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     

PbO2-based graphite-epoxy electrode for potentiometric determination of acids and bases in aqueous and aqueous-ethanolic media

The construction and analytical evaluation of a PbO2-based graphite-epoxy electrode sensitive to H3O+, based on incorporation of lead(IV) oxide in a graphite-epoxy matrix, are described. The data obtained from a variety of acid-base titrations in aqueous and aqueous-ethanolic media were compared with those obtained by use of a glass electrode under the same conditions. The proposed electrode provides a linear response in the pH range from 1 to 11 with a slope of -58.7+/-0.3 mV pH(-1) and -60.8+/-0.2 mV pH(-1) in aqueous and ethanolic media, respectively. The response time was less than 15 s and the lifetime of the electrode was at least eight months (ca. 5000 determinations) and its performance is good in pH determination and end-point detection in potentiometric acid-base titrations in both aqueous and aqueous-ethanolic media.     

Simple PVC–PPy electrode for pH measurement and titrations

Cobaltabis(dicarbollide) [3,3'-Co(1,2-C2B9H11)](-)-doped polypyrrole (PPy) films have been prepared galvanostatically on glassy carbon electrodes in acetonitrile solution. The potential response behavior of the film of this new material has been investigated in some common pH buffers and in acid-base titrations. The potentiometric characteristics of the resulting films are indicative of a quasi-Nernstian response (approximately 50 mV/pH unit), a linearity range from pH 12 to 3 and correlation coefficients (r2) of approximately 0.98. The electrode is suitable for pH measurements and for monoprotic titrations of strong alkalis with strong acids, and weak bases with strong acids, but the long response time hinders the use of this electrode for multiprotic titrations. The time response has been dramatically improved by reducing the film thickness by using the template effect of a non-conducting polymer (PVC) cast over the graphite surface before PPy deposition. PPy polymerization occurs in the free channels of PVC leading to the formation of PPy wires. The morphological change of PPy does not affect the slope or linearity range. The response of the PVC-PPy electrochemical sensor is rapid and the sensor is easy to prepare, at low cost, and its performance is comparable with that of commercial glass electrodes.     

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.     

Electrochemical characterization and analytical application of arsenopyrite mineral in non-aqueous solutions by voltammetry and potentiometry

Based on the cyclic voltammetric method, in the present study we have employed carbon paste for arsenopyrite mineral characterization in non-aqueous solution. Arsenopyrite yields well-defined cyclic voltammetric responses with well-defined oxidation (in the potential region from −0.7 to 0.7 V, versus Ag/AgCl) and reduction (from −1.0 to 0.8 V) peaks using this electrode. In addition, arsenopyrite mineral was studied as a new indicator electrode for the potentiometric titrations of acids (benzoic, anthranilic and salicylic acids) and bases (N,N′-diphenylguanidine, tributylamine and collidine) in acetonitrile and propionitrile. Potassium hydroxide, tetrabutylammonium hydroxide (TBAH) and perchloric acid proved to be very suitable titrating agents for these titrations.The investigated electrode showed a linear dynamic response for p-toluenesulfonic acid concentrations in the range 0.1-0.001 M, with a Nernstian slope of 38.5 mV in acetonitrile and 44.6 mV in propionitrile. The electrode showed a relatively fast response time and can be used without any time limit or without considerable divergence in potentials. The response time of the electrode was less than 10 s in both solvents. The standard deviation of the determination of the investigated acids and bases was less than 0.6% from those obtained with a glass electrode.The advantages of the electrodes are long-term stability, fast response and reproducibility, while the sensors are easy to prepare and are of low cost.     

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.     

Natural monocrystalline pyrite as electrode material for potentiometric titrations in water

The possibility of applying natural monocrystalline pyrite as sensor for the potentiometric titration of acids in water was investigated. The potential of this electrode in aqueous solutions exhibits a sub-Nernst dependence. In fresh solutions the slope (mV/pH) is 33.9. The potential jumps at the titration end-point obtained in titrations of HCl, H(3)PO(4) and CH(3) COOH do not differ much from those obtained by the application of the glass electrode as the indicator one. The potentials in the course of the titration and at the titration end-point (TEP) are rapidly established. The results obtained in the determination of the investigated acids deviated for 0.16-0.34% with respect to those obtained by using the glass electrode as the indicator one.     

