Oxalate membrane-selective electrode based on surfactant-modified zeolite

A novel polyvinyl chloride (PVC) membrane electrode for use in a potentiometric sensor for oxalate is described. The sensor comprises a surfactant-modified zeolite A (SMZ) as a modifier, dioctyl phthalate (DOP) as a plasticizer, and PVC matrix in the ratio 10:60:30 (modifier:DOP:PVC) (w/w). The membrane sensor showed a suitable response to oxalate in the concentration range of 1.0 × 10⁻⁶ to 3.0 × 10⁻¹ M (r = 0.9997), with a detection limit of 3.2 × 10⁻⁷ M and a Nernstian slope of −29.9 ± 0.6 mV per decade⁻¹ of oxalate concentration. The electrode response to oxalate remained constant in the pH range of 3.2–10.8. The selectivity coefficients for oxalate relative to a number of potential interfering substances were also determined. The sensor was highly selective for oxalate over a wide variety of other anions and exhibited a rapid response time of 5 s over a period of 2 months with good reproducibility. Thus, this novel sensor may be applied as an indicator electrode in the potentiometric titration of oxalate and Ca²⁺ ions.     

Cu(II) selective sensor based on 5,7,12,14-tetramethyldibenzo[b,i]-1,4,8,11-tetraazacyclotetradecane in PVC matrix

5,7,12,14-tetramethyldibenzo[b,i]-1,4,8,11-tetraazacyclotetradecane, Me₄Bzo₂[14]aneN₄. (I) was synthesized and used as an electroactive material for the fabrication of membrane electrode in PVC matrix for the determination of Cu²⁺. The best performance was given by the membranes of macrocycle (I) with composition 5:3:100:150 (I:NaTPB:DBBP:PVC). The sensor worked well over a concentration range 2.5 × 10^–5–1.0 × 10^–1 M of Cu²⁺ with a slope of 30.2 ± 0.3 mV (decade)^–1 of Cu²⁺ activity, a fast response time of 13 ± 2 s and a lifetime of five months. The working pH range of this sensor is 2.6–5.5 and it shows excellent selectivity for Cu²⁺ over other mono-, di- and trivalent cations. Its performance in partially nonaqueous medium was found to be satisfactory. The sensor can also be used as an indicator electrode in the potentiometric titration of Cu²⁺ against EDTA and its determination in real samples.     

Accumulation of Cu(II) cations in poly(3,4-ethylenedioxythiophene) films doped by hexacyanoferrate anions and its application in Cu-selective electrodes with PVC based membranes

Electrochemical properties of poly(3,4-ethylenedioxythiophene) doped with hexacyanoferrate(II,III) ions (PEDOT(HCF)) were studied in the presence of Cu²⁺ ions. Voltammetric and EDAX studies revealed retention of hexacyanoferrate anions in the polymer film and accumulation of Cu(II) cations, as well as formation of solid copper hexacyanoferrate near the polymer surface.Accumulation of Cu²⁺ ions was found to be advantageous from the point of view of PEDOT(HCF) applications as a solid contact (ion-to-electron transducer) in all-solid-state Cu²⁺-selective electrodes with solvent polymeric polyvinyl chloride (PVC) based membrane, containing Cu²⁺-selective ionophore. Binding of Cu²⁺ ions in the conducting polymer layer results in analyte ions flux into the transducer phase. Thus, pronounced enhancement of selectivity of the all-solid-state Cu²⁺-selective electrode or lower detection limit of the potentiometric response range was achieved, reaching under optimised conditions 10⁻⁷ M CuSO₄.     

