Ortho-nitrophenyloctyl Ether Research Articles

Screen-printed sensors for efficient potentiometric analysis of tolperisone hydrochloride in presence of its co-formulated drugs

Researchers seeking for green chemistry to help safeguard and boost the economy and the environment by discovering unique ways to decrease waste and find substitutes for dangerous chemicals. In this study, a green potentiometric ion-selective electrode (ISE) was developed for measurement of tolperisone HCl (TOLP) in bulk and Pharmaceutical dosage forms in presence of diclofenac sodium and paracetamol as co-formulated drugs. This paper presents the manufacture and characterization of a disposable potentiometric ion-selective strip with an enhanced detection limit for (TOLP) measurement in its tablet dosage form either alone or in presence of the co-formulated drugs. Numerous ion pairs (IPs), such as TOLP-tetraphenylborate (TOLP-TPB), TOLP-phosphotungstic acid (TOLP-PTA), and TOLP-ammonium Reinecke (TOLP- RKT) are tested in presence of different plasticizers. The optimal potentiometric response with a near Nernstian slope of 55.949 mV/decade was achieved within a linear concentration range of 5 times 10–5 − 1 times 10–2 M using (PTA) and ortho nitrophenyl octyl ether (o-NPOE) as a plasticizer. The effect of the nanoparticles on the membrane stability was studied using the graphene nanoplatelets which have an effective role in the enhancement of some constructed sensors stability. Finally, the developed technique is validated for the estimation of TOLP with high accuracy and precision.Graphical

A Clotrimazole-Selective Electrode and its Application to Pharmaceutical Analysis

The effect of measurement conditions and the nature of the plasticizer of an ion-selective electrode membrane (ortho-nitrophenyloctyl ether, dinonyl adipate, dibutyl phthalate) on the main performance characteristics of clotrimazole-selective electrodes with polyvinyl chloride ion-exchange membranes containing potassium tetrakis(4-chlorophenyl)borate as an ion exchanger was studied. The introduction of small (up to 20%) ethanol additives into the aqueous solution leads to a significant improvement of the potential stability and expands the working range of the electrodes. All of the studied electrodes have high selectivity to clotrimazole with respect to both inorganic and organic cations, slope of the electrode function close to the theoretical value, and low limits of detection (5.0 × 10–8–7.5 × 10–8 M). An electrode with a membrane plasticized with ortho-nitrophenyloctyl ether was the best for the combination of characteristics. It was demonstrated that clotrimazole can be determined in model solutions and various dosage forms (spray, cream, suppositories, tablets) using direct potentiometry and potentiometric titration with sodium tetraphenylborate. The proposed procedures are rapid (10–15 min) and characterized by excellent reproducibility (the relative standard deviation does not exceed 1.2%).

Ionophore Properties of Schiff Base Compounds as Ion Sensing Molecules for Fabricating Cu(II) Ion-Selective Electrodes

Bis(2-hydroxybenzaldehyde)-1,2-diaminoethane (LI), bis(2-hydroxybenzaldehyde)-1,3-diaminopropane (LII) and bis(2-hydroxybenzaldehyde)-4,4'-methylendianiline (LIII) were examined as ionophores for fabrication of polyvinylchloride (PVC) membrane Cu(II) ion-selective potentiometric sensors. The optimum composition (%) for the sensors was: 5 LI, 30 PVC, 6 sodium tetraphenylborate (NaTPB), 59 ortho-nitrophenyloctyl ether (NPOE); 4 LII, 30 PVC, 5 NaTPB, 61 dibutyl phthalate; 6 LIII, 30 PVC, 5 NaTPB, 59 NPOE. The linear response range of the electrodes was 5 × 10–4–0.05 (LI), 5 × 10–4–0.1 (LII) and 1 × 10–6–0.01 M (LIII), and the corresponding detection limits were 4 × 10–4, 4 × 10–4 and 2 × 10–7 M, respectively. The sensors were showed rapid response time (≈10 s). Their responses were independent on pH in the range 2.5–5.0 (LI), 3.2–4.7 (LII) and 4.0–5.0 (LIII). The selectivity of the prepared electrodes towards copper ions over some mono-, di- and trivalent metal ions was evaluated. The sensors were used as indicator electrode in potentiometric titration of copper ions in aqueous solutions.

