Differential potentiometric titrations of binary mixtures of halides with two ion-selective indicator electrodes

Differential potentiometric titrations with two different ion-selective indicator electrodes are described. Ion-selective electrodes for Cl^-, Br^-, I^-, F^-, S^2-, as well as glass and silver billet electrodes were used. The method was tested in the determination of binary mixtures of halides (Cl^-, Br^-, I^-, and F^-) by titration with solutions of silver nitrate, alone and mixed with lanthanum or thorium nitrate as required. Various factors influencing the determination were investigated. Results of simultaneous determinations of mixtures were in good agreement with the results of separate determinations within certain concentration limits. The method was successfully applied to the determination of a four-component halide mixture. Titrations of mixtures of fluoride with thiocyanate or hexacyanoferrate(III), and some other possibilities, are also reported.     

Amperometric ascorbimetric determination of cerium(IV) and Iron(III) with two polarized electrodes

Summary Amperometric ascorbimetric determinations of cerium(IV) and ferric iron have been carried out at 50°C with two polarized electrodes at 200 and 100 mV respectively. The results obtained are fairly accurate and precise within ±1.0 per cent. A simple method for successive determination of cerium and iron has been developed; and conditions for such estimations have been established. At an acidity of 2.5 M with respect to sulphuric acid, it is possible to ward off the reduction of ferric iron and thereby cerium(IV) is successfully titrated with ascorbic acid in this medium. After completion of the reaction and then lowering the acid concentration to p_H 1.5 with aid of ammonium hydroxide, Fe^III is titrated with standard ascorbic acid yielding good results.     

Semiautomatic and automatic catalytic amperometric and catalytic constant-current potentiometric titrations of gold(III)

Semiautomatic and automatic amperometry and constant-current potentiometry were used to follow the course of catalytic titration of gold(III) with potassium iodide. The Ce(IV)-As(III) system in the presence of sulfuric acid was used as the indicator reaction. The possibilities of the application of two types of graphite electrodes were investigated. The effect of concentration of the indicator reaction components, and the presence of organic solvents and acids on the shape of the catalytic titration curves was studied. Amounts of 80–900 μg of gold(III) were determined with a relative standard deviation less than 1.1%. The results obtained are in good agreement with those of comparable methods.     

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.     

Compleximetric titrations of iron(III) and iron(II) with triethylenetetraminehexaacetic acid

The stability constants of the iron(II) complexes of TTHA (triethylenetetraminehexaacetic acid) were calculated from measured pH and redox potentials. The values of the cumulative constants obtained were: log β_FeL= 15.37, log β_FeHL = 23.83, log β_FeH2L = 28.0, log β_Fe2L = 24.73. On the basis of these values and the previously determined constants ofiron(III) complexes, the possibilities of titrating iron(III) and iron(II) with TTHA were investigated. Depending on the experimental conditions, either FeL or Fe₂L formed. Actual titrations were in agreement with the developed theory. The influence of aluminium and titanium on titrations of iron(III) solutions was elucidated.     

Catalytic amperometric and catalytic constant-current potentiometric titrations of silver(I), palladium(II) and mercury(II)

Amperometry and constant-current potentiometry were used to follow the course of catalytic titrations of silver(I), palladium(II), and mercury(II) with potassium iodide. The Ce(IV)As(III) and Ce(IV)Sb(III) systems in the presence of sulphuric acid were used as indicator reactions. The possibilities of application of platinum, palladium, gold, graphite, and glassy-carbon indicator electrodes were investigated. Graphite appeared to be somewhat more advantageous than the other electrode materials. The effect of concentration of the components of the indicator reactions, the presence of organic solvents and acids on the shape of the catalytic titration curves was studied. Amounts of 30-3000 mug of silver(I) nitrate, 90-900 mug of palladium(II) chloride, 130-1300 mug of mercury(II) chloride, and 150-1500 mug of mercury(II) nitrate were determined with a relative standard deviation less than 1.0%. The results obtained were in good agreement with those of comparable methods. The catalytic titration method developed was applied to determination of mercury in Unguentum Hydrargyri.     

