Determination of insoluble azides by thermometric titrimetry

A method for determination of azide, based on the thermometric titration of this anion with hydrochloric acid, is described. Although this reaction has a large enthalpy change (DeltaH = -3.6 kcal/ mole), sulphate is added as an endothermic thermometric indicator to improve the end-point. The application of the method to the analysis of insoluble azides has been studied.     

Estimation of errors in differential thermometric titrimetry

Equations are derived predicting the error for applications of thermistors as temperature sensors in differential thermometric titrimetry. The predictions are compared with the error measured experimentally for a circuit with NTC thermistors.     

Determination of the purity of potassium iodate by constant-current coulometry

This paper describes a method of determining the purity of potassium iodate by constant-current coulometry. The determination can be divided into two steps. First, a Na₂S₂O₃ solution is prepared and its reductive value is determined. Second, the purity value of an oxidimetric quantity of potassium iodate is determined. This paper discusses the conditions of the reaction process and evaluates type A and B standard uncertainty of this method. The expanded relative uncertainty of this method is 0.02% (k=2). Received: 15 June 2000 Accepted: 27 December 2001     

Analysis of drugs by microcalorimetry Isothermal power-conduction calorimetry and thermometric titrimetry

Microcalorimetric analysis has been the subject of a few review's in recent years, but these reviews have mainly dealt with the wide-ranging capabilities of calorimetric assay. This review, however, discusses the experimental basis and practical exploitation of the method in the particularly important area of pharmaceuticals. This field of analysis embraces both conventional chemical assays and bioassays which involve living microbial species. The review highlights the design of calorimetric instruments appropriate for study of microbial metabolism and interaction with drug substances. For comprehensiveness, both microcalorimetric and thermometric assay systems are discussed and critically assessed.     

A cell for high-precision constant-current coulometry with external generation of titrant

A cell has been designed for the high-precision coulometric titration, with externally generated titrant, of materials which otherwise undergo undesirable reactions at the working electrodes. With this cell potassium dichromate has been titrated, via its hydrolysis reaction, with hydroxyl ion generated at the cathode, cathodic reduction of the chromium(VI) being circumvented. In this cell 99.9% of the titrant required is generated in one chamber and transferred to another for reaction; the titration is then completed with titrant generated at a second, drip-type electrode working at much lower current. By means of commercially available Leeds and Northrup coulometric titration electrical equipment, titration of NBS 136b Potassium Dichromate gave a purity of 99.976%, standard deviation 0.005%, and of NBS 84d Potassium Acid Phthalate (done as a check) 99.991%, standard deviation 0.005%, both values being in excellent agreement with other work.     

Borate-polyol complexes in aqueous solution: determination of enthalpies by thermometric titrimetry

Enthalpies for the reaction of borate with 1,2-ethanediol, 1,2-propanediol, 1,2,3-propanetriol and d-mannitol have been determined by thermometric titrimetry. From these enthalpies and equilibrium constants taken from the literature, corresponding entropies have been calculated. The data refer to aqueous solutions at 25 degrees and I = 1.0M (NaNO(3)). The results indicate reasons for the differences in the stabilities of the complexes.     

Assay of mixtures of hydrazine and other nitrogen bases by thermometric titrimetry

Summary Binary mixtures of hydrazine and one of the following N-containing bases: ammonia, aniline, hydroxylamine, thiocyanate and unsymmetrical dimethyl hydrazine have been assayed thermometrically. The titrations are based both on the basic and the reducing properties of the compounds. For example, whilst for mixtures of hydrazine and ammonia, the total base content is determined by an acid/base titration, and the hydrazine component is determined by oxidation with bromate ion; for mixtures containing aniline or hydroxylamine, serial titration with bromate ensures that all the hydrazine is oxidised before the onset of oxidation of the other component. Mixtures of hydrazine and UDMH have been assayed in both aqueous and non-aqueous media and a comparison of results has been reported. The main advantage of the proposed methods is that they can be applied to industrial samples, which would render other methods impossible.

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Analyse von Mischungen des Hydrazins mit anderen Stickstoff-haltigen Basen durch thermometrische Titration

Zusammenfassung Binäre Mischungen von Hydrazin mit Ammoniak, Anilin, Hydroxylamin, Thiocyanat und asymmetrischem Dimethylhydrazin wurden thermometrisch analysiert. Sowohl die basischen als auch die reduzierenden Eigenschaften des Hydrazins bilden die Grundlage der Titrationen. Zum Beispiel wird im Gemisch Hydrazin/Ammoniak der Gesamtbasengehalt acidimetrisch ermittelt und die Hydrazinkomponente durch Oxydation mit Bromat bestimmt. Im Gemisch Anilin/Hydrazin oder Hydroxylamin/Hydrazin wird mit Bromat zunächst alles Hydrazin oxydiert, bevor die Oxydation der zweiten Komponente einsetzt. Mischungen von Hydrazin mit asym. Dimethylhydrazin werden in wäßrigem und auch in nichtwäßrigem Medium ausgeführt und die Ergebnisse verglichen. Der Hauptvorteil der beschriebenen Verfahren besteht darin, daß auch industrielle Proben untersucht werden können, bei denen andere Verfahren versagen würden.