Phenoxy-substituted boron subphthalocyanine as a ionophore of ion-selective electrodes

Phenoxy-substituted boron subphthalocyanine was synthesized and studied as an ionophore of plasticized polyvinyl chloride membranes of ion-selective electrodes. The electrodes exhibit reversible response to dobutamine, demonstrating the cation function, as well as reversible response to the salicylate anion. The effects of concentration of the ionophore (0.2–5 wt %) and ionic components (sodium tetraphenylborate, TPhBNa, and tributylhexadecylphosphonium bromide, TBGDPBr), including ionic liquids (ILs), such as diphenylbutylethylphosphonium bis(triflyl)imide, diphenylbutylethylphosphonium hexafluorophosphate, and 1,3-dihexadecylimidazolium chloride, as well as plasticizers, such as ortho-nitrophenyloctyl ether and diethyl sebacate, on the electrochemical characteristics of membranes were studied. For the electrode containing 2% of the phenoxy-substituted boron subphthalocyanine in dobutamine and salicylate solutions, the slopes of the electrode function were 36 ± 1 mV/dec and–46 ± 3 mV/dec and the limits of detection (LODs) were 4 × 10–5 M and 3 × 10–4 M, respectively. The addition of an ionic liquid containing the diphenylbutylethylphosphonium cation and the bis(triflyl)imide and hexaflurophosphate anions to the membrane composition had no effect on the response of membrane electrodes to both dobutamine and salicylate. The use of phenoxy-substituted boron subphthalocyanine in an amount of 2% and the TPhBNa additive significantly improved sensor characteristics: the slope of the electrode function (S) for the dobutamine-selective electrode was (54 ± 1) mV/dec and LOD was 1 × 10–5 M. Dobutamine can be determined in the presence of dopamine, adrenalin, and glucose. Electrodes based on 2% phenoxy-substituted boron subphthalocyanine and 0.5% (C16H33)2ImCl, or TBGDPBr in salicylate solutions demonstrate the slope of the electrode function close to the theoretical one and a low limit of detection: S = (–59 ± 1) mV/dec, LOD = 2 × 10–5 M and S = (–57 ± 1) mV/dec, LOD = 4 × 10–5 M, respectively. The anti-Hofmeister selectivity of sensors was observed. The electrode based on phenoxy-substituted boron subphthalocyanine and (C16H33)2ImCl was used for the assay of acetylsalicylic acid in the drug Cardiomagnyl.

New Electrochemically-Modified Carbon Paste Inclusion β-Cyclodextrin and Carbon Nanotubes Sensors for Quantification of Dorzolamide Hydrochloride.

The present article introduces a new approach to fabricate carbon paste sensors, including carbon paste, modified carbon paste inclusion β-cyclodextrin, and carbon nanotubes for the quantification of dorzolamide hydrochloride (DRZ). This study is mainly based on the construction of three different carbon paste sensors by the incorporation of DRZ with phosphotungstic acid (PTA) to form dorzolamide-phosphotungstate (DRZ-PT) as an electroactive material in the presence of the solvent mediator ortho-nitrophenyloctyl ether (o-NPOE). The fabricated conventional carbon paste sensor (sensor I), as well as the other modified carbon paste sensors using β-cyclodextrin (sensor II) and carbon nanotubes (sensor III), have been investigated. The sensors displayed Nernstian responses of 55.4 ± 0.6, 56.4 ± 0.4 and 58.1 ± 0.2 mV·decade−1 over concentration ranges of 1.0 × 10−5–1.0 × 10−2, 1.0 × 10−6–1.0 × 10−2, and 5.0 × 10−8–1.0 × 10−2 mol·L−1 with lower detection limits of 5.0 × 10−6, 5.0 × 10−7, and 2.5 × 10−9 mol·L−1 for sensors I, II, and III, respectively. The critical performance of the developed sensors was checked with respect to the effect of various parameters, including pH, selectivity, response time, linear concentration relationship, lifespan, etc. Method validation was applied according to the international conference on harmonisation of technical requirements for registration of pharmaceuticals for human use ICH guidelines. The developed sensors were employed for the determination of DRZ in its bulk and dosage forms, as well as bio-samples. The observed data were statistically analyzed and compared with those obtained from other published methods.

