Potentiometric titrations of selenium with a fluoride-selective electrode

Selenite can be determined with a fluoride-selective electrode by two methods: a direct procedure based on the joint titration of selenite and standard fluoride with lanthanum and an indirect method based on precipitation of selenite with excess of lanthanum followed by back-titration with fluoride. In the first case the end-point is located by the second derivative method, and in the second case by means of a Gran plot. Direct titrations are suitable for selenite concentrations above 5 mM; indirect titrations are useful for concentrations as low as 0.5 mM.     

Potentiometric titrations in non-conducting solutions with an interfacial antimony electrode

The micro interfacial device described is based on an antimony/antimony scratch/ 0.1 M KCl/Hg₂Cl₂/Pt cell. Acid—base reactions occurring in solvents such as dry ligroin, benzene, cyclohexane, dichloroethane, chloroform and pentyl acetate are readily monitored.     

Potentiometric studies on organic compounds containing sulphur with a sulphide ion-selective membrane electrode

Phenylthiourea and N,N-diphenylthiourea can be determined in the concentration range 10¹–10^?3M by potentiometric titration with silver nitrate solution with a sulphide ion-selective membrane electrode. The influence of the alkali and acid concentration on the course of the reactions with the silver nitrate titrant was studied. When phenylthiourea is titrated in the presence of 0.1 M sodium hydroxide, silver sulphide is precipitated, and the phenylcyanamide formed simultaneously reacts further with silver nitrate to form a silver phenylcyanamide precipitate. When N,N-diphenylthiourea is titrated under similar conditions, silver sulphide is again formed, but no cyanamide-type compound can be formed owing to the presence of the second phenyl group. In 1 M sodium hydroxide both compounds studied react with two equivalents of silver to give silver sulphide and phenylurea or diphenylurea, respectively. In the presence of nitric acid both compounds react similarly with silver nitrate. Two molecules of the compounds react with one molecule of silver nitrate to give a white precipitate.     

Potentiometric determination of sulphate in fertilisers with cadmium sulphide membrane electrode

Summary A method is described for the determination of sulphur in fertilisers using reduction and evolution of hydrogen sulphide followed by a potentiometric titration with lead nitrate. Several procedures are tested for the destruction of the samples. The most accurate results are obtained after dissolution of the fertiliser in hydrochloric acid.

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Potentiometrische Bestimmung von Sulfat in Düngemitteln mit Hilfe der Cadmiumsulfid-Membranelektrode

Zusammenfassung Die vorgeschlagene Methode beruht auf Reduktion und Entwicklung von H₂S, gefolgt von einer potentiometrischen Titration mit Bleinitrat. Zum Aufschluß der Probe wurden verschiedene Verfahren getestet, wobei die Auflösung in verdünnter Salzsäure die besten Ergebnisse brachte.

     

Potentiometric studies on thioacetamide by means of a sulphide ion-selective membrane electrode

The sulphide ion-selective electrode has been found to be applicable to the determination of thioacetamide in the concentration range of 10^-1–10^-3 M by direct potentiometry and titration with silver nitrate. The effects of the acid and alkali content of the solutions on the titration reaction have been studied. In alkaline and slightly acidic solutions the product of the reaction is silver sulphide; in solutions in which the acid concentration exceeds 0.5 M, a precipitate of silver thioacetamide is formed. If the alkali concentration of the solution is lower than that corresponding to the amount of acid formed during the titration, another potential jump occurs before the end-point owing to the decrease of sulphide'concentration governed by hydrolysis.     

