Tripodal chelating ligand-based sensor for selective determination of Zn(II) in biological and environmental samples

Potassium hydrotris(N-tert-butyl-2-thioimidazolyl)borate [KTt^t-Bu] and potassium hydrotris(3-tert-butyl-5-isopropyl-l-pyrazolyl)borate [KTp^t-Bu,i-Pr] have been synthesized and evaluated as ionophores for preparation of a poly(vinyl chloride) (PVC) membrane sensor for Zn(II) ions. The effect of different plasticizers, viz. benzyl acetate (BA), dioctyl phthalate (DOP), dibutyl phthalate (DBP), tributyl phosphate (TBP), and o-nitrophenyl octyl ether (o-NPOE), and the anion excluders sodium tetraphenylborate (NaTPB), potassium tetrakis(p-chlorophenyl)borate (KTpClPB), and oleic acid (OA) were studied to improve the performance of the membrane sensor. The best performance was obtained from a sensor with a of [KTt^t-Bu] membrane of composition (mg): [KTt^t-Bu] (15), PVC (150), DBP (275), and NaTPB (4). This sensor had a Nernstian response (slope, 29.4 ± 0.2 mV decade of activity) for Zn²⁺ ions over a wide concentration range (1.4 × 10⁻⁷ to 1.0 × 10⁻¹ mol L⁻¹) with a limit of detection of 9.5 × 10⁻⁸ mol L⁻¹. It had a relatively fast response time (12 s) and could be used for 3 months without substantial change of the potential. The membrane sensor had very good selectivity for Zn²⁺ ions over a wide variety of other cations and could be used in a working pH range of 3.5–7.8. The sensor was also found to work satisfactorily in partially non-aqueous media and could be successfully used for estimation of zinc at trace levels in biological and environmental samples. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Cobalt(II)-selective membrane sensor based on a [Me2(13)dieneN4] macrocyclic cobalt complex

A new poly(vinyl chloride)-based membrane was fabricated with the cobalt(II) complex of 2,4-dimethyl-1,5,8,11-tetraazacyclotrideca-1,4-diene [Me₂(13)dieneN₄] as an ion carrier. The membrane composition was Co²⁺ complex/PVC/NaTPB/DBP 15:50:15:20 (w/w). The sensor exhibited a Nernstian response for Co²⁺ ions over a wide concentration range (7.94×10⁻⁶–1.0×10⁻¹ M) at pH 2.5–7.0, a response time of 10 s, and it could be used for 3 months without any significant divergence in potential. The proposed membrane sensor exhibited good selectivity for Co²⁺ over a wide variety of other metal ions and in mixtures containing up to 25% (v/v) non-aqueous content. The sensor was successfully used as an indicator electrode in the potentiometric titration of Co²⁺ with EDTA and the direct determination of Co²⁺ in real samples.     

Fabrication of an iron(III)-selective PVC membrane sensor based on a bis-bidentate Schiff base ionophore

A Fe³⁺ ion-selective membrane sensor was fabricated from polyvinyl chloride (PVC) matrix membrane containing bis-bidentate Schiff base (BBS) as a neutral carrier, sodium tetraphenyl borate (NaTPB) 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 best performance was obtained with a membrane containing 32% PVC, 62.5% NPOE, 3% BBS, and 2.5% NaTPB. The electrode shows a Nernstian behavior (slope of 19.3 ± 0.6) over a very wide iron ion concentration range (1.0 × 10⁻⁷–1.0 × 10⁻² M) and has a low detection limit (7.4 × 10⁻⁸ M). The potentiometric response of the sensor is independent of pH of the solution in the pH range 1.9–5.1. The proposed sensor has a very low response time (<15 s) and a good selectivity relative to a wide variety of other metal ions including common alkali, alkaline earth, heavy, and transition metal ions. The electrode can be used for at least 60 days without any considerable divergence in potentials. The proposed sensor was successfully applied as an indicator electrode for the potentiometric titration of 1.0 × 10⁻² M Fe³⁺ ions with a 1.0 × 10⁻⁴ M EDTA and the direct determination of Fe³⁺ in mineral water and wastewater samples.     

