Solid-state ion-selective electrodes for the potentiometric determination of phosphate

A number of solid-state ion-selective electrodes for the potentiometric determination of phosphate have been made and their properties investigated. The most successful of these electrodes, which had a membrane comprising silver sulphide, lead sulphide and lead hydrogen phosphate, had a theoretical Nernstian response to orthophosphate ion at concentrations down to 5 mug/ml total phosphate at pH 8.3. The electrode had a slow response and its standard potential changed with time. Anions such as sulphate, bicarbonate and nitrate did not interfere; chloride had a transient effect, but even at its worst the interference was less serious than with other phosphate electrodes. The electrode was used as an indicator in the potentiometric precipitation titration of phosphate and lanthanum.     

Direct potentiometric water hardness determination using ion-selective electrodes

Summary The use of ion-selective electrodes for direct potentiometric water hardness determinations is restricted to relatively soft waters if they are to be competitive with other techniques in terms of uncertainty on the water hardness scale. The selectivity factorK _MgCa ^Pot must be within 1.1% of unity if a hardness of 10 degrees on the German scale is to be measured to within 0.1 degrees in the composition rangec _Mg:c _Ca=0.25 to 25. The expressionK _MgNa ^Pot ·a _Na ² / (a _Mg+a _Ca) must be less than 0.001 if freedom from sodium interference is to be achieved. Under these conditions a 1% relative standard deviation can be obtained for an uncertainty of the EMF100V.

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Direkte potentiometrische Bestimmung der Wasserhärte mit ionen-selektiven Elektroden

Zusammenfassung Die direkte potentiometrische Bestimmung der Wasserhärte mit ionenselektiven Elektroden kann nur für relativ weiches Wasser verwendet werden, sofern sie mit anderen Methoden konkurrenzfähig sein soll. Der SelektivitätsfaktorK _MgCa ^Pot sollte nicht mehr als 1,1% von 1 abweichen, um eine Messung von 10 deutschen Härtegraden auf 0,1 Grad genau zu ermöglichen, wenn gleichzeitig das Mischungsverhältnisc _Mg:c _Ca im Bereich 0,25 bis 25 schwankt. Der AusdruckK _MgNa ^Pot ·a _Na ² /(a _Mg +a _Ca) sollte 0,001 nicht überschreiten, wenn eine Störung durch Natrium vermieden werden soll. Unter den obigen Bedingungen läßt sich eine Wasserhärte auf 1% genau bestimmen, wenn die Unsicherheit der gemessenen EMK100V.

     

Calixarene-based potentiometric ion-selective electrodes for silver

Four lipophilic sulphur and/or nitrogen containing calixarene derivatives have been tested as ionophores in Ag(I)-selective poly (vinyl chloride) membrane electrodes. All gave acceptable linear responses with one giving a response of 50 mV/dec in the Ag(I) ion activity range 10(-4)-10(-1)M and high selectivity towards other transition metals and sodium and potassium ions. This ionophore was also tested as a membrane coated glassy-carbon electrode where the sensitivity and selectivity of the conventional membrane electrode was found to be repeated. The latter electrode was then used in potentiometric titrations of halide ions with silver nitrate.     

New conventional coated-wire ion-selective electrodes for flow-injection potentiometric determination of chlordiazepoxide.

New chlordiazepoxide hydrochloride (Ch-Cl) ion-selective electrodes (conventional type) based on ion associates, chlordiazepoxidium-phosphomolybdate (I) and chlordiazepoxidium-phosphotungstate (II), were prepared. The electrodes exhibited mean slopes of calibration graphs of 59.4 mV and 60.8 mV per decade of (Ch-Cl) concentration at 25 degrees C for electrodes (I) and (II), respectively. Both electrodes could be used within the concentration range 3.16 x 10(-6)-1 x 10(-2) M (Ch-Cl) within the pH range 2.0-4.5. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficients of the electrodes, which were 0.00139 and 0.00093 V degrees C(-1) for electrodes (I) and (II), respectively. The electrodes showed a very good selectivity for Ch-Cl with respect to the number of inorganic cations, amino acids and sugars. The electrodes were applied to the potentiometric determination of the chlordiazepoxide ion and its pharmaceutical preparation under batch and flow injection conditions. Also, chlordiazepoxide was determined by conductimetric titrations. Graphite, copper and silver coated wires were prepared and characterized as sensors for the drug under investigation.     

