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.     

Ketoconazol‐Triiodide Ion Pair Complex as a Suitable Carrier in an Iodide Selective Membrane Electrode

A novel membrane sensor for selective monitoring of iodide, consisting of a triiodide‐ketoconazole ion pair complex dispersed in a PVC matrix, plasticized with a mixture of 2‐nitrophenyl octyl ether and dioctylphtalate with unique selectivity toward iodide ions, is described. The influence of membrane composition, pH of test solution and foreign ions on the electrode performance were investigated. The optimized membrane demonstrates a near‐Nernstian response for iodide ions over a wide linear range from 1.0 × 10^?2 to 1.0 × 10^?5 M, at 25 ± 1 °C. The electrode could be used over a wide pH range 3–10 and has the advantages of high selectivity, fast response time and good lifetime (over 4 months). It was successfully used as indicator electrode in potentiometric titrations and direct potentiometric assay of iodide ions.     

Copper(I)-bathocuproine complex as carrier in iodide-selective electrode

A PVC membrane electrode for iodide ions based on Cu(I)-bathocuproine as ionophore in membrane composition is prepared. The electrode exhibits a linear response over a wide concentration range 5.0×10⁻⁶ to 2.0×10⁻¹ mol l⁻¹ with a detection limit 1.0×10⁻⁶ mol l⁻¹. The proposed membrane electrode shows Nernstian behavior with a slope of −56.8 mV/decade, a fast response time 10 s and a lifetime at least 3 months. Iodide-selective electrode reveals good selectivities for iodide ion over a wide variety of the other anions and can be used in pH range of 3-9. It can also be used as an indicator electrode in potentiometric titration of iodide ion.     

A selective electrolytic sensor for nitrite based on a modified platinum electrode

The electrolytic sensor described is based on the oxidation of nitrite at a platinum electrode modified with chemisorbed iodine and coated with a thin layer of quaternized poly(4-vinylpyridine), qPVP. The sealed sensor uses an anion-exchange membrane to separate Donnan transport of nitrite across the membrane and controlled potential electrolysis at the Pt/qPVP indicator electrode. The sensor has a linear response to nitrate concentration in aqueous samples over the range 4 × 10^?6?2 × 10^?3 M nitrite. The detection limit is 2 × 10^?6 M nitrite. The sensor is free of interference by nitrate, dissolved oxygen, cations, and many neutral species. Anions that are electroactive at 0.7 V vs. Ag/ AgCl would interfere, but they are uncommon in most samples. Initial tests with lake water samples suggest that this sensor is unaffected by this matrix. The system was also evaluated for monitoring nitrite levels in spiked meat extracts.     

Construction of Suitable Iodide–Selective Electrode Based on Phenyl Mercury (II)(2‐mercaptobezothiozolate) Carrier

Abstract

Highly selective poly(vinyl chloride) (PVC) membrane electrode based on recently synthesized mercury complex i.e., phenyl mercury (II) (2‐mercaptobezothiozolate) (PMMBT) as new carrier for iodide‐selective electrode by incorporating the membrane ingredients on the surface of graphite electrode are reported. The effect of various parameters including the membrane composition, pH, and possible interfering anions were investigated on the response properties of the electrode. The developed sensor exhibited Nernstian responses toward iodide over a wide concentration range of 1×10^?7 to 0.1 M with slopes of 57.6±0.8 mV per decade of iodide concentration and detection limit of 8×10^?8 M, over a wide pH ranges of 2.0–11.5. The sensors have response time of 0.5 s and can be used for at least 2 months without any considerable divergence in their potential response. The proposed electrode show good ability to discriminate iodide over several inorganic and organic anions.

The electrode was successfully applied to direct determination of iodide in synthetic mixture, waste water and drinking water, and pharmaceutical samples in addition to applying as indicator electrode in precipitation titration.     

Enzyme electrode for urea with amperometric indication: Electrode with diffusional limitation

Urea can be determined amperometrically with an enzyme electrode consisting of urease trapped in a poly(vinyl alcohol) gel and confined by a dialysis membrane. A pH-dependent hydrazine oxidation at a platinum anode is used as the detector reaction. The current is a linear function of the urea sample concentration over the range 1–80 mM with 50-μl samples injected into 2 ml of hydrazine buffer in the cell. With enzyme loadings above 20 U cm^-2, the current became limited by the rate of mass transfer in the membrane arrangement. Forty samples per hour could be analyzed with negligible carry-over when the time derivative was used for quantitation.     

