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.     

Nitrate-containing ionic liquids as active membrane components of nitrate-selection electrodes

Two dialkylimidazolium nitrate ionic liquids (ILs) have been tested for use as an active component of plasticized PVC membranes in nitrate ion selective electrodes (ISEs). The potentiometric reversibility and the main electrochemical characteristics of the ISEs in KNO₃ solutions have been studied. The test membranes contain 5% of the active component and demonstrate a near-Nernstian response to NO ₃ ^? . The use of a more hydrophobic IL based on dioctadecylimidazolium increases the sensitivity and decreases the detection limit: the slope of the electrode function is 57 mV/pC, and C _min = 3.7 · 10^?6 mol/L. The pH range of the membrane performance has been studied, and the potentiometric selectivity to NO ₃ ^? in the presence of several foreign anions has been determined. The new electrode exceeds the commercially available analogue (an ELIT 021 nitrate-selective electrode) in the detection limit and response time. The utility of the new electrode for the direct potentiometric determination of nitrate ILs in aqueous solutions has been demonstrated.     

Cs+ -selective membrane electrodes based on ethylene glycol-functionalized polymeric microspheres

A new strategy for improving the robustness of membrane-based ion-selective electrodes (ISEs) is introduced based on the incorporation of microsphere-immobilized ionophores into plasticized polymer membranes. As a model system, a Cs⁺-selective electrode was developed by doping ethylene glycol-functionalized cross-linked polystyrene microspheres (P-EG) into a plasticized poly(vinyl chloride) (PVC) matrix containing sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate (TFPB) as the ion exchanger. Electrodes were evaluated with respect to Cs⁺ in terms of sensitivity, selectivity, and dynamic response. ISEs containing P-EG and TFPB that were plasticized with 2-nitrophenyl octyl ether (NPOE) yielded a linear range from 10⁻¹ to 10⁻⁵ M Cs⁺, a slope of 55.4 mV/decade, and a lower detection limit (log a_Cs) of −5.3. In addition, these membranes also demonstrated superior selectivity over Li⁺, Na⁺, and alkaline earth metal ion interferents when compared to analogous membranes plasticized with bis(2-ethylhexyl) sebacate (DOS) or membranes containing a lipophilic, mobile ethylene glycol derivative (ethylene glycol monooctadecyl ether (U-EG)) as ionophore.     

A potentiometric sensor for the determination of diclofenac

A diclofenacselective electrode with a plasticized poly(vinyl chloride) membrane containing an ion associate of diclofenac with Astrafloxin FF as an electrode-active substance was developed. The linearity range of the electrode function varied from 5 × 10^?5 to 5 × 10^?2 M; the slope of the electrode function was 59.0 ± 1.2 mV/pc, and the working pH range was 9–12. The effectiveness of the use of this electrode for monitoring diclofenac in pharmaceutical preparations was demonstrated.     

All-solid-state Fluoride Ion-selective Electrode using LaF3 Single Crystal with Poly(3,4-ethylenedioxythiophene) as Solid Contact Layer

An all-solid-state fluoride ion-selective electrode (ISE) was prepared using LaF₃ single crystal with poly(3,4-ethylenedioxythiophene (PEDOT) as the solid contact layer. In contrast to polymer-based ISEs, crystalline membrane-based ISEs have not been used for all-solid-state device, thereby prohibiting the integration of ISEs on a chip. The all-solid-state fluoride ISE developed in this study exhibited superior sensitivity (−56.0±0.9 mV/dec) and selectivity compared to those of conventional inner filling solution ISE. The effects of PEDOT as a solid contact layer were analyzed using chronopotentiometry and electrochemical impedance spectroscopy, which revealed that PEDOT promoted electrode stability. The all-solid-state device can miniaturize the fluoride ISE and facilitate environmental, industrial, agricultural, and physiological monitoring.     

