Hydrogen ion-selective poly(vinyl chloride) membrane electrode based on a p-tert-butylcalix[4]arene-oxacrown-4

Design and Characterization of Electrochemical Sensor for the Determination of Mercury(II) Ion in Real Samples Based upon a New Schiff Base Derivative as an Ionophore

The present paper provides a description of the design, characterization, and use of a Hg2+ selective electrode (Hg2+-SE) for the determination of Hg2+ at ultra-traces levels in a variety of real samples. The ionophore in the proposed electrode is a new Schiff base, namely 4-bromo-2-[(4-methoxyphenylimino)methyl]phenol (BMPMP). All factors affecting electrode response including polymeric membrane composition, concentration of internal solution, pH sample solution, and response time were optimized. The optimum response of our electrode was obtained with the following polymeric membrane composition (% w/w): PVC, 32; o-NPOE, 64.5; BMPMP, 2 and NaTPB, 1.5. The potentiometric response of Hg2+-SE towards Hg2+ ion was linear in the wide range of concentrations (9.33 × 10-8-3.98 × 10-3 molL-1), while, the limit of detection of the proposed electrode was 3.98 × 10-8 molL-1 (8.00 μg L-1). The Hg2+-SE responds quickly to Hg2+ ions as the response time of less than 10 s. On the other hand, the slope value obtained for the developed electrode was 29.74 ± 0.1 mV/decade in the pH range of 2.0-9.0 in good agreement with the Nernstian response (29.50 mV/decade). The Hg2+-SE has relatively less interference with other metal ions. The Hg2+-SE was used as an indicator electrode in potentiometric titrations to estimate Hg2+ ions in waters, compact fluorescent lamp, and dental amalgam alloy and the accuracy of the developed electrode was compared with ICP-OES measurement values. Moreover, the new Schiff base (BMPMP) was synthesized and characterized using ATR-FTIR, elemental analysis, 1H NMR, and 13C NMR. The PVC membranes containing BMPMP as an ionophore unloaded and loaded with Hg(II) are reported by scanning electron microscope images (SEM) along with energy-dispersive X-ray spectroscopy (EDX) spectra.

The effect of “on/off” molecular switching on the photophysical and photochemical properties of axially calixarene substituted activatable silicon(iv)phthalocyanine photosensitizers

Silicon(iv) phthalocyanines (4 and 5) bearing two calixarene groups as axial ligands were synthesized. Surprisingly, both phthalocyanines were obtained as two different isomers (4a–b and 5a–b).

Development of a pH sensing membrane electrode based on a new calix[4]arene derivative

A new pH sensing poly(vinyl chloride) (PVC) membrane electrode was developed by using recently synthesized 5,17-bis(4-benzylpiperidine-1-yl)methyl-25,26,27,28-tetrahydroxy calix[4]arene as an ionophore. The effects of membrane composition, inner filling solution and conditioning solution on the potential response of the proposed pH sensing membrane electrode were investigated. An optimum membrane composition of 3% ionophore, 67% o-nitrophenyl octyl ether (o-NPOE) as plasticizer, 30% PVC was found. The electrode exhibited a near-Nernstian slope of 58.7±1.1 mV pH(-1) in the pH range 1.9-12.7 at 20±1 °C. It showed good selectivity for H(+) ions in the presence of some cations and anions and a longer lifetime of at least 12 months when compared with the other PVC membrane pH electrodes reported in the literature. Having a wide working pH range, it was not only applied as a potentiometric indicator electrode in various acid-base titrations, but also successfully employed in different real samples. It has good reproducibility and repeatability with a response time of 6-7s. Compared to traditional glass pH electrode, it exhibited excellent potentiometric response after being used in fluoride-containing media.

Synthesis of silver embedded poly(o-anisidine) molybdophosphate nano hybrid cation-exchanger applicable for membrane electrode

Poly(o-anisidine) molybdophosphate was expediently obtained by sol-gel mixing of Poly(o-anisidine) into the inorganic matrices of molybdophosphate, which was allowed to react with silver nitrate to the formation of poly(o-anisidine) molybdophosphate embedded silver nano composite. The composite was characterized by Fourier Transform Infrared Spectroscopy, X-ray powder diffraction, UV-Vis Spectrophotometry, Fluorescence Spectroscopy, Scanning Electron Microscopy/Energy-dispersive X-ray Spectroscopy and Thermogravimertic Analysis. Ion exchange capacity and distribution studies were carried out to understand the ion-exchange capabilities of the nano composite. On the basis of highest distribution studies, this nano composite cation exchanger was used as preparation of heavy metal ion selective membrane. Membrane was characterized for its performance as porosity and swelling later on was used for the preparation of membrane electrode for Hg(II), having better linear range, wide working pH range (2–4.5) with fast response in the real environment.