Novel Ionophore for Aluminum Ion Sensors: Synthesis and Analytical Characterization

A new and rapid potentiometric method to quantify aluminum ions concentration was developed. The method involves the development of an aluminum ion sensor with a membrane consists of diethyl (2-azobenzoic acid) malonate (DAM) as a novel ionophore in poly (vinyl chloride) matrix membrane plasticized with orthonitrophenyl-octyl ether or dioctylphthalate. The structure of the synthesized ionophore (DAM) was identified using Fourier transform infrared, 1H Nuclear magnetic resonance, and elemental analysis. The proposed electrode reveals a Nernstian response over Al3+ ion in a concentration range $1\times 10^{\mathrm {-7}}$ – $1\times 10^{\mathrm {-2}}$ mol $\text{L}^{\mathrm {-1}}$ with the cationic slopes of 19.6 ± 0.3 and 19.3 ± 0.2 mV decade $^{\mathrm {-1}}$ , and the limits of detection $5 \times 10^{\mathrm {-8}}$ and $7 \times 10^{\mathrm {-8}}$ mol $\text{L}^{\mathrm {-1}}$ aluminum(III) for orthonitrophenyl-octyl ether and dioctylphthalate-based membrane sensors, respectively. The electrodes showed good discrimination toward Al3+ ion in the presence of the most common cations. The electrodes show response in a short time (10 s) for the entire concentration range and used for 11 weeks without significant variation in potentials. To evaluate the application of the investigated electrodes was used to determine Al3+ ion at different collected samples from environmental sources. In addition, these sensors have been used as indicator electrodes in the potentiometric titration of Al3+ ion against Ethylenediaminetetraacetic acid.

Ion selective electrode for uranium based on composite multiwalled carbon nanotube-benzo-15-crown-5 in PVC matrix coated on graphite rod

Development of a composite multiwalled carbon nanotube (MWNT) polyvinyl chloride (PVC) with benzo-15-crown-5 (B15C5) as ionophore sensor responsive to uranyl ion is described. The composite MWNT-PVC membrane containing the active ingredients was casted on the surface of a graphite rod. The sensor incorporates B15C5 as electroactive material, ortho-nitrophenyl octyl ether (o-NPOE) as a plasticizer and sodium tetraphenyl borate (NaTPB) as an ion discriminator. The sensor displays a rapid and linear response over the concentration range of 1 × 10−1 to 1 × 10−7 M with a slope of 29.9 ± 0.4 mV per decade. The detection limit of this electrode was found to be 5.4 × 10−8 M and the working pH range is from 2.5 to 4.5. Interference from many inorganic cations viz. Na+, K+, Sr2+, Zn2+ and Fe3+ is negligible for the sensor. Application to the determination of uranium in ores and effluent samples gives results with good correlation which are comparable with data obtained by inductively coupled plasma atomic emission spectrometry. The electrode has been characterized using surface techniques.

A solid-contact ion selective electrode for copper(II) using a succinimide derivative as ionophore.

All-solid-state sensors with polyvinyl chloride (PVC)-based membranes using off-the-shelf N-hydroxysuccinimide (NHS) and succinimide (Succ) ionophores were prepared using DOP (dioctyl phthalate) and NPOE (ortho-nitrophenyloctyl ether) as plasticizers. Good responses were obtained when NHS was used. The potentiometric response of the proposed electrode is independent of pH over the range 2–6. The electrode shows a fast response time of 0.25 s. The electrode exhibits a Super-Nernstian response, with 37.5 mV/decade, with a potentiometric detection limit of 4.4 μM. The proposed sensor revealed good selectivity towards a group of transition metal ions.

