Disopyramide-Selective Membrane Electrode∗

Abstract

A liquid membrane electrode based on disopyramide - dipicrylamine ion - pair complex, dissolved in nitrobenzene as solvent was proposed for the determination of disopyramide - an antiarrhythmic drug. The linear response covers the range from 10^?2 - 5 × 10^?6 M disopyramide solution, with a slope of 51.0 mV/decade (pH range 3.0 to 7.0). The detection limit is 4.7 × 10^?8 M. The electrode shows a good stability, reproducibility and fast response. The selectivity of the electrode is good. The strong interfering ion is thiamine (Vitamin B₁). These characteristics of the electrode made it to be used for the determination of disopyramide through direct and indirect potentiometric methods. Through indirect potentiometric method, disopyramide - as active substance can be determined with an average recovery of 99.98% and a relative standard deviation of 0.24%, and also this method can be used for its determination in pharmaceutical formulations such as capsules and ampoules with a relative standard deviation less than 1%. The electrode can be used at the dissolution tests of disopyramide capsules. The physical processes are numerically simulated by typical equations. The apparent first - order rate constants for disintegration and dissolution processes were calculated.

     

Potentiometric determination of the total acidity and concentration of citric acid in wines

The method of potentiometric titration with a copper electrode is used for the determination of the total acidity and concentration of citric acid (CA) in identifying the adulteration of wines. The procedure is suitable for the determination of citric acid in wines in the range from 0.1 to 3.5 g/L in the presence of 30-fold amounts of tartaric, acetic, malic, succinic acids and a 10-fold amount of oxalic acid after the separation of organic carboxylic acids on an AV-17-8 anion exchanger. The procedure was developed and certified for the potentiometric determination of the mass fraction of citric acid in table wines and wine materials with an error not exceeding 20%. The criteria (mass fraction of citric acid, the percentage of citric acid in the total acidity, and the shape of the curves of potentiometric titration) were proposed for revealing the adulteration of the acid composition of wines.     

Development of a Novel Solid‐State pH Sensor Electrode Based on Titanium Oxide Thin Film as an Indicator Electrode in Potentiometric Acid‐Base Titrations in Fused NaNO3 at 350°C

A solid‐state pH sensor was fabricated using a transparent conductive titanium oxide film on a glass substrate. The coating of the glass substrate was achieved by a novel simple chemical vapor deposition (CVD) procedure. The sensor slope was found to increase as the temperature of the solution was increased. The performance of the sensor was investigated in the pH range from 2.2 to 11.19. The E‐pH curve is linear with slope of 0.054 V at 298.15 K. This value is closed to the theoretical value 2.303RT/F (0.059 V at 298.15). The standard potential of this electrode, E°, is computed as 177.58 mV with respect to the SCE as reference electrode. Results obtained by the suggested sensor compares very well with conventional pH electrodes where the square of the correlation coefficient was 0.998. This electrode can be used as an indicator electrode in potentiometric acid‐base titration. This electrode behaves reversibly and responds to the oxide ion concentration in molten NaNO₃. K₂Cr₂O₇ was potentiometrically titrated with Na₂O₂ and K₂CO₃ as titrants in molten NaNO₃ at 350°C, using the above mentioned indicator electrodes. An acidity/basicity scale of the oxyanions was established in molten NaNO₃ at 350°C.     

A coated-metal enzyme electrode for urea determinations

A potentiometric enzyme electrode is reported in which an enzyme immobilized in polyvinyl chloride is used to coat an antimony metal electrode to detect changes in pH when the electrode is immersed in a solution of the enzyme substrat. As an example, urea is determined in solution by using immobilized urease on an antimony electrode, giving a linear concentration range of 5.0 × 10^-4–1.0 × 10^-2 M urea with a slope of 44 mV per decade change in urea concentration. The response slope is stable for about 1 week, with response times in the range 1–2 min, but with absolute potential changes occurring from day to day.     

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.     

Potentiometric determination of acids and bases using a silica gel based carbon-epoxy indicator electrode

The construction and the application of a silica gel based carbon-epoxy indicator electrode for the potentiometric determination of acids and bases are described. The effect of composition of silica gel and carbon-epoxy, slope (mV/pH), linear response (pH range) and the use for acid-base titrations were investigated. The data obtained for the acid-base titrations were compared with those obtained using a glass electrode in the same conditions. The electrode showed a linear response in the pH 2 to 13 range with a slope of –40.5 ± 0.4 mV/pH (at 25 °C) and a response time of less than 15 s. The lifetime of the electrode was higher than one year (over 6000 determinations) with a decrease of only 5% of the initial potentiometric response. The silica gel based carbon-epoxy electrode showed excellent results in the end-point indication potentiometric titrations in determination of acids and bases. The miniaturization of the proposed electrode for flow injection analysis was investigated. Received: 11 August 1999 / Revised: 4 October 1999 / Accepted: 7 October 1999     

