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.     

Drug selective poly(vinyl chloride)-based sensor of desipramine hydrochloride

The novel ion-pair ([TPB]⁻ [DH]⁺) of the quaternary ammonium drug desipramine hydrochloride, 3-(5,6-dihydrobenzo[b][1]benzazepin-11-yl)-N-methylpropan-1-amine, has been synthesized and incorporated into a poly(vinyl chloride)-based membrane sensor for the quantification of desipramine hydrochloride in different pharmaceutical preparations. The influence of the membrane composition on the potentiometric responses of the membrane sensor has been found to substantially improve the performance characteristics. The best performance was reported with membranes having the composition (in mg) of ([TPB]⁻ [DH]⁺) (5): PVC (150): o-NPOE (150). The proposed sensor (sensor no. 4) exhibits a Nernstian response in the concentration range of 2.2 × 10⁻⁶ to 1.0 × 10⁻² M with a detection limit of 1.2 × 10⁻⁶ M. The membrane sensor performs satisfactorily over the pH range of 2.8-7.4 with a fast response time of 12 s. The sensor no. 4 can tolerate a non-aqueous content of up to 20% and can be utilized for the determination of drug concentration in pharmaceutical preparation (tablets) and in body fluids such as urine and blood samples. The results were comparatively evaluated with liquid chromatography (LC). It was observed that the concentration of drug was greater in the blood sample than in the urine sample, as most of the drug is metabolized in the liver before discharge to urine.     

Direct determination of aluminium in foods and pharmaceutical preparations by potentiometry using an AlMCM-41 modified polymeric membrane sensor

A potentiometric aluminium sensor, based on the use AlMCM-41 as a neutral carrier, in poly(vinyl chloride) (PVC) matrix, is reported. The sensor exhibits significantly enhanced selectivity toward Al³⁺ ions over the concentration range 1.0 × 10⁻⁷ to 1.0 × 10⁻¹ M with a detection limit of 8.6 × 10⁻⁸ M and a Nernstian slope of 19.5 ± 0.4 mV/decade of activity. The best performance was obtained with membrane composition 30% poly(vinyl chloride), 67% acetophenone, 3% ionophore and 2 mL tetrahydrofuran. Fast and stable response, good reproducibility and long-term stability are demonstrated. The response time of the sensor is ∼10 s and membrane could be used over a period of 3 months without any considerable divergence in potentials. Selectivity coefficients were determined by matched potential method (MPM). The AlMCM-41-based sensor is suitable for use in aqueous solution of pH 3-6. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. It was used to determine Al³⁺ in drugs and food products.     

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.     

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.     

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.     

A novel potentiometric sensor for promethazine based on a molecularly imprinted polymer (MIP): The role of MIP structure on the sensor performance

A novel potentiometric sensor based on a molecularly imprinted polymer (MIP) for determination of promethazine (PMZ) was prepared. Promethazine MIP particles were prepared and dispersed in 2-nitrophenyloctyl ether and then embedded in a polyvinyl chloride matrix. The effect of the monomers type on the sensor performance was investigated, and an important role for this parameter was shown. It was shown that the membrane electrode with a MIP prepared by vinylbenzene and divinylbenzene had a better performance in comparison to membrane electrodes containing MIPs prepared with methacrylic acid-ethylene glycol dimethacrylate or vinylbenzene-ethylene glycol dimethacrylate. After optimization, the membrane electrode constructed with a MIP of vinylbenzene-divinylbenzene exhibited a Nernstian response (31.2 ± 1.0 mV decade⁻¹) over a wide concentration range, from 5.0 × 10⁻⁷ to 1.0 × 10⁻¹ M, with a low detection limit of 1.0 × 10⁻⁷ M and a response time of ∼50 s. The method has the requisite accuracy, sensitivity and precision to assay PMZ in syrup samples and biological fluids.     

Anion recognition using newly synthesized hydrogen bonding diamide receptors: PVC based sensors for carbonate

Novel hydrogen bonding diamide receptors viz., N,N^I-bis(phenyl)iso phthalohydrazide (I) and N,N^I-bis(2,4-dinitrophenyl)isophthalohydrazide (II), have been synthesized and characterized by IR, ¹H NMR and elemental analysis. Spectroscopic investigations indicate high affinity of these receptors for carbonate ion. Polyvinyl chloride (PVC) based membranes of (I) and (II) using tridodecylmethylammonium chloride (TDDMACl) as cation discriminator and diethylphthalate (DEP), dioctylphthalate (DOP), 1-chloronapthalene (CN), tris(2-ethylhexyl)phosphate (TEHP) and bis(2-ethylhexyl)sebacate (DOS) as plasticizing solvent mediators were prepared and investigated as CO₃²⁻ selective sensors. The best performance was shown by the membrane of composition (w/w) of (II) (4%):PVC (33%):CN (60%):TDDMACl (3%). This sensor works well over a wide concentration range 1.3 × 10⁻⁷ to 1.0 × 10⁻³ M with Nernstian compliance (29.0 mV decade⁻¹ of activity) at pH 8.6 with a fast response time of ∼7 s and showed good selectivity for carbonate over a number of anions. The sensor exhibits adequate shelf life (two and half months) with good reproducibility (S.D. ± 0.3 mV) and could be used successfully for the determination of total inorganic carbon in water samples.     