Construction of Promethazine Hydrochloride Selective Electrodes in A Pvc Matrix Membrane

Promethazine hydrochloride selective electrodes were constructed based on promethazine Molybdophosphoric acid ion pair. Promethazine hydrochloride electrodes (1, 2, 3, 4 and 5) using these plasticizers Di-butyl phthalate (DBPH); Di-octyl phthalate (DOP); Di-butyl phosphate (DBP); Tri-butyl phosphate (TBP); ortho-nitro phenyl octyl ether (ONPOE) in PVC matrix respectively. These electrodes give slopes (57.27, 54.08, 49.79, 46.76 and 44.52 mV/decade) and give linear ranges from (1×10 -5 -1×10 -1 , 1 ×10 -4 -1×10 -1 , 1 ×10 -5 - 1×10 -1 , 5 ×10 -4 -1×10 -1 and 1 ×10 -4 -1×10 -1 M) respectively. The best detection limit was 6 × 10 − 6 M for the electrode based on DBPH. The measurement interferences in the presence of (Na + , K + , Mn +2 , Cu +2 , Ca +2 , Fe +3 , Al +3 , Paracetamol, sucrose and Galaten) were studied using separate and mixed methods for selectivity coefficient determination. The pH and life time of the electrodes were also studied. The results were compared with UV-spectrophotometer technique by using F-test.

Graphite Disk Lanthanum(III)-Selective Electrode Based on Benzo-15-crown-5

In this study, construction of a new lanthanum selective disk electrode based on benzo-15-crown-5 (B15C5) as a neutral carrier has been described. The electrode has been composed of 2.5 mg of Benzo-15-crown5 as an ionophore, 7 mg of oleic acid (OA) as an additive, 60.5 mg of ortho-nitrophenyloctyl ether (NPOE) as a plasticizer, and 30 mg of polyvinyl chloride (PVC) as the membrane supporting matrix. The electrode shows a linear dynamic response in the concentration range of 5 × 10−7 to 1 × 10−2 M with a Nernstian slope of 19.5 mV per decade and a detection limit of 8.74 × 10−7 M. It has a response time of <15 s and can be used for at least 5 months without any significant divergence in potentials. The selectivity coefficients for mono, di, and trivalent cations indicate a good selectivity for La(III) ions over a large number of interfering cations. It could be used in a pH range of 3.0−6.0. The proposed electrode was applied as an indicator electrode in potentiometric titration of fluoride ion and also used for determination of F− ion in mouthwash solution, tap water and toothpaste samples.

A selective optical sensor for beryllium determination based on incorporating of 1,8-dihydroxyanthrone in a poly (vinyl chloride) membrane

A new optical sensor was fabricated for determination of beryllium ions. The optode membrane was prepared by incorporation of 1,8-dihydroxyanthrone and sodium tetraphenylborate (NaTPB) in a plasticized poly (vinyl chloride) membrane containing ortho-nitrophenyl octyl ether (o-NPOE) as a plasticizer. Color of the sensing membrane in contact with Be 2+ ions at pH 10.5, was changed from orange to red. The different variables affecting uptake efficiency were evaluated and optimized. Under the optimum conditions (i.e. 28.0% PVC, 60.0% o-NPOE, 8.0% 1,8-dihydroxyanthrone, 4.0% NaTPB and response time of 6 min), the proposed sensor displayed a linear range of 0.1–5 μg mL −1 with a detection limit of 0.03 μg mL −1. Also the precision (RSD%) was better than 2.9% for 7 replicate determinations of 1 μg mL −1 Be in various membranes. The selectivity of the probe was studied for some cations and anions. Experimental results showed that the sensor was high selective in the presence of ethylenediaminetetraacetic acid (EDTA) as a masking agent and could be used as an effective tool in analyzing the beryllium content of water samples.

Study on the mechanism of potential response of a ketamine‐sensitive membrane electrode

The response mechanism of a simple device for the rapid detection of ketamine with 'in the field' capabilities is investigated. The mechanism is a membranous ketamine ionic selective electrode (ISE) with partly carboxylated PVC as matrix and ortho-nitrophenyloctyl ether (o-NPOE) as plasticizer. The experimental results reveal that the inclusion of the plasticizer in the membrane significantly increased the response. A mechanism is proposed where the infiltration of a target species into the membrane is capable of producing a superior response. This response process is non-selective for species with similar molecular structure and size. This new research addresses some omissions and misapprehension in the literature where the mechanism was reported as an ion-exchange-induced response. In this research the ion-exchange-induced response was measurable after the elimination of the infiltration-induced response extending to lower concentration ranges and thus providing the potential for better sensitivity and selectivity.