Organic-inorganic composite cation-exchanger: poly-o-toluidine Zr(IV) phosphate-based ion-selective membrane electrode for the potentiometric determination of mercury

A new heterogeneous precipitate of an organic-inorganic composite cation-exchanger poly-o-toluidine Zr(IV) phosphate was utilized for the preparation of a Hg(II) ion-sensitive membrane electrode for the determination of Hg(II) ions in real aqueous as well as in real samples. The electrode showed good potentiometric response characteristics, and displayed a linear log[Hg(2+)] versus EMF response over a wide concentration range of 1 x 10(-1) - 1 x 10(-6) M with a Nernstian slope of 30 mV per decade change in concentration with a detection limit of 1 x 10(-6). The membrane electrode showed a very fast response time of 5 s and could be operated well in the pH range 2 - 8. The selectivity coefficients were determined by the mixed-solution method, and revealed that the electrode was selective in the presence of interfering cations; however most of these did not show significant interference in the concentration range of 1 x 10(-1) - 1 x 10(-4) M. The lifetime of the membrane electrode was observed to be 120 days. The analytical utility of this electrode was established by employing it as an indicator electrode in the potentiometric titrations of Hg(2+) ions from a synthetic mixture as well as drain water.     

Coated wire silver-ion selective electrode based on a N,N'-bis(2-thienylmethylene)-1,2-diaminobenzene.

A novel membrane coated platinum-wire electrode (MCPWE) based on N,N'-bis(2-thienylmethylene)-1,2-diaminobenzene (BTMD) for highly selective determination of Ag+ ion has been developed. The influences of membrane composition and pH on the potentiometric responses of electrode were investigated. The potentiometric responses are independent of the pH of the test solution in the range of 5.0 - 9.0. The electrode shows a linear response for Ag+ ion over the concentration range of 1.0 x 10(-60 to 1.0 x 10(-1) M with a lower detection limit of 6.0 x 10(-7) M. The electrode possesses a Nernstian slope of 59.7 mV decade(-1) and a fast response time of < or = 17 s and can be used for at least 2 months without any observable deviation. The proposed electrode displayed very good selectivity for Ag+ ion with respect to NH4+ and alkali, alkaline earth and some common transition metal ions. The practical utility of the electrode has been demonstrated by its use as the indicator electrode in the potentiometric titration of an AgNO3 solution with a NaI solution and in determination of the silver content of a developed radiological film.     

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.     

聚苯胺修饰电极酸碱示波电位滴定法——Ⅰ.水溶液中的酸碱滴定

示波电位滴定具有终点直观、仪器便宜、操作简便、快速、准确等特点。本文将对氢离子响应敏锐、使用寿命长、制备简单的聚苯胺修饰电极(PAME)^[4,5]应用于酸碱示波电位滴定中,使电位突跃更加明显,化学计量点更易判断(与双铂电极体系比较),可滴定多元弱酸、弱碱、混合酸和混合碱.与pH玻璃电极比较,具有阻抗低,响应灵敏、迅速,终点电位突跃大,不易损坏,不需预处理,制备简单等特点.     

Hydralazine-selective PVC membrane electrode based on hydralazinium tetraphenylborate

A hydralazine ion-selective PVC membrane electrode based on hydralazinium tetraphenylborate has been prepared with dioctyl phthalate as plasticizer. The electrode showed linear response with a slope factor of 57.5 mV/concentration decade at 20 degrees over the concentration range from 4 x 10(-4) to 10(-1)M hydralazine. The effects, on the electrode performance, of membrane composition, pH of the test solution and the time of soaking were studied. The electrode exhibited good selectivity for hydralazine with respect to a large number of inorganic cations and organic substances of biological importance. The standard-addition method and potentiometric titrations were used to determine hydralazine concentrations in pure solutions and in a pharmaceutical preparation, with satisfactory results.     

A liquid state Hg(2+)-sensitive electrode

The construction and basic characteristics of a liquid-state Hg(2+)-sensitive electrode are discussed. The membrane consists of the Hg(2+) chelate of diketohydrindylidene-diketohydrindamine (DYDA) in chloroform. The range of linear response of the electrode is 10(-1)-10(-5)M Hg(2+) with a slope of 31 mV/decade. The response time of the electrode is a few seconds in concentrated solutions. The electrode may be used with good results in potentiometric titrations involving Hg(2+).     

Flow injection analysis with tubular membrane ion-selective electrode and coated wires for buspirone hydrochloride

New Plastic membrane ion-selective electrode for buspirone hydrochloride based on buspironium tetraphenylborate was prepared. The electrode exhibited mean slope of calibration graph of 58.4 mV per decade of BusCl concentration at 25 degrees C. The electrode can be used within the concentration range 6.3 x 10(-5) - 10(-2) M BusCl at a pH range of 2.5-7.0. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal temperature coefficient of the electrode, amounting to 0.00056 V degrees C(-1). The electrode showed a very good selectivity for BusCl with respect to a number of inorganic cations, sugars and amino acids. The electrode was applied to the potentiometric determination of the buspirone ion and its pharmaceutical preparation under batch and flow injection conditions. Also, buspirone was determined by conductimetric titrations. Graphite rod, copper and silver coated wire electrodes were prepared and characterized as sensors for the drug under investigation.     