A Potentiometric Multisensor System of Anion-Selective Electrodes Based on Ionic Liquids

The possibility of using solid-state and liquid PVC-membrane electrodes based on ionic liquids to design a potentiometric multisensor system is assessed. Ionic liquids with 1,3-dihexadecylimidazolium cation and chloride, bromide, iodide, and nitrate anions are used. The sensitivity parameters of the sensors are determined. A multisensor array is applied to detect chloride and iodide anions in the multicomponent mixture. The designed system is used to discriminate between mineral waters of different compositions by applying the method of principal component analysis (PCA).     

Solid Contact Ion-selective Electrodes on Printed Circuit Board with Membrane Displacement

Multiplexed solid-contact ion-selective electrodes (SCISEs) are fabricated using printed circuit board (PCB) and mesoporous carbon black (MCB) as ion-to-electron transducer (solid contact). Four sensor configurations were examined and showed that in addition to MCB, the sensor configuration plays crucial role in the stability of the potential response. The enhanced sensor stability was also linked with suppression of transmembrane flux of water. The sensors exhibited near-Nernstian sensitivity (58.1 mV/dec for K⁺ ISEs and −55.1 mV/dec for NO₃^- ISEs), low detection limits (1.5–2.2 μM), and good short-term stability (∼0.1 mV/min). Sensors can be stored dry and used without preconditioning. This work demonstrates a promising approach to combining PCB technology and carbon black for large-scale production of low cost ISEs for point-of-care testing, wearables, or in situ field measurements.     

Use of Tin (IV) Porhyrins as Ionophores for the Construction of Phthalate‐Selective Electrodes: Influence of the Structure and Membrane Composition on their Response Properties

Tin(IV) porphyrins derivatives were used as ionophores for phthalate selective electrodes preparation. The influence of ionophore structure and membrane composition (amount of incorporated ionic sites) on the electrode response, selectivity and long‐term stability were studied. Poly(vinyl chloride) polymeric membranes plasticized with o‐NPOE (o‐nitrophenyloctylether) and containing Sn(IV)‐tetraphenylporphyrin (TPP) dichloride (Sn(IV)[TPP]Cl₂) or Sn(IV)‐octaethylporphyrin (OEP) dichloride (Sn(IV)[OEP]Cl₂), and in some cases incorporating lipophilic cationic (tetraocthylammonium bromide ‐ TOABr) and anionic (sodium tetraphenylborate – NaTPB and potassium tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate‐KTFPB) additives, were prepared and their potentiometric characteristics compared. Both ionophores are shown to operate via a neutral mechanism, and the addition of 10 mol % of lipophilic quaternary ammonium salt derivative to the membrane is required to achieve optimal electrode performance. The potentiometric units prepared, with Sn(IV)[TPP]Cl₂ (Type A) or Sn(IV)[OEP]Cl₂ (Type B) without additives, presented a slope of ?52.8 mV dec^?1 and ?58.8 mV dec^?1 and LLLR of 9.9×10^?5 mol L^?1 and 9.9×10^?6 mol L^?1, respectively. The units prepared using the same metalloporphyrins and incorporating 10% mol TOABr presented a slope of ?55.0 mV dec^?1 and ?57.8 mV dec^?1 and LLLR of 5.0×10^?7 mol L^?1 and 3.0×10^?7 mol L^?1. Their analytical usefulness was assessed by potentiometric determinations of phthalate in water and industrial products providing results that presented recoveries of about 100%.     

Micro Solid‐Contact Ion‐Selective Electrode Using a Carbon Nanotube Tower as Ion‐to‐Electron Transducer and Conductive Substrate

Solid contact (SC) ion‐selective electrodes (ISEs) have been recognized as the next generation of ISEs. In this work, the electrical conductivity and mechanical strength of a carbon nanotube (CNT) tower enable it to play the dual roles of transducer and substrate for micro SC‐ISEs. The electrode had a close to Nernstian slope of 35 mV/decade a_Ca2+, a linear range of four orders of magnitude of calcium ion activity (10^?5.6 to 10^?1.8 M), and a detection limit of 1.6×10^?6 M. The simplified fabrication by a one‐step drop casting makes miniaturizing SC‐ISEs and fabricating sensor arrays easier to achieve.     