Electroanalytical studies on cobalt(II) selective potentiometric sensor based on bridge modified calixarene in poly(vinyl chloride)

A bridge modified 4-tert-butylthiacalix[4]arene (I) has been employed as electroactive material in the preparation of cobalt selective sensor. Polyvinyl chloride (PVC)-based membranes of (I) using sodium tetraphenylborate (NaTPB) as anion discriminator and bis(2-ethylhexyl) sebacate (DOS), chloronaphthalene (CN), tri-n-butylphosphate (TBP), o-nitrophenyl octyl ether (NPOE), tris(2-ethylhexyl)phosphate (TEHP) as plasticizers were prepared and investigated as cobalt selective sensors. A number of membranes of different compositions were prepared and investigated. The best performance was observed with the membrane having composition of 2:66:1.5:127 (mg) = I:NaTPB:PVC:NPOE. The potential response of this membrane is linear to Co²⁺ ions in the concentration range 5.3 × 10⁻⁶ to 1.0 × 10⁻¹ M with near-Nernstian slope of 30.0 mV/decade of activity and a detection limit of ∼0.3 ppm. This membrane also showed lowest response time of 10 s and works satisfactorily in partially non-aqueous medium. The selectivity studies of this sensor, evaluated with fixed interference method and matched potential method, show that the sensor under consideration possesses excellent selectivity for Co²⁺ over a large number of mono-, bi- and trivalent cations such as Na⁺, K⁺, Ag⁺, Ca²⁺, Mg²⁺, Cu²⁺, Hg²⁺, Pb²⁺, Li⁺, Ba²⁺, Zn²⁺, Sr²⁺, Cr³⁺, Ni²⁺, etc. The sensor could be used as an indicator electrode in the quantification of Co²⁺ by potentiometric titration against EDTA as well as in determination of cobalt content in wastewater and beer samples.     

Electrochemical sensors for the determination of Zn ions based on pendant armed macrocyclic ligand

The construction and performance characteristics of polymeric membrane electrodes based on two newly synthesized macrocyclic ligands 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,8,12,14-tetraene-9,12-N₂-1,5-O₂ (L₁) and 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,14-diene-9,12-dimethylacrylate-9,12-N₂-1,5-O₂ (L₂) for the quantification of Zn²⁺ ions are described here. Several membranes having different compositions of PVC, plasticizers, ionic additives and ionophores were fabricated and the best response was observed for the membrane having composition L₂:PVC:TBP:NaTPB in the ratio of 4:37:57:2 (w/w; mg). The response characteristics of the membrane based on L₂ were compared with polymeric membrane electrode (PME) as well as with coated graphite electrode (CGE). The electrode exhibits Nernstian slope for Zn²⁺ ions with limits of detection of 3.3 × 10⁻⁷ mol L⁻¹ for PME and 7.9 × 10⁻⁸ mol L⁻¹ for CGE with response time of 12 s and 10 s for PME and CGE respectively. Furthermore, the electrodes generated constant potentials in the pH range of 3.0–8.0 for PME and 2.5–9.0 for CGE. The practical utility of the CGE has been demonstrated by its usage as an indicator electrode in potentiometric titration of EDTA with Zn²⁺ ion solution. The high selectivity of CGE also permits their use in the determination of Zn²⁺ ions in water, biological, milk and tea samples.     

Aluminium (III)-selective PVC membrane sensor based on a Schiff base complex of N,N′-bis (salicylidene)-1, 2-cyclohexanediamine

A potentiometric aluminium sensor, based on the use N,N′-bis(salicylidene)-1,2-cyclohexanediamine (NBSC) as a neutral carrier, in poly(vinyl chloride) (PVC) matrix, is reported. Effect of various plasticizers; 2-nitrophenyloctylether (o-NPOE), tri-n-butyl phosphates (TBP), dioctylpththalate (DOP) & chloronapthalen (CN), and anion excluder, sodium tetraphenylborate (NaTPB) was studied. The best performance was obtained with a membrane composition of PVC: o-NPOE: NBSC: NaTPB ratio (w/w; mg) of 150:150:5:5. The sensor exhibits significantly enhanced selectivity toward Al³⁺ ions over the concentration range 1.0 × 10⁻⁸-1.0 × 10⁻¹ M with a lower detection limit of 5.0 × 10⁻⁹ M and a Nernstian slope of 20.3 ± 0.1 mV decade⁻¹ of activity. Influence of the membrane composition and possible interfering ions was investigated on the response properties of the electrode. Fast and stable response, good reproducibility and long-term stability are demonstrated. The sensor shows response time of <5 s and can be used for about 3 months without any considerable divergence in their potential response. Selectivity coefficients determined by matched potential method (MPM) indicate high selectivity for aluminium (III) ion. The proposed electrode shows fairly good discrimination of aluminium (III) from many metal ions. It was successfully applied for direct determination of aluminium (III) in biological, industrial and environmental samples. The electrode can be used in the pH range of 2.0-9.0 and mixtures containing up to 20% (v/v) non-aqueous content. It was used as an indicator electrode in potentiometric titration of aluminium ion vs. EDTA.     

