Potentiometric membrane sensor based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene for detection of Sn(II) in real samples

A Sn²⁺ ion-selective electrode which was prepared with a polymeric membrane based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene (NDDBH) as a ionophore. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, the amount of additive and concentration of internal solution on the potential response of Sn²⁺ sensor were investigated. The electrode exhibited a Nernstian slope of 28.8 ± 1.1 mV/decade of Sn²⁺ over a concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M of Sn²⁺ in an acidic solution (pH 1). The limit of detection was 4.0 × 10⁻⁶ M. The results show that this electrode can be used in ethanol media until 20% (v/v) concentration without interference. It can be used for more than 6 weeks without any considerable divergence in the potentials. The proposed membrane electrode revealed very good selectivity for Sn(II) ions over a wide variety of other cations and could be used in acidic media. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The stability constant (log K_s) of the Sn(II)-ionophore complex was determined at 25 °C by potentiometric titration in mixed aqueous solution. It was used as indicator electrode in potentiometric determination of Sn(II) ion in real samples.     

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.     

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.     

Silver(I)-selective membrane potentiometric sensor based on two recently synthesized ionophores containing calix[4]arene

Two new PVC membrane electrodes that are highly selective to Ag(I) ions were prepared using (L₁) calyx[4]arene (L₂) as two suitable neutral carriers. The silver(I) ion selective electrodes exhibit a good response for silver ion over a wide concentration range of 1.0 × 10⁻¹ to 4.2 × 10⁻⁶ M (L₁) and 1.0 × 10⁻¹ to 6.5 × 10⁻⁶ M (L₂) with a Nernstian slope of 60 mV per decade (L₁) and 58 mV per decade (L₂) at 25°C, and was found to be very selective, precise, and usable within the pH range 4.0–8.0. They have a response time of <15 s and can be used for at least 3 months without any measurable divergence in potential. The proposed sensors show a fairly good discriminating ability towards Ag⁺ ion in comparison to some hard and soft metal ions. The electrodes were used as indicator electrodes in the potentiometric titration of silver ion and in the determination of Ag⁺ in photographic emulsion and radiographic and photographic films. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 7, pp. 862–868. The article is published in the original.     

Novel potentiometric copper (II) selective membrane sensors based on cyclic tetrapeptide derivatives as neutral ionophores

Two novel membrane sensors sensitive and reasonably selective for Cu²⁺ ions are described. These are based on the use of newly synthesized cyclic tetrapeptide derivatives as neutral ionophores and sodium tetraphenylborate (NaTPB) as an anionic excluder in plasticized PVC membranes. The sensors exhibit fast and stable near-Nernstian response over the concentration range 1.0 × 10⁻⁶ mol l⁻¹ to 1.0 × 10⁻² mol l⁻¹ Cu²⁺ with a cationic slope of 30.2-25.9 mV per decade at pH 4.5-7 with a lower detection limit of 0.05-0.13 μg ml⁻¹. Effects of plasticizers, lipophilic salts and various foreign common ions are tested. The sensors display long life-span, long term stability, high reproducibility, and short response time. Selectivity of both sensors is significantly high for Cu²⁺ over Fe³⁺, Al³⁺, Zn²⁺, Cd²⁺, Hg²⁺, Ni²⁺, Co²⁺, Mn²⁺, alkaline earth and alkali metal ions. The sensors are used for direct measurement of copper content in different rocks and industrial wastewater samples from electroplating factories. The results agree fairly well with data obtained using atomic absorption spectrometry.     