Solid-state reference electrodes for potentiometric sensors

The availability and application of solid-state reference electrodes for potentiometric electrochemical sensors are briefly reviewed. For a long time, considerable efforts have been made to combine solid-state indicator electrodes with equivalent reference electrodes to take advantage of the absence of liquid system components to full capacity. In spite of various suggestions to solve the problem, no type of solid-state reference electrode is so far available with properties completely identical to conventional ones.     

Single-point potentiometric titrations with ion-selective electrodes

A single-point potentiometric titration method is described for the determination of silver(I), chloride and sulphate with ion-selective electrodes. Relative standard deviations in the range 0.1–1.25% can be obtained, depending on the quality of the electrodes used.     

Studies on bis(crown ether)-based ion-selective electrodes for the potentiometric determination of sodium and potassium in serum

Bis(crown ether)-based ion-selective electrodes for sodium and potassium are described, based on the bis[(12-crown-4)-2-ylmethyl]-2-dodecyl-2-methyl malonate sensor(I) for sodium and the bis[(benzo-15-crown-5)-15-ylmethyl] pimelate sensor(II) for potassium. The best results were obtained when the sensors were used in association with 2-nitrophenyl octyl ether as plasticising solvent mediator and potassium tetrakis(4-chlorophenyl)borate as anion excluder in poly(vinyl chloride) matrices. Electrode slopes were near-Nernstian, with detection limits of less than 10(-5) M. The electrode features are compared with those of a sodium glass membrane electrode, for sensor I, and with a valinomycin-based potassium electrode, for sensor II. The electrodes are also discussed in relation to others reported for sensors I and II and are shown to be superior. However, although the electrodes described offer promising alternatives to glass electrodes for sodium and valinomycin electrodes for potassium, data for sodium and potassium measurements in blood serum indicate a need for further research in order to improve the correlation with flame photometric measurements.     

New polyacrylate-based lead(II) ion-selective electrodes

A novel polyacrylate-based matrix for potentiometric ion-selective electrodes has been developed. Isododecyl acrylate, acrylonitrile and hexanedioldiacrylate co-monomers along with the thermo-initiator 2,2-dimethoxy-2-phenylacetophenone were used as polymeric matrix components. A lead(II)-selective electrode (Pb-ISE) was constructed using the above matrix. The electrode showed comparable analytical performance in the micromolar range to Pb-ISEs with conventional poly(vinyl chloride)-based membranes containing neutral ionophore and with solid-state membranes containing a mixture of lead sulphide and silver sulphide. Electrochemical impedance spectroscopy studies revealed much lower ion mobility in the polyacrylate membrane than in plasticized poly(vinyl chloride) membranes. This result additionally indicates the possibility of obtaining a lower detection limit for ISEs using the new acrylate matrix.     

A microcomputer-based system for potentiometric measurements with ion-selective electrodes

A comparison, on completely equal terms, of a microcomputer-based system with manual measurements is described in detail. The main features compared are the precision and accuracy of the results and the number of determinations per time unit. The example used is a standard addition measurement of fluoride in toothpaste. The microcomputer system and its interfacing to the peripheral units are also described. The microcomputer system for control, supervision and evaluation of the measurements results in a significant gain in precision and speed. Accuracy requires the use of a non-theoretical value of the Nernstian slope. The memory effect of the ion-selective electrode is large when the type of sample is changed.     

Studies of copper(II) sulphide ion-selective electrodes

Changes in liquid junction potentials in copper(II) solutions were measured when different reference electrodes were used. The slope and intercept of a calibration curve for a copper-selective electrode will depend on the selection of reference electrode. The condition of the electrode surface of an Orion copper-selective electrode was studied microscopically and the influence of redox potential on stability of the electrode against corrosion is discussed. Oxidizing solutions will produce pits at dislocations in the material and there will be a mixed electrode potential. The slope, stability, and speed of response are much lower when the surface contains pits. Diamond-polishing was shown to improve the electrode significantly.     