Surfactant modified zeolite carbon paste electrode (SMZ-CPE) as a nitrate selective electrode

A nitrate-selective electrode based on surfactant-modified zeolite (SMZ) particles into carbon paste was proposed (SMZ-CPE). The electrode was fully characterized in terms of composition, response time, ionic strength, thermal stability and usable pH range. The electrode containing 10% SMZ exhibited linear response range to nitrate species in the range of 1.00 × 10⁻⁶ to 1.00 × 10⁻³ M with a detection limit of 1.00 × 10⁻⁶ M and a Nernstian slope of 59.4 ± 0.7 mV per decade of nitrate concentration. The response of the electrode to nitrate remains constant in the pH ranges of 3.5–9.8 and 1.7–10.5 for 1.00 × 10⁻⁴ and 1.00 × 10⁻² M nitrate, respectively, and in presence of 1 × 10⁻⁴ to 1 × 10⁻³ M NaCl. The response of the electrode reaches to its equilibrium value within several seconds (10 s) after immersing the electrode in nitrate solution. Selectivity coefficients showed multivalent anions (such as arsenate, dichromate and sulfate) have higher interferences than monovalent anions (such as iodide, fluoride, bromide, chloride and thiocyanate). The electrode was used for determination of nitrate in an ammonium nitrate fertilizer sample, using direct potentiometry, and the satisfactory results were obtained. The electrode was also used for the potentiometric titration of nitrate. The validation of the obtained results in each case was proved by statistical “t” and “g” tests.     

Construction of barium (II) PVC membrane electrochemical sensor based on 3-deoxy-d-erythro-hexos-2-ulose bis (thiosemicarbazone) as a novel ionophore

In this study, a new ion-selective electrode for Ba²⁺ is described, illustrating 3-deoxy-d-erythro-hexos-2-ulose bis (thiosemicarbazone) (DHUT) in a poly(vinylchloride) (PVC) membrane with benzyl acetate (BA) as a plasticizer and sodium tetraphenyl borate (NaTPB) as an anionic additive. This sensor presented very good selectivity and sensitivity towards the Ba²⁺ ions over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The electrode revealed a great improvement in the selectivity coefficients for the Ba²⁺ ions in comparison with the formerly reported Ba²⁺ sensors. The proposed electrode exhibited a significantly enhanced response towards the Ba²⁺ ions across the concentration range of 1.0 × 10^− 6-1.0 × 10^− 2 M for the pH variation from 2.6 to 11 with a lower detection limit of 5.6 × 10^− 7 M. Moreover, the sensors displayed the Nernstian slope of 29.6 ± 0.5 mV per decade, having a fast response time within 15 s over the entire concentration range. It could also be used for at least 2 months with no potential divergence. As a result, the developed sensor was successfully applied to the direct barium ion determination in solutions, rock samples and as an indicator electrode in the Ba²⁺ ion potentiometric titration with EDTA.     

