₄ ^–- und NO₃ ^–-Ionen keine Störungen.

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The authors thank Dr. S. Kisaka, Dr. K. Sugihara, Dr. S. Hayakawa and Dr. S. Mori for their encouragement in this work.     

Lead-sensitive membrane electrode based on chelating ion exchanger

A new selective membrane electrode for the measurement of lead activities is proposed. The preparation of active components of the membrane is described. The ready made electrode insert was used in which the PVC membrane was replaced by the prepared membrane. Experimental results document the emf response of profile, the selectivity, the detection limit and the effect of the sample media. The prepared electrode was applied for the measurement of the lead concentration in water samples. Activated alumina micro-column was used for the pre-concentration of lead in the analyzed water samples. The obtained results were compared with those determined by atomic absorption spectrometry.     

Potentiometric determination of sulphate in fertilisers with cadmium sulphide membrane electrode

Summary A method is described for the determination of sulphur in fertilisers using reduction and evolution of hydrogen sulphide followed by a potentiometric titration with lead nitrate. Several procedures are tested for the destruction of the samples. The most accurate results are obtained after dissolution of the fertiliser in hydrochloric acid.

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Potentiometrische Bestimmung von Sulfat in Düngemitteln mit Hilfe der Cadmiumsulfid-Membranelektrode

Zusammenfassung Die vorgeschlagene Methode beruht auf Reduktion und Entwicklung von H₂S, gefolgt von einer potentiometrischen Titration mit Bleinitrat. Zum Aufschluß der Probe wurden verschiedene Verfahren getestet, wobei die Auflösung in verdünnter Salzsäure die besten Ergebnisse brachte.

     

Thermodynamic parameters related to the specific adsorption of iodide ion on the mercury electrode

The thermodynamic functions for the specific adsorption of the iodide ion on mercury have been determined from capacity measurements at 5°C, 25°C and 45°C. The experimental values of the standard electrochemical free energy, enthalphy and entropy of adsorption at zero charge, Δ$\text{G}$⁰_I^?, Δ$\text{H}$⁰_I^?, and Δ$\text{S}$⁰_I^?, are in good agreement with previous values for chloride and thiocyanate ion adsorption. They show that most of the free energy change comes from the entropy change, suggesting that the structural contributions play an important role in the ion-specific adsorption. The thermodynamic functions are compared with the values calculated using the Andersen—Bockris model.     

A polystyrene based membrane electrode for cadmium(II) ions

A polystyrene based membrane of 3,4:12,13-dibenzo-2,5,11,14-tetraoxo- 1,6,10,15-tetraazacyclooctade-cane shows a Nernstian response to Cd(II) ions over a wide concentration range (3.16 x 10(-6) - 1.00 x 10(-1) mol L(-1) with a Nernstian slope of 29.8 mV/decade of concentration, between pH 2.0 and 6.0. This electrode has been found to be chemically inert and of adequate stability with a response time of 20s. The electrode gives reproducible results with a lifetime of 130 days. The membrane works satisfactorily in a partially non-aqueous medium up to a maximum 35% (v/v) content of methanol and ethanol. The practical utility of the proposed chemical sensor has been observed by using it as end-point indicator in the titration of Cd(II) ions with EDTA. The potentiometric selectivity coefficient values indicate that the membrane sensor is highly selective for Cd(II) ions over a number of cations. Small amounts of surfactants do not disturb the functioning of the sensor. This electrode has also been used to estimate cadmium ions in real samples.     

Controlled release of model drugs through a molecular recognition ion gating membrane in response to a specific ion signal

A controlled-release device that responds to a specific molecular signal is an ideal goal in drug delivery and tissue engineering. A molecular recognition ion gating membrane, in which a copolymer of N-isopropylacrylamide and benzo[18]-crown-6-acrylamide was grafted onto the surface of the porous polyethylene film, was used to control the permeability of vitamin B12 and lysozyme in response to a specific ion signal. The observed response depended on the amount of grafted copolymer. When the grafting ratio was below 15%, the membrane pores opened by Ca2+ and closed by Ba2+. The permeability of model drugs became higher by opening of the pores. On the other hand, when the grafting ratio was above 15%, the properties of the membrane changed. The permeability of model drugs became lower by Ca2+ due to dehydration of the grafted copolymer. The opposite responses were observed at different grafting ratios.     