Fabrication of novel coated graphite electrodes for the selective nano-level determination of Cd ions in biological and environmental samples

Novel cadmium selective coated graphite electrodes were prepared using three different ionophores N¹, N²-dicyanoethyl-N¹, N²-bis(pyridin-2-ylmethyl)benzene-1, 2-diamine [L₁], N¹, N²-dicyanoethyl-N¹, N²-bis(thiophen-2-ylmethyl) benzene-1, 2-diamine [L₂] and N¹, N²-dicyanoethyl-N¹, N²-bis(furan-2-ylmethyl)benzene-1, 2-diamine [L₃], and their potentiometric characteristics were determined. Membranes having different compositions of poly(vinylchloride) (PVC), the plasticizer o-nitrophenyloctylether (o-NPOE), sodium tetraphenylborate (NaTPB) as an anionic additive and ionophores were coated onto the graphite surface. The potential response measurements showed that the best performance was exhibited by the electrodes with membranes having the composition L₁: o-NPOE:NaTPB:PVC as 4:51:2.5:42.5 (wt.%), L₂: o-NPOE:NaTPB:PVC as 3:52.5:1.5:43 (wt.%) and L₃: o-NPOE:NaTPB:PVC as 7:49:3.5:40.5 (wt.%). These electrodes had the widest working concentration range, Nernstian slope and fast response times of 12 s, 7 s and 17 s for L₁, L₂ and L₃, respectively. The selectivity studies showed that these electrodes have higher selectivity towards Cd²⁺ over a large number of cations and could tolerate up to 20 vol.% non-aqueous impurities. Furthermore, the electrodes generated constant potentials in the pH range 2.0–8.0, with a shelf life of approximately four to six weeks. The high selectivity of these electrodes permits their use in the detection of the Cd²⁺ content in some medicinal plants, soil and industrial wastewater samples. The electrodes could also be used as an indicator electrode in the potentiometric titration of Cd²⁺ with EDTA.     

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.     

The ultrasonic electropolymerization of an 5-[o-(4-bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) film electrode and its electrocatalytic properties to dopamine oxidation in aqueous solution

5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H₂SO₄ between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s⁻¹. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L⁻¹ phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10⁻⁷ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹. The electrode had a detection limit of 6.0 × 10⁻⁸ mol L⁻¹(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s⁻¹, the transfer coefficient α = 0.709, the electron number involved in the rate determining step n_α = 0.952, and the diffusion coefficient D_o = 3.54  10⁻⁵ cm² s⁻¹ were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.     

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.     

Study of the potentiometric response of the doped spinel Li1.05Al0.02Mn1.98O4 for the optimization of a selective lithium ion sensor

In this paper, we studied the development of a selective lithium ion sensor constituted of a carbon paste electrode modified (CPEM) with an aluminum-doped spinel-type manganese oxide (Li_1.05Al_0.02Mn_1.98O₄) for investigating the influence of a doping ion in the sensor response. Experimental parameters, such as influence of the lithium concentration in the activation of the sensor by cyclic voltammetry, pH of the carrier solution and selectivity for Li⁺ against other alkali and alkaline-earth ions were investigated. The sensor response to lithium ions was linear in the concentration range 5.62 × 10⁻⁵ to 1.62 × 10⁻³ mol L⁻¹ with a slope 100.1 mV/decade over a wide pH 10 (Tris buffer) and detection limit of 2.75 × 10⁻⁵ mol L⁻¹, without interference of other alkali and alkaline-earth metals, demonstrating that the Al³⁺ doping increases the structure stability and improves the potentiometric response and sensitivity of the sensor. The super-Nernstian response of the sensor in pH 10 can be explained by mixed potential arising from two equilibria (redox and ion-exchange) in the spinel-type manganese oxide.     

Preparation and characterization of thiocyanate-selective electrodes based on new complexes of copper(II) as neutral carriers

The complexes of hydroxycitronellal (o-aminobenzoic acid) copper(II) (Cu(II)-HXAB) and salicylaldehyde (o-aminobenzoic acid) copper(II) (Cu(II)-SHAB) were used as neutral carriers in PVC-based membrane ion-selective electrodes. The electrode based on Cu(II)-HXAB exhibited near-Nernstian potential response to thiocyanate (SCN⁻) in a linear range of 1.0 × 10^− 6 to 1.0 × 10^− 1 M with a detection limit of 8.5 × 10^− 7 M and a slope of − 57.3 mV/decade in 0.01 M phosphate buffer solution (pH 5.0). The electrode exhibited high selectivity to SCN⁻ over other tested anions with an anti-Hofmeister selectivity sequence. The selectivity behavior might be discussed in terms of UV-Vis spectrum and infrared spectrum. The transfer process of thiocyanate across the membrane interface was investigated by making use of the AC impedance technique. The electrode containing Cu(II)-HXAB could be applied to thiocyanate analysis in waste water with satisfactory results.     