Potentiometric determination of acids and bases using a silica gel based carbon-epoxy indicator electrode

The construction and the application of a silica gel based carbon-epoxy indicator electrode for the potentiometric determination of acids and bases are described. The effect of composition of silica gel and carbon-epoxy, slope (mV/pH), linear response (pH range) and the use for acid-base titrations were investigated. The data obtained for the acid-base titrations were compared with those obtained using a glass electrode in the same conditions. The electrode showed a linear response in the pH 2 to 13 range with a slope of -40.5 +/- 0.4 mV/pH (at 25 degrees C) and a response time of less than 15 s. The lifetime of the electrode was higher than one year (over 6000 determinations) with a decrease of only 5% of the initial potentiometric response. The silica gel based carbon-epoxy electrode showed excellent results in the end-point indication potentiometric titrations in determination of acids and bases. The miniaturization of the proposed electrode for flow injection analysis was investigated.     

A ferrocene-modified platinum electrode as a potentiometric sensor for l-ascorbic acid

A half-oxidized platinum electrode modified with a monolayer of ferrocene is proposed as a potentiometric sensor for l-ascorbic acid in an aqueous glycine buffer pH 2.2. The ferrocene was covalently attached to the surface by a silane carbon chain. The potentials of 15 electrodes were measured and a slope of (50 ± 8.8) mV per decade change in concentration of ascorbic acid was obtained over the concentration range 10^?3-10^?6 M. Recovery experiments with pure l-ascorbic acid solutions showed a relative standard deviation of 1.9%, in the analysis of fresh orange juice, the relative standard deviation was 6.1%.     

Determination of L-Ascorbic Acid by Adsorption Potentiometry with Carbon Paste Electrode

Abstract

This paper reports the potentiometric measurement of ascorbic acid in the solution of 0.10 mol/L NaOH-0.1 mol/L NaCl using carbon paste (the mixture of spectroscopic graphite powder and di-iso-octyl phthalate) electrode(room temperature 15°C), with the linear range 7.0 × 10^?7 × 4.0 × 10^?5mol/L, average response slope 95mV/decade and detection limit 1 × 10^?7mol/L. Phenol, sulfite, Mn²⁺ and so on pose no interference to the measurement of ascorbic acid. This method is characterized by fine selectivity, reproducibility and accuracy. The potential response behavior is caused chiefly by chemisorption of ascorbic acid to the surface of the carbon.

Each year yields a number of papers concerning the determination of ascorbic acid by various methods, including gas chromatographymass spectrometry¹, capillary electrophoresis², spectrophotometry³, voltammetry⁴, titrimetric method⁵, biosensor⁶ and so on, Each method has its merits and defects in analyzing different samples. M. Petersson⁷ worked out the potentiometric sensor for determining ascorbic acid by modifying monolayer of ferrocene upon the surface of half-oxidized platinum electrode with an average response slope 50±8.8mV/decade, but this sensor suffers from inadequate selectivity. In our study, carbon paste electrode (without ionophore) is applied in the determination of ascorbic acid by potentiometry with an average response slope 95mV/decade. This method displays fine selectivity, accuracy, convenience and rapidity of determination.     

Performance and Characteristics of New Cyproheptadine Hydrochloride Selective Plastic Membrane Electrodes Based on Cyproheptadine Tetraphenylborate

Abstract

A new cyproheptadine hydrochloride (CHDHC1) ion selective F VC membrane electrode based on the ion-pair complex of CHDHC1 with sodium tetraphenylborate was prepared and its performance characteristics were studied. The electrode exhibited a Jinear response with a good Nernstian slope over a relatively wide range of concentration. Up to 21 days of continuous soaking, the calibration graph slope was constant at 57.1 mV/concentration decade, at 25°C, then it decreased as the time of soaking increases reaching 32.9 mV/decade after 37 days. The change in pH did not affect the electrode performance within the range 2–6. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of electrode. The electrode showed very good selectivity for CHDHC1 with respect to a large number of inorganic and organic cations. The standard addition method and potentiometric titration were used to determine (CHDHC1) in pure solution and in a. pharmaceutical preparation.     