Sensitive quantification of iodide by ion-exchange chromatography with electrochemical detection at a modified platinum electrode

A rapid and very sensitive method for the accurate determination of free iodide in real samples is described. The method is based on anion-exchange chromatographic separation coupled with amperometric detection at a modified platinum electrode under constant applied potential (+0.85 V vs. Ag AgCl). An experimental setup with an in-line and very effective method of electrode modification is proposed using an amperometric thin-layer cross-flow detector and a flowing solution 300 mg/L of iodide; the working electrode is polarised to the limiting current for oxidation of iodide to iodine in acidic solutions with the consequent formation of an iodine-based film. The results indicated that the modified electrode exhibits high analytical response for iodide electrooxidation with good stability and long-life. The signal intensity of daily experimental sessions (8 h), during which standards and real samples were repeatedly injected, exhibits a moderate lowering (i.e. <6%). Using a mixture of 25 mM HNO₃ and 50 mM NaNO₃ as an eluent phase in ion-exchange chromatography, the detection limit of iodide was estimated to be 0.5 g/L (S/N=3) with an injection volume of 50 L. This method was applied successfully to quantify the iodide content of milk samples and in wastewaters as well as trace amounts in common vegetables and solutions containing high chloride levels.     

Selective separations by reactive ion exchange: Part 4. Preconcentration of cadmium and zinc by in situ precipitation as hexacyanoferrate(II) salts on gel and macroporous ion-exchange resins

The in situ precipitation of traces of cadmium(II) and zinc(II) ions as hexacyanoferrates from aqueous matrices was studied on conventional polystyrene gel and macroporous cation- and anion-exchange resins. Coprecipitation with each other or with copper(II) ions present in binary cation resins or in solution, and the influence of added nonprecipitating ions of the same charge type such as magnesium(II) were investigated. Microporous (gel) cation exchangers gave reasonable recoveries and macroporous cation exchangers gave very good recoveries; but macroporous anion exchangers performed best, suggesting macroporous hexacyanoferrate(II) resin as an ideal phase for collection/preconcentration of traces of Cu²⁺, Cd²⁺, Zn²⁺, and possibly Co²⁺, Ni²⁺, and Pb²⁺ from waters. As expected, very low yields were obtained with conventional anion exchange resin in the hexacyanoferrate form. Uniform distribution of Cu²⁺, Zn²⁺, and Cd²⁺ over macroporous anion-exchange resin phases were established by means of electron probe scans and taken as evidence for the formation of a uniform, well-developed precipitate layer covering the entire resin particle surface.     

Automated on-line preconcentration of palladium on different sorbents and its determination in environmental samples

The determination of noble metals in environmental samples is of increasing importance. Palladium is often employed as a catalyst in chemical industry and is also used with platinum and rhodium in motor car catalytic converters which might cause environmental pollution problems. Two different sorbents for palladium preconcentration in different samples were investigated: silica gel functionalized with 1,5-bis(di-2-pyridyl)methylene tbiocarbohydrazide (DPTH-gel) and [1,5-Bis(2-pyridyl)-3-sulphophenyI methylene thiocarbonohydrazide (PSTH) immobilised on an anion-exchange resin (Dowex lx8-200)]. The sorbents were tested in a micro-column, placed in the auto-sampler arm, at the flow rate 2.8 mL min(-1). Elution was performed with 4 M HCl and 4 M HNO3, respectively. Satisfactory results were obtained for two sorbents.     

Perchlorate Ion-Selective Electrodes with the Liquid Membranes of the O-Phenanthroline Chelate or its Related Compounds

Abstract

The metal chelates of o-phenanthroline, a, a′-dipyridyl or bathophenanthroline were used as the ion exchanger in the liquid membrane of the perchlorate ion-selective electrode. The electrode with a nitrobenzene membrane containing tris(bathophenanthroline)ferrous perchlorate is the highest sensitive one and gives a linear Nernstian response up to about 1 × 10 ^?5 M perchlorate. The membrane electrode having the ferrous ion-chelate of o-phenanthroline as an ion exchanger shows an excellent selectivity for perchlorate ion over nitrate or iodide Ion. The effects of the chelate concentration in the membrane and the central metal species of the chelate are examined on the electrode performance.     