Potentiometric and visual titrations with bromamine-B

Bromamine-B is proposed as an oxidimetric titrant for potentiometric and visual end-point titrations of arsenic(II), hexacyanoferrate(II), antimony(III), hydroquinone, semicarbazide hydrochloride, isonicotinic acid hydrazide, hydrazine sulphate, ascorbic acid, phenylhydrazine hydrochloride and metol. Quinoline Yellow, naphthidine, dimethylnaphthidinedisulphonic acid, o-dianisidine, diphenylbenzidine, Variamine Blue, alpha-naphthoflavone, Amaranth, Methyl Orange and Methyl Red are proposed as indicators in macro and micro titrations of the reductants with bromamine-B. The transition potentials of Quinoline Yellow, naphthidine, dimethylnaphthidinedisulphonic acid, and o-dianisidine in the titration of ascorbic acid are reported. Arsenic(III) and hexacyanoferrate(II) are suggested for the standardization of bromamine-B solutions.     

Potentiometric titrations in nonaqueous cerimetry

Summary Potassium iodide and hydroquinone can be estimated potentiometrically in nonaqueous medium using ammonium nitrato cerate as oxidant. A platinum indicator electrode coupled with either a glass electrode or an antimony electrode as reference electrode, can be used in nonaqueous medium satisfactorily, for following the potentiometric titration. Direct potentiometric titration of xanthate with ammonium nitrato cerate in nonaqueous medium yields slightly lower values than the actual values in presence of platinum indicator electrode.

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Zusammenfassung Kaliumjodid und Hydrochinon können in nichtwÄ\rigem Medium mit Ammoniumnitratocerat als Oxydationsmittel potentiometrisch bestimmt werden. Dabei wird eine Platin-Indicatorelektrode und eine Glasoder Antimon-Bezugselektrode mit gutem Erfolg benutzt. Die direkte potentiometrische Titration von Xanthat mit Ammoniumnitratocerat in nichtwÄ\rigem Medium gibt mit der Platin-Indicatorelektrode etwas zu niedrige Werte.

     

Electrometric titrations with the gold electrode

Summary Massive gold because of the passivity of the oxide formed on its surface can be used as a substitute for platinum in electrometric titrations including acid-base and oxidation-reduction systems. The end points are attended with large jumps on the curves and coincide satisfactorily with those obtained using the hydrogen or platinum electrode or by other method.     

Potentiometric titrations with ion-exchanging membrane electrodes : Experimental results

Potentiometric titrations with ion-exchanging membrane electrodes for end point detection are described for simple precipitation and acid-base reactions. When only monovalent ions are present,there is a qualitative agreement between the titration curves obtained and the theoretically calculated curves.     

Potentiometric titration of tellurium with a fluoride-selective electrode

Tellurium, as tellurite, can be determined with a fluoride-selective electrode by means of an indirect procedure based on precipitation of tellurite with excess of lanthanum(III), followed by back-titration with standard fluoride. The end-point is located by using the Gran method, and the titrations are suitable for tellurite concentrations above 1 mM.     

Potentiometric titrations using dual microband electrodes.

We present a novel method of analysis using potentiometric end-point detection and dual microband electrodes in generator-collector mode. The titrant is electrogenerated using either a constant current or a current that increases linearly with time, and the fluxes of reactive material rather than molar amounts are balanced. The advantage of the ramp current system over the constant current method is that all of the information needed for a full titration curve and a proper analysis can be obtained during a single scan. The method was applied to the determination of vitamin C with ferricyanide and to the determination of thiosulfate and sulfite with iodine using gold microband electrodes. As a new type of analysis, a potentiometric titration that uses dissolving silver microband electrodes in order to generate the titrant is demonstrated. The system was applied to the detection of chloride, iodide, thiosulfate and cyanide. The accuracy of the analysis is +/-10%, limited mainly by the present screen-printing process, and the method is well adapted for measurements on the millimolar scale.     

High-molecular-weight hydrolyzed polyacrylamides. II. Potentiometric titrations

Potentiometric titrations in water of high-molecular-weight partly hydrolyzed polyacrylamides were analyzed by the Lifson—Katchalsky rodlike model. A fair concordance was found between theory and experimental curves with pK₀ of acid functions of about 4.75 when 0 < τ < 0.49. Two methods were derived to calculate the parameter n of the extended Henderson-Hasselbach equation by using a series expansion of pK_a vs. α, not yet reported in the literature. A new equation for n was established and comparison between two sets of values of n, obtained by using the theoretical ΔpK curves and series expansion is discussed.     