Copper Incorporated [Me2(15)dieneN4] Macrocyclic Complex for Fabrication of PVC based Membrane Electrode for Copper

Copper (II) complex of 2,4-dimethyl-1,5,9,12-tetraazacyclopentadeca-1,4-diene, [Me₂(15)dieneN₄] was synthesized and used in the fabrication of Cu²⁺ – selective ISE membrane in PVC matrix. The membrane having Cu(II) macrocyclic complex as electroactive material along with sodium tetraphenyl borate (NaTPB) as anion discriminator. Dibutyl phthalate (DBP) as plasticizer in poly(vinyl chloride) (PVC) matrix was prepared for the determination of Cu²⁺. The best performance was observed by the membrane having Cu(II) complex–PVC–NaTPB–DBP with composition 1:5:1:3. The sensor worked well over a concentration range 1.12 × 10⁻⁶ M–1.0 × 10⁻¹ M between pH 2.1–6.2 and a fast response time 10±2 s and a lifetime of 6 months. Their performance in partially non-aqueous medium was found satisfactory. Electrodes exhibited excellent selectivity for Cu²⁺ ion over other mono-, di-, trivalent cations. It can also be used as indicator electrode in the potentiometric titration of Cu²⁺ against EDTA as well as in the determination of Cu²⁺ in real samples.     

Samarium(III)-PVC-Membrane Sensor Based on Ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline

Abstract

2-Ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EED) was found to be a suitable neutral ionophore for the preparation of a highly selective samarium (Sm)(III) membrane sensor. Poly vinylchloride (PVC)–based membranes of EED with sodium tetraphenyl borate (NaTPB) as an anionic additive and dibutylphthalate (DBP), nitrobenzene (NB), and acetophenone (AP) as plasticizing solvent mediators were prepared and investigated as Sm(III) sensors. The sensor exhibited a Nernstian response over a concentration range of 1.0 × 10^?6 to 1.0 × 10^?2 M, with a detection limit of 5.0 × 10^?7 M. The best performance was achieved with a membrane composition of 30% PVC, 66% dibutyl phthalate (DBP), 2% EED, and 2% sodium tetraphenyl borate (NaTPB). It has a very short response time, in the whole concentration range (～10s), and can be used for at least 10 weeks. The proposed electrode shows a very good selectivity toward Sm(III) ions over a wide variety of cations, including alkali, alkaline earth, transition-metal, and heavy-metal ions. The sensor was applied to the determination of Sm ions in binary mixtures.     

Azide-selective sensor based on tripodal iron complex for direct azide determination in aqueous samples

A potentiometric azide-selective sensor based on the use of iron(III) hydrotris(3,5-dimethylpyrazolyl)borate acetylacetonate chloride [Tp^Me2Fe(acac)Cl] as a neutral carrier for an azide-selective electrode is reported. Effect of various plasticizers, viz. o-nitrophenyloctyl ether (o-NPOE), dioctylphthalate (DOP), dibutylphthalate (DBP), and benzylacetate (BA), and an anion excluder, hexadecyltrimethylammonium bromide (HTAB), with [Tp^Me2Fe(acac)Cl] complex in poly(vinyl chloride) (PVC) were studied. The best performance was obtained with a membrane composition of [Tp^Me2Fe(acac)Cl]/HTAB/DOP/PVC in a ratio of 5:2:190:100 (w/w). The sensor exhibits significantly enhanced selectivity toward azide ions over the concentration range 6.3 × 10⁻⁷ to 1.0 × 10⁻² M with a lower detection limit of 3.8 × 10^–7 M and a Nernstian slope of 59.4 ± 1.1 mV decade⁻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 and applicability over a wide pH range (3.5–9.0) are demonstrated. The sensor has a response time of 14 s and can be used for at least 45 days without any considerable divergence in the potential response. The proposed electrode shows fairly good discrimination of azide from several inorganic and organic anions. It was successfully applied to the direct determination of azide in orange juice, tea extracts and human urine samples.     

All Solid State Nickel(II)‐Selective Potentiometric Sensor Based on an Upper Rim Substituted Calixarene

A new ionophore, i.e. p‐(2‐thiazolazo)calix[4]arene ( I ) has been explored for its selective behavior towards Ni(II) ions. A poly(vinyl chloride) based membrane containing ( I ) as an electroactive material along with sodiumtetraphenylborate (NaTPB), and nitrophenyloctyl ether in the ratio 10 : 100 : 3 : 150 (I:PVC:NaTPB:NPOE) (w/w) was used to fabricate an all solid state nickel(II)‐selective sensor. The developed sensor exhibited a working concentration range of 1.0×10^?6–1.0×10^?1 M, with a Nernstian slope of 28.9±1.0 mV/decade of activity and a response time of 10–15 s. This sensor shows a detection limit of 9.0×10^?7 M. Its potential response remains unaffected of pH in the range 3.0–7.6, and the cell assembly could be used successfully in partially nonaqueous medium (up to 10 % v/v) without any significant change in the slope value or the working concentration range. The sensor worked satisfactorily for about ten weeks and exhibited excellent selectivity over a number of mono‐, bi‐, and tri‐valent cations including alkali, alkaline earth metal, and transition metal ions. It could be used as an indicator electrode for the end point determination in the potentiometric titration of nickel ions against ethylenediaminetetraacetic acid (EDTA) as well as for the determination of nickel ion concentration in real samples.     