     

High-precision analysis of nuclear materials by constant-current coulometry: Part I Determination of uranium

Work is described on the application of constant-current coulometry for the highly precise and accurate assay of uranium and its compounds. Uranium is reduced to the tetravalent state by titanium(III) in nitric acid solution containing sulphamate and reacted with excess of iron(III) to give an equivalent amount of iron(II) which is titrated with electrogenerated cerium(IV). Factors governing the overall titration efficiency are discussed and results for the assay of a number of standard uranium materials presented. The procedure gives a standard deviation of 0.004% at the 40-mg level and an accuracy exceeding 0.01 %.     

Potentiometric determination of the total acidity of humic acids by constant-current coulometry

A straightforward method for both the quantitative and the equilibrium analysis of humic acids in solution, based on the combination of potentiometry with coulometry, is presented. The method is based on potentiometric titrations of alkaline solutions containing, besides the humic acid sample, also NaClO₄ 1 M; by means of constant current coulometry the analytical acidity in the solutions is increased with a high precision, until the formation of a solid phase occurs. Hence, the total acid content of the macromolecules may be determined from the e.m.f. data by using modified Gran plots or least-squares sum minimization programs as well. It is proposed to use the pK_w value in the ionic medium as a check of the correctness of each experiment; this datum may be readily obtained as a side-result in each titration. Modelling acid-base equilibria of the HA samples analysed was also performed, on the basis of the buffer capacity variations occurring during each titration. The experimental data fit, having the least standard deviation, was obtained assuming a mixture of three monoprotic acids (HX, HY, HZ) having about the same analytical concentration, whose acid dissociation constants in NaClO₄ 1 M at 25 °C were pK_HX = 3.9 ± 0.2, pK_HY = 7.5 ± 0.3, pK_HZ = 9.5 ± 0.2, respectively. With the proposed method the handling of alkaline HA solutions, the titration with very dilute NaOH or HCl solutions and the need for the availability of very small volumes of titrant to be added by microburettes may be avoided.     

High-precision analysis of nuclear materials by constant-current coulometry : Part II. Determination of thorium

A constant-current coulometric method is described for the precise determination of thorium by titration with EDTA, elcctrogenerated from its mercury complex in acetate-buffered solution at pH 4.5. With polarised mercury electrodes for end-point detection, relative standard deviations of 0.02 and 0.3% for 30 mg and 30 μg respectively were obtained; the method was applied to the analysis of zone-refined thorium of high purity.     

Elucidation of coordination polymer stoichiometry via thermometric titrimetry: Metal complexes of trithiocyanuric acid

An attempt has been made to elucidate the stoichiometry of the coordination polymers formed by trithiocyanuric acid with some metals in both dimethyl formamide and aqueous solution. It is possible, using the technique of thermometric titrimetry, to assign stoichiometries to a number of these complexes. In some cases, however, the solid phases that separate are non-stoichiometric. Comparison is made with the stoichiometries of metal complexes of the related ligands, cyanuric acid and melamine as determined via thermometric titrimetry. This technique is shown to be successful and rapid, in contrast with the conventional procedure.     

Rapid analysis of dosage forms of some pharmaceuticals by nonaqueous thermometric titrimetry

The use of the technique of solution thermochemistry is proposed for the rapid assay for quality control and quality assurance of dosage amounts of some ethical formulations of some antimalarial drugs. The active ingredients are chloroquine, hydroxychloroquine, dapsone, proguanil hydrochloride, and pyrimethamine.Assay is done without the separation of the excipients and without isolation or derivatisation of the analytes. The titrations are done in glacial acetic acid and utilise the catalysed hydrolysis of acetic anhydride by perchloric acid to indicate the endpoint of the reactions.The time taken for a typical assay, of a typical dosage amount is about 3–5 minutes. The reproducibility is of the order of 1% for the milligramme amounts of analyte present in the dosage amounts of the drugs.