A selective membrane electrode for iodide ion based on a thiopyrilium ion derivative as a new ionophore

A highly selective electrode for iodide ion based on a thiopyrilium derivative as an excellent ionophore is described. At pH 5.5-8.0, the electrode responds to iodide ion in a linear range from 1.0×10⁻¹ to 8.0×10⁻⁷ M with a slope of 60.2 mV per decade, and a detection limit of 2.0×10⁻⁷ M. Selectivity coefficients determined with the match potential method (MPM) indicate that the interference from inorganic and organic anions is very small. The proposed sensor shows a fast response time of approximately 15 s. It was applied as an indicator electrode in titration of iodide with Ag⁺.     

Osmotic pressure control in response to a specific ion signal at physiological temperature using a molecular recognition ion gating membrane

A molecular recognition gating ion membrane was prepared by graft copolymerization of N-isopropylacrylamide and benzo[18]crown-6-acrylamide onto the pore surface of porous polyethylene film. This membrane captured Ba2+ with its crown ether receptors and generated osmotic pressure in response to Ba2+ autonomously and reversibly. However, the membrane never generated osmotic pressure in response to Ca2+. In addition, the concentration gradient of both the ion and other solute such as dextran could be used as the driving force; using a dextran concentration gradient, we can control the critical concentration and the duration time of the osmosis response.     

低检出限聚合物膜镉离子选择性电极的研制及应用

基于痕量电位分析原理,研制出了一种新型的聚合物膜镉离子选择性电极.通过优化电极内充液组成及聚合物膜组分,电极在10-8～10-4mol/L镉浓度范围内呈现良好的能斯特响应,响应斜率为24.9 mV/dec.,检出限可达5.9nmol/L.该电极应用于实际湖水样品中镉含量的检测,结果与ICP-MS法数据较为吻合.     

An approach to membrane fouling characterization by confocal scanning laser microscopy

Confocal scanning laser microscopy (CSLM) is an optical microscopic technique that, among other advantages, can provide high-resolution images from different depths of a three-dimensional object, therefore rendering invasive techniques unnecessary for sample preparation. CSLM in fluorescence mode is a powerful technique in biological applications and in the microscopy of food materials. The main goal of the present study is to develop the appropriate strategies so that CSLM can be used for membrane fouling characterization during the filtration of protein solutions. Single and binary solutions of BSA–fluorescein and ovalbumin–Texas red conjugates were filtered using 0.8 μm polycarbonate membranes. Samples of the membranes at the end of the filtration runs were analyzed by CSLM. A standardized protocol for sample analysis by CSLM was developed and applied in this study. The most significant results show that CSLM can be used to visualize BSA–fluorescein and ovalbumin–Texas red conjugates on top of and inside the membranes, and that they can be distinguished when they jointly foul the membrane. Finally, if the appropriate sectioning is applied a 3D reconstruction of the membrane and the adsorbed/deposited protein can be obtained which give information on the fouling morphology.     

Radioactive tracer study of adsorption and exchange reaction of lead ion selective electrode membrane

Summary The amount of adsorption and exchange of lead on the electrode membrane as a function of time was correlated to the potential measurement stability. The adsorption and exchange of lead in various organic solvents tend to be increased relating to the increase in the dielectric constant of solvents. Removal of O₂ and CO₂ and addition of methanol and formaldehyde are very effective means to improve the potential stability. The behavior of lead ISE exposed to solutions containing lead and other interfering ions was also studied.