Combinatorial screening of potentiometric Pb(II) sensors from polysulfoaminoanthraquinone solid ionophore

A potentiometric Pb(II)-selective sensor was fabricated by a combinatorial screening of electrically conducting polysulfoaminoanthraquinone (PSA) nanoparticles as a solid ionophore, ion exchangers (oleic acid (OA) and NaTPB), plasticizers in a polyvinyl chloride (PVC) matrix, membrane thickness, inner filling ion species, and concentration. The membrane sensor with the composition of PSA/PVC/DOP (dioctyl phthalate)/OA (1.0:33:61:5.0) exhibited the best performance, including a slope of 29.3 mV decade(-1) in the concentration range 10(-6.3)-10(-1.6) M, detection limit of 1.6 × 10(-7) M, response time of 16 s, lifetime of five months, and good response reversibility. The proposed sensor has demonstrated good selectivity for Pb(II) over other monovalent, divalent and trivalent interfering ions, and could be used in a pH range of 3.62-5.22. The Pb(II) sensor has been successfully applied for the determination of Pb(II) concentration in real-world samples and also as an indicator electrode for potentiometric titration of lead ions.

A low pH sensor from an esterified pillar[5]arene

An esterified pillar[5]arene, incorporated into a PVC membrane, displays a non-Nernstian response to changes in pH.

Ion-exchange studies on poly-o-anisidine Sn(IV) phosphate nano composite and its application as Cd(II) ion-selective membrane electrode

An organic-inorganic composite, poly-o-anisidine Sn(IV) phosphate, was chemically synthesized by mixing ortho-anisidine into gels of Sn(IV) phosphate with different mixing volume ratios. Studies on the effect of eluant concentration, elution behavior and separation of metal ions were carried out to understand the ion-exchange capabilities. Due to Cd(II) selective nature of composite, revealed by distribution studies, Cd(II) ion selective membrane electrode was fabricated. The analytical utility of the electrode was established by employing it as an indicator electrode in electrometric titrations having fast response time, 3–5s, and long life span of six months. Some physical parameters like self-diffusion coefficient (D0), activation energy (Ea) and entropy of activation (ΔS0) have been evaluated under conditions favoring a particle diffusion-controlled mechanism by studying ion-exchange kinetics.

Blank membranes versus ionophore-based membranes for the selective determination of H+

A pH electrode for the selective determination of H+ was introduced. Both phosphorated calix[6]arene and a N,N'-bisethoxycarbonyl-1,10-diaza-4,7,13,16-tetraoxacyclo-octadecane (DZCE) were used as new H+-ionophores. The calibration graphs of the obtained electrodes exhibits satisfactory Nernstian slopes. The electrodes were compared to blank membranes (without any ionophoric substances) for the first time. Selectivity coefficients of the studied electrodes towards several inorganic cations were calculated. The relative selectivity coefficient (RSC) was applied for evaluating the selectivity properties of H+-electrode using a mathematical equation. The electrodes were applied for the determination of different inorganic and organic acids.

Synthesis and Characterization of Organic-Inorganic Nanocomposite Poly-o-anisidine Sn(IV) Arsenophosphate: Its Analytical Applications as Pb(II) Ion-Selective Membrane Electrode

Poly-o-anisidine Sn(IV) arsenophosphate is a newly synthesized nanocomposite material and has been characterized on the basis of its chemical composition, ion exchange capacity, TGA-DTA, FTIR, X-RAY, SEM, and TEM studies. On the basis of distribution studies, the exchanger was found to be highly selective for lead that is an environmental pollutant. For the detection of lead in water a heterogeneous precipitate based ion-selective membrane electrode was developed by means of this composite cation exchanger as electroactive material. The membrane electrode is mechanically stable, with a quick response time, and can be operated over a wide pH range. The selectivity coefficients were determined by mixed solution method and revealed that the electrode is sensitive for Pb(II) in presence of interfering cations. The practical utility of this membrane electrode has been established by employing it as an indicator electrode in the potentiometric titration of Pb(II).

