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It is shown that the improvement of the steric accessibility of exchange centers of higher quaternary ammonium salts by replacing three long-chain radicals (octadecyl) with three methyl radicals and the addition of a neutral carrier, p-trifluoroacetylbenzoic acid heptyl ester, significantly enhance the selectivity of an oxalate-selective electrode and lower the detection limit. An electrode reversible to oxalate ions is proposed. A procedure is developed for determining oxalate ions in green and black tea. [ABSTRACT FROM AUTHOR]

N,N,N tris(2-pyridyloxymethyl) ethane (TPOME) has been used as an ionophore in a polyvinylchloride (PVC)-based membrane. Membrane electrode with a composition 30:5:62:3 (PVC:TPOME: o-NPOE:NaTPB) exhibits Nernstian response towards Pb(II) ions with a slope of 30 mV/decade, over a concentration range of 1 × 10 M to 1 × 10 M. Potential response remains almost unchanged over pH range of 3.7-6.4. The electrode shows fast response time of 15 ± 2 s and a lifetime of four months. It shows good selectivity for Pb(II) ions over other mono-, di- and trivalent cations. Electrode response is satisfactory in mixed solvent media up to 30% (v/v) non-aqueous contents. Selectivity of the ionophore for Pb(II) ions was determined by spectrophotometric method. The electrode can also be used as an indicator electrode in potentiometric titration of Pb(II) ions with standard chromate solution and its determination in real-life samples. Surface morphology of membrane electrode at different stages of its development and use is also discussed. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: A PVC membrane Cu2+ ion-selective electrode has been constructed using a new compound ethyl 1,2,3,4-tetrahydro-4-(4-methoxyphenyl)-6-methyl-2-oxopyrimidine-5-carboxylate (ETMOC) as a neutral ionophore. The electrode works properly. It responds to Cu2+ ion with a sensitivity of 29.5±0.2mV/decade over the range of 1.0×10−9 to 5.0×10−1 M at pH 3.0–8.0. The limit of detection was 4.5×10−10 M. It has a response time of <6s and can be used for at least 3months without any divergence in potentials. The proposed electrode shows fairly good discrimination of Cu2+ ion from several cations. The effect of organic solvents on electrode response shows that this electrode can be used in methanol and ethanol media until 15% (v/v) concentration without interference. This sensor was used to determination of Cu2+ concentration in Tea leaves, Milk powder and Drinking water samples. [Copyright &y& Elsevier]

In the present paper, the potentiometric response characteristics of a metalloporphyrin-based electrode in plasticized polyvinyl chloride PVC) membranes are presented for a set of monovalent anions. As membrane ionophore, 5,10,15,20-tetrakis-(3,4-dimethoxyphenyl)-porphyrin-Fe(III) (FeMeOPP) was used. To establish the optimum composition of the membrane, different ionic additives (mol.% relative to ionophore) were used. Electrodes formulated with membranes containing 1 wt.% ionophore, 66 wt.% o-NPOE, 33 wt.% PVC (plasticizer: PVC = 2:1) and the lipophilic cationic derivative TDMACl (20mol%) are shown to exhibit high selectivity for thiocyanate with a near-Nernstian slope in the working concentration range of 1.0x10-1-5.0x10-6 M, with a good stability in time. [ABSTRACT FROM AUTHOR]

Abstract: The potentiometric response characteristics of zinc ion selective PVC-based membrane electrode employing 1,12,14-triaza-5,8-dioxo-3(4),9(10)-dibenzoyl-1,12,14-triene as an inophore was investigated. The proposed electrode exhibits a Nernstian behavior with a slope of 29.2±0.4mV per decade with a working concentration range of 1.3×10−7–1.0×10−1 molL−1 and a detection limit of 1.0×10−8 molL−1. The membrane having the composition as TDODBCPT:O-NPOE:PVC:OA; 7:57:30:6 wt.% exhibits the best results. It has a fast response time of 7s and can be used for at least 100days without any considerable divergence in potential. The proposed electrode show good discrimination of Zn2+ ion from diverse ions. The potential response remains constant over a pH range of 3.5–9.2. The electrode found well work under laboratory conditions. The proposed sensor directly used for determination of zinc ions in human hair sample, wastewater and an indicator electrode with EDTA titration. [Copyright &y& Elsevier]