Silver(I)-selective electrode based on [Bz2Oxo4(18)dieneS4] tetrathia macrocyclic carrier

A polystyrene-based membrane of 7,8:16,17-dibenzo-6,9,15,18-tetraoxo-1,5,10,14-tetrathiacyclooctadeca-7,16-diene [Bz₂Oxo₄(18)dieneS₄] was fabricated using sodium tetraphenylborate (NaTPB) and dioctyl phthalate (DOP) as anion excluder and plasticizing agent. The best performance was obtained from the membrane with the composition ionophore [Bz₂Oxo₄(18)dieneS₄]:polystyrene:DOP:NaTPB, 5:100:150:10 (w/w). The response of the electrode was linear over a wide range of concentration, 1.26×10^–6–1.00×10^–1 mol L⁻¹ for silver ion with a Nernstian slope of 58.4±0.1 mV per decade and a detection limit of 1.0×10⁻⁶ mol L⁻¹. The electrode was found to be chemically inert and of adequate stability with a response time of 10 s and could be used for a period of 3 months without change of potential. It worked satisfactorily in mixtures containing up to 35% (v/v) non-aqueous content. The proposed membrane sensor had good selectivity for Ag⁺ over a wide variety of metal ions in the pH range 2.2–8.5. It was successfully used as an indicator electrode in potentiometric titration of silver ion. The electrode was also useful for determination of Ag⁺ in waste from photographic films.     

Copper(II) ion selective electrode based on a newly synthesized Schiff-base chelate

A new Cu (II) ion-selective electrode has been fabricated in poly (vinyl chloride) matrix based on a recently synthesized Schiff-base chelate. The addition of sodium tetraphenylborate (NaTPB) and various plasticizers viz. TBP, TEHP, DOS, and CN have been found to substantially improve the performance of the electrode. The membrane of various compositions of the ionophore (I) were investigated and it was found that the best performance was obtained with the membrane having (I): PVC: NaTPB: CN in the ratio 4: 140: 3: 80 (mg). The electrode exhibits a Nernstian response over a wide concentration range (1.9 × 10⁻⁶–1.0 × 10⁻¹ M) with 30.0 mV/decade of concentration between pH 3.0 and 7.5. The response time of the electrode is about 12 s and it can be used over a period of 3 months without any divergence in potential. The potentiometric selectivity coefficient values as determined by fixed interference method indicate excellent selectivity for Cu²⁺ ions over interfering cations. The electrode has also been used successfully in partially non-aqueous media having a 25% (v/v) methanol, ethanol or acetone content without showing any considerable change in the value of slope or working concentration range. The electrode has been used in the potentiometric titration of Cu²⁺ with EDTA.     

Mercury-selective membrane electrode based on methyl substituted dibenzo tetraphenyl tetraaza macrocycle

A new polystyrene based membrane electrode of methyl substituted 6,7:13,14-dibenzo-2,4,9,11-tetraphenyl-1,5,8,12-tetraazacyclotetradeca-1,4,6,8,11,13-hexaene (I) with sodium tetraphenylborate (NaTPB) and dibutyl phthalate (DBP) as anion excluder and plasticizing agent was prepared and investigated as Hg (II)-selective electrode. The electrode exhibits a Nernstian response for Hg (II) ions over a wide concentration range of 1.0 × 10⁻¹–8.9 × 10⁻⁶ M with a slope of 30 ± 1 mV per decade concentration. It has a response time of 10 s and can be used for at least 4 months without any divergence in potentials. The membrane works satisfactorily in a partially non-aqueous medium up to a maximum 30% (v/v) content of methanol and ethanol. The proposed sensor revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metal ions and could be used in a pH range of 2.5–5.0. Normal interferents like Ag⁺, Cd²⁺ and Pb²⁺ low interfere in the working of the electrode. The electrode was successfully used in the direct determination of Hg²⁺ in aqueous solution.     