Capillary Melt Method for Micro Antimony Oxide pH Electrode

In this work, a new approach named “capillary melt method” was developed to fabricate micro antimony wires, and the wire surface was then oxidized in a nitrate melt at high temperature to obtain an antimony/antimony oxide pH electrode. Characterization results show that the oxide layer on the wire surface is porous, and consists of Sb₂O₃ crystal phase. The pH electrode, made using this method, showed good sensing performance in buffer solutions in the tested pH range of 2–12. Its EMF signal was found to have a linear relationship with pH value of the solution, with a sensitivity of 54.1 mV/pH and a fitting correlation coefficient of R²=1.00. The advantages of the electrode are long‐term stability, fast response, reproducibility and low cost.     

Evaluation of GaN and In0.2Ga0.8N Semiconductors as Potentiometric Anion Selective Electrodes

The response of potentiometric anion selective electrodes consisting of undoped GaN or In_0.2Ga_0.8N films grown on Al₂O₃ (sapphire) was measured in electrolyte solutions of F^?, NO₃^?, Cl^?, SCN^?, ClO₄^? or Br^? anions at concentrations ranging from 10^?6 to 10^?1 M. The slope of the linear regions varied between ?32.8 and ?51.9 mV/decade for the GaN electrode and between ?31.0 and ?72.0 mV/decade for the In_0.2Ga_0.8N electrode. The drift of the GaN electrode reached 1.57 mV/day in KNO₃ solutions, whereas the drift of the In_0.2Ga_0.8N electrode could not be evaluated due to large drops in the slope of its linear range over time. Both electrodes were sensitive to pH variations over the pH range from 12.8 to 1.3. The GaN electrode surface could be electrochemically etched under anodic polarization; however, both GaN and In_0.2Ga_0.8N electrodes remained chemically stable and mechanically intact under open circuit conditions even after prolonged use.     

An Easy Process to Prepare a Copper(I)/Copper Sulfide Electrode and Its Behavior in Alkalimetric Titrations

Abstract

A copper sulfate (Cu₂S) film is formed on the surface of a copper wire by immersion in melted (>55°C) sodium thiosulfate, Na₂S₂O₃·5H₂O. This Cu₂S/Cu electrode is sensitive to sulfide ions and can be used in potentiometric titration of Na₂S solutions with copper(II) cations. Besides, as a novelty, it gives a good response to H⁺ cations at a wide pH range, even in alkaline medium, as checked in potentiometric titration of acetic and phosphoric acids. An analysis of a number of potentiometric measurements leads to interpretation of the electrode response in acidic/basic medium.     

Ion-selective electrode for the determination of prenalterol

A new prenalterol (Pr) ion-selective PVC membrane electrode based on the ion-pair complex of Pr with sodium tetraphenylborate was prepared and its performance characteristics were studied. The electrode exhibited a linear response with a good Nernstian slope over a relatively wide range of concentration. The electrode whose membrane was made of 8.0% (w/w) of ion pair, 49.5% (w/w) of dioctyl phthalate (DOP) and 43.5% (w/w) of PVC showed characteristics higher than those obtained with the other ones, namely, slope of 56.3 mV per concentration decade, at 25 °C; usable concentration range 1.2×10⁻⁵–3.2×10⁻² M prenalterol; response time ≤20 s. Up to 24 h continuous soaking, the calibration graph slope was constant at 56.0 mV per concentration decade, at 25 °C, then it decreased gradually as the time of soaking increases reaching 41 mV per decade after 11 days. The changes in pH did not affect the electrode performance within the range 2.2–7.5. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The electrode showed very good selectivity for Pr with respect to a large number of inorganic and organic cations. The standard addition method and potentiometric titration were used to determine Pr in pure solutions and in pharmaceutical formulations. The relative standard deviations (R.S.D.) of the three methods used for the determination of prenalterol in pharmaceutical formulations were 0.8, 2.1 and 1.9% of the extrapolation, standard addition and potentiometric methods, respectively.     

A New Highly Selective Neodymium(III) Polyvinylchloride Membrane Electrode Based on 4-Hydroxypyrrolidine-2-Carboxylic Acid as an Active Material

The present paper describes the fabrication of a new polyvinylchloride (PVC) membrane electrode for the determination of Nd(III) ion based on 4-hydroxypyrrolidine-2-carboxylic acid (LHP) as an active material along with sodium tetraphenyl borate (NaTPB) as an anionic additive and acetophenone (AP) as solvent mediator. The optimum composition (%, w/w) of the best performing membrane contained 66 AP, 30 PVC, 2 NaTPB and 3 LHP. The basic analytical parameters of this electrode such as slope characteristics, detection limit, response time, selectivity and pH effect were assessed. The electrode displayed a Nernstian response in terms of slope (20.5 ± 0.4 mV per decade) and response time (~8 ± 1 s) over a wide neodymium ion concentration range of 10^–6 to 10^–2 M with a detection limit of 7.5 × 10^?7 M. The potentiometric response of the electrode was constant in the pH range of 3.2?8.9. According to the selectivity coefficients determined by the matched potential method, the interference of many common alkaline, alkaline earth, transition, heavy metals and specially lanthanide ions in determination of Nd(III) ion was very low. The proposed electrode has been successfully used as an indicator electrode in the potentiometric titration of Nd(III) ion with EDTA and applied for determination of Nd(III) ion in mixtures of different ions.     