Developments in the Field of Conducting and Non-conducting Polymer Based Potentiometric Membrane Sensors for Ions Over the Past Decade

Many research studies have been conducted on the use of conjugated polymers in the construction of chemical sensors including potentiometric, conductometric and amperometric sensors or biosensors over the last decade. The induction of conductivity on conjugated polymers by treating them with suitable oxidizing agents won Heeger, MacDiarmid and Shirakawa the 2000 Nobel Prize in Chemistry. Common conjugated polymers are poly(acetylene)s, poly(pyrrole)s, poly(thiophene)s, poly(terthiophene)s, poly(aniline)s, poly(fluorine)s, poly(3-alkylthiophene)s, polytetrathiafulvalenes, polynapthalenes, poly(p-phenylene sulfide), poly(p-phenylenevinylene)s, poly(3,4-ethylenedioxythiophene), polyparaphenylene, polyazulene, polyparaphenylene sulfide, polycarbazole and polydiaminonaphthalene. More than 60 sensors for inorganic cations and anions with different characteristics based on conducting polymers have been reported. There have also been reports on the application of non-conducting polymers (nCPs), i.e. PVC, in the construction of potentiometric membrane sensors for determination of more than 60 inorganic cations and anions. However, the leakage of ionophores from the membranes based on these polymers leads to relatively lower life times. In this article, we try to give an overview of Solid-Contact ISE (SCISE), Single-Piece ISE (SPISE), Conducting Polymer (CP)-Based, and also non-conducting polymer PVC-based ISEs for various ions which their difference is in the way of the polymer used with selective membrane. In SCISEs and SPISEs, the plasticized PVC containing the ionophore and ionic additives govern the selectivity behavior of the electrode and the conducting polymer is responsible of ion-to-electron transducer. However, in CPISEs, the conducting polymer layer is doped with a suitable ionophore which enhances the ion selectivity of the CP while its redox response has to be suppressed.

Schiff bases as cadmium(II) selective ionophores in polymeric membrane electrodes

The construction and performance characteristics of polymeric membrane electrodes based on two neutral ionophores, N,N'-[bis(pyridin-2-yl)formylidene]butane-1,4-diamine (S1) and N-(2-pyridinylmethylene)-1,2-benzenediamine (S2) for quantification of cadmium ions, are described. The influences of membrane compositions on the potentiometric response of the electrodes have been found to substantially improve the performance characteristics. The best performance was obtained with the electrode having a membrane composition (w/w) of (S1) (2.15%):PVC (32.2%):o-NPOE (64.5%):KTpClPB (1.07%). The proposed electrode exhibits Nernstian response in the concentration range of 7.9x10(-8) to 1.0x10(-1) M Cd2+ with limit of detection 5.0x10(-8) M, performs satisfactorily over wide pH range (2.0-8.0) with a fast response time (10 s). The sensor has been found to work satisfactorily in partially non-aqueous media up to 30% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 2 months. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of cadmium in real samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.

A Novel Membrane Sensor for Histamine H1-Receptor Antagonist "Fexofenadine"

The construction and general performance of thirteen new polymeric membrane sensors for the determination of fexofenadine hydrochloride based on its ion exchange with reineckate, tetraphenylborate and tetraiodomercurate have been studied. The effects of membrane composition, type of plasticizer, pH value of sample solution and concentration of the analyte in the sensor internal solution have been thoroughly investigated. The novel sensor based on reineckate exchanger shows a stable, potentiometric response for fexofenadine in the concentration range of 1 x 10(-2) - 2.5 x 10(-6) M at 25 degrees C that is independent of pH in the range of 2.0 - 4.5. The sensor possesses a Nernstian cationic slope of 62.3+/-0.7 mV/concentration decade and a lower detection limit of 1.3 x 10(-6) M with a fast response time of 20 - 40 s. Selectivity coefficients for a number of interfering ions and excipients relative to fexofenadine were investigated. There is negligible interference from almost all studied cations, anions, and pharmaceutical excipients, however, citrizine that has a structure homologous to that of fexofenadine was found to interfere. The determination of fexofenadine in aqueous solution shows an average recovery of 99.83% with a mean relative standard deviation (RSD) of 0.5%. Direct potentiometric determination of fexofenadine in tablets gave results that compare favorably with those obtained by standard spectrophotometric methods. Potentiometric titration of fexofenadine with phosphomolybdic acid as a titrant has been monitored with the proposed sensor as an end point indicator electrode.