Determination of two metals from a single potentiometric titration curve The application of two indicator electrodes

The advantages of applying two indicator electrodes in complexometric potentiometric multicomponent titration are shown by means of simulated titration curves. Two measurement arrangements have been considered, one in which the indicator electrodes are directly connected to a voltmeter and the other in which the electrodes are connected to the voltmeter through a summing operational amplifier. They have been compared with the conventional arrangement of a single indicator electrode and a reference electrode. The influence of the stability constants of the complexes in solution and of the electrode parameters on the shape of titration curves has been examined. It is shown that the use of two indicator electrodes may significantly increase the applicability of multicomponent potentiometric titrations.     

Potentiometric titration of hydrogen peroxide with an electropolished stainless steel electrode

The preparation and use of a stainless steel indicator electrode in the accurate potentiometric titration of aqueous hydrogen peroxide are described. The results agree excellently with those obtained by a standard colorimetric weight-titration procedure. The nature of the titration curves, potential changes and the factors affecting them are discussed. Rapid potentiometric titrations directly to the equivalence-point potential are possible, owing to the nature of the titration curve.     

Titrations using an apparatus for recording the antilogarithm of pH or pM

A titration apparatus plotting either the concentration of sample ion or the concentration of titrant ion has been tested. An antilog apparatus, converting measured e.m.f. values into concentrations is connected to ordinary titration equipment. The instrument has been tested by means of acid—base titrations (titrations of mixtures of weak acids and of a weak and a strong acid), precipitation titrations (determination of the chloride concentration in tap-water, titration of mixtures of halides), titrations with ion-selective electrodes (determination of the fluoride content of toothpaste) and complexometric titrations (determination of copper with EDTA, using mercuric ion as indicator ion and amalgamated silver rod as indicator electrode, or using a copper-selective indicator electrode). The method considerably simplifies the evaluation of the results as compared to conventional potentiometric titrations.     

Voltammetric behavior of the iron(II)-(III) and cerium(III)-(IV) couples in potentiometric titrations at constant current and amperometric titrations with two indicator electrodes

The voltammetric behavior at the rotated platinum electrode of the iron(II)-(lII) and cerium (III)-(IV) couples in sulfuric and hydrochloric acids has been investigated The iron and cerium couples are not reversible at a platinum electrode when current flows in the system, and the current-potential curves deviate considerably from those predicted on the basis of reversibility Titration curves for potentiometric titrations at constant current using one and two indicator electrodes are predicted from the current-potential curves and compared with the experimental curves.The degree of reversibility of the iron couple depends greatly on the pretreatment of the electrode The current-potential curves of the iron couple at a platinum electrode coated with a monomolecular film of platinum oxide approach reversibility while those at a clean electrode are highly irreversible Experimental and calculated titration lines for amperometric titrations using two indicator electrodes are compared, and the effects of medium and applied e.m.f. upon the characteristics of the titration curves are considered.     

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.     

Ti/TiO2 indicator electrodes formed by plasma electrolytic oxidation for potentiometric analysis

Ti/TiO₂ indicator electrodes were prepared by plasma electrolytic oxidation (PEO) method in the tetraborate electrolyte and were used for potentiometric indication of chemical reactions of different types and for analysis of surface and industrial wastewaters on the example of potentiometric determination of alkalinity and chloride. The electrodes formed at current densities of 0.05, 0.1, 0.15 and 0.2 A/cm² are different in composition, surface morphology and electroanalytical properties. The electrodes formed at a current density of 0.05 A/cm² exhibit the highest pH-sensitivity and generate the highest analytical signal at the equivalence point in the acid–base and precipitation titrations. The maximum analytical signal at the equivalence point, exceeding in magnitude the analytical signal, obtained by classical Pt electrode in oxidation–reduction and complexometric titrations generates PEO layers formed at a current density of 0.05 A/cm² and a platinum-modified nanoparticles. The results of the potentiometric titration of the surface and technogenic waters using as indicator Ti/TiO₂ electrodes are comparable with the conventionally used glass electrode (to determine alkalinity) and Ag electrode (to the determine chloride) and the results of visual titration. The advantage of the obtained metal oxide systems is the ability to determine two hydrochemical parameters due to their multifunctionality and opportunity to work with a single electrode. In addition, these sensors offer some analytical characteristics such as sensitivity, good reproducibility, high mechanical stability and a simple preparation procedure.     

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.     

Elektroden-probleme in der potentiometrie

The variations of the potential, calculated and observed during a potentiometric titration, are independent of the nature of the electrode used. The influence of changing the rate of agitation upon the potential of silver electrodes of different surfaces is studied. A halide-free reference electrode is described as a suitable simplification in argentometric titrations.     