Sm3+ Potentiometric Membrane Sensor as a Probe for Determination of Some Pharmaceutics

The increase use of ion sensors in the fields of environmental, agricultural, and medical analysis is stimulating analytical chemists to develop new sensors for fast, accurate, reproducible, and selective determination of various ions. In this study a new samarium membrane sensor was constructed and for the first time, it was applied as a probe in indirect determination of hyoscine, homatropine, and tramadol drugs in their pharmaceutical formulation. The proposed membrane sensor was constructed based on a membrane containing 2% sodium tetraphenyl borate (NaTPB) as an anionic additive, 63% dibutyl phthalate (DBP) as solvent mediator, 5% ionophore, and 30% poly(vinyl chloride) (PVC). The proposed Sm(III) electrode exhibits a Nernstian response of 19.35±0.2 mV per decade of samarium concentration, and has a lower detection limit of 1.0×10^?7 M. The linear range of the sensors was 1.0×10^?7–1.0×10^?1 M. It works well in the pH range of 3.0–8.0.     

Comparative Studies of Tridentate Sulfur and Nitrogen‐Containing Ligands as Ionophores for Construction of Cadmium Ion‐Selective Membrane Sensors

New polymeric membrane cadmium‐ion selective sensors have been prepared by incorporating nitrogen and sulfur containing tridentate ligands as the ionophores into the plasticized PVC membranes. Poly(vinyl chloride) (PVC) based membranes of potassium hydrotris[N‐(2,6‐xylyl)thioimdazolyl) borate] (KTt^2,6‐xylyl) and potassium hydrotris(3‐phenyl‐5‐methylpyrazolyl) borate (KTp^Ph,Me) with sodium tetraphenyl borate (NaTPB) as an anionic excluder and dibutylphthalate (DBP), tributylphthalate (TBP), dioctylsebacate (DOS), and o‐nitrophenyloctyl ether (o‐NPOE) as plasticizing solvent mediators were investigated in different compositions. KTt^2,6‐xylyl was found to be a selective and sensitive ion carrier for Cd(II) membrane sensor. A membrane composed of KTt^2,6‐xylyl:NaTPB:PVC:DBP with the % mole ratio 2.3 : 1.1 : 34.8 : 61.8 (w/w) works well over a very wide concentration range (7.8×10^?8–1.0×10^?2 M) with a Nernstian slope of 29.4±0.2 mV/decades of activity between pH values of 3.5 to 9.0 with a detection limit of 4.37×10^?8 M. The sensor displays very good discrimination toward Cd(II) ions with regard to most common cations. The proposed sensor shows a short response time for whole concentration range (ca. 8 s). The effects of the cationic (tetrabutylammonium chloride, TBC), anionic (sodium dodecyl sulfate, SDS) and nonionic (Triton X‐100) surfactants were investigated on the potentiometric properties of proposed cadmium‐selective sensor. The proposed sensor based on KTt^2,6‐xylyl ionophore has also been used for the direct determination of cadmium ions in different water samples and human urine samples.     

An optical chemical sensor for mercury ion based on 2-mercaptopyrimidine in PVC membrane

An optical chemical sensor based on 2-mercaptopyrimidine (2-MP) in plasticized poly(vinyl chloride) (PVC) membrane incorporating (N,N-diethyl-5-(octadecanoylimino)-5H benzo[a]phenoxazine-9-amine (ETH 5294) and sodium tetraphenyl borate (NaTPB) for batch and flow-through determination of mercury ion is described. The response of the sensor is based on selective complexation of Hg²⁺ with 2-MP in the membrane phase, resulting in an ion exchange process between H⁺ in the membrane and Hg²⁺ in the sample solution. The influences of several experimental parameters, such as membrane composition, pH, and type and concentration of the regenerating reagent, were investigated. The sensor has a response range of 2.0 × 10⁻⁹ to 2.0 × 10⁻⁵ mol L⁻¹ Hg²⁺ with a detection limit of 4.0 × 10⁻¹⁰ mol L⁻¹ and a response time of ≤45 s at optimum pH of 6.5 with high measurement repeatability and sensor-to-sensor reproducibility. It shows high selectivity for Hg²⁺ over several transition metal ions, including Ag⁺, Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Fe³⁺, Mn²⁺, Ni²⁺, and common alkali and alkaline earth ions such as Na⁺, K⁺, Mg²⁺, Ca²⁺, and Pb²⁺. The sensor membrane can be easily regenerated with dilute acid solutions. The sensor has been used for the determination of mercury ion concentration in water samples.     