Abstract: New binuclear metallic complexes of thiomacrocyclic Schiff base, 3,9,13,19 -tetraphenyl-6,16-dithione-1,11-dithio-4,5,7,8,14,15,17,18-octaazacycloeicosa-3,8,13,18-tetraene binuclear metal(II) [M(II)2-TDDOCT] (M=Cu, Co, Ni), were synthesized and their anion response characteristics were investigated. The performances of the electrodes are considerably influenced by the nature of the central metals. The Cu(II) complex-based electrode exhibited a good selectivity to salicylate anion with an anti-Hofmeister selectivity pattern: Sal− >ClO4 − >SCN− >I− >Benzoate>Br − >Acetate>F− >SO3 2− >NO2 − >Cl− >NO3 − >SO4 2− >H2PO4 −. The electrode had an excellent linear response to Sal− from 9.0×10−7 to 1.0×10−1 M with a slope of −59.3mV per decade，a detection limit of 5.0×10−7 M, and a fast response time within 15s over the entire concentration series in phosphate buffer solutions of pH 5.0 at 25°C. Spectroscopic techniques and the influence of lipophilic charged additives on the electrode behavior were used to investigate the response mechanism to Sal−. The electrode can be applied to the direct determination of salicylate in human urine and pharmaceutical samples and the results obtained are in accord with the results from a standard method. [Copyright &y& Elsevier]

Abstract: A new PVC membrane strontium ion-selective electrode has been constructed using 6-(4-nitrophenyl)-2-phenyl-4,4-dipropyl-3,5-diaza-bicyclo[3,1,0] hex-2-ene (NPDBH) as a neutral ionophore. The electrode was prepared with 7% NPDBH (as ionophore), 57% acetophenone (as plasticizer), 30% PVC and 6% oleic acid (as lipophilic additive). The electrode responds to Sr2+ ion with a sensitivity of 28.2±0.5mV/decade over the range 1.0×10−6–1.0×10−1 molL−1 and in a pH range of 3.0–10.0. The limit of detection was 2.4×10−7 molL−1. It has a response time of <20s and can be used for at least three months without any divergence in potentials. The proposed electrode shows good discrimination of Sr2+ ion from several cations. The effect of organic solvents on electrode response was examined. The results show that this electrode can be used in ethanol media up to 15% (v/v) concentration without interference. The isothermal temperature coefficient of this electrode amounted to 0.00019V/°C. The electrode was found to work well under laboratory conditions. It was successfully applied to the determination of strontium ions in human urine and bone digests. [Copyright &y& Elsevier]

Abstract: A potentiometric thiocyanate-selective sensor based on the use of zinc-tris(N-tert-butyl-2-thioimidazolyl)hydroborate complex [Tt t-Bu–Zn] as a neutral carrier for a thiocyanate-selective electrode is reported. Effect of various plasticizers viz., o-nitrophenyloctyl ether (o-NPOE), dioctylphthalate (DOP), dibutylphthalate (DBP), benzylacetate (BA), and anion excluder, hexadecyltrimethylammonium bromide (HTAB), with Tt t-Bu–Zn complex in poly (vinyl chloride) (PVC) were studied. The best performance was obtained with a membrane composition of DOP:PVC:Tt t-Bu–Zn:HTAB percent ratio (w/w) of 60:33:5:2. The sensor exhibits significantly enhanced selectivity toward thiocyanate ions over the concentration range 6.3×10−7 to 1.0×10−2 M with a lower detection limit of 3.16×10−7 M and a Nernstian slope of 59.4±1.1mVdecade−1. Influences of the membrane composition, pH, and possible interfering anions were investigated on the response properties of the electrode. Fast and stable response, good reproducibility, long-term stability, applicability over a wide pH range (3.5–9.0) are demonstrated. The sensor has a response time of 14s and can be used for at least 45 days without any considerable divergence in their potential response. The proposed electrode shows fairly good discrimination of thiocyanate from several inorganic and organic anions. It was successfully applied to direct determination of thiocyanate within physiological fluids and environmental samples. [Copyright &y& Elsevier]