A potentiometric and voltammetric sensor based on polypyrrole film with electrochemically induced recognition sites for detection of silver ion

Conducting polypyrrole membranes were deposited on glassy carbon electrodes by electropolymerizing pyrrole in the presence of Eriochrome Blue-Black B (EBB) as the counter anion. The electrodes were then subjected to several oxidation/reduction potential steps in pure silver nitrate solution for successive accumulation/stripping of silver species. This electrochemically mediated doping/templating generated selective recognition elements in the EBB/PPy film for silver ions. The resulting sensor exhibited a considerable enhancement in the potentiometric and voltammetric response characteristics: extending the linear dynamic range and lowering the detection limit. In the potentiometric mode, the sensor showed highly reproducible response with a Nernstian slope of 58.5 ± 0.3 mV per decade of Ag⁺ activity over a linear range spanning seven orders of magnitude (1 × 10⁻⁸ to 1 × 10⁻¹ M Ag⁺), with a detection limit of ∼6 × 10⁻⁹ M. The electrodes demonstrated high selectivity over a large number of cations including alkali, alkaline earth and several transition and heavy metal ions, and could be used over a wide pH range of 1-8.5. The EBB/PPy modified electrode was also used for preconcentration and differential pulse anodic stripping voltammetric (DPASV) measurements. The DPASV peak current was dependent on the concentration of Ag⁺ over the range 3 × 10⁻¹⁰ to 1 × 10⁻⁴ M. The presence of 1000-fold excess of Cd²⁺, Cu²⁺, Cr³⁺, Co²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Ni²⁺ and Pb²⁺ can be tolerated in the determination of silver ion.     

Novel coated graphite electrode for the selective determination of Gd(III) in rocks and waste water samples

A novel gadolinium selective coated graphite electrode based on 2,6-bis-[1-{N-cyanopropyl,N-(2-methylpridyl)}aminoethyl]pyridine [P] is described. The best performance was exhibited by the electrode having membrane composition P:NaTPB:PVC:NPOE as 8:4:30:58 (%, w/w). The electrode demonstrates excellent potentiometric characteristics towards gadolinium ion over several interfering ions. The electrode exhibited a Nernstian response to Gd³⁺ ion over a wide concentration range 2.8 × 10⁻⁷ to 5.0 × 10⁻² M with a detection limit (6.3 ± 0.1) × 10⁻⁸ M and slope 19.6 ± 0.1 mV decade⁻¹ of a_Gd³⁺. Furthermore, it showed a fast response time (12 s) and can be used for 2.5 months without significant divergence in its characteristics. Noticeably, the electrode can tolerate the concentration of different surfactants up to 1.0 × 10⁻⁴ M and can be used successfully in 30% (v/v) ethanol media and 10% (v/v) methanol and acetonitrile water mixture. The useful pH range of this sensor is 2.0 to 8.0. It is sufficiently selective and can be used for the determination of Gd³⁺ ions in waste water and rock samples. It also serves as a good indicator in the potentiometric titration of GdCl₃ with EDTA.     

Highly selective and sensitive Th<Superscript>4+</Superscript>-PVC-based membrane sensor based on 2-(diphenylphosphorothioyl)-<Emphasis Type="Italic">N</Emphasis>′,<Emphasis Type="Italic">N</Emphasis>′-diphenylacetamide

A Th⁴⁺ ion-selective membrane sensor was fabricated from poly (vinyl chloride) (PVC) matrix membrane containing 2-(diphenylphosphorothioyl)-N′,N′-diphenyl acetamide (DPTD) as a neutral carrier, potassium tetrakis (p-chlorophenyl) borate (KTpClPB) as anionic excluder and o-nitrophenyloctyl ether (NPOE) as a plasticizing solvent mediator. The effects of the membrane composition, pH and additive anionic influence on the response properties were investigated. The sensor, comprising 30% PVC, 63% solvent mediator, 4% ionophore and 3% anionic additive demonstrates the best potentiometric response characteristics. It displays Nernstian behavior (15.2 ± 0.5 mV per decade) over the concentration range 1.0 × 10⁻²–1.0 × 10⁻⁶ M. The detection limit of the electrode is 6.3 × 10⁻⁷ M (∼140 ng/ml). The response time of the electrode is 30 s .The sensor can be used in the pH range 3.0–9.0 for about 6 weeks. The membrane sensor was used as an indicator electrode in the potentiometric titration of Th⁴⁺ ions with EDTA. It was successfully applied to the determination of thorium ions in binary mixture.     

