The aluminium indicator electrode in acid-base potentiometric titrations

Aluminium has been employed as an indicator electrode in potentiometric acid-base titrations. The titration curves obtained were approximately 3.6 times broader than those obtained with the antimony electrode.     

Natural pyrite as an electrochemical sensor for potentiometric titrations with EDTA, mercury(II) and silver(I)

The results obtained in potentiometric titrations of copper(II), mercury(II) and iron(III) with standard EDTA solutions are presented. The titration of copper(II) at pH values in the range from 8.11 to 10.99 (ammonia buffer) and the titration of mercury(II) and iron(III) at pH values from 3.59 to 5.65 (acetate buffer) were performed. The titration end-point (TEP) was detected with an indicator electrode made from natural crystalline pyrite as an electrochemical sensor. The results obtained in potentiometric titration with the pyrite electrode were compared with those obtained using a platinum electrode (Fe³⁺), a Cu ion selective electrode (Cu²⁺) and a Hg electrode (Hg²⁺). Accurate and reproducible results with good agreement were obtained, but higher potential changes at the TEP were obtained using the pyrite electrode. In the course of the titration the potential was established within less than 1 min, whereas at the TEP it was within about 2–3 min. The potential changes at the TEP were in the range from 60 to 200 mV per 0.1 ml EDTA, according to the stability constant of the complex formed. The highest potential changes, ranging from 160 to 200 mV, were obtained in the titration of iron(III) at pH 3.59. Reverse titration was also performed and accurate and reproducible results were obtained. Moreover, titration of halogenide and thiocyanate with standard mercury(II) solutions, as well as cyanide with silver(I) solution, were performed and accurate and reproducible results were again obtained. Received: 20 February 1998 / Accepted: 19 November 1999     

Polypyrrole-calcion film as a membrane and solid-contact in an indicator electrode for potentiometric titrations

This paper shows the application of conducting polymers (CPs) for constructing potentiometric indicator electrodes. Two types of polypyrrole (PPy)-based calcium sensors are presented, one sensor with PPy-calcion film as the active part and the other sensor with PPy-calcion as a solid-state contact coated with a conventional membrane selective towards calcium ions. It is shown that the PPy-calcion film, due to the complexing properties of calcion ensuring high loading of the film with calcium, is sufficiently selective to be used as the active part or as a mediating layer of the indicator electrode. The electrode, with PPy-calcion film as the active part, was used as the indicator electrode in potentiometric titrations of calcium in mixed solvents, where conventional PVC-based electrode can not be used. For the first time, the practical applicability of PPy-based electrodes in titrations is demonstrated.     

Mercury-mercurous acetate indicator electrode for potentiometric titrations in anhydrous acetic acid

The authors describe a metallic mercury electrode covered with a mercurous acetate coating, its preparation, its use as an indicator electrode in anhydrous acetic acid neutralization titrations and its properties as compared with other electrodes used for the same purpose.     

Iodine--iodide reference electrode for potentiometric titrations of bases in acetic acid

The suitability of the half-cell Pt/I2, KI in glacial acetic acid as reference electrode for potentiometric titrations of weak bases in the same medium was investigated. This electrode is easily prepared. It has been found very convenient in use and performing at least as well as the best electrodes used for the same purpose. Some phenomenological aspects of the behaviour of the above half-cell, of interest for the use as the reference electrode in the laboratory practice have been observed, that show important differences respect aqueous medium and other organic solvents.     