Abstract: Plasticized membranes using 1-phenyl-3-(2-thiazolyl)-2-thiourea (PTT) and 1-phenyl-3-(2-thiazolyl)-2-urea (PTU) have been prepared and explored as ytterbium ion-selective sensors. Effect of various plasticizers, viz. chloronaphthalene (CN), o-nitrophenyloctyl ether (o-NPOE), dibutylphthalate (DBP), dioctylsebacate (DOS) and anion excluders, sodium tetraphenylborate (NaTPB) and oleic acid (OA) was studied and improved membrane performance was observed. Optimum performance was noted with membrane of PTT having composition of PTT (3.5):PVC (80):DOS (160):NaTPB (1.5) in mg. The sensor works satisfactorily in the concentration range 1.2×10−7 to 1.0×10−2 M (detection limit 5.5×10−8 M) with a Nernstian slope of 19.7mVdecade−1 of activity. Wide pH range (3.0–8.0), fast response time (10s), non-aqueous tolerance (up to 20%) and adequate shelf life (12 weeks) indicate the vital utility of the proposed sensor. The proposed electrode comparatively shows good selectivity for Yb3+ ion with respect to alkali, alkaline earth, transition and rare earth metals ions and can be used for its determination in binary mixtures and sulfite determination in white and red wine samples. [Copyright &y& Elsevier]

Three kinds of transition metal chelates of unsymmetrical tetradentate Schiff base, o‐hydroxybenzophenone‐1,2‐diaminobenzene‐pyrrole‐2‐carbaldehyde(H2L), were synthesized to prepare anion‐selective electrodes and their anion response characteristics were investigated. The results show that the performances of the electrodes are considerably influenced by the nature of the central metals. The proposed electrode with the Cu(II)‐chelate and cationic additive demonstrated an anti‐Hofmeister selectivity sequence with a good selectivity towards thiocyanate in the following order: Thiocyanate>iodide>salicylate>perchlorate>bromide>nitrite>chloride>acetate>fluoride>nitrate>sulfite>sulfate. The electrode had an excellent linear response to thiocyanate from 3.4×10-7 to 1.0×10-1 M in phosphate buffer solution at pH 5.0 with a slope of -58.7 mV per decade, a detection limit of 1.6×10-7 M, and a fast response time within 5 s over the entire concentration series. Spectroscopic techniques and AC impedance were used to investigate the response mechanism to thiocyanate of the membrane doped with Cu(II)‐chelate. The preliminary application of the electrode for determination of thiocyanate in wastewater and urine samples is reported. [ABSTRACT FROM AUTHOR]

Abstract: The quantitative structure–activity relationship (QSAR) for neutral carriers used to prepare hydrogen ion sensors has been studied. A series of synthesized carrier compounds were taken as the training set. Five molecular structure parameters of the compounds were calculated by using CNDO/2 algorithm and used as feature variables in constructing QSAR model. The lower and upper limits of the linear pH response range were taken as the activity measure. The corresponding model equations were derived from the stepwise regression procedure. With the established QSAR model, a new pH carrier, (4-hydroxybenzyl) didodecylamine (XIII) was proposed and synthesized. The PVC membrane pH electrode based on carrier XIII with a wide pH linear response range of 2.0–12.5 was prepared. Having a theoretical Nernstian response slope of 57.2±0.3mV/pH (n =5 at 25°C) without a super-Nernstian phenomenon, the sensor had low resistance, short response time, high selectivity and good reproducibility. Moreover, the sensor was successfully applied to detecting the pH value of serum samples. [Copyright &y& Elsevier]