Development of a selective optical sensor for Cr(VI) monitoring in polluted waters

An optical sensor is described for the sensitive and selective determination of the Cr(VI) ion in aqueous solutions. The optode membrane is prepared by incorporating Aliquat 336 as an ionophore and a chromoionophore (4′,5′-dibromofluorescein octadecyl ester) in a poly(vinyl chloride) (PVC) membrane containing ortho-nitrophenyloctyl ether ( o-NPOE) as a plasticizer. The response to Cr(VI) is indicated by co-extraction of the target species and of hydrogen ions into the bulk of the membrane yielding large absorbance changes which can easily be measured in the visible spectral range. The optode membrane shows a reversible response in the concentration range of 1.1 × 10 −5–1.0 × 10 −3 M and has been shown to be more selective towards the HCr O 4 − ion than other anions with a selectivity pattern HCrO 4 − > SCN − ≈ ClO 4 − > NO 3 − ≈ I − ≈ NO 2 − ≫ H 2PO 4 − ≈ Cl − ≈ SO 4 2−. The sensing method developed has successfully been applied to the determination of Cr(VI) in spiked river water as well as in electroplating rinse waters.

Stability Indicating Electrochemical Methods for the Determination of Meclophenoxate Hydrochloride and Pyritinol Dihydrochloride Using Ion-Selective Membrane Electrodes

The construction and electrochemical response characteristics of polyvinyl chloride (PVC) membrane sensors for the determination of meclophenoxate hydrochloride (I) and pyritinol dihydrochloride (II) in presence of their degradation products are described. The sensors are based on the use of the ion-association complexes of (I) and (II) cation with sodium tetraphenyl borate and ammonium reineckate counteranions as ion-exchange sites in the PVC matrix. In addition beta-cyclodextrin (beta-CD) membranes were used in the determination of I and II. These ion pairs and beta-CD were then incorporated as electroactive species with ortho nitrophenyl octyl ether (oNPOE) as a plasticizer. Three PVC sensors were fabricated for each drug, i.e. meclophenoxate tetraphenyl borate (meclo-TPB), meclophenoxate reineckate (meclo-RNC) and meclophenoxate beta-cyclodextrin (meclo-beta-CD), and the same was done for pyritinol (pyrit-TPB), (pyrit-RNC) and (pyrit-beta-CD). They showed near Nernestian responses for meclophenoxate over the concentration range 10(-5)-10(-2) with slopes of 52.73, 51.64 and 54.05 per concentration decade with average recoveries of 99.92+/-1.077, 99.96+/-0.502 and 100.03+/-0.763 for meclo-TPB, meclo-RNC and meclo-beta-CD respectively. Pyritinol also showed near Nernestian responses over the concentration range of 3.162 x 10(-6) - 3.162 x 10(-4) for pyrit-TPB and pyrit-RNC, and 10(-6) - 3.162 x 10(-4) for pyrit-beta-CD with slopes of 30.60, 31.10 and 32.89 per concentration decade and average recoveries of 99.99+/-0.827, 100.00+/-0.775 and 99.99+/-0.680 for pyrit-TPB, pyrit-RNC and pyrit-beta-CD respectively. The sensors were used successfully for the determination of I and II in laboratory prepared mixtures with their degradation products, in pharmaceutical dosage forms and in plasma.