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Radiochemische Untersuchung der Adsorptions- und Austauschreaktionen bleiionenspezifischer Elektroden

Zusammenfassung Adsorption und Austausch von Blei an der Elektrodenmembran als Funktion der Zeit wurden zur Stabilität der Potentialmessung in Beziehung gesetzt. In verschiedenen organischen Lösungsmitteln steigen Adsorption und Austausch mit der Dielektrizitätskonstante an. Die Entfernung von O₂ und CO₂ sowie der Zusatz von Methanol und Formaldehyd verbessern die Stabilität des Potentials. Das Verhalten von bleiionenspezifischen Elektroden gegenüber Lösungen, die Blei und andere störende Ionen enthalten, wurde untersucht.

     

KTiOPO4单晶膜钾离子选择性电极的研究

本文采用KTiOPO4单晶薄片作为离子活性传感膜, 制备了钾离子选择性电极。20℃时, 其线性响应范围为1.2×10^-^5～1.0mol.dm^-^3氯化钾溶液, 平均响应斜率为58mV/-lgak, 对钠离子的电位选择性系数为4.0×10^-^4。该电极的优点是电极斜率受酸度变化影响小, 稳定性和重现性好, 寿命长。     

The preparation and analytical evaluation of a new heterogeneous membrane electrode for cadmium(ii)

The preparation of a new cadmium-selective heterogeneous membrane electrode obtained by hot-pressing a mixture of cadmium and silver sulfides with polythene in a moulding press is described. Nernstian response to cadmium ion was achieved only when the mixture of salts was purified by heat treatment at 600° in an atmosphere of hydrogen sulfide for several hours. This behaviour is discussed in terms of the purity of the salts. Interferences and analytical applications in aqueous and nonaqueous solvents are described.     

Chitosan solubilization by bipolar membrane electroacidification: Reduction of membrane fouling

Chitosan, a biopolymer obtained from chitin deacetylation, was solubilized by bipolar membrane electroacidification (BMEA). We showed earlier that limitation in solubilization process was mainly due to chitosan precipitation in the acidified compartment. If fouling can be reduced or prevented, BMEA could be an environmentally attractive method for chitosan solubilization. The purpose of the present work was to identify process conditions that could reduce chitosan fouling in BMEA. The factors studied were: the type of salt in the acidified compartment (NaCl or CH₃COONa); the type of electrolyte in the basified compartment (KCl or HCl); and the current density (4 or 20 mA/cm²). Chitosan fouling was successfully reduced by a combination of NaCl salt and HCl electrolyte, while 98% chitosan solubilization yield was achieved by operating at a current density of 4 mA/cm² with NaCl/KCl configuration with no apparent fouling. This work showed that water dissociation at the interface of the anionic membranes was the main factor responsible for chitosan precipitation.     

A polystyrene-based membrane electrode sensitive to molybdate ions

A polystyrene-based zirconium oxide membrane has been used to determine the concentration of molybdate ions in the range 0.5-10(-3)M and pH range 7-11. The response time is about 20 sec and the electrode remains usable for at least 6 months. It can also be used as an indicator electrode for titrations involving molybdate ions. Univalent anions interfere more strongly than bivalent and multivalent anions.     

Feed-water pretreatment: methods to reduce membrane fouling by natural organic matter

The prevention of fouling of polysulphone ultrafiltration membranes, used for the purification of natural brown water, was investigated by pretreating the feed-water prior to filtration. Natural brown water was pretreated by changing the pH of the feed solution and by coagulation with metal-ions prior to filtration. Specific characterisation techniques, developed by Maartens et al. (1998) [A. Maartens, P. Swart, E.P. Jacobs, Humic membrane foulants in natural brown water: characterization and removal, Desalination 115 (3) (1998) 215–227] and Jucker and Clarke (1994) [C. Jucker, M.M. Clark, Adsorption of aquatic humic substances on hydrophobic ultrafiltration membranes, J. Membrane Sci. 97 (1994) 37–52], were used to determine and compare the effects induced by the adsorption of natural organic matter on the permeability of capillary ultrafiltration membranes. The extent of foulant adsorption and the quality of the resultant permeate solutions were determined by UV–VIS-light spectroscopy. Results indicated that adsorption of natural organic matter can be minimised by adjusting the pH of the feed solution to 7. The findings of this investigation provides information of importance for the operation of future natural brown water ultrafiltration plants.