A novel thiocyanate (SCN−)-selective PVC membrane electrode based on a zinc-phthalocyanine (ZnPc) complex as neutral carrier is described. The membrane electrode containing ZnPc with 5.1% (w/w) ionophore, 29.2% (w/w) PVC, and 65.7% (w/w) 2-nitrophenyl octyl ether ( o-NPOE) as plasticizer displayed an anti-Hofmeister selectivity sequence % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX!% MathType!MTEF!2!1!+-% feaafaart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX% garmWu51MyVXgatuuDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wz% aebbnrfifHhDYfgasaacH8qrps0lbbf9q8WrFfeuY-Hhbbf9v8qqaq% Fr0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qq% Q8frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeWaeaaakeaaca% qGOaGaae4uaiaaboeacaqGobWaaWbaaSqabeaacqGHsislaaGccqGH% +aGpcaqGtbGaaeyyaiaabYgadaahaaWcbeqaaiabgkHiTaaakiabg6% da+iaabMeadaahaaWcbeqaaiabgkHiTaaakiabg6da+iaaboeacaqG% SbGaae4tamaaBaaaleaacaqG0aaabeaakmaaCaaaleqabaGaeyOeI0% caaOGaeyOpa4JaaeOqaiaabkhadaahaaWcbeqaaiabgkHiTaaakiab% g6da+iaaboeacaqGSbWaaWbaaSqabeaacqGHsislaaGccqGH+aGpci% GGobGaai4tamaaBaaaleaacaGGZaaabeaakmaaCaaaleqabaGaeyOe% I0caaOGaeyOpa4JaaeOtaiaab+eadaWgaaWcbaGaaeOmaaqabaGcda% ahaaWcbeqaaiabgkHiTaaakiabg6da+iaabIeadaWgaaWcbaGaaeOm% aaqabaGccaqGqbGaae4tamaaBaaaleaacaqG0aaabeaakmaaCaaale% qabaGaeyOeI0caaOGaeyOpa4Jaae4uaiaab+eadaWgaaWcbaGaaein% aaqabaGcdaahaaWcbeqaaiaaikdacqGHsislaaGccaGGPaGaaiilaa% aa!67CA! $${\text{(SCN}}^ - > {\text{Sal}}^ - > {\text{I}}^ - > {\text{ClO}}_{\text{4}} ^ - > {\text{Br}}^ - > {\text{Cl}}^ - > \operatorname{NO} _3 ^ - > {\text{NO}}_{\text{2}} ^ - > {\text{H}}_{\text{2}} {\text{PO}}_{\text{4}} ^ - > {\text{SO}}_{\text{4}} ^{2 - } )$$ , and exhibited near-Nernstian potential response to thiocyanate ranging from about 1.0×10−1 to 1.0×10−6 mol L−1 with a detection limit of 7.5×10−7 mol L−1 and a slope of 58.1±0.5 mV per decade in pH 3.0 phosphate buffer solution at 25 °C. This preferential response is believed to be associated with the unique coordination between the central metal of the carrier and thiocyanate. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Three main types of creatinine potentiometric membrane sensors are described. They are based on the use of dibenzo-30-crown-10 (DB30C10) with potassium tetrakis(p-chlorophenyl)borate type (I), dibenzo-30-crown-10 alone type (II), and potassium tetrakis(p-chlorophenyl)borate alone type (III), incorporating in poly(vinyl chloride) matrix membrane plasticized with either o-nitrophenyl octyl ether or dioctylphthalate. The sensors are used for quantification of creatinine after soaking the membranes in 0.1M creatinine solution for 2 days. The sensors show almost the same potentiometric response characteristics. Sensor type (I) exhibits Nernstian responses over a concentration range of 5.0×10−5 moll−1–1.0×10−2 moll−1 creatinine with cationic slopes of 59.5±0.1 and 60±0.2mVdecade−1 and detection limits of 1.1×10−5 moll−1 and 8×10−6 moll−1 creatinine, over the pH range of 3.5–6.5 and 3.5–7.0, for o-NPOE and DOP solvent mediators, respectively. Sensor type (II) displays Nernstian responses over a concentration range of 6.0×10−5 moll−1–1.0×10−2 moll−1 creatinine with cationic slopes of 60.0±0.1 and 65.0±0.2mVdecade−1 and detection limits of 1.5×10−5 moll−1 and 1.4×10−5 moll−1 creatinine over the pH range of 2.6–6.2 and 2.5–6.0, for o-NPOE and DOP solvent mediators, respectively. Sensor type (III) shows Nernstian responses over a concentration range of 7.0×10−5 moll−1–1.0×10−2 moll−1 creatinine with cationic slopes of 60±0.1 and 62.0±0.2mVdecade−1 and detection limits of 2.7×10−5 moll−1 and 2.0×10−5 moll−1 creatinine over the pH range of 2.5–6.0, for o-NPOE and DOP solvent mediators, respectively. The response times of the sensors for 10−3 moll−1 creatinine solution are instantaneous (4–10s). The sensors show long-term stability with life span of ∼6 months. The sensors are used for determination of serum creatinine of rats (Rattus Norvigicus) with mean R.S.D. of 2.62%, and the results agreed well with the Jaffe kinetic method. [Copyright &y& Elsevier]