The platinum-20% rhodium electrode in potentiometry

The performance of a platinum-20% rhodium alloy indicator electrode is studied in a number of potentiometric redox and acid-base titrations and compared with that of the conventional platinum electrode. The potential breaks obtained with the alloy electrode are always smaller than those obtained with the platinum electrode. The end-points are also usually indicated later than the true end-points. The bimetallic electrode system comprising platinum and platinum-rhodium electrodes gives a peak at the correct end-point even with 0.001N concentration titrations, where the ordinary potentiometric systems do not always give good results.     

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.     

用卡尔曼滤波作非平衡电位滴定

用长链四烷基锡为中性载体制备了性能优良的十二烷基磺酸根PVC膜电极。用其为指示电极,以非平衡方式进行快速电位滴定。借卡尔曼滤波方法可靠地确定等当点。引入的滤波算法具有通用性,能有效地节省电位滴定分析时间。     

The chalcocite copper membrane electrode

The membrane electrode based on a synthetic chalcocite (Cu(2)S) single crystal responds primarily to the activity of copper(I) ions in solution. The experimental selectivity coefficient with respect to copper(II) ions is in good agreement with the value calculated on the basis of solubility products of both sulphides. The electrode has been calibrated with metal-ion buffers containing a strongly complexing ligand. TETREN, and can be used as an indicator in titrations of copper with EDTA and TETREN. Comparison of an experimental titration curve with one calculated with the aid of the program HALTAFALL showed good agreement in the case of TETREN, but there were discrepancies for the EDTA titration, which are attributed to the presence and complexation of copper(I) ions. The electrode has also been applied in metal titrations with Cu(2+) as indicator ion, though the potential changes observed were smaller than predicted. All titrations showed errors less than 1%.     

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.     

Ion-selective electrodes in potentiometric titrations; a new method for processing and evaluating titration data

A new method to convert the potential of an ion-selective electrode to concentration or activity in potentiometric titration is proposed. The advantage of this method is that the electrode standard potential and the slope of the calibration curve do not have to be known. Instead two activities on the titration curve have to be estimated e.g. the starting activity before the titration begins and the activity at the end of the titration in the presence of large excess of titrant. This new method is beneficial when the analyte is in a complexed matrix or in a harsh environment which affects the properties of the electrode and the traditional calibration procedure with standard solutions cannot be used. The new method was implemented both in a method of linearization based on the Grans's plot and in determination of the stability constant of a complex and the concentration of the complexing ligand in the sample. The new method gave accurate results when using titrations data from experiments with samples of known composition and with real industrial harsh black liquor sample. A complexometric titration model was also developed.     

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.     

Titrations of weak acids in 1,1,3,3-tetramethylguanidine

The use of 1,1,3,3-tetramethylguamdine (TMG) as a medium for the titrations of weak acids has been investigated. The hydrogen electrode behaves reversibly in this solvent and can serve as an indicator electrode in titration reactions. The titrant was a o.1 M solution of tetrabutylammonium hydroxide in a 90-10% mixture of TMG and methanol. A hydrogen electrode dipping into a TMG solution saturated with benzoic acid served as reference electrode. Potentiometric titrations of a number of weak acids gave results accurate to at least ±0.5%. It was found that in most cases curcumin could be used as an end-point indicator with an accuracy comparable to that of the potentiometric titration.     

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.     

Zero-current bipotentiometric indication using two differently pretreated electrodes

A new potentiometric technique of zero-current bipotentiometry using differently pretreated platinum electrodes is described, and its application to various redox titrations discussed. The potential across the electrodes appears to be generated by differences in kinetics of the reactions occurring on the two dissimilar electrode surfaces.     

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.     

Metal and metalloid indicator electrodes for the non-aqueous potentiometric titration of weak acids: comparative evaluation of group III, IV and V main-group elements

Indicator electrodes constructed from aluminium, gallium, indium, thallium, carbon, silicon, germanium, tin, lead, arsenic, antimony and bismuth have been evaluated for the potentiometric titration of solutions of benzoic acid in dimethylformamide and 4-methyl-2-pentanone. The aluminium, gallium, silicon and arsenic electrodes have also been evaluated for the determination of 3,5-xylenol in the same two solvents. Aluminium, gallium, indium, silicon, germanium, antimony and bismuth electrodes are superior to, or compare favourably with, a glass electrode for the determination of benzoic acid, when the criterion of efficiency is the sharpness of the end-point inflexion. In non-aqueous titrations of 3,5-xylenol, aluminium and gallium electrodes are similar in efficiency to the glass electrode for determinations in dimethylformamide solution, while the gallium electrode is superior to the glass electrode when 4-methyl-2-pentanone is the solvent. Possible relationships between the properties of the electrode element and the end-point sharpness when it is used as an indicator electrode are briefly considered.