Oxoacidity reactions in molten LiCl+KCl eutectic (at 470°C): Potentiometric study of the equilibria of exchange of O2− between Al(III) systems and carbonate and water systems

The reactions between aluminium chloride and oxide anion were studied in molten LiCl+KCl eutectic at 470°C. For that purpose, a pO^2? indicator electrode made with a membrane in yttria-stabilized zirconia has been used and tested by means of a carbonate ion whose dissociation constant, 10^?2.15 atm, was determined. Then, the electrode has allowed us to obtain the formation constant of AlO⁺ (solvated by Cl^?) and the solubility product of Al₂O₃ (S): 10^10.7 and 10^?27.4, respectively (molality scale). The equilibrium constant of the following system: 2HCl (g)+O^2? agH₂O (g)+2Cl^? has also been determined: 10^?9.93 atm mol kg^?1. The conditional solubility of alumina in LiCl+KCl melt is discussed.     

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.     

Copper(II)-selective electrode based on dithioacetal

A PVC membrane electrode for copper ion based on 1,3-dithiane,2-(4-methoxy phenyl) as ionophore and o-nitrophenyl octyl ether as a plasticizer is demonstrated. The electrode exhibits a Nernstian slope of 29.5±1 mV per decade in a linear range of 3.0×10⁻⁶ to 5.0×10⁻² M for Cu²⁺ ion. The detection limit of this electrode is 1.0×10⁻⁶ mol/l. This sensor has a very short response time of about 5 s and could be used in a pH range of 4.0-7.0. High selectivity was obtained over a wide variety of metal ions. The proposed electrode was successfully applied as an indicator electrode for the potentiometric titration of copper ion with EDTA and for the direct determination of copper in river water.     

Response of polyacrylamide—acyclic poly(oxyethylene)-coated ion-selective electrodes to alkali and alkaline earth metal ions in propylene carbonate and its thermodynamic application

The response of ion-selective electrodes with a membrane of polyacrylamide (PAA) coupled to acyclic poly(oxyethylene) neutral carriers to lithium, sodium, potassium, magnesium and barium ions in propylene carbonate (PC) was investigated. Tetraethylene glycol monododecyl ether (POE4) and hexaethylene glycol monododecyl ether (POE6) were used as the acyclic poly(oxyethylene). Both the PAA-POE4 and the PAA-POE6 electrodes showed a more rapid dynamic response in PC than that in acetonitrile. Nernstian responses to lithium, magnesium and barium ions were obtained with the PAA-POE4 electrode. The selectivity coefficients, logk_Ba²⁺,M^x+, for lithium, sodium, potassium and magnesium ions vs. barium ion obtained in PC with the PAA-POE4 electrode were 3.6, 0.23, 0.02 and 1.1, respectively. The PAA-POE4 electrode was applied to obtain the successive formation constants of the barium ion in PC with N, N-dimethylacetamide (DMA). From the successive formation constants obtained in PC-rich solutions, the Gibbs free energies of transfer of the barium ion from PC to DMA and to PC-DMA mixtures were calculated. The electrode was also used to obtain directly the Gibbs free energies of transfer of the barium ion from PC to PC-DMA mixtures. The calculated values of the free energies were in good agreement with the values obtained experimentally, suggesting that the electrode responded to variations in solvation energy for the barium ion.     

Hydrogen ion-selective poly(vinyl chloride) membrane electrode based on a p-tert-butylcalix[4]arene-oxacrown-4

A hydrogen ion-selective poly(vinyl chloride) (PVC) membrane electrode was developed using p-tert-butylcalix[4]arene-oxacrown-4 as ionophore. Apart from the ionophore, plasticisers and lipophilic anions were blended, in various proportions, with PVC in tetrahydrofurane and mixtures so prepared were poured onto glass surfaces to form the membrane. 2-Nitrophenylpentylether has proved to be the best alternative as plasticiser and the lipophilic anions tried have turned out to have an adverse effect on the pH response. The electrode of the optimum characteristics had a composition of 2% p-tert-butylcalix[4]arene-oxacrown-4, 68.3% o-NPPE and 29.7% PVC. The electrode showed an apparent Nernstian response in the pH range 2-11 with a slope of 54.2±0.4 mV pH⁻¹ at 20±1 °C. It has a rapid potential-response to changes of pH, high ion selectivity towards lithium, sodium and potassium, and other characteristics comparable to those reported for the conventional pH glass membrane electrode. It appears to be a suitable potentiometric indicator electrode specifically for hydrofluoric acid solutions.     