Polymeric membrane and coated graphite electrode based on newly synthesized tetraazamacrocyclic ligand for trace level determination of nickel ion in fruit juices and wine samples

Novel polymeric membrane electrode (PME) and coated graphite electrode (CGE) for nickel ion were prepared based on 2,9-(2-methoxyaniline)₂-4,11-Me₂-[14]-1,4,8,11-tetraene-1,5,8,12-N₄ as a suitable neutral ionophore. The addition of lipophilic anion excluder (NaTPB) and various plasticizers viz o-nitrophenyloctylether (o-NPOE), dioctylphthalate (DOP), dibutylphthalate (DBP), 1-chloronaphthalene (CN) and tri-n-butylphosphate (TBP) have found to improve the performance of the sensors. The best performance was obtained for the membrane sensor having a composition of I:NaTPB:TBP:PVC in the ratio 6:4:100:90 (w/w; mg). The electrodes exhibit Nernstian slopes for Ni²⁺ ions over wide concentration ranges of 4.6 × 10^?7–1.0 × 10^?1 M for PME and 7.7 × 10^?8–1.0 × 10^?1 M for CGE with limits of detection of 2.7 × 10^?7 M for PME and 3.7 × 10^?8 M for CGE. The response time for PME and CGE was found to be 10 and 8 s respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 3.0–8.0. The proposed electrodes revealed good selectivities over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions. The coated graphite electrode was used as an indicator electrode in the potentiometric titration of nickel ion with EDTA and in direct determination in different fruit juices and wine samples.     

Barium(II)-PVC Membrane Sensor Based on 4-4′-Methylenediantipyrine as a Neutral Carrier

Abstract

A highly selective and sensitive poly(vinyl chloride) membrane electrode, using 4-4′-Methylenediantipyrine as an ionophore, has been prepared and examined as a Ba²⁺-selective electrode. The influence of the anion excluder (sodium tetraphenyl borate, NaTPB) and the effect of the plasticizers dibutyl phthalate (DBP), nitrobenzene (NB), and benzyl acetate (BA) were studied. The best performance was obtained with the sensor having a membrane composition (w/w) of (MAP, 2.0%), (PVC, 30%), (NB, 66%), (NaTPB, 2.0%) with a wide working concentration range of 1.0 × 10^?6 to 1.0 × 10^?2 M between the pH values of 3.4 and 10.6. Furthermore, a Nernstian slope of 29.7±0.3 mV/decade of activity was demonstrated with a response time of 15 s. The sensor could be used over a period of 2 months with no potential divergence, revealing a good selectivity for a broad variety of cations including alkali, alkaline earth, heavy and transition metals. Regarding the practical applicability of this sensing device, it was successfully applied for the Ba²⁺ ions detection in a lithophone pigment and as an indicator electrode in the potentiometric titration of the under study cations.     

Aluminium(III)-selective electrode based on a newly synthesized glyoxal-<Emphasis Type="Italic">bis</Emphasis>-thiosemicarbazone Schiff base

A PVC membrane electrode for Al³⁺ based on glyoxal-bis-thiosemicarbazone (GBTC) as an ion carrier was developed. The electrode exhibits a Nernstian slope of 20.1 mV per decade and a linear range of 1.8 × 10⁻⁵−1.0 × 10⁻¹ M for Al(NO₃)₃ with a detection limit of 8.7 × 10⁻⁶ M. It has a fast response time of about 10 s and can be used for at least 1 month. The proposed membrane sensor revealed a good selectivity for Al³⁺ over a wide variety of other metal ions and could be used in the pH range of 2.5–4.5. The text was submitted by the authors in English.     

A simple optical sensor for cadmium ions assay in water samples using spectrophotometry

A new simple and inexpensive optical chemical sensor for cadmium(II) ions is presented. The cadmium sensing system was prepared by incorporating 2-amino-cyclopentene-1-dithiocarboxylic acid (ACDA) on a triacetylcellulose membrane. The absorption spectra of the optical sensor membrane in Cd(II) solution showed a maximum peak at 430 nm. The proportionality in intensity of the membrane color on the optode to varying amounts of Cd(II) suggests its potential applications for screening Cd(II) in aqueous samples by visual colorimetry. The sensor provided a wide concentration range of 3.0 × 10⁻⁶–3.4 × 10⁻⁴ M of Cd(II) ions with a detection limit of 1.0 × 10⁻⁶ M (0.2 μg/mL). The relative standard deviations for eight replicate measurements of 8.0 × 10⁻⁶ and 5.0 × 10⁻⁵ M Cd(II) were 2.7 and 2.3%, respectively. The response time of the optode was 6 min. The influence of interfering ions on the determination of 1.0 × 10⁻⁵ M Cd(II) was studied and the main interferences were removed by extraction method. The sensor was applied to the determination of Cd(II) in water samples.     