Natural monocrystalline chalcopyrite and galena as electrochemical sensors in non-aqueous solvents. Part I: potentiometric titrations of weak acids in γ-butyrolactone and propylene carbonate

Natural monocrystalline chalcopyrite and galena as new indicator electrodes for the potentiometric titrations of benzoic, anthranilic, -nitroso--naphthol and salicylic acids in -butyrolactone (GBL) and propylene carbonate have been used. Potassium hydroxide in methanol was employed as the titrating agent. The results are compared with those obtained using a glass electrode. The investigated electrodes showed a linear dynamic response for p-toluensulfonic acid concentrations in the range from 0.1 to 0.001 M, with a Nernstian slope of 63 mV for chalcopyrite, 66 mV per decade for galena in GBL, 77 mV for chalcopyrite and 98 mV per decade for galena in propylene carbonate. Both electrodes showed a relatively fast response time and can be used without any time limit or without considerable divergence in potentials. The standard deviation of the determination of the investigated acids was less than 0.5%.     

A mercury(II) ion-selective electrode based on N,N-dimethylformamide-salicylacylhydrazone as a neutral carrier.

A new PVC membrane mercury(II) ion electrode based on N,N-dimethylformamide-salicylacylhydrazone (DMFAS) as an ionophore is described, which shows excellent potentiometric response characteristics and displays a linear log[Hg(2+)] versus EMF response over a wide concentration range between 6.2 x 10(-7) and 8.0 x 10(-2) M with a Nerstian slope of 29.6 mV per decade and a detection limit of 5.0 x 10(-7) M. The response time for the electrode is less than 30 s and the electrode can be used for more than 2 months with less than a 2 mV observed divergence in a potentials. The proposed electrode exhibits very good selectivity for mercury(II) ions over many cations in a wide pH range (pH 1 - 4). The electrode was also applied to the determination of a mercury(II) ion in vegetables and in Azolla filiculoides.     

Potentiometric Determination of Acids and Bases using Silicone Rubber Based Graphite Electrode

Abstract

A silicone rubber based graphite electrode has been used as an indicator electrode for potentiometric acid-base titrations. The electrode potential changes an average of 30 mV per pH-unit. If the electrodes are pretreated with a solution of an oxidant before use, the pH-sensitivity is increased. The electrode can be used in both aqueous and non-aqueous solutions. A measuring cell, composed of a silicone rubber based graphite electrode of small surface area and a chloride-selective reference electrode, can be used for acid-base titrations in the micro range.     

A deuterium-palladium electrode as a new sensor in non-aqueous solutions: potentiometric titration of weak acids in acetonitrile and benzonitrile

A deuterium-palladium electrode was employed as a new indicator electrode for the titration of weak acids in acetonitrile and benzonitrile. The investigated electrode showed a linear dynamic response for p-toluenesulfonic acid in the concentration range from 0.001 M to 0.1 M with a Nernstian slope of 48 mV in acetonitrile. Sodium methylate, potassium hydroxide and tetrabutylammonium hydroxide proved to be very suitable titrating agents for these titrations. The response time was less than 10-11 s and the lifetime of the electrode was limitless. Advantages of the electrode are: long-term stability, fast response, reproducibility, easy preparation and low cost.     

Clotrimazole-triiodide ion association as an ion exchanger for a triiodide ion-selective electrode.

A novel triiodide ion-selective electrode based on a clotrimazole-triiodide ion pair as a membrane carrier was prepared. It has a linear response to triiodide from 8 x 10(-6) to 5 x 10(-3) M with a slope of -68.9 mV per decade and a detection limit of 5 x 10(-6) M. The electrode response is independent of the pH of the solution in the pH range 2-9. It has a very short response time and can be used for at least 3 months without any considerable divergence in the potentials. The proposed sensor revealed very good selectivities for I3- over a variety of other anions. It was used as an indicator electrode in the potentiometric titration of triiodide ions and in an indirect potentiometric determination of clotrimazole in pharmaceutical preparations.     

Flow Injection Potentiometric Determination of Coke Acidity and Acetic Acid Content in Vinegar Using an Antimony Electrode

Abstract

A flow injection potentiometric procedure is proposed for the determination of acidity of several samples using an antimony/ antimony oxide electrode. The ΔE/pH curve in phosphate buffer solutions in the pH range from 1.58 to 12.00 showed a linear sub-Nernstian behavior with an operational slope S =-42.1mV/pH_c and a conditional standard potential of 264.8mV. This flow potentiometric electrode responds linearly to low acidity variations of dilute acetic acid solutions from 3.16 to 100mM with a slope of 30.1mV/dec and analytical frequency of 23 results/h. Good reproducibility and an average standard deviation of ±0.5% was obtained. The application of this sensor for the determination of coke acidity and acetic acid in vinegar is reported.