A novel cobalt(II)-selective potentiometric sensor based on p-(4-n-butylphenylazo)calix[4]arene

A new poly(vinyl chloride)-based membranes containing p-(4-n-butylphenylazo)calix[4]arene (I) as an electroactive material along with sodiumtetraphenylborate (NaTPB), and dibutyl(butyl)phosphonate in the ratio 10:100:1:200 (I:DBBP:NaTPB:PVC) (w/w) was used to fabricate a new cobalt(II)-selective sensor. It exhibited a working concentration range of 9.2 × 10⁻⁶ to 1.0 × 10⁻¹ M, with a Nernstian slope of 29.0 ± 1.0 mV/decade of activity and the response time of 25 s. This sensor shows the detection limit of 4.0 × 10⁻⁶ M. Its potential response remains unaffected of pH in the range, 4.0-7.2, and the cell assembly can be used successfully in partially non-aqueous medium (up to 10%, v/v) without significant change in the slope of working concentration range. The sensor has a lifetime of about 3 months and exhibits excellent selectivity over a number of mono-, bi-, and tri-valent cations including alkali, alkaline earth metal, heavy and transition metal ions. It can be used as an indicator electrode for the end point determination in the potentiometric titration of cobalt ions against ethylenediaminetetraacetic acid (EDTA) as well as for the determination of cobalt ion concentration in real samples.     

Batch and flow measurement of hydrogen ions in highly acidic media using 2-(4-methoxy phenyl) 6-(4-nitrophenyl)-4-phenyl-1,3-diazabicyclo [3.1.0] hex-3-ene as an H-selective ionophore

A hydrogen ion-selective poly(vinyl chloride) (PVC) membrane electrode was developed using 2-(4-methoxy phenyl) 6-(4-nitrophenyl)-4-phenyl-1,3-diazabicyclo [3.1.0] hex-3-ene as ionophore. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, and the amount of additive on the potential response of pH sensor were investigated. This H⁺-selective membrane electrode gave a linear response over the pH range 0-4 (10⁻⁴ to 1 mol L⁻¹ HCl) with slope of 57.4 ± 0.3 mV pH⁻¹ and limit of detection 6.3 × 10⁻⁵ mol L⁻¹ at 20 °C. Also, hydrofluoric acid did not influence the surface of this electrode and thus it was maintained without showing any changes in potentials after being used in a hydrofluoric acid solution. The equilibrium water content of the electrode was determined in the presence of two different plasticizers as membrane solvent. The alkaline cation binding affinity of ionophore was very low that prove these cations do not have specific interaction with this ionophore. The electrode had fairly low electrical resistance, good potential stability and reproducibility. It has a rapid potential response to changes of pH (10 s), easily used in a single channel wall-jet flow injection system with good reproducibility (RSD% = 1.67%) and high reversibility. It was used as indicator electrode in potentiometric determination of pH in real samples.     

Application of artificial neural network to simultaneous potentiometric determination of silver(I), mercury(II) and copper(II) ions by an unmodified carbon paste electrode

The response characteristics and selectivity coefficients of an unmodified carbon paste electrode (CPEs) towards Ag⁺, Cu²⁺ and Hg²⁺ were evaluated. The electrode was used as an indicator electrode for the simultaneous determination of the three metal ions in their mixtures via potentiometric titration with a standard thiocyanate solution. A three-layered feed-forward artificial neural network (ANN) trained by back-propagation learning algorithm was used to model the complex non-linear relationship between the concentration of silver, copper and mercury in their different mixtures and the potential of solution at different volumes of the added titrant. The network architecture and parameters were optimized to give low prediction errors. The optimized networks were able to precisely predict the concentrations of the three cations in synthetic mixtures.     