Development of membrane electrodes for selective determination of some antiepileptic drugs in pharmaceuticals,plasma and urine

Newly developed, simple, low-cost and sensitive ion-selective electrodes have been proposed for determination of some antiepileptic drugs such as lamotrigine, felbamate, and primidone in their pharmaceutical preparations as well as in biological fluids. The electrodes are based on poly(vinyl chloride) membranes doped with drug–tetraphenyl borate (TPB) or drug–phosphotungstic acid (PT) ion-pair complexes as molecular recognition materials. The novel electrodes displayed rapid Nernstian responses with detection limits of approximately 10⁻⁷ M. Calibration graphs were linear over the ranges 5.2 × 10⁻⁷–1.0 × 10⁻³, 1.5 × 10⁻⁶–1.0 × 10⁻³, and 2.6 × 10⁻⁷–1.0 × 10⁻³ M for drug–TPB and 5.8 × 10⁻⁷–1.0 × 10⁻³, 1.8 × 10⁻⁷–1.0 × 10⁻³, and 6.6 × 10⁻⁷–1.0 × 10⁻³ M for drug–PT electrodes, respectively, with slopes ranging from 52.3 to 62.3 mV/decade. The membranes developed have potential stability for up to 1 month and proved to be highly selective for the drugs investigated over other ions and excipients. The results show that the selectivity of the ion-selective electrodes is influenced significantly by the plasticizer. The proposed electrodes were successfully applied in the determination of these drugs in pharmaceutical preparations in four batches of different expiry dates. Statistical Student’s t test and F test showed insignificant systematic error between the ion-selective electrode methods developed and a standard method. Comparison of the results obtained using the proposed electrodes with those found using a reference method showed that the ion-selective electrode technique is sensitive, reliable, and can be used with very good accuracy and high percentage recovery without pretreatment procedures of the samples to minimize interfering matrix effects. Figure Structure of lamotrigine, felbanate and primidone     

Highly sensitive modified glassy carbon sensor based on TDAN for nitrate detection in real water

Glassy carbon electrodes modified with a plasticized PVC membrane including tetradodecyl ammonium nitrate (TDAN) and two different plasticizers [bis(2-etheylhexyl) sebacate (DOS) and dibutyl phthalate (DBP)]. TDAN is a quaternary ammonium salt, used in nitrate-selective field-effect transistor membrane, and it is applied as an ionophore for sensor development. Membranes were prepared as sensing matrix for nitrate detection through the intensity of its reduction peak using cyclic voltammetry. Under optimum conditions, the detection limits of nitrate obtained with TDAN + DOS and TDAN + DBP, are 10–6 mol/dm3 and 10–9 mol/dm3, respectively. As a result, the developed sensors based on TDAN + DOS and TDAN + DBP matrices demonstrate satisfactory quantified amounts in determination of nitrate in water where the measured values were less than 0.57 × 10–7 mol/dm3 and 0.73 × 10–10 mol/dm3, respectively.     

Subnanomolar determination of a beryllium ion by a novel Be(II) microsensor based on 4-nitrobenzo-9-crown-3-ether

In this work, for the first time, we introduce a highly selective and sensitive Be(II) microsensor. 4-nitrobenzo-9-crown-3-ether (NBCE) was used as a membrane-active component to prepare a Be(II)-selective polymeric membrane microelectrode. The electrode exhibits a Nernstian response toward Be(II) ions over a very wide concentration range (1.0 × 10⁻⁴–1.0 × 10⁻¹⁰ M), with a detection limit of 3.5 × 10⁻¹¹ M (∼350 pg/L). In fact, the electrode presents a fast response time in the whole concentration range (6 s). The proposed microelectrode can be used for at least six weeks without any considerable divergence in the potentials. The proposed membrane sensor revealed a selectivity toward Be(II) ions over a wide variety of other metal ions including common alkali, alkaline-earth, and rare-earth ions. It could be used in the pH range of 3.0–11.5. The microelectrode was successfully used as an indicator electrode for the titration of 20 mL of 1.0 × 10⁻⁶ M Be²⁺ solution with 1.0 × 10⁻⁴ M of EDTA. It was also applied to the direct determination of beryllium ions in beryl and binary mixtures. The text was submitted by the authors in English.