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Zusammenfassung Es wird die Anwendung eines lösungsthermochemischen Verfahrens zu Schnellbestimmungen bei der Qualitätskontrolle und — sicherung von Wirkstoffeinsatzmengen einiger rezeptpflichtiger Präparate von einigen antimalarischen Arzneimitteln empfohlen. Die aktiven Bestandteile sind Chloroquin, Hydroxychloroquin, Dapson, Proguanilhydrochlorid und Pyrimethamin.Die Bestimmungen werden ohne jegliche Abtrennung der Bindestoffe und ohne Isolierung oder Derivatisierung der zu bestimmenden Substanzen durchgeführt. Die Titrierungen werden in Eisessig durchgeführt und bedienen sich der katalytischen Hydrolyse von Essigsäureanhydrid durch Perchlorsäure als Endpunktindikation der Reaktion.Die Dauer für eine typische Probe bei einer typischen Wirkstoffmenge beträgt etwa 3–5 Minuten. Die Reproduzierbarkeit liegt in der Größenordnung von 1% für Milligrammengen der zu analysierenden Stoffe im Arzneimittel.

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We acknowledge the Nigerian Government for the provision of a grant to one of us (S.I.A.). We acknowledge the following for the gifts of samples of the authentic drugs and the tablets assayed in this work: Imperial Chemical Industries plc; May and Baker plc; Winthrop Laboratories plc; Wellcome Foundation (Medical Division).     

Surfactant media for constant-current coulometry. Application for the determination of antioxidants in pharmaceuticals

Effect of surfactant presence on electrochemical generation of titrants has been evaluated and discussed for the first time. Cationic (1-dodecylpyridinium and cetylpyridinium bromide), anionic (sodium dodecyl sulfate) and nonionic (Triton X100 and Brij^® 35) surfactants as well as nonionic high molecular weight polymer (PEG 4000) do not react with the electrogenerated bromine, iodine and hexacyanoferrate(III) ions. The electrogenerated chlorine chemically interact with Triton X100 and Brij^® 35. The allowable range of surfactants concentrations providing 100% current yield has been found. Chain-breaking low molecular weight antioxidants (ascorbic acid, rutin, α-tocopherol and retinol) were determined by reaction with the electrogenerated titrants in surfactant media. Nonionic and cationic surfactants can be used for the determination of antioxidants by reaction with the electrogenerated halogens. On contrary, cationic surfactants gives significantly overstated results of antioxidants determination with electrogenerated hexacyanoferrate(III) ions. The use of surfactants in coulometry of α-tocopherol and retinol provides their solubilization and allows to perform titration in water media. Simple, express and reliable coulometric approach for determination of α-tocopherol, rutin and ascorbic acid in pharmaceuticals using surfactant media has been developed. The relative standard deviation of the measurements does not exceed of 5%.     

Influence of AgCl precipitates on the precipitation titration of sodium chloride by constant-current coulometry.

The precipitation titration of sodium chloride with electrogenerated silver ion was studied. The production of a precipitate of silver chloride had a significant effect on the titration results because the precipitate involved unreacted chloride or unreacted silver ion. The accuracy of the method was investigated by changing the introduction time of a sodium chloride solution to the coulometric cell during the process of electrolysis, and examining the dependency on the sample size. The accuracy of the measurement of the precipitation titration is discussed.     

Determination of the purity of acidimetric standards by constant-current coulometry, and the intercomparison between CRMs

The accuracy and uncertainty of the coulometric measurement results of reference materials for acidimetric titration were examined in this study. The results for amidosulfuric acid and potassium hydrogen phthalate are presented. The uncertainty was investigated by examining the dependency on the sample size and on the electrolysis current. Changes in the titration parameters did not result in any significant effects on the titration results. Acidimetric standards with the certified value linked to the SI were developed. In addition, the intercomparison of acidimetric standards was carried out by gravimetric titration, and the relationship between our coulometric results was determined. Furthermore, due to recent internationalization, not only the traceability to the SI but also the relationship and consistency of their analytical data have gained increasing importance. Our results were validated using certified reference materials (CRMs) obtained from different National Metrology Institutes (NMIs), and their relationships are presented. Presented at -- “BERM-10” -- April 2006, Charleston, SC, USA.     

A rapid method for the determination of some antihypertensive and antipyretic drugs by thermometric titrimetry

A simple and rapid method is described for the direct thermometric determination of milligram amounts of methyl dopa, propranolol hydrochloride, 1-phenyl-3-methylpyrazolone (MPP) and 2,3-dimethyl-1-phenylpyrazol-5-one (phenazone) in the presence of excipients. The compounds are reacted with N'-bromosuccinimide and the heat of reaction is used to determine the end-point of the titration. The time required is approximately 2 min, and the accuracy is analytically acceptable.     

Investigation of the use of thermometric titrimetry for the determination of acidic substances in wine

The use of thermometric titrimetry in the determination of acidic substances in red wine is described. The titration curve obtained in the thermometric titration of red wine with strong base presents two inflections. The stoichiometry corresponding to the first inflection presents good agreement with the so-called "total acidity" of wine, and is proposed for its determination. The second inflection is related to the content of phenolic substances in red wine.