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.     

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.     

Acid-base strengths in 1,2-dichloroethane

The pK_a value of hydriodic acid in 1,2-dichloroethane was determined from conductivity measurements. A glass electrode was calibrated for dichloroethane in the potentiometric titration of hydriodic acid with tetramethylguanidine. From potentiometric titrations, the pK_a values in dichloroethane of hydrobromic acid, hydrochloric acid, picric acid and some sulfonphthaleins as well as some protonated nitrogen bases were determined. In the curves of the titrations of the carboxylic acids and the hydrogen halides with TMG, evidence was found for the formation of the complex B(HX)₂.     

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.     

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.     

The coulometric titration of acids and bases in dimethylsulfoxide media

The coulometric titration of 20–200 μeq of acids and bases in DMSO media is described. In the titration of bases, the electro-oxidation of hydrogen at a platinized platinum electrode is used as the source of protons. The conditions for 100 % current efficiency at this electrode are low current density to avoid passivity and regular treatment of the electrode with potassium dichromate—sulfuric acid to remove a poisoning sulfide layer. The accuracy of the titrations is better than ±1 %. Very weak acids like phenols (pK_a (DMSO) ≈16) can be titrated successfully. Tris(hydroxymethyl)aminomethane is the weakest base titrated.     

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%.     

An evaluation of some simple sulfonic acids as nonaqueous titrants

The simple aliphatic and aromatic sulfonic acids show evidence of possibilities as new titrants in a glacial acetic acid medium. Excellent precision is obtained in potentiometric titrations with both ethane- and methane sulfonic acids with a standard deviation of 0.2%. Benzenemonosulfonic and naphthalenesulfonic acids both give an average precision of 0.4%. In visual titrations with with crystal violet indicator, the color changes at the end-point are very sharp. The chief advantage of these acids as titrants lies in the fact that they dissolve readily in glacial acetic acid and can be titrated to give reproducible results with the glass-calomel electrode system. None of the sulfonic acids tested was as strong a titrant as perchloric acid, but, unlike perchloric acid, they did not form precipitates or gels in the titration with potassium acid phthalate.     

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.     

Signal processing with a summing operational amplifier in multicomponent potentiometric titrations

It has been proved that application of two indicator electrodes connected to the ordinary titration apparatus through an auxiliary electronic device (a summing operational amplifier) significantly extends the scope of multicomponent potentiometric titrations in which the analytes are determined simultaneously from a single titration curve. For each analyte there is a corresponding potential jump on the titration curve. By application of the proposed auxiliary device, the sum of the electrode potentials is measured. The device also enables the relative sizes of the potential jumps at the end-points on the titration curve to be varied. The advantages of the proposed signal processing are exemplified by complexometric potentiometric titrations of Fe(III) and Cu(II) in mixtures, with a platinum electrode and a copper ion-selective electrode as the indicator electrodes.     

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.     

Comparison of a single-use pH test strip and a glass electrode for potentiometric titration

The potentiometric titration of a carbonate mixture or an acetate solution is a common experiment in analytical laboratories. Typically, a glass electrode combined with a calomel or Ag/AgCl reference electrode is used to locate the equivalence points in neutralization titrations. The dissociation constants of weak acids and bases can be calculated from the pH at the half-neutralization point. Recently, a new commercial product for measuring pH has been developed. This novel acid–base detection strip is a single-use sensor that requires neither storage in a preservation liquid nor calibration prior to use. This study examined its suitability for the continuous monitoring of pH changes in potentiometric titrations of carbonate mixtures, acetate solutions, or ammonia solutions. There were no significant differences in the concentrations of solutions tested using a glass electrode and a pH test strip. The pK_a, pK_b, and pH values determined using the two systems differed by less than 5%. The results confirmed that the pH strips are suitable for continuously monitoring pH changes during neutralization titrations. However, the strips can only be used once.     

A deuterium–palladium electrode as a new sensor in non-aqueous solutions: potentiometric titration of weak acids in N,N-dimethylformamide and N-methylpyrrolidone

A deuterium–palladium electrode was employed as a new indicator electrode for the titration of weak acids in N,N-dimethylformamide and methylpyrrolidone. The investigated electrode showed a linear dynamic response for p-toluenesulfonic acid in the concentration range from 0.1 to 0.001 M, with a nernstian slope of 78.0 mV in N,N-dimethylformamide and of 64 mV per decade in N-methylpyrrolidone. Sodium methylate, potassium hydroxide, and tetrabutylammonium hydroxide proved to be very suitable titrating agents for these titrations. The potential in the course of the titration and at the titration end point was rapidly established. The response time was less than 10–11 s, and the lifetime of the electrode is long. The experimental results obtained for the proposed electrochemical sensor and a conventional glass electrode were in good agreement. The advantages of the electrode are log-term stability, fast response, reproducibility, and easy preparation.     

Effect of EDTA/NaF solutions on the orion Cu(II) ion-selective electrode

The titration of ethylenediaminetetra-acetic acid in fluoride medium with Cu(II) solution with the Orion Cu(II) ion-selective electrode as indicator, results (after several titrations) in a broad end-point which is unsatisfactory for exact analytical purposes. This effect has been found to arise from an enhanced rate of response to changes in EDTA concentration when the electrode has been exposed to an EDTA/NaF medium for prolonged periods.     

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.     

交流示波极谱滴定的研究(ⅩⅢ)——有机碱及有机酸盐类药物在水溶液中的中和滴定

本文用交流示波极谱中和滴定技术,在水溶液中直接滴定有机碱和有机酸的盐类药物,简便、快速、准确。     

Metal oxide electrodes as sensors in complexometric titrations

EDTA titrations of lead and manganese, and of some other ions by using these as indicator ions, have been followed potentiometrically with PbO(2) and MnO(2) electrodes. Explanations are put forward for the anomalies observed in the titration curves. With the MnO(2) electrode, formation of an Mn(III)-EDTA complex is responsible for the diminished potential breaks. With the PbO(2) electrode the decrease in the potential break and the distortion of the curves in acid solution may be due to reaction between electrode coating and titrant. The MnO(2) electrode has been used for titrations of Ba(2+) Ca(2+), Cd(2+) and Cu(2+) with errors < 1%.     

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.     

Developments in indicators

The use of metal ion-metallochromic indicator complexes as narrow-range pH indicators is shown to be advantageous for the titration of weak acids in aqueous media. The Cu-DBAH and the Mg-Azo Violet complexes with apparent pK values of 7.7 and 11.5 have been used for the titrations of benzoic acid and of glycine and phenol, respectively, with good precision.     

The conductometric titration of carboxylic and phenolic acids in non-aqueous solutions : Preliminary experiments

The present study deals with the conductometric titration of weak organic acids and alkylphenols in non-aqueous solution.It is shown that the results are highly dependent on the bases and solvents used. A detailed account is given of experience gained with this method.A series of successful titrations of some types of acids is described in order to illustrate the versatility of conductometric titration.