Intercalation Compounds as Inner Reference Electrodes for Reproducible and Robust Solid‐Contact Ion‐Selective Electrodes

With billions of assays performed every year, ion‐selective electrodes (ISEs) provide a simple and fast technique for clinical analysis of blood electrolytes. The development of cheap, miniaturized solid‐contact (SC‐)ISEs for integrated systems, however, remains a difficult balancing act between size, robustness, and reproducibility, because the defined interface potentials between the ion‐selective membrane and the inner reference electrode (iRE) are often compromised. We demonstrate that target cation‐sensitive intercalation compounds, such as partially charged lithium iron phosphate (LFP), can be applied as iREs of the quasi‐first kind for ISEs. The symmetrical response of the interface potentials towards target cations ultimately results in ISEs with high robustness towards the inner filling (ca. 5 mV dec^?1 conc.) as well as robust and miniaturized SC‐ISEs. They have a predictable and stable potential derived from the LiFePO₄/FePO₄ redox couple (97.0±1.5 mV after 42 days).     

Iodide‐Selective Electrode Based on Copper Phthalocyanine

Copper phthalocyanine was used as ion carrier for preparing polymeric membrane selective sensor for detection of iodide. The electrode was prepared by incorporating the ionophore into plasticized poly(vinyl chloride) (PVC) membrane, coated on the surface of graphite electrode. This novel electrode shows high selectivity for iodide with respect to many common inorganic and organic anions. The effects of membrane composition, pH and the influence of lipophilic cationic and anionic additives and also nature of plasticizer on the response characteristics of the electrode were investigated. A calibration plot with near‐Nernestian slope for iodide was observed over a wide linear range of five decades of concentration (5×10^?6?1×10^?1 M). The electrode has a fast response time, and micro‐molar detection limit (ca. 1×10^?6 M iodide) and could be used over a wide pH range of 3.0–8.0. Application of the electrode to the potentiometric titration of iodide ion with silver nitrate is reported. This sensor is used for determination of the minute amounts of iodide in lake water samples.     

Solid-state ion-selective electrodes based on ionic liquid solid at room temperature for detecting amino acids

An ion-selective electrode based on tetraoctylammonium N-lauroyl sarcosinate ionic liquid, which is solid at room temperature, is responsive to anionic forms of amino acids. Preconditioning in copper sulfate solution and the introduction of more high-melting and hydrophobic ionic liquid (1,3-dihexade-cylimidasolium bromide) allowed the limit of detecting phenylalanine to be lowered by several times (c_min = 2.7 × 10^–5 M) and significantly improves the service life of the ion-selective electrode. The possibility was shown for using two ionic liquids for designing ISE with one of them that serves as an inert solid matrix for immobilizing the second one, which in turn ensured the analyte binding and the generation of a potentiometric signal.     

Robust Polyoxometalate/Nickel Foam Composite Electrodes for Sustained Electrochemical Oxygen Evolution at High pH

The development of technologically viable electrodes for the electrochemical oxygen evolution reaction (OER) is a major bottleneck in chemical energy conversion. This article describes a facile one‐step hydrothermal route to deposit microcrystals of a robust Dexter–Silverton polyoxometalate oxygen evolution catalyst, [Co_6.8Ni_1.2W₁₂O₄₂(OH)₄(H₂O)₈], on a commercial nickel foam electrode. The electrode shows efficient and sustained electrochemical oxygen evolution at low overpotentials (360 mV at 10 mA cm⁻² against RHE, Tafel slope 126 mV dec⁻¹, faradaic efficiency (96±5) %) in alkaline aqueous solution (pH 13). Post‐catalytic analyses show no mechanical or chemical degradation and no physical detachment of the microcrystals. The results provide a blueprint for the stable “wiring” of POM catalysts to commercial metal foam substrates, thus giving access to technologically relevant composite OER electrodes.     