A Solid Fe2O3 Based Carbon–Epoxy Electrode for Potentiometric Measurements of pH

A solid Fe₂O₃ based carbon-epoxy composite electrode was investigated for use as a potentiometric pH sensor. The electrode was constructed using a mixture of sulfated iron(III) oxide, carbon power, and epoxy resin, which was deposited directly onto a glass tube. The effect of composition (Fe₂O₃, carbon and epoxy resin) on the electrode response and its calibration curve (mV/pH) were investigated. The analytical behavior of the electrode in acid–base titrations was compared with that of a glass electrode. A linear response from pH 1.7 to 12.2 with a slope of –39.7 ± 0.6 mV/pH (at 25°C) was observed.     

Non-aqueous redox determination of ascorbic acid with copper (II)

Hydrated copper (II) perchlorate (in acetonitrile) has been used for the direct visual and potentiometric determination of ascorbic acid in acetic acid-acetonitrile media. Diphenylamine and diphenylbenzidine are suitable indicators. A bright platinum wire is used as indicator electrode and a modified calomel or an antimony electrode as reference electrode for the potentiometric titration. Ascorbic acid is oxidized to dehydroascorbic acid. The proposed method is simple, accurate and reliable. The reverse titration also works well.     

Electrochemical characterization and application of Ni-RuO2 as a pH sensor for determination of petroleum oil acid number

Electrochemical characterization and application of nickel ruthenium dioxide (Ni-RuO₂) as a pH sensor for the determination of petroleum oil acid number is described. The sensor consists of RuCl₃ thermally decomposed onto the upper side of a polycrystalline nickel electrode at 400 °C in an open furnace. The advantages of the sensor are: (i) easy preparation, (ii) fast response in a large pH range, (iii) high physical and chemical stability, and (iv) excellent reproducibility as determined by the reproducible linear variation of charge transfer resistance (R_ct) as a function of overpotential (η) obtained by electrochemical impedance spectroscopy (EIS), and the Nernstian slope of the electrode potential in a wide range of pH (1.5–12.5) obtained by potentiometric measurements. The potentiometric selectivity coefficients of the sensor toward some anions and cations were evaluated in aqueous solution. The characterized Ni-RuO₂ pH sensor was successfully tested for the determination of petroleum oil acid number.     

Palladium metal electrode and its analytical application to precipitation and acid–base analysis in aqueous and non-aqueous media

Electrochemical characterization of palladium electrode has been reported. The investigated electrode showed a linear dynamic response for p-toluensulfonic acid and iodide ions in the concentrations range between 5?×?10^?1 and 1?×?10^?5 mol L^?1 with a Nernstian slope of 55 mV for p-toluensulfonic acid and 63 mV per decade for iodide ions in water, as well as 53 mV for p-toluensulfonic acid and 51 mV per decade for iodide ions in dioxane. The response time of the electrodes was less than 10 s in the used solvents. Some potential analytical applications of the sensors have been pointed. Palladium electrode for the potentiometric titrations of acids (citric, barbituric, and p-toluensulfonic acid), bases (N,N’-diphenylguanidine, tributylamine, and 2,2'–bipyridine), halides, and some real samples in aqueous and non-aqueous solutions were studied. Тetrabutylammonium hydroxide, perchloric acid, and silver nitrate proved to be very suitable titrating agents for these titrations. The standard deviation of the determination of the investigated compounds was less than 0.9 % from those obtained with a glass electrode, i.e., silver electrode.     

Chemically modified electrode based on poly[tetra(4-aminophenyl)porphyrin] as a pH sensor

A chemically modified platinum electrode with coated poly[tetra(4-aminophenyl)porphyrin] has been used as a potentiometric pH sensor. It gives a linear response over the pH range 1.5-13.7 with a slope of 55 mV/pH (at 20 degrees ). The sensor has fair resistance to erosion of hydrofluoric acid and to interference of a coexisting redox couple. The sensor can be used for pH determination and end-point indication for potentiometric titration of hydrofluoric acid with sodium hydroxide. The a.c. impedance of the polymer membrane has also been studied.