Natural monocrystalline chalcopyrite and galena as electrochemical sensors in non-aqueous solvents. Part II: potentiometric titrations of weak acids in N,N-dimethyformamide and N-methylpyrrolidone

Natural monocrystalline chalcopyrite and galena as new indicator electrodes for the potentiometric titration of weak acids in N,N-dimethylformamide and N-methylpyrrolidone were used. The investigated electrodes showed a linear dynamic response for p-toluenesulfonic acid concentrations in the range from 0.1 to 0.001 M, with a Nernstian slope of 59.0 mV for chalcopyrite and 33 mV per decade for galena in N,N-dimethylformamide, 56.1 mV for chalcopyrite, and 32.0 mV per decade for galena in N-methylpyrrolidone. The potential in the course of the titration and at the titration end point was rapidly established. 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 electrodes is limitless. The advantages of the electrodes are log-term stability, fast response, reproducibility, easy preparation, and low cost. The results obtained in the determination of the investigated weak acids deviated on average by ±0.04–0.34% from those obtained with a glass electrode.     

On the use of the mercury electrode in chelatometric potentiometric titrations

Summary Information is given on the applicability of the mercury electrode in chelatometric potentiometric titrations. The influence of ternary complex formation, the formation of precipitates on the electrode and possible errors, due to the asymmetric shape of the titration curves are discussed.

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Über die Verwendung der Quecksilberelektrode bei chelatometrisch-potentiometrischen Titrationen

Zusammenfassung Einige Betrachtungen werden angestellt über die Anwendung der Quecksilberelektrode für komplexometrische Titrationen mit potentiometrischer Endpunktsanzeige. Der Einfluß der Bildung ternärer Komplexe, die Bildung von Niederschlägen auf der Elektrode und die Fehler infolge der Asymmetrie der Titrationskurven werden besprochen.

     

Polycrystalline and monocrystalline antimony, iridium and palladium as electrode material for pH-sensing electrodes

Different ways of making pH-sensing electrodes from monocrystalline or polycrystalline antimony, iridium and palladium have been investigated. Monocrystalline antimony and iridium are superior to the polycrystalline elements with respect to reproducibility between electrodes and stability of the electrode potential over long periods of time. No good palladium/palladium oxide electrode could be obtained by electrochemical oxidation and the thermal preparation method could not take advantage of the properties of the monocrystalline palladium. Therefore, only polycrystalline palladium was used to study this type of electrodes. The different electrodes were compared with respect to the manner of preparation, the pH-response (reproducibility and time response) and the effect that different complexing ligands present in the measuring solutions may have on the electrode response. Also, the redox-response of the electrodes and the effect of different oxygen pressures on the electrode potentials were studied. The monocrystalline antimony electrodes have the best reproducibility and long-term stability but also respond to complexing ligands and to variations in the oxygen pressure. Monocrystalline iridium electrodes can be obtained by continuously cycling the potential between -0.25 and +1.25 V (SCE) in 0.5M sulphuric acid. They do not respond to the complexing ligands tested, and have fairly good long-term stability, but the reproducibility between electrodes is inferior to that of the monocrystalline antimony electrodes. Polycrystalline antimony and iridium electrodes were inferior to the monocrystalline ones. The properties of the palladium electrodes were similar to those of the iridium ones.     

Equivalence volumes in potentiometric titrations

The development of methods for finding the equivalence volume by using linear regression methods is reviewed. The methods discussed are mainly those developed and used at the Department of Analytical Chemistry at the Royal Institute of Technology in Stockholm. No attempt has been made to cover the large number of methods of finding the equivalence volume in potentiometric titrations developed elsewhere.     

Quinquevalent tungsten as a reducing agent in potentiometric titrations

Qmnquevalcnt tungsten prepared by the electrolytic reduction of tungstate in ION HC1 is sufficiently stable when kept in strong acid solutions under COg to be used as an effective reducing agent in potcntiometric titrations. It can be accurately standardised with dichromate. The formal redox potentials of the $\text{W}{}^{\mathrm{+6}}\text{W}{}^{\mathrm{+5}}$ system as determined at different acidities indicate that quinquevalent tungsten is more reducing than the corresponding molybdenum compound.Quinquevalent tungsten can be applied successfully as a volumetric reagent in the potentiometric titration of ferric iron in 8-ioN HC1 or in a mixture of HCl and H3PO4 0.5.N each and of cupric copper in 8N HCl at 80° C. It can also be applied for the estimation of iodate, provided that the latter is used as the titrant.     