Efficient electrocatalyst utilization: electrochemical deposition of Pt nanoparticles using nafion membrane as a template

We deposit Pt particles electrochemically on an electrode covered with a Nafion membrane. Platinum ions travel through the hydrophilic channels of the membrane, and platinum deposits are formed at the place where the channels make contact with the planar electrode. This procedure deposits the catalyst only at the end of the hydrophilic channels that cross the membrane; no catalyst is placed under the hydrophobic domains, where it would not be in contact with the electrolyte. By performing a series of cyclic voltammograms with this system, we show that deposition of the platinum through the membrane achieves better platinum utilization than deposition of platinum on the naked electrode followed by the placement of the membrane on top.     

Flow-injection system with ion-exchange separation and potentiometric detection for the determination of three halides

The use of ion exchangers in flow-injection systems is reviewed briefly. In the method described, halides are separated on a short column of a strongly basic ion-exchange resin (Dowex 1-X8) placed in the flow-injection conduit, with a laboratory-made tubular silver/silver halide ion-selective electrode as potentiometric sensor. The response capabilities of the different halide-selective electrodes to a wide concentration range (20-5000 mg dm^?3) of single and mixed halide solutions with and without the incorporated ion-exchange column are compared. By careful selection of suitable concentrations of the potassium nitrate carrier/eluent stream to satisfy the requirements of both the ion-exchange column and the halide-selective electrode, it is possible to separate and determine chloride, bromide and iodide in mixed halide solutions with a detection limit of 5 mg dm^?3. The bromide-selective electrode is the most satisfactory detector.     

Oleophilic ion-exchange resins. IV. Swelling of quaternary ammonium polymers in mixed solvents

The swelling characteristics of an oleophilic anion-exchange resin in methanol–benzene and ethanol–chloroform mixed solvent systems were compared with those of a conventional anion-exchange resin. The oleophilic resin was prepared by amination of chloromethylated polystyrene 1% DVB with N,N-dimethyldodecylamine. It showed a large shift of the swelling peak from polar to less polar solution compositions in both methanol–benzene and ethanol–chloroform systems as compared with the swelling of conventional resins. Total solvent uptake and solvent distribution between resin and solvent phases were also determined. The less polar solvent (benzene or chloroform) was sorbed preferentially by the oleophilic resin over a wide range of composition, while preference for the more polar solvent (methanol or ethanol) by the conventional resin was shown over the entire composition of the mixed solvent systems. The Newman-Krigbaum treatment of mixed solvents was applied to swelling data on the ethanol–chloroform–oleophilic resin system, where the volume of the gel network plus the solvent imbibed was relatively constant over the entire range of composition. The result suggests a strong similarity of the liquid–liquid interaction terms in this gel phase compared with those in the pure binary liquid phase.     

Reactions of aromatic and heteroaromatic compounds bearing electron-acceptor substituents

Dimethyl(2-thienyl)sulfonium salts were synthesized for the first time. The corresponding triiodomercurates were obtained by the reaction of methyl 2-thienyl sulfide or its substituted derivatives with methyl iodide and mercuric iodide. Sulfonium perchlorates are formed as a result of the reaction of thiophene compounds with dimethyl sulfoxide in the presence of POCl₃ and perchloric acid. The HgI₃ ^– anion was replaced by NO₃ ^– by means of an anion-exchange resin. The methods for the dimethylation of sulfonium salts with conversion of them to the corresponding sulfides were studied; the conditions for obtaining quantitative yields from these reactions by means of an anion exchange resin in the acetate form were found.See [1] for communication VII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 165–168, February, 1972.     

Detection of additional impurities in the UV-chromatogram of <Emphasis Type="SmallCaps">l</Emphasis>-[<Emphasis Type="Italic">S</Emphasis>-methyl-<Superscript>11</Superscript>C]methionine

Samples of l-[S-methyl-¹¹C]methionine prepared by on-column [¹¹C]methylation on a C18 cartridge were analyzed by HPLC under different conditions in order to explain some anomalies observed in the UV-chromatograms. By so doing, two new unlabelled impurities were found and identified as iodide and homocystine. Their amounts are still compatible with the safe human use of the radiotracer solution. Nevertheless, if needed, iodide can be totally removed by elution through an anion-exchange resin, while homocystine can be reduced by either decreasing the amount of precursor used in the synthesis or preventing its air oxidation.     

Screen‐Printed Electrodes for Amperometric Determination of Iodide

An amperometric method for the determination of iodide ions has been developed using disposable, screen‐printed electrodes. The used sensors have a gold, graphite and platinum working electrodes with an area of about 7 mm². Calibration curves exhibit a linear relationship between the electrode response and the iodide concentration up to 3.00 mM. The correlation coefficients for all calibration curves varied from 0.988 to 0.998. The relative standard deviations were equal to or less than 5.26 % (n=5). The lowest iodide concentration measured was 100 µM.     

