Determination of Ionol by Voltammetry and Coulometric Titration

Procedures were developed for determining ionol by voltammetry and by coulometric titration with electrogenerated chlorine using the amperometric indication of the titration end point. Possible mechanisms of ionol oxidation with electrogenerated chlorine and its electrochemical oxidation at a glassy carbon and a gold electrode were discussed. Procedures were developed for determining ionol in mineral oil in analytical ranges from 1.0 × 10^–4 to 1.0 × 10^–2 M (RSD = 9%) and from 3.0 × 10^–5 to 4.0 × 10^–3 M (RSD = 9%) using a glassy carbon and a gold electrode, respectively. The detection limits for ionol at the glassy carbon and gold electrode were 2.8 × 10^–4 and 1.0 × 10^–5 M, respectively. The detection limit in coulometric titration was 20 g/mL.     

Die Acidität von Silanolgruppen. Vorläufige Mitteillung

The intrinsic acidity constant K_int. of surface silanol groups has been determined by coulometric titration of silicagel at 25° in solutions of the constant ionic strength 0,1M consisting primarily of sodium perchlorate. The experimental data are consistent with      

Nickel‐catalyzed coupling of CO2 and amines: improved synthesis of carbamates

The electrochemical incorporation of carbon dioxide into amines catalyzed by an electrogenerated Ni complex afforded carbamates in moderate yields under very mild conditions (p = 1 atm, room temperature) without any addition of probases. Mechanistic and electrochemical studies revealed the role of reduced nickel species in the activation of CO₂ and electrogenerated CO as a base in the synthesis of carbamates. The influence of number of faradays per mole of amine supplied to the electrodes (Q), cathode materials, temperatures, supporting salts and amounts of catalyst was studied to optimize the electrolytic conditions. A plausible reaction mechanism for the reduction of CO₂ was proposed. Copyright © 2007 John Wiley & Sons, Ltd.     

In Situ Synthesis Kinetics of Salicylic Acid Terbium Complexes in Sol-Gel Derived Host Materials

In situ synthesis kinetics of salicylic acid terbium complexes in sol-gel derived host materials has been investigated. With the increase of the heat treatment time, the broad excitation band in the excitation spectra of the salicylic acid and terbium chloride co-doped gel glass was formed gradually and the luminescence intensity increased gradually, which indicated the gradual synthesis of the salicylic acid terbium complexes in the gel glass during the heat treatment. In situ synthesis reactions of the salicylic acid terbium complexes in 90°C, 120°C, 150°C were found to be second-order reactions, and can be described by the integrated rate equation: , where x is the fractional concentration of the synthesized complex and t the reaction time. According to Arrhenius equation, the activation energy of in situ synthesis of the salicylic acid terbium complexes in the gel glasses was calculated to be 46.39 KJ/mol.     

Determination Coulometrique de L'acide β Amino-Naphtylamido Thioglycolique (Thionalide)

Abstract

Mercury and silver were determined by precipitation from aqueous solution with β amino-naphthylamido thioglycolic acid (thionalid). The metallic thionalidate phases were separated, dissolved in ethanol and analyzed by coulometric titration of the thionalid with electrogenerated iodine.     

Determination of Fat-Soluble Antioxidants by Galvanostatic Coulometry Using Electrogenerated Oxidants

It was found that vitamin E reacts with electrogenerated chlorine and bromine, as well as with silver (I) and vanadium(V) in the ratio 1 : 1 to form -tocopherylquinone. Vitamin A reacts with electrogenerated halogens in the ratio 1 : 3. Individual fat-soluble antioxidants were determined in model solutions at the milligram level with RSD between 1 and 4%. The bromine-scavenging antioxidant capacity of some vegetable oils and animal fats was evaluated.     

Coulometric Titration of Free Cyanide with Electrogenerated Hypobromite

Abstract

A rapid and sensitive method is described for the direct determination of cyanide by coulometric titration with electrogenerated hypobromite. A biamperometric end point was utilized. From 0.498 – 9.980 ueq of cyanide were analyzed with an average error of 0.36% and an average standard deviation of 0.045.     

Determination coulometrique d'alcaloides et de sels de bases organiques apres precipitation sous forme de tetraphenylborates

A coulometric microdetermination of salts of certain organic bases and alkaloids is described, based on precipitation as the tetraphenylborates and the coulometric determination of the tetraphenylborate content of the precipitate with electrogenerated silver ion. Eleven compounds were determined with satisfactory accuracy.     

Precise coulometric determination of uranium,plutonium and americium-application to small samples

Summary Isotopic dilution followed by mass spectrometry is currently used for the determination of microquantities of actinides, but for this method it is necessary to prepare certified solutions of isotopic diluents. The isotopes used are very expensive and often available only in small quantities. New methods have been developed for the accurate and precise determination of small amounts of uranium, plutonium and americium. By using controlled-potential coulometry 0.5eq of uranium and plutonium can be determined with a precision of 0.1% (coefficient of variation). For americium a constant-current coulometric titration allows the determination of 1eq with a precision of 0.3%. The equipment, coulometric cells and procedures are described. The results obtained for standard materials and comparisons with results from other analytical methods are given.