Construction of a permanganate ion-selective electrode and its application to potentiometric titrations

The construction of a liquid-membrane type permanganate ion-selective electrode and its application to potentiometric titrations are described. The benzylcetyldimethylammonium-permanganate ion-pair in the aqueous phase is easily extracted into nitrobenzene and the extract is employed as the liquid ion-exchange membrane of the ion-selective electrode. The electrode gives Nernstian response to permanganate in the concentration range from 10(-6) to 10(-1)M, and the potential is almost independent of pH over the range from 3.0 to 10.5. The electrode can be used as indicator electrode in potentiometric titrations with permanganate.     

Aluminum as a superior endpoint sensor in some potentiometric titrations

Summary Aluminum rod and wire sensors surpassed conventional sensors in the magnitude of potentiometric breaks obtained in the titration of halides vs. silver ions, aluminum vs. fluoride ions, fluoride vs. lanthanum ions, and phosphate vs. lead, cerous, and lanthanum ions. In the titration of fluoride vs. aluminum or thorium, sulfate vs. lead, and phosphate vs. silver ions, however, conventional sensors were superior to aluminum. In the titration of phosphate vs. lead, cerous, or lanthanum ions endpoint breaks occurred in the negative direction, unlike the usual breaks in the titration of anions vs. cations. The theoretical basis for these phenomena remains unexplained.

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Aluminium als vorteilhafter Endpunkt-Sensor bei potentiometrischen Titrationen

Zusammenfassung Stab- und Draht-Sensoren aus Aluminium übertreffen konventionelle Sensoren durch die Grö\e der potentiometrischen Stufe bei folgenden Titrationen: Halogenide gegen Silber, Aluminium gegen Fluorid, Fluorid gegen Lanthan, Phosphat gegen Blei, Cer(III) oder Lanthan. Dagegen sind bei Titrationen von Fluorid gegen Aluminium oder Thorium sowie von Sulfat gegen Blei und Phosphat gegen Silber konventionelle Sensoren vorteilhafter. Bei der Titration von Phosphat gegen Blei, Cer(III) oder Lanthan verlaufen die Endpunktstufen in negativer Richtung, im Gegensatz zu den üblichen Stufen bei der Titration von Kationen vs. Anionen. Die theoretischen Grundlagen für diese Erscheinungen sind noch ungeklÄrt.

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Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-ENG-48.     

以锑电极作参比电极测定废水中硫化物

提出了以锑电极作为参比电极与Ag2 S电极组成无液接测量电池测定废水中硫化物的新方法。并研究了电极的性能 ,测定条件及干扰物质的影响。方法的线性范围 1 .0× 1 0 - 2 mol/L～ 5 .0× 1 0 - 7mol/L[S2 - ],回收率为 99%～1 0 3%     

Voltammetric,potentiometric and amperometric studies with a rotated aluminum wire electrode: The R.Al.E. as indicator electrode in potentiometric and amperometric acid-base titrations

The effect of varying concentrations of fluoride on the potential of the R.AI.E. in acid buffer solutions is reported. In the pH range between 1 and 5.5 the potential becomes 30 mV more negative per unit increase in pH at fluoride concentrations between 10^-3 and 10^-4M. At a given pH the potential becomes 100 mV more negative when the fluoride concentration is increased from 10^-4 to 10^-3it. No depolarization occurs and no reproducible potentials can be measured in phosphate buffers of pH 6 to 8, even in the presence of 10^-3M fluoride. This concentration of fluoride causes depolarization and establishment of reproducible potentials in veronal buffers of reproducible pH 6 to 8. At a pH greater than 9 fluoride has no effect on the electrode potential which now becomes determined by pH. In the presence of fluoride, oxygen shifts the electrode potential to less negative values (mixed potential). Examples of potentiometric and amperometric titrations of strong and weak acids are given with the R.AI.E. as indicator electrode.     