PVC-based membranes of dicyclohexano-24-crown-8 as Cd(II) selective sensor

Membranes of dicyclohexano-24-crown-8 (I) as an ion-selective compound in poly(vinyl chloride) (PVC) based matrix have been tried for cadmium(II)-selective sensors. The effect of anion excluder, sodiumtetraphenylborate (NaTPB) and plasticizers dibutylphthalate (DBP), dioctylphthalate (DOP), di(butyl)butylphosphonate (DBBP), 1-chloronaphthalene (CN), tri-butylphosphate (TBP) and tris-(2-ethyl hexyl)phosphate (TEHP) on the performance of the membrane sensor has also been studied. It was observed that the membrane having the composition I: NaTPB:DBBP:PVC in the ratio 10:1:100:100 exhibited the best performance with a wide working concentration range of 3.0 × 10⁻⁵ to 1.0 × 10⁻¹ M, a Nernstian slope of 30.0 ± 1.0 mV/decade of activity, and with a response time of 23 s. It was found selective to cadmium ions over a number of mono-, bi- and trivalent cations. The sensor works satisfactorily in the pH range of 2.0-5.4 and can successfully determine cadmium ions in partially non-aqueous medium having up to 40% (v/v) non-aqueous content. The sensor could be used as an indicator electrode in the titration of Cd²⁺ ions with EDTA.     

Electrochemical characterization of cetyltrimethyl ammonium bromide modified carbon paste electrode and the application in the immobilization of DNA

A cetyltrimethyl ammonium bromide modified carbon paste electrode (CTAB/CPE) was developed in this work based on the surface modification method. The improved electrochemical response of K₄Fe(CN)₆ at this electrode indicated that CTAB could change the surface property of carbon paste electrodes (CPEs), which was demonstrated by the electrochemical impedance spectroscopy (EIS). In 0.1 mM [Fe(CN)₆]^3−/4−, a low exchange current (i₀) of 2.72×10⁻⁷ A at bare CPE was observed while that at CTAB/CPE was 6.79×10⁻⁵ A. The effect of CTAB concentration on the electrode quality revealed that CTAB formed a compact monolayer on the electrode surface with high density of positive charges directed outside the electrode. This electrode showed strong accumulation ability toward Fe(CN)₆⁴⁻ and can also accumulate Co(phen)₃²⁺ by the adsorption of the organic ligands in the hydrophobic area of the monolayer. The electrode was applied to the immobilization of DNA, which was characterized by the isotherm adsorption of Co(phen)₃²⁺.     

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.     

Microfabrication, characterization and analytical application of a new thin-film silver microsensor

The present research demonstrates the microfabrication of a novel thin-film silver microelectrode based on an ion-selective PVC organic membrane. First, the gold substrate thin-film surface is treated by depositing a thin-layer of Ag electrochemically. This pretreatment step is followed by applying the organic-membrane-sensitive layer using a new nebulization technique, which gives a high stability to the organic-membrane-sensitive layer. The performance of the resulting thin-film silver microelectrode is investigated by potentiometric measurements. The microelectrode provides a linear Nernstian response of high sensitivity (58 ± 0.5 mV/decade) covering the range of 1 × 10⁻⁶-1 × 10⁻¹ mol L⁻¹ of Ag⁺ ions with a fast response time (<20 s) and a relatively long life span (>3 months). The suggested microelectrode is successfully used in the analytical evaluation of Cl⁻ ions in some real environmental samples as well as in the simultaneous determination of halides using potentiometric titration. The results obtained are compared with those obtained by the commercial silver billet electrode and the conventional bulk ion-selective electrode based on the same ionophore.     

Electrochemical tolazoline sensor based on gold nanoparticles and imprinted poly-o-aminothiophenol film

Amperometric detection of tolazoline (TL) was carried out on a gold nanoparticles (AuNPs)/poly-o-aminothiophenol (PoAT)-modified electrode by a molecular imprinting technique and electropolymerization method. The modification procedure was characterized via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The recognition between the imprinted sensor and target molecule was observed by measuring the variation of amperometric response of the oxidation-reduction probe, K₃Fe(CN)₆ on electrode. Under the optimal experimental conditions, the peak currents were proportional to the concentrations of tolazoline in two ranges of 0.05-5.0 μg mL⁻¹ and 5.0-240 μg mL⁻¹ with the detection limit of 0.016 μg mL⁻¹. Meanwhile the prepared sensor showed sensitive and selective binding sites for tolazoline. The enhancement of sensitivity was attributed to the presence of AuNPs which decreased the electron-transfer impedance.     

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.