A simple differential titrator for automatic potentiometric titration at zero current, with two identical indicator electrodes

A simple differential titrator for automatic potentiometric titration at zero current, with two identical indicator electrodes, is described. The autoburette is a normal microburette connected to one tube of a peristaltic pump, and the differentiating system is a closed-flow circuit in a second tube of the pump, this tube containing two electrodes 5 cm apart. The apparatus has been applied to the determination of halides and sulphide-disulphide mixtures, with electrodes coated with an appropriate silver salt.     

Determination of EDTA by catalytic amperometric and catalytic potentiometric titration at a small constant current

Summary Amperometric and potentiometric methods at a small constant current were developed to follow the course of catalytic titrations. In ammoniacal medium EDTA was determined by titration with 0.1 M copper(II) chloride in the presence of hydrogen peroxide as the indicator. Amounts of 42.26–126.87 mg of EDTA were determined with a maximal average deviation of 0.55 %. The results obtained are in good agreement with those of comparable methods.

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Bestimmung von ÄDTA mit Hilfe der katalytischen amperometrischen und der katalytischen potentiometrischen Titration bei kleinem konstantem Strom

Zusammenfassung Die amperometrische und die potentiometrische Methode bei kleinem konstantem Strom wurden für die Verfolgung katalytischer Titrationen ausgearbeitet. ÄDTA wurde in Ammoniakmedium mit 0,1 M Kupfer(II)-chlorid in Anwesenheit von Wasserstoffperoxid als Indicator titriert. Mengen von 42,26–126,87 mg ÄDTA wurden mit einer mittleren Abweichung von 0,55% bestimmt. Die Ergebnisse stimmen gut mit denen vergleichbarer Methoden überein.

The authors thank the SIZ for researchs of SAP Vojvodina for the partial financial support of the present work.     

Amperometric iodimetric determination of nickel(II) at constant voltage with two polarised electrodes

Summary The amperometric iodimetric determination of nickel(II) in presence of excess dimethylglyoxime in ammoniacal medium atph 6.5, has been carried out at 30 millivolts with two polarised electrodes. The redox reaction is quantitative and the results obtained are accurate and satisfactory. The formation of complexes alters the oxidation potential of Ni²⁺/Ni⁴⁺ to a lower value, so as the former is titrable with iodine. The method is simple, sensitive and convenient; and has the advantage that it permits determination of trace amounts of nickel of the order of 10^–4 M with fair degree of accuracy. At higher dilutions, error exceeds 5 percent.

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Zusammenfassung Die amperometrische jodometrische Bestimmung von Nickel(II) wurde in Gegenwart von überschüssigem Dimethylglyoxim in ammoniakalischem Medium (ph 6,5) bei 30 mV mit zwei polarisierten Elektroden durchgeführt. Die Redoxreaktion verläuft quantitativ und liefert genaue Ergebnisse. Durch die Komplexbildung mit Dimethylglyoxim wird das Redoxpotential Ni²⁺/Ni⁴⁺ erniedrigt und dadurch die jodometrische Titration des Ni²⁺ ermöglicht. Das Verfahren ist empfindlich, einfach und bequem und hat den Vorteil, daß auch Spuren (10^–4 m) mit guter Genauigkeit bestimmt werden können. Bei größeren Verdünnungen beträgt der Fehler mehr als 5%.

     

Determination of some steroidal bases in non-aqueous media by potentiometric titrations at a small constant current

In this work the volumetric and coulometric titrations of some newly synthesized androstene steroidal compounds with pyridine ring are carried out. The titrations were followed potentiometrically at a small constant current using pairs of identical platinum or glassy carbon electrodes, both in presence of quinhydrone. As the titration reagent, in volumetric titrations served 0.01 mol dm^?3 perchloric acid, and in coulometric titrations hydrogen ions were anodically generated in situ from quinhydrone at the platinum electrode. Sodium perchlorate served as the supporting electrolyte.Amounts of 1.18-5.35 mg of the investigated steroidal compounds were determined with a relative standard deviation less than 1.4% at volumetric and 1.2% at coulometric determinations. A negative influence of the supporting electrolyte on magnitude of the signal change in potentiometric determinations was observed. Glassy carbon electrodes are more advantageous over platinum ones.The achieved results are in good agreement with those of catalytic thermometric titrations.     