Logarithmic diagrams and gran-curves as an aid in potentiometric titrations in complexometry

A detailed exposition is given of the use of logarithmic diagrams and Gran plots to construct titration curves and to determine accurately the equivalence point in potentiometric complexometric titrations.     

Calculated equivalence volume in potentiometric acid-base titrations

Summary Using a pH meter, a motorized burette and a programmable pocket calculator potentiometric acidbase titrations may be carried out with a high degree of precision, a high degree of accuracy and in a time comparable to the time needed to perform a titration with a visual indicator. With the exception of the lowest concentration of the weak acid a precision higher than 0.01 ml of the reagens is easily obtainable, whereas the accuracy may be as high as 0.1 %. The method is suitable over a wide range of concentrations of either strong or weak acids.

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Berechnetes Äquivalenzvolumen bei potentiometrischen Säure-Base-Titrationen

Zusammenfassung Mit Hilfe eines pH-Meßgeräts, einer Motorbürette und einem programmierbaren Taschenrechner können potentiometrische Säure-Base-Titrationen mit hoher Reproduzierbarkeit und Richtigkeit in einer mit der Verwendung von visuellen Indicatoren vergleichbaren Zeit durchgeführt werden. Mit Ausnahme der niedrigsten Konzentration einer schwachen Säure wurde eine Reproduzierbarkeit von besser als 0,01 ml und eine Richtigkeit von 0,1 % erhalten. Das Verfahren ist für einen weiten Konzentrationsbereich von starken und schwachen Säuren geeignet.

     

Cetylpyridinium-iodomercurate PVC membrane ion selective electrode for the determination of cetylpyridinium cation in Ezafluor mouth wash and as a detector for some potentiometric titrations

A potentiometric method is described for the determination of cetylpyridinium (CP) cation using a polyvinyl chloride powder (PVC) membrane sensor based on CP-iodomercurate ion pair as an electroactive material. The sensor shows a linear response for CP ion over the concentration range of 2x10(-6)-1x10(-3) M at 25 degrees C. The electrode posses a sub-Nernstian slope of 29.0+/-0.4 mV decade(-1), which has been thoroughly discussed.The electrode shows a fast potential response of approximately 50 s, which is almost constant over a pH range of 3.0-6.0. Selectivity coefficient data for some common ions show negligible interference, however, cetyltrimethylammonium bromide (CTMAB) interferes significantly. An average recovery of 98.8% for CP with an average relative standard deviation (R.S.D.) of 1.2% has been achieved. The determination of CPC in Ezafluor mouth wash gave result that compare favorably with those obtained by the British Pharmacopoeia method. The CP electrode has been utilized as an end point indicator electrode in potentiometric titration of some anions, and applied for the determination of anionic surfactants in some commercial detergents and waste water.     

Method for determination of the equivalence point in potentiometric titrations

A method is developed for calculating the end-point and the ionization constant in a potentiometric titration. The influence of dilution is studied. The method is compared with the procedure of KOLTHOFF and that of HAHN.     

Critical evaluation of potentiometric redox titrations in enology

Measurements of the zero current potential of a platinum electrode immersed in solutions of tanins or in wines of various origins, were performed during the additions of a solution of Ti(III), or of a solution of dichlorophenolindophenol (DCPIP), in order to obtain a global indication for the resistance to oxidation of some wines. The steady state intensity-potential curves on a platinum electrode highlight the occurrence of mixed potentials between the oxidation of ethanol or catechin and the reduction of oxygen present at very low concentrations, as well as the irreversibility of the redox system Ti(IV)/Ti(III). The adsorption of various species on the platinum and the slowness of the oxidation reactions by DCPIP exclude use of potentiometric titration theory. The shape of the potential-reagent volume curves depends on the nature of the solution and on the rate of reagent introduction. Generally, due to the slowness of the oxidation reactions with DCPIP it is impossible to find a linear relationship between the volume of titrant solution necessary to reach the inflexion point of the curves and the solution composition.