Sub-Micro Molar Monitoring of La3+ by a Novel Lanthanum PVC-Based Membrane Sensor Based on 3-Hydroxy-N'-(pyridin-2-ylmethylene)-2-naphthohydrazide

A La (III) ion-selective membrane sensor has been fabricated from poly vinyl chloride (PVC) matrix membrane, containing 3-hydroxy-N'-(pyridin-2-ylmethylene)-2-naphthohydrazide (HPMN) as a neutral carrier, potassium tetrakis (p-chlorophenyl) borate (KTpClPB) as an anionic excluder and ortho-nitrophenyloctyl ether (NPOE) as a plasticizing solvent mediator. The effects of membrane composition and pH as well as the influence of the anionic additive on the response properties were investigated. The sensor with 30% PVC, 62% solvent mediator, 6% ionophore and 2% anionic additive, shows the best potentiometric response characteristics. It displays a Nernstian behavior (19.2 mV per decade) across the range of M. The detection limit of the electrode is M (10 ng/mL) and the response time is 15 s from up to M and 30 s in the range of M. The sensor can be used in the pH values of 3.0-9.0 for about seven weeks. The membrane sensor was used as an indicator electrode in the potentiometric titration of lanthanum ions with EDTA. It was successfully applied to the lanthanum determination in some mouth wash preparations.

Highly selective single-use fluoride ion optical sensor based on aluminum(III)-salen complex in thin polymeric film

A highly selective optical sensor for fluoride ion based on the use of an aluminum(III)-salen complex as an ionophore within a thin polymeric film is described. The sensor is prepared by embedding the aluminum(III)-salen ionophore and a suitable lipophilic pH-sensitive indicator (ETH-7075) in a plasticized poly(vinyl chloride) (PVC) film. Optical response to fluoride occurs due to fluoride extraction into the polymer via formation of a strong complex with the aluminum(III)-salen species. Co-extraction of protons occurs simultaneously, with protonation of the indicator dye yielding the optical response at 529 nm. Films prepared using dioctylsebacate (DOS) are shown to exhibit better response (e.g., linear range, detection limit, and optical signal stability) compared to those prepared using ortho-nitrophenyloctyl ether ( o-NPOE). Films formulated with aluminum(III)-salen and ETH-7075 indicator in 2 DOS:1 PVC, exhibit a significantly enhanced selectivity for fluoride over a wide range of lipophilic anions including salicylate, perchlorate, nitrate, and thiocyanate. The optimized films exhibit a sub-micromolar detection limit, using glycine-phosphate buffer, pH 3.00, as the test sample. The response times of the fluoride optical sensing films are in the range of 1–10 min depending on the fluoride ion concentration in the sample. The sensor exhibits very poor reversibility owing to a high co-extraction constant (log K = 8.5 ± 0.4), indicating that it can best be employed as a single-use transduction device. The utility of the aluminum(III)-salen based fluoride sensitive films as single-use sensors is demonstrated by casting polymeric films on the bottom of standard polypropylene microtiter plate wells (96 wells/plate). The modified microtiter plate optode format sensors exhibit response characteristics comparable to the classical optode films cast on quartz slides. The modified microtiter is utilized for the analysis of fluoride in diluted anti-cavity fluoride rinse samples and the results obtained are shown to correlate well with the analysis performed using the LaF 3 single crystal ion-selective electrode.

Optical determination of ionophore diffusion coefficients in plasticized poly(vinyl chloride) sensing films

The knowledge of accurate diffusion coefficients of electrically neutral ionophores in solvent polymeric membranes is important in view of understanding and optimizing important sensor characteristics of ion-selective electrodes (ISEs) and their corresponding optical sensors. A spectroscopic imaging technique is introduced here to determine the diffusion coefficient of the chromoionophore ( N, N-diethyl-5-(octadecanoylimino)-5 H-benzo[a]phenoxazine-9-amine, ETH 5294) in solvent polymeric membranes with different types of plasticizers and varying polymer–plasticizer ratio. This method is based on following the changes in the absorbance profiles of the chromoionophore as a function of space and time. The desired membrane composition is solvent cast onto a glass slide and placed under a microscope objective. The membrane is then exposed to light from a mercury arc lamp which photobleaches the dye in a circular area, providing an interface from which the time rate of absorbance change is studied. Spectral images are acquired over fixed time intervals with a microscope equipped with a charge-coupled device (CCD) camera providing 0.41 μm nominal resolution. Two plasticizers, ortho-nitrophenyl octyl ether ( o-NPOE) and bis(2-ethylhexyl) sebacate (DOS), are examined in poly(vinyl chloride) (PVC) by varying the ratio of polymer to plasticizer content and measuring the diffusion coefficient of the chromoionophore. Corresponding membrane compositions containing 10 wt.% of an inert lipophilic salt (ETH 500) are also examined. Near linear relationships between the logarithmic diffusion coefficients and the PVC content are observed that obey the following relationships: log D=−6.17 –0.0459 wt.% PVC (for PVC–DOS), log D=−6.46 –0.0468 wt.% PVC (for PVC–DOS–ETH 500), log D=−5.89 –0.0508 wt.% PVC (for PVC–NPOE), log D=−6.22 –0.0473 wt.% PVC (for PVC–NPOE–ETH 500).