The potentiometric titration of fluoride without fluoride ion-selective electrodes

Graphite and platinum sensors were investigated as indicators in the potentiometric titration of fluoride vs lanthanum(III) and thorium(IV). In every case a partially nonaqueous medium yielded larger breaks than in aqueous solution, similar to the fluoride electrode. All the sensors yielded endpoint breaks which were smaller than those obtained with a fluoride ion-selective electrode. The largest breaks were obtained with the vitreous carbon, pyrolytic graphite, and platinum sensors. Conditioning in neutral permanganate solution significantly enhanced the breaks for all types of graphite, except vitreous carbon. The break obtained with the platinum electrode can be enhanced by application of a polarizing current of 2.0 μA in the reducing direction.     

Mercury(II) ion-selective electrodes based on heterocyclic systems

Mercury ion-selective electrodes (ISEs) were prepared with a polymeric membrane based on heterocyclic systems: 2-methylsulfanyl-4-(4-nitro-phenyl)-l-p-tolyl-1H-imidazole (I) and 2,4-diphenyl-l-p-tolyl-1H-imidazole (II) as the ionophores. Several ISEs were conditioned and tested for the selection of common ions. The electrodes based on these ionophores showed a good potentiometric response for Hg2+ ions over a wide concentration range of 5.0 x 10(5-) - 1.0 x 10(-1)M with near-Nernstian slopes. Stable potentiometric signals were obtained within a short time period of 20 s. The detection limits, the working pH range of the electrodes were 1.0 x 10(-5) M and 1.6-4.4 respectively. The electrodes showed better selectivity for Hg2+ ions over many of the alkali, alkaline-earth and heavy metal ions. Also sharp end points were obtained when these sensors were used as indicator electrodes for the potentiometric titration of Hg2+ ions with iodide ions.     

Solid-state halide ion-selective electrodes: studies of quaternary ammonium halide solutions and determination of surfactants

The feasibility of using homogeneous membrane-type halide ion-selective electrodes in solutions containing cationic surfactant compounds was examined. The results established the applicability of these electrodes for monitoring halide ions in solution without interference by the surfactants. The data also provided a basis for estimation of the surfactant in solution through the halide content. Two typical plating-bath compositions containing CTAB have been successfully analysed for their surfactant content by this procedure.     

Construction of different types of ion-selective electrodes and validation of direct potentiometric determination of phenytoin sodium

The construction and performance characteristics of phenytoin sodium selective electrodes are detailed. Two types of electrodes: plastic membrane I and coated wire II, were constructed based on the incorporation of phenytoin sodium with tungstosilicic acid. The influence of membrane composition, kind of plasticizer, pH of the test solution, soaking time and the electrodes’ foreign ions were investigated. The electrodes showed a Nernstian response with a mean calibration graph slope of 30.9±0.1 and 28.9±0.1 mV decade⁻¹ at 25°C for electrode I and II respectively, over a phenytoin sodium concentration range of 5×10⁻³−5×10⁻⁶ M and 1×10⁻³−1×10⁻⁶ M with a detection limit 1.3×10⁻⁶ M and 2.5×10⁻⁷ M for electrode I and II, respectively. The electrodes gave average selective precision and were usable within the pH range 6–10. Interference studies from common cations, alkaloids, sugars, amino acids and drug excipients are reported. The results obtained by the proposed electrodes were also applied successfully for the determination of the drug in pharmaceutical preparations and biological fluids.     

Comparison of copper(II) ion-selective electrodes for measurements at micromolar concentrations

Four types of copper ion-selective electrodes have been tested for determining copper at concentrations below lO^-6 mol 1^l-1. None of the electrodes has a Nemstian response in dilute copper solutions in this concentration range, though their responses are linear in pCu buffer solutions. The causes of the deviations are a direct redox effect in the case of an electrode with a Cu_1.8,Se single crystal membrane, production of copper ions by oxidation of the membrane itself in Ag₂S—CuS membrane electrodes, and a combination of the two in the case of the R??i?ka Selectrode. The electrode potentials are affected by the oxygen content and pH of the sample solution and the condition of the membrane surface. Precision tests on two types of electrode are described.     