A selective fluorescent chemosensor with 1, 2, 4-triazole as subunit for Cu (II) and its application in imaging Cu (II) in living cells

A chemosensor based on rhodamine B with 1, 2, 4-triazole as subunit was synthesized and characterized. It exhibits high selectivity and sensitivity for Cu²⁺ in ethanol/water (6:4, v:v) of pH 7.0 HEPES buffer solution and undergoes ring opening mechanism, and a 2:1 metal-ligand complex is formed. The chemosensor displays a linear response to Cu²⁺ in the range between 1.0 × 10⁻⁷ M and 1.0 × 10⁻⁶ M with a detection limit of 4.5 × 10⁻⁸ M. Its capability of biological application was also evaluated and the results show that this chemosensor could be successfully employed as a Cu²⁺-selective chemosensor in the fluorescence imaging of living cells.     

Electroanalytical studies on cadmium(II) selective potentiometric sensors based on t-butyl thiacalix[4]arene and thiacalix[4]arene in poly(vinyl chloride)

Cd²⁺-selective sensors have been fabricated from poly(vinyl chloride) (PVC) matrix membranes containing t-butyl thiacalix[4]arene (I) and thiacalix[4]arene (II) as electroactive materials. The addition of sodium tetraphenylborate and the plasticizer 2-nitrophenyl octyl ether has been found to improve the performance of the sensors substantially. The membranes of various compositions of the two thiacalixarenes have been investigated and it was found that the best performance was obtained for the membrane of composition II:PVC:NaTPB:NPOE in the ratio 5:120:3:150. The sensor shows a linear potential response for Cd²⁺ over a wide activity range 3.2 × 10⁻⁶ to 1.0 × 10⁻¹ M with Nernstian compliance (29.5 mV decade⁻¹ of activity) in pH range 4.5-6.5 and a fast response time of ∼8 s. The potentiometric selectivity coefficient values determined by matched potential method indicate excellent selectivity for Cd²⁺ ions over mono-, di- and trivalent interfering cations. The sensor exhibits adequate shelf life (∼3 months) with good reproducibility (S.D. ±0.2 mV) and can also be used in partially non-aqueous media having up to 20% (v/v) methanol, ethanol or acetone content with no significant change in the value of slope or working activity range. The sensor has been used in the potentiometric titration of Cd²⁺ with EDTA. The sensor could be successfully used for the quantification of cadmium in river water samples.     

Novel all-solid-state copper(II) microelectrode based on a dithiomacrocycle as a neutral carrier

A novel dithiomacrocycle (4-phenyl-11-decanoyl-1,7-dithia-11-azacyclotetradecane-4-sulfide) has been synthesized and used as a new ionophore in order to develop a plasticized poly(vinyl chloride) membrane for copper ion detection. The performance of these novel planar copper(II)-selective potentiometric microelectrodes was investigated using potentiometric measurements. The developed microelectrodes exhibits a good linear response of 29.5 ± 1 mV per decade within the concentration range of 1.0 × 10⁻⁶ to 1.0 × 10⁻² M (r = 0.9995) of Cu²⁺. The detection limit was determined as 5.62 × 10⁻⁷ M and the selectivity coefficients for possible interfering cations were evaluated. The microelectrodes are suitable for use with aqueous solutions of pH 3.5-6.0 and were found to be insensitive to the nature of the anions used in the sample.     

Application of surfactant modified zeolite carbon paste electrode (SMZ-CPE) towards potentiometric determination of sulfate

A sulfate-selective electrode based on surfactant modified zeolite (SMZ) particles into carbon paste has been proposed (SMZ-CPE). The electrode was fully characterized in terms of composition, response time, ionic strength range, thermal stability and usable pH range. The electrode containing 10% of the SMZ was exhibited linear response range to sulfate species in the range of 2.0 × 10⁻⁶-3.1 × 10⁻³ M with detection limit of 2.0 × 10⁻⁶ M and Nernstian slope of 29.8 ± 0.8 mV per decade of sulfate concentration. The electrode response remains constant in the pH range of 4-10 and in the presence of 1 × 10⁻⁴-2 × 10⁻³ M NaNO₃. The response of the electrode reaches equilibrium within several second after immersing the electrode in sulfate solution. A successful application of sulfate determination sulfate in real sample of a pharmaceutical zinc sulfate capsule, using direct potentiometry, is presented. The electrode was also used for potentiometric titration of sulfate. The validation of the obtained results in each case was proved by statistical methods.     