Ion-selective characteristics of heavy metal myristate liquid membrane electrodes

Liquid membrane electrodes of myristate soaps of heavy metals, namely copper, cadmium, zinc, nickel, cobalt, strontium and barium in a benzene-n-butanol mixture were prepared. Each electrode showed nernstian response in common metal ion test solution. The range of concentration of the test solution for the Nernstian behaviour lies between 10^?4 and 10^?1M. With a dissimilar metal ion in test solution the metal soap liquid membrane electrode indicates deviations from Nernst's equation depending on the nature of the metal ion, suggesting different selectivities for different ions. The selectivity ratios are therefore calculated.     

Ni(II) selective sensors based on Schiff bases membranes in poly(vinyl chloride)

The two nickel chelates of Schiff bases, 3-hydroxy-N-{2-[(3-hydroxy-N-phenylbutyrimidoyl)-amino]-phenyl}-N′-phenylbutyramidine (M₁) and bis-4-(ethyliminomethyl)naphthalene-1-ol (M₂), have been synthesized and explored as ionophores for preparing PVC-based membrane sensors selective to nickel ion. The influences of membrane compositions on the potentiometric response of the electrodes have been found to substantially improve the performance characteristics. The best performance was obtained with the electrode having a membrane composition (w/w; mg) of (M₁): PVC:NaTPB:CN in the ratio 5:150:5:150. The sensor shows a linear potential response for Ni²⁺ over a wide concentration range 1.6 × 10⁻⁷ to 1.0 × 10⁻² M with Nernstian compliance (30.0 ± 0.2 mV/decade of activity) within pH range 2.5-9.5 and a fast response time of 10 s. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol, and acetonitrile and could be used for a period of 4 months. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of nickel in real samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.     

A lead(II)-selective PVC membrane based on a Schiff base complex of N,N'-bis(salicylidene)-2,6-pyridinediamine

PVC membrane electrodes for lead ion based on N,N’-bis(salicylidene)-2,6-pyridinediamine as membrane carrier were prepared. Among their membranes, a membrane electrode (m-3) containing o-NPOE as a plasticizer and 50 mol% additive displays an excellent Nernstian response (29.4 mV/decade) and the limit of detection of −log a (M) = 6.04 to Pb²⁺ in Pb(NO₃)₂ solutions at room temperature. It has a rapid response time within 10 s over the entire concentration range. The proposed electrode revealed good selectivity and response for Pb²⁺ over a wide variety of other metal ions in a pH 5.0 buffer solutions, and good reproducibility of base line in subsequent measurements.     

Interaction of calcium ion with sodium triphosphate determined by potentiometric and calorimetric techniques

The stoichiometry of the interaction of Ca²⁺ with sodium triphosphate was determined using a Ca²⁺ sensitive electrode, divalent ion sensitive electrode, a glass electrode and by titration calorimetry, A 2:1 and 1:1 complex of Ca²⁺ and P₃O^5?₁₀ is found when titrating calcium chloride with sodium triphosphate by the calcium ion sensitive electrode and tritation calorimetry. However, only by titration calorimetry is the 2:1 and 1:1 complex found when titrating sodium triphosphate with calcium chloride. Thermodynamic value (log K, ΔH and ΔS) are reported for the formation of CaP(in3)O^?3₁₀ and Ca₂P₃O^?₁₀ in aqueous solution.     

Carbonate ion electrode based on HTPP sites

Several quaternary phosphonium salts have been used as the site materials for construction of carbonate ion electrodes. Among them the electrode based on hexadecyltriphenylphosphonium salt showed best performance characteristics. The Nerstian response range of the electrode is from 1 × 10^?2 down to 6.3 × 10^?7 mol · dm^?3 with a detection limit of 1.8 × 10^?7 mol · dm³. The selectivity order of ions can be altered by the introduction of trifluoroacetyl-tert-butylbenzene as a solvent mediator. The strong solvatoin of the primary ion of interest in the membrane phase by the solvent mediator favors the improvement of the selectivity of the proposed electrode.     

Lead-Selective Membrane Potentiometric Sensor Based on a Recently Synthesized Bis(Anthraquinone) Sulfide Derivative

Abstract

A new PVC membrane electrode for lead ions, based on bis[(1-hydroxy-9,10-anthraquinone)-2-methyl]sulfide as membrane carrier, was prepared. The sensor exhibits a Nernstian response for Pb²⁺ over a wide concentration range (5.6 × 10^?3-4.0 × 10^?6 M). It has a response time of about 30 s and can be used for at least 3 months without any divergence in potentials. The proposed membrane sensor revealed good selectivities for Pb²⁺ over a wide variety of other metal ions. It was used as an indicator electrode in potentiometric titration of lead ion.     