The potentiometric titration of surfactants and soaps using ion-selective electrodes

Summary Several quaternary ammonium halides have been evaluated for the precipitation titration of anionic surfactants and soaps. The titrants were hexadecyltrimethylammonium chloride and bromide, hexadecylpyridinium chloride, and diisobutylphenoxyethoxyethyl(dimethyl)benzylammonium chloride. Hexadecylpyridinium chloride yielded the highest precision and largest potentiometric break. Titrations were monitored with a commercically available fluoroborate ion-selective indicator electrode and a double-junction reference electrode. Commercially available perchlorate, nitrate, and calcium electrodes may also be used for emf monitoring. This obviates the need of preparing special liquid membrane or other electrodes mostly used heretofore in the potentiometric titration of surfactants and soaps. Electrophoresis purity reagent sodium dodecylsulfate is recommended for the standardization of the quaternary ammonium halides. The reverse titration, of cationic surfactants vs. standard sodium dodecylsulfate, is similarly feasible.Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore Laboratory under contract number W-7405-ENG-48.     

Lead(II) and copper(II) ion-selective electrodes based on two heterocyclic compounds

In this paper, two nitrogen, sulphur or oxygen containing heterocyclic compounds were used as ionophores in ion-selective electrodes. In these two ion-selective electrodes, 2,6-di(5-methyl-1,3,4-oxadiazol-5-yl)pyridine (DMOP) gives the best Pb²⁺ sensitivity and 2,5-di(2′-methylpyridinethio)thiadiazole (DPTD) gives the best sensitivity for Cu²⁺. These electrodes are composed of KTpClPB as anion excluder and DOS as plasticizer. The two membrane electrodes show Nernstian or near-Nernstian response towards Pb²⁺ or Cu²⁺ (29.3 and 27.3 mV/decade, respectively) over the concentration range 10⁻⁵∼10⁻² and 10⁻⁶∼10⁻³ M, respectively. The response time was less than 20 sec and a good reproducibility over a period of 2 months was observed. The electrodes exhibited good selectivities over a number of alkali, alkaline earth and transition metal ions. The proposed electrodes have also been used for the direct determination of Pb²⁺ and Cu²⁺ ions in real samples.     

Real-time probing of the growth dynamics of nanoparticles using potentiometric ion-selective electrodes

This Communication demonstrates the ability of potentiometric ion-selective electrodes (ISE) to probe the growth dynamics of metal nanoparticles in real-time. The new monitoring capability is illustrated using a solid-contact silver ISE for monitoring the hydroquinone-induced precipitation of silver on gold nanoparticle seeds. Potential-time recordings obtained under different conditions are used to monitor the depletion of the silver ion during the nanoparticle formation and shed useful insights into the growth dynamics of the nanoparticles. Such potentiometric profiles correlate well with the analogous optical measurements. The new real-time electrochemical probing of the particle growth process reflects the direct, rapid and sensitive response of modern ISE to changes in the level of the precipitated metal ion from the bulk solution and holds considerable promise for probing the preparation of different nanoscale materials.     

PVC membrane electrodes for potentiometric determination of tripelennamine

The construction of PVC matrix type tripelennamine ion selective electrodes and their use for direct potentiometry, potentiometric titration and flow injection analysis of tripelennamine cation are described. The membranes of these electrodes consist of tripelennamine-tetraphenylborate, reineckate and picrylsulfonate ion-association complexes dispersed in PVC matrix with tributyl phosphate (TBP) plasticizer. The electrodes exhibit near-Nernstian response over the concentration range of 10^–1-10^–4 M tripelennamine over the pH range 4.5–8.0. Selectivity coefficients data obtained for 17 different organic and inorganic ions are presented. The results obtained for the determination of 29 g/ml-29 mg/ml of tripelennamine with the proposed electrodes show average recoveries of 99.5–99.9% and mean standard deviations of 0.6–1.2%. The data agree well with those obtained by the standard methods.