Plastic membrane electrodes for the determination of flavoxate hydrochloride and cyclopentolate hydrochloride

Four novel ion-exchangers (Fx-Rt (I), Fx-TPB (II), Cp3-PMA (III) and Cp3-PTA (IV)) of antispasmodic and anticholinergic drugs, flavoxate hydrochloride (FxCl), 2-piperidinoethyl-3-methyl-4-oxo-2-phenyl-4h-1-benzopyran-8-carboxylate hydrochloride, cyclopentolate hydrochloride (CpCl) and (2-(dimethylamino)ethyl (RS)-(1-hydroxycyclopentyl)phenylacetate) hydrochloride were synthesized and incorporated into poly(vinyl chloride)-based membrane electrodes for the quantification of FxCl and CpCl in different pharmaceutical preparations. The influence of membrane composition on the potentiometric response of the membrane electrodes was found to substantially improve the performance characteristics. The best performance was reported with membranes having compositions (w/w) of Fx-Rt (2%):PVC (49%):DOP (49%), Fx-TPB (7%):PVC (46.5%):DOP (46.5%), Cp3-PMA (8%):PVC (46%):DOP (46%) and Cp3-PTA (9%):PVC (45.5%):DOP (45.5%). The proposed sensors exhibited Nernstian responses in the concentration ranges of 1.39 × 10⁻⁶-5.00 × 10⁻⁴, 9.90 × 10⁻⁷-3.75 × 10⁻⁵, 1.39 × 10⁻⁵-2.53 × 10⁻³ and 3.21 × 10⁻⁶-8.62 × 10⁻⁴ M, with detection limits of 5.50 × 10⁻⁷, 9.8 × 10⁻⁷, 9.8 × 10⁻⁶ and 2.95 × 10⁻⁶ M for the (I), (II), (III) and (IV) electrodes, respectively. The membrane electrodes performed satisfactorily over pH ranges of 2.0-5.5, 2.0-5.5, 2.0-5.0 and 2.0-7.5, with fast response times of 20, 30, 15 and 20 s for the (I), (II), (III) and (IV) electrodes, respectively. The practical utility of the sensors was demonstrated by the determination of FxCl and CpCl in pure solutions and pharmaceutical preparations using standard additions and potentiometric titration.     

A comparative study of Pb selective sensors based on derivatized tetrapyrazole and calix[4]arene receptors

Two neutral ionophores, 2,12-dimethyl-7,17-diphenyltetrapyrazole (I) and 5,11-dibromo-25,27-dipropoxycalix[4]arene (II) have been explored for preparing PVC based membrane sensors selective to Pb²⁺. The addition of sodium tetraphenylborate and various plasticizers viz. DOS, TEHP, DBP, DOP and TBP has been found to substantially improve the performance (working concentration range, slope and response time) of the sensors. The best performance was obtained with the sensor having a membrane of composition (w/w) of (I) (1%):PVC (33%):TBP (65%):NaTPB (1%). The sensor exhibits Nernstian response in the concentration range 2.5 × 10⁻⁶ to 5.0 × 10⁻² M Pb²⁺, performs satisfactorily over wide pH range (1.6-6.0) with a fast response time (∼10 s). The sensor was found to work satisfactorily in partially non-aqueous media up to 25% (v/v) content of acetone, methanol or ethanol and could be used over a period of 5 months. Potentiometric selectivity coefficients as determined by match potential method (MPM) indicate excellent selectivity for Pb²⁺ ions. The sensors could be used successfully in the estimation of lead in Eveready battery waste and also as an indicator electrode in potentiometric titration.     