Selective determination of rubidium ions by a solid membrane electrode

An araldite-based titanium tungstoarsenate solid membrane electrode has been developed to estimate rubidium ion concentration in the range 10^?1 to 4×10^?5M. The electrode shows considerable selectivity for rubidium ions over other cations. Treatment with a 10^?4M solution of the anionic surfactant, sodium dodecyl sulphate, not only makes the membrane immune to detergent effects but the selectivity and validity range of the electrode assembly are also improved.     

Solid contact Zn2+ -selective electrode with low detection limit and stable and reversible potential

A new solid contact Zn²⁺ polyvinylchloride membrane sensor with 2-(2-Hydroxy-1-naphthylazo)-1,3,4 -thiadiazole as an ionophore has been prepared. For the electrode construction, ionic liquids, alkylmethylimidazolium chlorides are used as transducer media and as a lipophilic ionic membrane component. The addition of ionic liquid to the membrane phase was found to reduce membrane resistance and determine the potential of an internal reference Ag/AgCl electrode. The electrode with the membrane composition: ionophore: PVC: o-NPOE: ionic liquid in the percentage ratio of (wt.) 1:30:66:3, respectively, exhibited the best performance, having a slope of 29.8 mV decade^?1 in the concentration range 3×10^?7–1×10^?1 M. The detection limit is 6.9×10^?8 M. It has a fast response time of 5–7 s and exhibits stable and reproducible potential. It has a fast response time of 5–7 s and exhibits stable and reproducible potential, which does not depend on pH in the range 3.8–8.0. The proposed sensor shows a good and satisfactory selectivity towards Zn²⁺ ion in comparison with other cations including alkali, alkaline earth, transition and heavy metal ions. It was successfully applied for direct determination of zinc ions in tap water and as an indicator electrode in potentiometric titration of Zn²⁺ ions with EDTA.      

PVC membrane electrode based on triheptyl dodecyl ammonium iodide for the selective determination of molybdate(VI)

Novel polyvinyl chloride (PVC) membrane electrodes based on triheptyl dodecyl ammonium iodide have been developed. In the presence of 12.5 mM H₂O₂, these electrodes are capable of determining molybdate(VI) ion. The electrodes exhibit near-Nernstian responses over a wide concentration range (2.0 × 10⁻⁶ to 5.0 × 10⁻³ M). The proposed electrodes demonstrate satisfying selectivity for molybdate(VI) ion in the presence of a wide variety of anions other than iodide, and can be used in the pH range 5.0-7.0. Moreover, the electrodes show an average response time of 2-3 min and can be used over a period of 2 months without any significant deviation being observed. In the light of our results, the response mechanism of the electrode is discussed and HMoO₂(O₂)₂⁻ is suggested as the response ion. The proposed electrode has been used to measure molybdenum in ore samples, and the results were in agreement with those obtained by means of ICP analysis.     

Sulfite-sensitive solvent/polymeric-membrane electrode based on bis(diethyldithiocarbamato)mercury(II)

A new solvent/polymeric-membrane electrode which exhibits significant potentiometric response toward sulfite ion in the 1 × 10_?6?1 × 10^?3 M range is described. The membrane is prepared by incorporation of neutral bis(diethyldithiocarbamato)mercury (II) in a thin film of plasticized poly (vinyl chloride). In sharp contrast to classical Hofmeister behavior, the resulting membrane displays little or no response to a wide range of anions (log K^pot_i,j ? ?4, i being sulfite) including sulfate, nitrate, nitrite, chloride, perchlorate, salicylate, and alkylsulfonates. Bromide and thiocyanate are moderate interferents, while significant response to iodide, thiosulfate, and sulfide is observed. These selectivity data, along with other response characteristics of the membrane, are used to postulate the mechanism by which the electrode responds to sulfite. Preliminary studies demonstrate that the electrode can be used in conjunction with an outer gas-permeable membrane for highly selective detection of total sulfite species in the form of sulfur dioxide.     

A highly selective thallium(I) electrode based on a thia substituted macrocyclic ionophore

A new highly Tl(I)-selective PVC membrane electrode based on tetrathia macrocycle 6,7: 14,15-dibenzo-5,8,13,16-tetraoxo-1,4,9,12-tetrathiacyclohexadecane [Bz₂O₄(16)aneS₄] (I) as membrane carrier, o-nitrophenyloctyl ether (o-NPOE) as solvent mediator and potassium tetrakis(p-chlorophenyl)borate (KTpClPB) as lipophilic additive has been developed. The best performance was given by the membrane of macrocycle (I) with composition 3:120:1.5:50 (I:o-NPOE:KTpClPB:PVC). This electrode exhibits a Nernstian response to Tl(I) ions in the concentration range 1.0 × 10⁻¹-2.23 × 10⁻⁶ M with a slope of 58.2 mV/decade of concentration and a detection limit of 1.58 × 10⁻⁶ M. The response time of the sensor is 12 s and can be used over a period of 4 months with good reproducibility. The proposed electrode revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metals. The electrode works well over a pH range of 3.2-11.5 and in partially non-aqueous medium with up to 30% organic content. The sensor was also used as an indicator electrode in potentiometric titration of Tl(I) ions with KI solution.     