Preparation of ethambutol-copper(II) complex and fabrication of PVC based membrane potentiometric sensor for copper

Copper(II) complex of ethambutol (I) was prepared and used in the fabrication of Cu(2+) selective ISE membrane. The membrane having Cu(II)-ethambutol complex (I) as electroactive material, along with sodium tetraphenylborate (NaTPB) as anion discriminator, dioctylphthalate (DOP) as plasticizer in poly(vinyl chloride) (PVC) matrix in the percentage ratio 6:2:190:200 (I:NaTPB:DOP:PVC) (w/w) gave a linear response in the concentration range 7.94x10(-6) to 1.0x10(-1) M of Cu(2+) with a slope of 29.9+/-0.2 mV per decade of activity and a fast response time of 11+/-2 s. The sensor works well in the pH range 2.1-6.3 and could be satisfactorily used in presence of 40% (v/v) methanol, ethanol and acetone and is selective for copper over a large number of cations with slight interference from Na(+) and Co(2+) if present at a level 1.5x10(-5) and 6.5x10(-5) M, respectively. It works well over a period of 6 months and can also be used as indicator electrode for the end point determination in the potentiometric titration of Cu(2+) against EDTA as well as in the determination of Cu(2+) in real samples.     

Novel fluorimetric bulk optode membrane based on 5,8-bis((5′-chloro-8′-hydroxy-7′-quinolinyl)methyl)-2,11-dithia-5,8-diaza-2,6-pyridinophane for selective detection of lead(II) ions

A novel fluorescence chemical sensor for the highly sensitive and selective determination of Pb²⁺ ions in aqueous solutions is described. The preliminary potentiometric and spectrofluorimetric complexation studies in solution revealed that the lipophilic ligand 5,8-bis((5′-chloro-8′-hydroxy-7′-quinolinyl)methyl)-2,11-dithia-5,8-diaza-2,6-pyridinophane (L2) forms a highly stable and selective [PbL2]²⁺ and [Pb(L2)₂]²⁺ complexes which results in a strong fluorescence quenching of the ligand. Thus, a novel fluorescence Pb²⁺ sensing system was prepared by incorporating L2 as a neutral lead-selective fluoroionophore in the plasticized PVC membrane containing tetrakis(p-chlorophenyl) borate as a liphophilic anionic additive. The response of the sensor is based on the strong selective fluorescence quenching of L2 by Pb²⁺ ions. At pH 5.5, the proposed sensor displays a calibration curve over a wide concentration range of 3.0 × 10⁻⁷ to 2.5 × 10⁻² M with a relatively fast response time of less than 5 min. In addition to high stability, reversibility and reproducibility, the sensor shows a unique selectivity towards Pb²⁺ ion with respect to common coexisting cations. The proposed fluorescence optode was successfully applied to the determination of lead in plastic toys and tap water samples.     

A new fluorescent sensor bearing three dansyl fluorophores for highly sensitive and selective detection of mercury(II) ions

A novel fluorometric sensor bearing three dansyl moieties based on tris[2-(2-aminoethylthio)ethyl]amine was prepared by a simple approach using a conventional two-step synthesis. The sensor exhibits highly Hg²⁺-selective ON-OFF fluorescence quenching behavior in aqueous acetonitrile solutions and is shown to discriminate various competing metal ions, particularly Cu²⁺, Ag⁺, and Pb²⁺ as well as Ca²⁺, Cd²⁺, Co²⁺, Fe³⁺, Mn²⁺, Na⁺, Ni²⁺, and Zn²⁺, with a detection limit of 1.15 × 10⁻⁷ M or 23 ppb.     

An efficient and selective flourescent chemical sensor based on 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane as a new fluoroionophore for determination of iron(III) ions. A novel probe for iron speciation

A novel fluorescent chemical sensor for the highly sensitive and selective determination of Fe³⁺ ions in aqueous solutions is prepared. The iron sensing system was prepared by incorporating 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a neutral Fe³⁺-selective fluoroionophore in the plasticized PVC membrane containing sodium tetraphenylborate as a liphophilic anionic additive. The response of the sensor is based on the strong fluorescence quenching of L by Fe³⁺ ions. At pH 5.5, the proposed sensor displays a calibration curve over a wide concentration range from 6.0 × 10⁻⁴ to 1.0 × 10⁻⁷ M, with a relatively fast response time of less than 2 min. In addition to a high stability and reproducibility, the sensor shows a unique selectivity toward Fe³⁺ ion with respect to common coexisting cations. The proposed fluorescence optode was applied to the determination of iron(III) content of straw of rice, spinach and different water samples. The fluorescent sensor was also used as a novel probe for Fe³⁺/Fe²⁺ speciation in aqueous solution.     