Abstract: A new highly selective silver(I) electrode was prepared with a PVC membrane using 5,10,15-tris(pentafluorophenyl)corrole as an electroactive material, 2-nitrophenyl octyl ether (o-NPOE) as a plasticizer and sodium tetraphenylborate (NaTPB) as an additive in the percentage ratio of 3:3:62:32 (corrole:NaTPB:o-NPOE:PVC, w:w). The electrode exhibited linear response with a near Nernstian slope of 54.8mV/decade within the concentration range of 5.1×10−6 to 1.0×10−1 M silver ions, with a working pH range from 4.0 to 8.0, and a fast response time of <30s. Selectivity coefficients for Ag(I) relative to a number of interfering ions were investigated. The electrode is highly selective for Ag(I) ions over a large number of mono-, bi-, and tri-valent cations. Common interferents like Hg2+ and Cd2+ show very low interfering effect on the silver assay, which is valuable property of the proposed electrode. Several electroactive materials and solvent mediators have been compared and the experimental conditions were optimized. The sensor was applied to the determination of silver in real ore samples with satisfied results. [Copyright &y& Elsevier]

Abstract: Some novel PVC membrane electrodes based on N,N′-bis-(benzaldehyde)-glycine metallic complexes of Cu(II), Ni(II), Zn(II) and Co(II) as neutral carriers are described. The results showed that the electrode based on the N,N′-bis-(benzaldehyde)-glycine copper(II) complex [Cu(II)-BBAG] had a near-Nernstian response to the thiocyanate ion ranging from 1.0×10−1 to 9.0×10−7 M in a phosphate buffer solution of pH 4.0 with a detection limit of 7.0×10−7 M and a slope of −57.6 mV/decade at 25°C. The electrode displays an anti-Hofmeister selectivity sequence in the following order: SCN−>ClO− 4>Sal−>I−>Br−>NO− 2>NO− 3>SO2− 3>SO2− 4>Cl−>H2PO The response mechanism is discussed in view of both AC impedance and UV spectroscopy techniques. The [Cu(II)-BBAG]-based electrode was successfully applied to the determination of the thiocyanate ion in wastewater and human saliva. [Copyright &y& Elsevier]

Abstract: The upper rim of calix[6]arene-hexaacetic acid hexaethyl esters was modified with various alkyl substituents to develop ionophores for constructing organic ammonium ion-selective membrane electrodes. We found that the substitution of bulkier alkyl groups enabled a more effective discrimination of simple aliphatic ammonium ions such as methylammonium and ethylammonium. In particular, an electrode based on p-1,1,3,3-tetramethylbutylcalix[6]arene-hexaacetic acid hexaethyl ester showed the highest response to methylammonium among various organic ammonium ions and inorganic cations, giving the following selectivity coefficients; : C2H5NH3+, -0.2; C3H7NH3+, -1.4; C4H9NH3+, -1.9; C6H13NH3+, -1.6; phenethylammonium, -1.9; Na+, -2.8; K+, -1.8; Rb+, -1.6; Cs+, -0.2; NH4+, -2.8. The electrode exhibited a near Nernstian response to methylammonium in the concentration range of 1×10-5 to 1×10-2M with a slope of 58.5mV per concentration decade in 0.1M MgCl2. The limit of detection was 3×10-6M. The electrode could be used over a pH range of 2–10. Formation of a 1:1 complex between p-1,1,3,3-tetramethylbutylcalix[6]arene-hexaacetic acid hexaethyl ester and methylammonium was confirmed by electrospray ionization mass spectrometry. The response characteristics of the methylammonium-selective electrode were compared with those of NH4+-selective electrodes so far developed. [Copyright &y& Elsevier]

A new solvent polymeric membrane electrode based on a tricoordinate Schiff base copper(II) complex as neutral carrier is described, that demonstrates excellent selectivity to thiocyanate relative to many common anions and over a wide linear range of 2.6 × 10-6 -10 × 10-1 M with a detection limit of 8.0 × 10-7 M and a near-Nernstian slope of - 57.6 mV/decade in pH 4.0 of phosphate buffer solution at 25°C. The electrode displays an anti-Hofmeister selectivity sequence in the following order SCN- > Sal- > ClO4- > I- > NO2- > Br- > NO3- > Cl-> SO&frac;23- > So&frac24;- > H2PO4-. The response mechanism is discussed in view of the AC impedance technique and the ultraviolet (UV) spectroscopy technique. The electrode was successfully applied to the determination of thiocyanate ion in wastewater and human saliva. [ABSTRACT FROM AUTHOR]