Miniature Ion-selective Electrodes with Mesoporous Carbon Black as Solid Contact

Herein, we demonstrated miniature solid-contact ion-selective electrodes (ISEs) using a commercial mesoporous carbon black (MCB) as ion-to-electron transducer. MCB is attractive in its high surface area, good conductivity, relative low cost and availability. ISEs for potassium (K⁺) and nitrate (NO₃⁻) ions were prepared by subsequently coating the sealed glass capillaries (1.5 mm) with MCB and ion-selective membranes. Addition of MCB substantially stabilized electrode response by providing adequate double-layer capacitance and lowering resistance by more than 100× compared to the coated-wire electrodes. The electrodes exhibited near-Nernstian slopes of 59.6 (K⁺ ionophore), 57.8 (K⁺ ion-exchanger) and −54.8 (NO₃⁻ ion-exchanger) with standard solutions in the range of 10⁻⁵ to 10⁻¹ M. Fast response (∼10 s) and reproducible sensitivities were also obtained in a mixed electrolyte containing interfering ions, although with a baseline drift of 2–10 mV/day in the long term. Importantly, the electrodes can be simply stored in air between measurements and used directly without conditioning in solutions. With simple fabrication and free maintenance, these sensors offer a low cost and convenient alternative to bulk ISEs, especially when sample volumes or space are limited.     

Fabrication of Membrane Sensitive Electrodes for the Validated Electrochemical Quantification of Anti-Osteoporotic Drug Residues in Pharmaceutical Industrial Wastewater

Accurate and precise application of ion-selective electrodes (ISEs) in the quantification of environmental pollutants is a strenuous task. In this work, the electrochemical response of alendronate sodium trihydrate (ALN) was evaluated by the fabrication of two sensitive and delicate membrane electrodes, viz. polyvinyl chloride (PVC) and glassy carbon (GC) electrodes. A linear response was obtained at concentrations from 1 × 10⁻⁵ to 1 × 10⁻² M for both electrodes. A Nernstian slope of 29 mV/decade over a pH range of 8–11 for the PVC and GC membrane electrodes was obtained. All assay settings were carefully adjusted to obtain the best electrochemical response. The proposed technique was effectively applied for the quantification of ALN in pure form and wastewater samples, acquired from manufacturing industries. The proposed electrodes were effectively used for the determination of ALN in real wastewater samples without any prior treatment. The current findings guarantee the applicability of the fabricated ISEs for the environmental monitoring of ALN.     

Characterization of home-made silver sulphide based iodide selective electrode

Polycrystalline silver sulphide/silver iodide ion selective electrodes (ISEs) with four different compositions, 9:1, 2:1, 1:1, 1:9 Ag₂S-AgI mole ratios, have been fabricated in the laboratory and characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). X-ray diffraction studies show the presence of Ag₃SI, Ag₂S and AgI crystalline phases in the electrode material. The electrode surfaces have been found to become smoother and lustrous with increasing percentage of silver sulphide in silver iodide. ISE 1:1, ISE 2:1 and ISE 9:1 all responded in Nernstian manner with slopes of about 60 mV/decade change in iodide ion concentration in the linear range of 1 × 10⁻¹ to 1 × 10⁻⁶ M while ISE 1:9 showed sub-Nernstian behavior with slope of about 45 mV up to the concentration 1 × 10⁻⁵ M. Two capacitive loops, one corresponding to the charge transfer process at metal electrode and the back contact and a second loop corresponding to the charge transfer process at membrane-electrolyte interface have been observed at high and low frequency ranges, respectively. Mott-Schottky analysis shows that the materials are n-type semiconductors with donor defect concentrations in the range of 5.1 × 10¹⁴ to 2.4 × 10¹⁹/cm³.     