Poly(vinyl chloride)-membrane ion-selective bulk optode based on 1,10-dibenzyl-1,10-diaza-18-crown-6 and 1-(2-pyridylazo)-2-naphthol for Cu and Pb ions

An ion-selective bulk optode (ISBO) for sensing Cu²⁺ and Pb²⁺ ions based on plasticized poly(vinyl chloride) containing 1,10-dibenzyl-1,10-diaza-18-crown-6 (DBzDA18C6) as ionophore and 1-(2-pyridylazo)-2-naphthol (PAN) as chromoionophore was prepared. The effects of DBzDA18C6/PAN and NaTPB/PAN mole ratios on the response behavior of the ISBO were investigated. The ISBO membrane shows enhanced selectivities for Cu²⁺ (at 530 nm) and Pb²⁺ (at 467 nm) over alkali, alkaline earth and other transition metal ions. The optical selectivity coefficients were measured using the separate solution method (SSM) in the two corresponding wavelengths at pH=5. The detection limit for Cu²⁺ and Pb²⁺ are 3.2×10⁻⁷ and 1.0×10⁻⁸ M, respectively.     

Intramolecular hydrogen bonds in the copper(II) complex withcis,cis-1,3,5-tri[2-(diphenylphosphoryl)ethylamino]cyclohexane

The formation of intramolecular hydrogen bonds in the complex ofcis,cis-1,3,5-tri[2-(diphenylphosphoryl)cthylamino]cyclohexanc with the Cu²⁺ cation in different solvents has been studied by IR spectroscopy. Conformational analysis of the complex has been performed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1537–1542, June, 1996.     

Lower rim substituted p-tert-butyl-calix[4]arene. Part 16. Synthesis of 25,26,27,28-tetrakis(piperidinylthiocarbonylmethylene)-p-tert-butylcalix[4]arene and its interaction with metal ions

The synthesis, characterisation and X-ray crystal structures of p-tert-butyl-calix[4]arene-thioamide L and its complex with lead L-Pb²⁺ is reported. The cation-binding properties in solution have been assessed by liquid-liquid extraction of the metal picrates from water into dichloromethane and by stability constants determination in acetonitrile using UV-absorption spectrophotometry or potentiometry. The compound was used as active material in Pb-ion-selective membrane electrodes. The characteristics of these electrodes as well as the selectivity coefficients for Pb²⁺ cation versus many metal ions tested were obtained. Complex formation constants within the electrode membranes were determined using the sandwich membrane method and were compared to those obtained in acetonitrile. The lead concentration in the scrap-lead was determined with the use of electrodes incorporating the ligand studied.     

Highly sensitive and selective determination of Hg2+ by using 3-((2-(1H-benzo[d]imidazol-2-yl)phenylimino)methyl)benzene-1,2-diol as fluorescent chemosensor and its application in real water sample

A new receptor 3-((2-(1H-benzo[d]imidazol-2-yl)phenylimino)methyl)benzene-1,2-diol (1) was synthesised and developed as a highly selective fluorescent chemosensor for the detection of Hg²⁺ in semi-aqueous media. The fluorescence of receptor 1 was dramatically and selectively quenched on complexation with Hg²⁺ ion with the detection limit down to 0.20 μM. The developed sensor was successfully applied for the determination of Hg²⁺ content in water samples. Density Functional Theory (DFT) calculations were performed to study the mechanistic behaviour behind the binding of Hg²⁺ with receptor 1.     