Potentiometric studies of dithiooxamide with a sulphide-selective membrane electrode

The sulphide-selective electrode is applicable to the determination of dithiooxamide by titration with silver nitrate. The effect of the alkali content of the solutions on the reaction has been studied. The reaction products are silver sulphide, oxalic acid, and nitric acid. If the alkali concentration of the solution is lower than that equivalent to the acid formed during the titration, the amount of sulphide produced by hydrolysis decreases and the equilibrium potential is established more slowly.The determination is rapid and accurate in the presence of 1 M sodium hydroxide.     

Potentiometric determination of sulfonamides with a silver sulfide electrode

The silver sulfide membrane electrode shows well-defined responses to several pharmaceutically important sulfonamides over the concentration range 10^-1–10^-4 M. Both direct and titrimetric determinations of sulfonamides are described and applied to pharmaceutical dosage forms.     

Potentiometric titrations with ion-exchanging membrane electrodes: Part II. Theoretical aspects of simple precipitation titrations

Titration curves were derived for potentiometric titrations with zero electric current, utilizing a membrane electrode as indicating electrode, the membrane consisting of permselective, ion-exchanging material. As a first example, calculations were made for simple precipitation titrations with only +1 or -1 charged ions present in the solution to be titrated and in the reagent. For the calculations of the membrane potentials the theory of TEORELL and MEYER and SIEVERS was used. The influence of several parameters, such as the diffusion coefficients of the ions, the capacity of the membrane and the concentration of the solutions, was examined.     

Potentiometric iodimetric titrations with an interfacial voltaic cell for end-point detection

The simple cheap interfacial (antimony scratch) voltaic cell provides sharp sensitive end-point signals in titrations of inorganic and organic compounds directly with iodine or in backtitrations with thiosulfate. Recoveries were in the range 98.3–101.7% for 2–10 mg of sample. The results were the same as those obtained by classical iodimetric titrations.     

Potentiometric titrations of organotin chlorides with tetraphenylarsonium chloride in acetonitrile media

Tetraphenylarsonium chloride was used for the potentiometric titration of R₄-_nSnCl_n compounds (R = Me, Et, Pr, Bu, Ph ; n = 2,3) in acetonitrile media. Evidence for penta-coordinated R₄-_nS_nCl_n+1- complexes was obtained. A stability scale as a function of R groups is given.     

Potentiometric stripping analysis at a stationary electrode

The feasibility of controlling the transport mechanism of the oxidizing species at the working electrode during the stripping step of potentiometric stripping analysis is demonstrated. When linear diffusion of the oxidizing species is the rate-determining mechanism at the working electrode/solution interface and when the physical properties of the medium are considered to lower the diffusion coefficient of the oxidizing species, the relative sensitivity of the technique is enhanced by a factor of 50 for all the common ions studied by potentiometric stripping analysis. Examples and comparison with the normal procedure are given for Cu, Cd, Zn, Pb, Bi, Tl and Ga. The “stationary electrode” procedure is compatible with the normal instrumentation without great modification; it is self-optimizing with respect to time and resolution and preserves all the inherent advantages of potentiometric stripping analysis compared to other electrochemical techniques of trace analysis. The enhancement of the relative sensitivity by this modification permits measurements in the 0.01–0.1 ppb range for metal ions; the total time required is 2–4 min for a single determination and the relative standard deviations are about 3%.     

Potentiometric determination of some common alkaloids with a picrate-selective electrode

Potentiometric methods are described for the determination of alkaloids, based on the formation of insoluble alkaloid picrate salts, using a picrate ion-selective indicating electrode. Micro-amounts of strychnine, papaverine, quinine and cocaine were determined by direct potentiometry and titrimetrically, using Gran plots, with average errors of about 4% and 2%, respectively. The method was successfully applied to pharmaceutical preparations.