A novel salicylate-selective poly(vinyl chloride) (PVC) membrane electrode based on N,N'-bis-(furaldehyde)-glycine copper(II) complex [Cu(II)-BFAG] as neutral carrier is reported, which exhibits anti-Hofmeister selectivity sequence: Sal- > ClO-4 > SCN- > I- > NO-3 > Br- > Cl- > SO2-3 > SO2-4 and a near-Nernstian potential linear range for salicylate from 1.0 x 10-1 to 4.0 x 10-6 mol/L, with a detection limit of 8.0 x 10-7 mol/L and a slope of -56.8 mV/pSal- in pH 5.0 of phosphate buffer solution at 25°C. The response mechanism is discussed in view of the A,C, impedance and the ultraviolet (UV) spectroscopy technique. The effects of the electrode membrane compositions and the experimental conditions were studied. The electrode based on copper(II) compound was applied to the determination of salicylate ion in drug pharmaceutical preparations with satisfactory results. [ABSTRACT FROM AUTHOR]

A novel solvent polymeric membrane electrode based on bis(1,3,4-thiadiazole) complexes of Hg(II) is described which has excellent selectivity and sensitivity toward iodide ion. The electrode, containing 1,4-bis(5-methyl-1,3,4-thiadiazole-2-yl-thio)butanemercury(II) [Hg(II)BMTB(NO3)4], has a Nernstian potentiometric response from 2.0×10-8 to 2.0×10-2 mol L-1 with a detection limit of 8.0×10-9 mol L-1 and a slope of -59.0±0.5 mV/decade in 0.01 mol L-1 phosphate buffer solution (pH 3.0, 20°C). The selectivity sequence observed is iodide>bromide>thiocyanate>nitrite>nitrate>chloride>perchlorate>acetate>sulfate. The selectivity behavior is discussed in terms of the UV-Vis spectrum, and the process of transfer of iodide across the membrane interface is investigated by use of the AC impedance technique. The electrode was successfully applied to the determination of iodide in Jialing River and Spring in Jinyun Mountains, with satisfactory results. [ABSTRACT FROM AUTHOR]

Polypyrazolylmethanes, represented by the general formula H4−nC(pz)n (pz: 1-pyrazolyl), form a six-membered MN4C chelate ring of a shallow boat configuration, acting as tridentate or bidentate ligands. We have developed novel ion-selective membrane electrodes based on polypyrazolylmethanes and report the first results of their use here. HC(pz)3 (1), HC(3,5-Me2pz)3(2), HC(3-Phpz)3 (3), HC(3-iPrpz)3 (4), HOCH2C(pz)3 (5), and C(pz)4 (6) were prepared as described in the literature and incorporated as an ionophore in PVC membrane. The selectivity of the electrodes changed with the substituents of polypyrazolylmethanes. The electrodes of 3, 4 and 6 were selective for Cu2+ at pH 5.5. The electrode of 5 was selective for Pb2+ and Cu2+ at pH 5.5. Since the selectivity coefficient log KCu,Mpot of electrode 4 was less than −6.4 for the divalent cations, it was most selective for Cu2+ among Cu2+ selective electrodes ever reported. The detection limit and dynamic range for Cu2+ were 2×10−6 and 10−6 to 5×10−3 M, respectively. The electrode 4 showed rapid response time (∼10 s) and reproducible results for more than 4 months, and successfully applied to potentiometric titration of Cu2+ with EDTA. [Copyright &y& Elsevier]

A novel selective thiocyanate PVC membrane electrode based on bis-bebzoin-semitriethylenetetraamine binuclear copper(II) [Cu(II)2–BBSTA] as neutral carrier is reported, which displays an anti-Hofmeister selectivity sequence in following order: SCN− > ClO4− > I− >Sal− >SO32− >NO3− > H2PO4− > Cl− >NO2− > SO42−. The electrode exhibits Nernstian potential linear range to thiocyanate from 1.0 × 10−1 to 9.0 × 10−7 mol/l with a detection limit 7.0 × 10−7 mol/l and a slope of −57.0 mV/decade in pH 5.0 of phosphorate buffer solution at 25 °C. The response mechanism is discussed in view of the AC impedance technique and the UV spectroscopy technique. From comparison of potentiometric response characteristics between the binuclear metallic complex copper(II) [Cu(II)2–BBSTA] and mononuclear copper(II) metallic complex [Cu(II)–BBSDA], an enhanced response towards thiocyanate from the electrode based on binuclear metallic complex copper (II) [Cu(II)2–BBSTA] was observed. The electrode based on binuclear copper(II) compound was used to determine the thiocyanate content in waste water with satisfactory results. [Copyright &y& Elsevier]