Poly (Vinyl Chloride) Matrix Membrane Electrodes Responsive to Thiocyanate,Perchlorate and Periodate

Abstract

Three types of PVC matrix membrane ion-selective electrodes (ISEs) are described. These are based on membranes containing nitron thiocyanate with 2-nitro-phenyl phenyl ether, 2-nitrophenyl phenyl ether alone and tetraphenylarsonium thiocyanate with 2-nitrophenyl octyl ether. Each type is conditioned and stored in 0.1M sodium thiocyanate. The first two electrodes have been evaluated for thiocyanate and perchlorate response and the best linear long range (linear range down to 2.5×10^?5M) response was obtained for perchlorate. The third electrode is suitable as a periodate ISE with linear calibration range down to 2×10^?4M. The plasticized (2-nitrophenyl phenyl ether) PVC electrode for thiocyanate and perchlorate had a much longer pH interference free range (1.5–12.5) than either of the other electrodes.     

Iodide‐Selective Electrodes Based on Bis[N(2‐methyl‐phenyl) 4‐Nitro‐thiobenzamidato]mercury(II) and Bis[N‐phenyl 3,5‐Dinitro‐thiobenzamidato]mercury(II) Carriers

Highly selective poly(vinyl chloride) (PVC) membrane electrodes based on recently synthesized mercury complexes including Hg(Nmpntb)₂ and Hg(Npdntb)₂ as new carriers for iodide‐selective electrodes by incorporating the membrane ingredients on the surface of graphite electrodes are reported. The effect of various parameters including the membrane composition, pH and possible interfering anions were investigated on the response properties of the electrodes. Both sensors exhibited Nernstian responses toward iodide over a wide concentration range of 7×10^?7 to 0.1 M and 1×10^?6 to 0.1 M, with slopes of 59.6±0.8 and 58.9±0.9 mV per decade of iodide concentration and detection limit of 3×10^?7 M and 7×10^?7 for Hg(Npdntb)₂ and Hg(Nmpntb)₂, respectively, over a wide pH range of 3–11. The sensors have response times of ≤5 s and can be used for at least 2 months without any considerable divergence in their potential response. The proposed electrodes show good ability to discriminate iodide over several inorganic and organic anions. The electrodes were successfully applied to direct determination of iodide in synthetic mixture, waste water and drinking water and as indicator electrodes in precipitation titrations.     

Electrochemical Study of Indium in a Water‐Stable 1‐Ethyl‐3‐Methylimidazolium Chloride/Tetrafluoroborate Room Temperature Ionic Liquid

The electrochemistry of indium species was investigated at glassy carbon, tungsten and nickel electrodes in a basic 1‐ethyl‐3‐methylimidazolium chloride/tetrafluoroborate ionic liquid. Amperometric titration experiments suggest that In(III) chloride is complexed as [InCl₅]^2? in this ionic liquid. The electrochemical reduction of [InCl₅]^2? to indium metal is preceded by overpotential driven nucleations. The effective anodic dissolution of indium to indium(III) requires, however, the presence of sufficient chloride ions at the electrode surface. The electrodeposition of indium at glassy carbon and tungsten electrodes proceeds via three‐dimensional instantaneous nucleation with diffusion‐controlled growth of the nuclei. At the nickel electrode, the deposition proceeds via three‐dimensional progressive nucleation with diffusion‐controlled growth of the nuclei. Raising the deposition temperature decreases the average radius of the individual nuclei, r. Scanning electron microscopic and x‐ray diffraction data indicated that bulk crystalline indium electrodeposits could be prepared on nickel substrates within a temperature range between 30 and 120 °C.     

Coated wire thorium ion selective electrode: Part I

Coated wire ion selective electrode for thorium ion selective potentiometry was developed. Thorium ion selective coated wire electrodes were prepared by depositing a membrane comprising of Aliquat-336 loaded with Th(NO₃)₆²⁻ ions and poly vinyl chloride in varying proportion. A linear near-Nernstian response with a slope of −29.5 ± 0.3 mV over thorium concentration range of 1 × 10⁻¹–3 × 10⁻⁵ M in constant total nitrate concentration of 6 M was obtained for the electrodes of almost all the composition studied. In spite of small drift in response potential from composition to composition, day to day as well as from electrode to electrode, the slope of potential response line was constant within experimental error. Moreover, the electrode once prepared could be conveniently used over a period of one and half month.