Novel Nitrite Membrane Sensor Based on Cobalt(II) Salophen for Selective Monitoring of Nitrite Ions in Biological Samples

A novel PVC-based membrane sensor based on the Co(II)-salophen complex (CSC) is described. The electrode revealed a Nernstian response over a wide nitrite ion concentration range (1.0×10−6–1.0×10−1 M). The detection limit of the sensor is 8.0×10−7 M. The best performance was obtained with a membrane composition of 33% PVC, 61% ortho-nitrophenyloctyl ether, 3% cobalt(II)-salophen, and 3% hexadecyltrimethylammonium bromide. The potentiometric response of the sensor is independent of the pH of solution in the pH range 4.5–11.9. The electrode exhibits a very fast response time and good selectivity over a variety of common inorganic and organic anions, including fluoride, bromide, iodide, sulfite, nitrate, thiocyanate, thriiodide and perchlorate. The selectivity behavior of the proposed sensor shows substantial improvements compared to the previously reported electrodes for nitrite ion. The membrane sensor can be used for at least 2 months without any divergence in potential. The electrode was successfully applied to the monitoring of nitrite ion in water, sausage, flour, wheat, cheese and milk.

PVC-based dicyclohexano-18-crown-6 sensor for La(III) ions

A new ion-selective electrode (ISE) based on dicyclohexano-18-crown-6 (DC18C6) as a neutral carrier is developed for lanthanum(III) ions. The electrode comprises of dicyclohexano-18-crown-6 (6%), PVC (33%), and ortho-nitrophenyl octyl ether ( o-NPOE) (61%). The electrode shows a linear dynamic response in the concentration range of 10 −6 to 10 −1 M with a Nernstian slope of 19 mV per decade and a detection limit as 5×10 −7 M. It has a response time of <30 s and can be used for at least 5 months without any significant divergence in potentials. The selectivity coefficients for mono-, di-, and trivalent cations indicate good selectivity for La(III) ions over a large number of interfering cations. The sensor has been used as an indicator electrode in the potentiometric titrations of La(III) with EDTA. The membrane is successfully applied in partially non-aqueous medium. It can be used in the pH range 4–9.

Novel Beryllium Membrane Sensor Based on 2,4-Dinitrophenylhydrazinebenzo-9- crown -3 Coated Graphite

A novel sensor based on 2,4-dinitrophenylhydrazinebenzo-9-crown-3 (NPHC) for selective determination of ultra trace amount of beryllium is reported. The plasticized PVC membrane containing 30% PVC, 58% ortho-nitrophenyloctyl ether (NPOE), 3% sodium tetra phenyl borate (NaTPB) and 9% NPHC was directly coated on a graphite electrode works well over a wide range of concentration (1.0 × 10−1 to 4.0 × 10−7 M) with a Nernstian slope of 29.5 mV per decade. The electrode shows a fast response time of 10 s and operates in the pH range 3.0–9.0. The sensor can be used for more than five months without any divergence in the potential. The selectivity of the electrode was studied and it was found that the electrode exhibits very good selectivity for beryllium ion over alkali, alkaline earth, heavy, and transition metal ions. The beryllium ion-selective electrode was used as an indicator electrode for the potentiometric titration of beryllium ion in solution using a standard solution of EDTA, a sharp potential change occurs at the end-point. The applicability of the sensor to Be(II) ion measurement in water samples spiked with beryllium chloride is illustrated.