Calix[6]arene-hexaacetic acid hexaethyl ester, originally developed as a cesium ionophore, is quite suitable for making a thallium(I) (Tl+)-selective membrane electrode. An electrode constructed using this ionophore, with potassium tetrakis(p-chlorophenyl)borate (20 mol% relative to the ionophore) as an ionic additive and bis(2-ethylhexyl)sebacate as a solvent mediator in a poly(vinyl chloride) (PVC) membrane matrix, showed better selectivity for Tl+ than Cs+ (log kTl+,Cs+Pot=−0.7). Thus, the electrode markedly avoided interference from various inorganic and organic cations, because the ionophore is known to well recognize Cs+. The electrode exhibited a near-Nernstian response to Tl+ in the concentration range of 1×10−6 to 1×10−2 M with a slope of 55 mV per concentration decade in 0.1 M Mg(NO3)2. The limit of detection was 0.3 μM. The electrode could be used over a pH range of 2.5–12. Calix[5]arene-hexaacetic acid hexaethyl ester also exhibited good selectivity for Tl+ and showed much less interference from Cs+ than the corresponding calix[6]arene derivative, though interference from alkali metal ions such as Na+ and K+ was significantly increased. The corresponding calix[6]arene and calix[5]arene derivatives with tert-butyl groups were less effective for recognition of Tl+. [Copyright &y& Elsevier]

In recent years squarines received attention as fluorescent labels. Their very promising spectral properties such as long wavelength absorption and emission, high extinction coefficients and quantum yields could lead novel sensing technologies. In this work newly synthesized fluoroinophores named bis[4-N-(1-aza-4,7,10,13-tetraoxacyclopentadecyl)-3,5-dihydroxyphenyl]squaraine, azacrown-1 and 2 bis[4-N-(1-aza-4,7,10,13,16-pentaoxacyclooctadecyl)-3,5-dihydroxyphenyl]squaraine, azacrown-2 have been used for sodium and potassium sensing in plasticized PVC matrix. The squaraine derivatives exhibited fluorescence emission based optical responses to sodium and potassium with a detection limit of 1.10−9 M. The sensor compositions exhibited wide response ranges between 10−9 and 10−5 M Na+or K+, and, therefore, may be an alternative method to flame emission spectroscopy. The sensor is fully reversible within the dynamic range and the response time is 3 min under batch conditions. Cross sensitivity to pH is negligible in the pH range of 6.2–7.3. Throughout fiber optic based studies a relative signal change of 54–56% has been achieved. The azacrown dyes have the advantage that they can be excited with long wavelength light and, are, therefore, LED compatible. The cross sensitivity of azacrown-1 and -2 to Ba2+, Ca2+ and NH4+were also tested in separate solutions. [Copyright &y& Elsevier]

Carbonate-selective membranes were prepared by incorporating a molecular tweezer-type carbonate-selective neutral carrier [N,N-dioctyl-3α,12α-bis(4-trifluoroacetylbenzyloxy)-5β-cholan-24-amide] into a room temperature vulcanizing-type silicone rubber (3140 RTV-SR) matrix, and deposited on the planar-type electrodes (Pt containing Ag/AgCl electrodes formed on a ceramic plate) with and without an intermediary conducting polymer layer. Two types of solvent-soluble conducting polymers [poly(1-hexyl-3,4-dimethyl-2,5-pyrrolylene) or poly(3-octylthiophene-2,5-diyl)] have been examined as the solid contact material. Potentiometric properties of the resultant all-solid-state electrodes were evaluated in terms of their carbonate selectivity, response slope, potential stability and reproducibility. The sensitivity and carbonate selectivity of the SR membrane-based all-solid-state electrodes with conducting polymer solid contact were comparable to those of conventional electrodes. Experimental results also showed that the intermediary conducting polymer layer used in the all-solid-state electrodes greatly reduces the interference from dissolved oxygen. [Copyright &y& Elsevier]