Preconcentration of Nickel(II) in White Wine Using Quinoxaline-2,3-dithiol and a Finely Divided Anion-Exchange Resin for the Determination by Solid-Phase Spectrophotometry

A simple and sensitive method for the determination of trace amounts of nickel(II) is described. The method is based on the adsorptive enrichment of nickel(II) as the complex with quinoxaline-2,3-dithiol using a finely divided anion-exchange resin, collection of the resin on a membrane filter by filtration, and direct measurement of the absorbance of the resultant circular thin layer by reflective spectrophotometry at 605 nm. In the presence of interfering cations such as copper(II) and cobalt(II) a sample solution is first filtered, after the addition of ammonium thiocyanate and Zephiramine, to extract these cations onto a membrane filter as the ion-pair precipitate formed between the metal-thiocyanate complex anions and Zephiramine cations, then nickel(II) in the filtrate is determined. Interferences from iron(III), silver(I), bismuth(III), cadmium(II), mercury(II), indium(III), palladium(II), platinum(IV), tin(IV), and zinc(II) can also be eliminated. The proposed method was applied to the determination of nickel in white wine. The concentrations of nickel found in 5-ml aliquots of 10 different wine samples were in the range 16.1-68.0 ng ml⁻¹.     

Improved interfacial adhesion of membrane electrode assemblies using polymer binders and pore-filling membranes in alkaline membrane fuel cells

The development of alkaline membrane fuel cells (AMFCs) will enable the use of non-platinum catalysts and hydrocarbon-based electrolyte membranes. Such catalysts are intrinsically stable and have activities similar to that of platinum in an alkaline environment. A pore-filling membrane has been made from a porous, high-density polyethylene substrate to fabricate durable, AMFC membrane electrode assemblies (MEAs). Because of the low binding ability of the hydrocarbon ionomer in the preparation of AMFC MEAs, polymer binders were added to the catalyst slurries to form a firmly bound interface. A content of 20 wt% polyethylene (PE) binder, the same material as the porous substrate in the pore-filling membrane, exhibits the best attachment of the non-platinum catalyst particles to the pore-filling, hydrocarbon anion-exchange membranes. The addition of a PE binder improves adhesion at the MEA interface and diminished contact resistance. The improved durability of the MEA is confirmed by continuous, constant-voltage operation. Adhesion between the cathode catalyst layer and the pore-filling membrane is also investigated after mild hot-pressing to test the use of decal method in the fabrication of AMFCs. The catalyst layer with the PE binder was completely transferred to the pore-filling membrane at 50 °C and 30 bar?cm^?2, but not for the PTFE binder.     

Electrochemical determination of iodide by poly(3-aminophenylboronic acid) film electrode at moderately low pH ranges

A new potentiometric sensor for the determination of iodide based on poly(3-aminophenylboronic acid) (PAPBA) film electrode was constructed. Poly(3-Aminophenylboronic acid) films were synthesized electrochemically on platinum electrode by cyclic voltammetry. The effect of film thickness, pH, and preconditioning parameters on the electrode performance were examined. The analytical performance was evaluated and linear calibration graphs were obtained in the concentration range of 10⁻⁶ to 10⁻¹ M iodide ion. The limit of detection was found to be 8 × 10⁻⁷ M. The response time of the sensor was 5 s and its lifetime is about one week. To check the selectivity of the PAPBA film for iodide ion, potential interferences such as Cl⁻, Br⁻, F⁻, CN⁻, IO₃⁻, Ca²⁺, and Mg²⁺ were tested. The PAPBA electrode was also employed as a sensing platform for the determination of iodide ions in commercial table salt.     

Quasi-solid-state dye-sensitized solar cells assembled with polymeric ionic liquid and poly(3,4-ethylenedioxythiophene) counter electrode

Poly(3,4-ethylenedioxythiophene) nanofibers (PEDOT-NF) with high catalytic activity were synthesized and employed as a counter electrode in dye-sensitized solar cells (DSSCs). A polymeric ionic liquid (PIL) was used as a gelling agent and an iodide source for making a highly conductive gel polymer electrolyte. A quasi-solid-state DSSC assembled with this PIL-based gel polymer electrolyte and PEDOT-NF counter electrode exhibited high conversion efficiency of 8.12% at 100 mW cm^− 2.