Strontium(II)-selective electrode based on a macrocyclic tetraamide

A new PVC membrane electrode based on 5,7,12,14-dibenzo-2,3,9,10-tetraoxa-1,4,8,11-tetraazacyclotetradecane (I) as an ion carrier, o-nitrophenyloctyl ether (o-NPOE) as solvent mediator and sodium tetraphenylborate (NaTPB) as lipophilic additive was fabricated and investigated as Sr²⁺-selective electrode. The best performance was exhibited by the membrane having composition 8:200:4:120 (I:o-NPOE:NaTPB:PVC). The electrode exhibited a Nernstian response for strontium ion over a wide concentration range 3.98 × 10⁻⁶ to 1.0 × 10⁻¹ M with a slope of 29.0 ± 0.1 mV/decade of concentration and a detection limit of 2.82 × 10⁻⁶ M. It showed a response time of less than 10 s and could be used for at least 3 months without any divergence in potential. The proposed electrode showed a good discriminating ability towards strontium(II) ion over a wide variety of other metal ions including alkali, alkaline earth, transition, and heavy metal ions. The electrode can be used in the pH range of 2.5-10.5 and in mixtures containing up to 35% (v/v) non-aqueous content. It was used as an indicator electrode in potentiometric titration of strontium ion against EDTA.     

Schiff bases as cadmium(II) selective ionophores in polymeric membrane electrodes

The construction and performance characteristics of polymeric membrane electrodes based on two neutral ionophores, N,N′-[bis(pyridin-2-yl)formylidene]butane-1,4-diamine (S₁) and N-(2-pyridinylmethylene)-1,2-benzenediamine (S₂) for quantification of cadmium ions, are described. The influences of membrane compositions on the potentiometric response of the electrodes have been found to substantially improve the performance characteristics. The best performance was obtained with the electrode having a membrane composition (w/w) of (S₁) (2.15%):PVC (32.2%):o-NPOE (64.5%):KTpClPB (1.07%). The proposed electrode exhibits Nernstian response in the concentration range of 7.9 × 10⁻⁸ to 1.0 × 10⁻¹ M Cd²⁺ with limit of detection 5.0 × 10⁻⁸ M, performs satisfactorily over wide pH range (2.0-8.0) with a fast response time (10 s). The sensor has been found to work satisfactorily in partially non-aqueous media up to 30% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 2 months. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of cadmium in real samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.     

A bio-selective membrane electrode prepared with living bacterial cells.

A novel potentiometric sensor has been devised by coupling intact microorganisms (Streptococcus faecium) with an ammonia gas-sensing membrane electrode. The resulting electrode provides a linear response to arginine over the concentration range 5.0 × lO^-5–1. 0 × 10^-3 M in phosphate buffer pH 7.4, with selectivity over other amino acids. The slope of the calibration graph is -40 to -45 mV/decade during the period 2–20 days after preparation. This membrane electrode with living bacterial cells may serve as a model for the development of other new sensing systems.     

A mercury(II) ion-selective electrode based on neutral salicylaldehyde thiosemicarbazone

A new ion-selective PVC membrane electrode based on salicylaldehyde thiosemicarbazone as an ionophore is developed successfully as sensor for mercury(II) ions. The electrode shows excellent potentiometric response characteristics and displays a linear log[Hg²⁺] versus EMF response over a wide concentration range of 1.778×10⁻⁶-1.0×10⁻¹ M with Nernstian slope of 29 mV per decade with the detection limit of 1.0×10⁻⁶ M. The response time of the electrode is less than 30 s and the membrane electrode operates well in the pH range of 1.0-3.0. The lifetime of the sensor is about 2 months. The electrode shows better selectivity towards Hg²⁺ ions in comparison with the alkali, alkaline and some heavy metal ions; most of these metal ions do not show significant interference (K^Pot_Hg,M values of the order of 10⁻³-10⁻⁴). The present sensor showed comparable or even better performance vis-à-vis similar PVC based ion-selective electrodes reported in literature. The sensor was also applied as an indicator electrode for potentiometric titration of Hg²⁺ions with I⁻ and Cr₂O₇²⁻.