A calcium ion-selective PVC membrane electrode based on neutral carrier n,n,n',n'-tetracyclohexyl-3-oxapetanediamide, using di-(2-ethylhexyl) phthalate as the plasticizer and potassium tetrakis (4-chlorophenyl) borate as the additive is reported in this paper. The ion selective membrane consists of 1 wt % of the Ca selective ligand, 65 wt % of the plasticizer, 1 wt % of the additive and 33 wt % of poly (vinyl chloride) powder. The electrode has the linear response range of 2.0 × 10 -10 mol/L with the Nernstian slope of 28 mV/decade at 25 °C and the detection limit of 2.0 × 10 mol/L. The response time of the calcium ion-selective electrode is 4s as the concentration of calcium ion is rapidly shifted from 10 to 10 mol/L. The potential stability and reproducibility are good. The free calcium in blood serum was determined by the calcium ion-selective electrode with satisfactory results. [ABSTRACT FROM AUTHOR]

Two types of Mg-selective microelectrodes baed on a synthetic neutral carrier and containing poly-(vinyl chloride) (PVC) are described. The first is applicable to intracellular Mg assays and suffers no interference from alkali and all other alkaline-earth metal cations. The second can be used for determining intra- as well as extracellular Mg activities, but Ca and especially lipophilic cations (e.g. acetylcholine) may interfere. Cyclohexanone is used for dissolving the PVC-containing membrane phases thus avoiding problems encountered with the much more volatile tetrahydrofuran. The procedure gives a higher output of working microelectrodes and can also be applied with other membrane phases. [ABSTRACT FROM AUTHOR]

A liquid-membrane microelectrode (≤1 μm tip diameter) using macrotetrolide antibiotics as ion-selective components is described. The electrode shows selectivities of NH over K, Na and H of 3.8, 100 and 150, respectively. The stability and reproducibility of the sensor signal and the response time are determined in solutions with a typical intracellular ion background. The microelectrode does not suffer from significant interference by inorganic and organic inhibitors and lipophilic cations, but high concentrations of lipophilic anions may interfere considerably. [ABSTRACT FROM AUTHOR]

In intracellular electrolyte solutions a Ca-selective microelectrode based on the synthetic electrically neutral carrier N,N,N′,N′-tetracyclohexyl-3-oxapentanediamide (ETH 129) shows an improved detection limit when compared with the so far widely used Ca microelectrodes based on the neutral carrier ETH 1001. Detection limits are found at pCa=9.2 in Ca buffers containing an intracellular background of K (125 mM). Selectivity studies in mixed solutions show a preference of Ca over Na of 6·10, over K of 1.6·10, and over Mg of 5·10. The microelectrode does not suffer from significant interference by inorganic and organic inhibitors and by lipophilic cations and anions. The low detection limit is unchanged at least during the first eight hours of continuous contact with Ca solutions. The EMF drift during the first hour of use is between 5 and 10 mV and is then reduced to about 1 mV/h. The changes in EMF induced between solution of pCa=7 and pCa=8 are reproducible within 24.7±0.4 mV (SD, n=8, about 3 h). These electrode characteristics were found for single-barrelled microelectrodes of one micrometer diameter front-filled with a PVC-containing membrane phase. In the absence of poly(vinyl chloride) in the membrane phase irregular EMF response curves were obtained throughout. Preliminary punctures of ferret ventricular muscle cells indicate that the Ca electrode response is not disturbed by the contact of a cytosolic milieu. [ABSTRACT FROM AUTHOR]

The intracellular potential in gallbladder epithelial cells is about −59 mV with respect to both mucosal and serosal media. It is a diffusion potential mainly due to K; Na conductance seems to be very low. Entrance of Cl into cells appears to be coupled with Na on a neutral carrier and exit towards blood side seems to be due to a NaCl neutral pump. [ABSTRACT FROM AUTHOR]

The ionophore N,N,N′,N′-tetracyclohexyl-1,2-phenylenedioxydiacetamide (4) shows higher lipophilicity and superior Na/K selectivity than the previously described N,N′-dibenzyl-N,N′-diphenyl-1,2-phenylenedioxydiacetamide (2). It is a suitable component of Na-selective liquid membrane electrodes for the assay of Na in clinical analysers. [ABSTRACT FROM AUTHOR]