Solid substrate-room temperature phosphorimetry for the determination of trace protein using ion association complex [Cu(BPY)2]·[(Fin)2] as a phosphorescent probe

Fluorescein (HFin) emitted strong and stable room temperature phosphorescence (RTP) on filter paper after set at 50 °C for 10 min using Li⁺ as the ion perturber. HFin existed as Fin⁻ when the pH value was in the range of 5.45–7.36. Fin⁻ could react with [Cu(BPY)₂]²⁺ (BPY: α,α-bipyridyl) to produce ion association complex [Cu(BPY)₂]²⁺·[(Fin)₂]²⁻, which could enhance the RTP signal of Hfin. In the presence of bovine serum albumin (BSA), the –COOH group of Fin⁻ in the [Cu(BPY)₂]²⁺·[(Fin)₂]²⁻ could react with the –NH₂ group of BSA to form the ion association complex [Cu(BPY)₂]²⁺·[(Fin-BSA)₂]²⁻, which contained –CO–NH– bond. This complex could sharply enhance the RTP signal of Hfin and the ΔI_p was directly proportional to the content of BSA. According to the facts above, a new solid substrate-room temperature phosphorimetry (SS-RTP) for the determination of trace protein had been established using the ion association complex [Cu(BPY)₂]²⁺·[(Fin)₂]²⁻as a phosphorescent probe. This method had wide linear range (0.40 × 10⁻⁹–280 × 10⁻⁹ mg l⁻¹), high sensitivity (the detection limit (LD) was 1.4 × 10⁻¹⁰ mg l⁻¹), good precision (RSD: 3.4–4.9%) and high selectivity (the allowed concentration of coexistent ions or coexistent materials was high). It had been applied to the determination of the content of protein in 10 kinds of real samples, and the result agreed well with pyrocatechol violet-Mo (VI) method (P.V.M.M.), which indicated it had high accuracy. Meanwhile, reaction mechanism for the determination of trace protein with [Cu(BPY)₂]²⁺·[(Fin)₂]²⁻ phosphorescent probe was also discussed. The academic thought of this research could not only be used to develop many kinds of ion association complex phosphorescent probes, but also provided a new way to promote the sensitivity of SS-RTP.     

A fiber-optic evanescent wave sensor for dissolved oxygen detection based on novel hybrid fluorinated xerogels immobilized with [Ru(bpy)3]2+

We have prepared a novel fiber-optic evanescent wave sensor (FEWS) for dissolved oxygen (DO) detection. The sensor fabrication was based on coating a decladded portion of an optical fiber with a microporous coating, which was prepared from 3,3,3-trifluoropropyltrimethoxysilane and n-propyltrimethoxysilane. The fluorophores were immobilized in the porous coating and excited by the evanescent wave field produced on the core surface of the optical fiber. The sensitivity of the sensor was quantified by the ratio of the fluorescence intensities in pure deoxygenated (I ₀) and in pure oxygenated environments (I). Results show that the quenching response of DO is increased with the enhancement of the coating surface hydrophobicity using the presented hybrid fluorinated ORMOSILs. The calibration curve of I ₀/I to [O₂] is linear from 0 to 40 ppm and the detection limit is 0.05 ppm (3σ) with a short response time of 15 s for DO detection. Figure       

Spectroscopic and photoelectrochemical differences between racemic and enantiomeric [Ru(phen)3] ions intercalated into layered niobate K4Nb6O17

Chirality effects have been observed in the intercalation, spectroscopic and photoelectrochemical behavior when enantiomeric and racemic [Ru(phen)₃]²⁺ complexes were intercalated in the interlayer spaces of K₄Nb₆O₁₇. The results were interpreted in terms of a [Nb₆O₁₇]⁴⁻-chelate and chelate–chelate interactions. The faster luminescence decay and higher photocurrent of the enantiomeric [Ru(phen)₃]²⁺–K₄Nb₆O₁₇ compounds than the racemic ones suggest that the emission of adsorbed [Ru(phen)₃]²⁺ ions was not only quenched by adsorbed complexes (or concentration quenching) but also by the semiconductive host lattices.