PVC membrane and coated graphite potentiometric sensors based on 1-phenyl-3-pyridin-2-yl-thiourea for selective determination of iron(III)

The construction and performance characteristics of PVC membrane (PME) and coated graphite (CGE) Fe³⁺ ion selective electrodes based on 1-phenyl-3-pyridin-2-yl-thiourea (PPT) are described. The electrodes exhibit a Nernstian slope of 20.2 ± 0.8 (CGE) and 19.9 ± 0.4 (PME) mV decade⁻¹ of activity in Fe³⁺ ion over a wide concentration range from 3.0 × 10⁻⁷ to 1.0 × 10⁻² M for CGE and 6.9 × 10⁻⁷ to 1.0 × 10⁻² M Fe³⁺ for PME. The lower detection limits by CGE and PME are 2.0 × 10⁻⁷ and 3.9 × 10⁻⁷ M, respectively, in the pH range of 1.8-5.6 for PME and 1.8-5.8 for CGE with a fast response time (<10 s). The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the PME. The PME showed the working temperature range of 22-55 °C with isothermal temperature coefficient of 1.33 × 10⁻³ V/°C and it was also used in non-aqueous solvents. The electrodes were successfully applied to determine iron(III) in water samples.     

Fabrication of a novel holmium(III) PVC membrane sensor based on 4-chloro-1,2-bis(2-pyridinecarboxamido)benzene as a neutral ionophore

This paper introduces the development of an original PVC membrane electrode, based on 4-chloro-1,2-bis(2-pyridinecarboxamido)benzene (CBPB) as a suitable carrier for the Ho³⁺ ion. The electrode presents a Nernstian slope of 19.7 ± 0.3 mV per decade for the Ho³⁺ ions across a broad working concentration range from 1.0 × 10⁻⁶ to 1.0 × 10⁻² M. The lower detection limit was 8.5 × 10⁻⁷ M in the pH range 2.7–9.8, while the response time was rapid (<15 s). Therefore, this potentiometric sensor displayed good selectivity for a number of cations such as alkali, alkaline earth, transition and heavy metal ions. The practical applicability of the electrode was demonstrated by its use as an indicator electrode in the potentiometric titration of Ho³⁺ ions with EDTA and in the determination of F^- in mouth wash samples.     

Chloride selective potentiometric sensor based on a newly synthesized hydrogen bonding anion receptor

A new potentiometric chloride sensor based on the use of anion receptor 2-(1-H-imidazo [4,5-f][1,10]phenanthroline-2-yl)-6methoxyphenol (HIPM) in poly(vinyl chloride) (PVC) matrix is reported. Effect of various plasticizers: 2-nitrophenyloctylether (o-NPOE), di-n-butylphthalate (DBP), diethyl phthalate (DEP), dioctylpthalate (DOP), tri-n-butyl phosphates (TBP), chloronapthalene (CN) and cation excluder, cetryltrimethylammoniumbromide (CTAB) was studied. The best performance was obtained with a membrane composition of PVC: o-NPOE:HIPM: CTAB ratio (w/w, %) of 31:60:7:3. The sensor exhibits significantly enhanced selectivity towards chloride over the concentration range 5.0 × 10⁻⁸ to 1.0 × 10⁻¹ M with a lower detection limit of 1.0 × 10⁻⁸ M and a Nernstian slope of 59.8 mV decade⁻¹ of activity. Influence of the membrane composition and possible interfering ions was investigated on the response properties of the electrode. Fast and stable response, good reproducibility and long-term stability are demonstrated. The sensor shows response time of <10 s and can be used for about 3 months without any considerable divergence in their potential response. Selectivity coefficients determined with matched potential method (MPM) indicate high selectivity for chloride. The proposed electrode shows fairly good discrimination of chloride from anions. It was successfully applied to determination of chloride ion in packed drinking water. The electrode can be used in the pH range of 6.5-8.0 and mixtures containing up to 20% (v/v) non-aqueous content. It was used as an indicator electrode in potentiometric titration of chloride ion against silver nitrate.