Voltammetric determination of iron(II) and iron(III) in standard rocks and other materials

Voltammetry at a rotating platinum electrode in concentrated electrolyte solutions containing HCl and LiCl is described for simultaneous determinations of iron(II) and iron(III) in a variety of materials. Applications of the method to some U.S. Geological Survey standard rocks, a Georgian clay, and an iron-containing multiple vitamin tablet are described. For materials which can be dissolved without altering the original iron(II)/ iron(III) ratio, this method enables the two valence states to be determined rapidly and simultaneously. The technique is precise (r.s.d. ≈ 2%) and relatively free from interference, and requires only a recording d.c. polarograph.     

Some observations on the redox behaviour of N-phenylanthranilic acid indicator in iron(II) titrations

The optimum conditions for the successful use of N-phenylanthranilic acid as indicator in titrations of iron(II) with dichromate, cerium(IV) sulphate and vanadate have been established. The influence of iron(III) on the indicator action, and the nature of a green compound formed from the indicator in iron(II) titrations, have been investigated spectrophotometrically.     

Anodic generation of cerium (IV) at glassy carbon in acetic acid and coulometric titrations with the generated reagent

Conditions for electrochemical generation of cerium(IV) at glassy carbon in acetic acid in the presence of alkali-metal acetates and sodium perchlorate, respectively, were investigated. A high current efficiency was achieved in anodic oxidation of cerium(III) in acetate supporting electrolytes. Coulometric titration methods for the determination of reducing substances with the generated oxidant were also developed. The end-points were determined by the biamperometric and bipotentiometric methods. The error of the determinations was less than + 2%.     

Titrimetric determination of vanadium(IV) with cerium (IV)sulphate at room temperature using ferroin as indicator

A procedure has been developed for the visual titrimetric determination of vanadium(IV) with cerium(IV) sulphate, using ferroin is redox indicator. The method has been extended to the determination of iron(II) and vanadium(IV) in mixtures.     

Electrometric titrations of Bi(III), Cu(II), Pt(IV), Te(VI) and Te(IV) with standard iron(II) solution in alkaline medla containing hexitols

Potentiometric, bipotentiometric and biamperometric titrations with an iron(II) salt in alkaline solutions containing sorbitol are reported. Suitable conditions are discussed for determinations based on the Bi(III) → Bi°, Cu(II) → Cu(I) → Cu°, Pt(IV) → Pt(II) → Pt° and Te(VI) → Te(IV) → Te° → telluride systems.     

Sequential titration of iron(II) and vanadium(IV) mixtures with cerium(IV) sulphate, with ferroins as indicators

The titration of vanadium(IV) with cerium(IV) sulphate, with nitroferroin as indicator, is proposed. Unlike ferroin, the indicator does not need a catalyst in this system. By suitable choice of experimental conditions iron(II) can be titrated first to a ferroin end-point and then vanadium(IV) to a nitroferroin end-point.     

Spectrofluorimetric determination of pharmaceutical compounds with the cerium(IV)—cerium(III) system

The compounds to be determined are oxidised by cerium(IV). The concentration of cerium(III) formed is measured spectrofluorimetrically. The method has been used both in solution and, by fluorodensitometry, on t.l.c. plates. Detection limits of some substances are 15 ng ml^-1 for the solution method and 5 ng per spot for the t.l.c. method.     

Behaviour of ferroin indicator in iron(ii)- dichromate titrations A Critical study

A critical evaluation has been made of the optimum conditions for a successful direct and reverse titration of iron(II) with dichromate, with ferroin as indicator, taking into account the influence of acidity, the catalytic effect of iron(III) and the induction effect of the iron(II)-dichromate reaction on the indicator oxidation reaction. The difference in the behaviour of the indicator in the direct and reverse titrations is believed to be due to the presence of a slow : step in the indicator oxidation mechanism ; this is however surmounted in the reverse titration, making it possible to use the indicator even in a 2N sulphuric add medium for this titration. The higher potentials recorded in the reverse titration are believed to be due to the oxide film on the platinum metal electrode. While iron(III) seems to help lower the kinetic barrier of the slow step sufficiently in the indicator oxidation mechanism, the ferriin-ferroin system seems to help m a similar way toe establishment of a more positive potential of the Ct(VI)/Cr(III) system at the platinum electrode in me direct titration; this value explains the feasibility of the direct visual titration in 2N sulphuric acid, although the colour change at the end-point is slow for other reasons.