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Genaue coulometrische Bestimmung von Uran, Plutonium and Americium; Anwendung auf kleine Proben

Zusammenfassung Isotopenverdünnung und nachfolgende Massenspektrometrie werden laufend für die Bestimmung kleiner Mengen von Actiniden verwendet; dazu ist es aber notwendig, genaue Lösungen von Isotopen zur Verdünnung herzustellen. Die dazu verwendeten Isotopen sind sehr teuer und oft nur in sehr kleinen Mengen zu haben. Für die genaue Bestimmung kleiner Mengen Uran, Plutonium und Americium wurden neue Methoden ausgearbeitet. Unter Verwendung der potential-kontrollierten Coulometrie lassen sich 0,5eq Uran und Plutonium mit einer Genauigkeit von 0,1% (Variations-Koeffizient) bestimmen. Gleichstromcoulometrische Titration ermöglicht die Bestimmung von 1eq Americium mit einer Genauigkeit von 0,3%. Einrichtung samt coulometrischer Zellen und Arbeitsweise wurden beschrieben. Die mit Standardproben erzielten Resultate wurden mit den Ergebnissen anderer Verfahren verglichen.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Investigation on drying conditions and assays of amidosulfuric acid and sodium carbonate by acidimetric coulometric titration and gravimetric titration

Amidosulfuric acid and sodium carbonate as standards for acid–base titrimetry were assayed by coulometric titration and gravimetric titration. Amidosulfuric acid was directly assayed by coulometric titration with electrogenerated hydroxide ions, and sodium carbonate was assayed by gravimetric back-titration. For sodium carbonate, excess amount of sulfuric acid, whose concentration was determined by coulometric titration, was added to sodium carbonate, and then gravimetrically back-titrated using a sodium hydroxide solution whose concentration was determined by gravimetric titration using the sulfuric acid. The accuracy of the coulometric titration for amidosulfuric acid and sulfuric acid was evaluated by examining the current efficiency of pulse electrolysis, the amount of the electrolysis current used, and the time spent for a titration. In addition, the drying conditions for high purity primary standards have a significant effect on the titration results due to changes in the acid–base assay. The suitable drying conditions for amidosulfuric acid and sodium carbonate were evaluated by mass-change measurements, coulometric titration and gravimetric titration. The measurement uncertainties were estimated from the uncertainties on the titration processes. Finally, the assays of amidosulfuric acid and sodium carbonate were 99.986% ± 0.010% (k = 2) after drying at 50 °C for 2 h, and 99.970% ± 0.016% (k = 2) after drying at 280 °C for 4 h, respectively. In addition, the international consistency was confirmed by measuring certified reference materials (CRMs) available from different National Metrology Institutes, and the compatibility of values among CRMs was experimentally ascertained.     

Electrochemical Determination of Lipoic Acid

Procedures for determining lipoic acid by voltammetry and coulometric titration with electrogenerated halogens using the biamperometric indication of the titration end-point were developed. Possible mechanisms of lipoic acid oxidation with electrogenerated halogens are discussed. Microgram amounts of lipoic acid were determined in model solutions with an RSD of 1–2%. The analytical range of lipoic acid found by voltammetry at a glassy-carbon electrode lies between 1.15 × 10^–5 and 1.73 × 10^–4 M. The detection limit for lipoic acid is 5.75 × 10^–6 M.     

Simultaneous determination of platinum(II) and platinum(IV) by controlled-reagent coulometry

Both platinum(II) and the total amount of platinum were determined in the 5-μmole range with a precision of 0.3%. First, platinum(II) was determined dy oxidation with electrogenerated bromine,the equivalent quantity of electricity being measured. After reduction to platinum(II) with electrogenarated tin(II), the total amount of platinum was determined by a second oxidation with electrogenerated bromine.The reduction with tin(II) was too slow for manual control, and an electronic coulometric titrator was used.The construction of the tritator is described. The underlying coulometric principle, called controlled-reagent coulometry, and its adventages are discussed. A number of other substances were also tested.     

Coulometric titration with complexones in inorganic ultramicro analysis

Summary Coulometry is a very useful technique for ultramicroanalysis, particularly when suitable titrants and methods of end-point detection are available. The choice of method for end-point detection must depend on consideration of (a) the precision required and (b) the feasibility of the method with small volumes of solution. The best method is one which will give correct results when used with a microcell of simple design; amperometric detection with two metallic electrodes meets these requirements. The choice of a titrant depends to some extent on the same criteria as the choice of a titrant for a macrotitration, but for ultramicro work certain criteria (such as solubility of reaction products, rate of reaction) are relatively more important. Complexones make useful titrants for many cations, and can be used in coulometric ultramicro titrations to determine 10^–10–10^–7 g of metal in 3–5l of solution. Generally, the more complex the complexone used, the greater the sensitivity of the titration. For example, if DTPA (diethylenetriaminepentaacetic acid) is used instead of EDTA, the limit for detection of zinc is lowered by 1–2 orders of magnitude. By use of suitable complexones and masking agents, elements can be determined in the presence of each other. For example, zinc can be determined by coulometric ultramicrotitration (with electrogenerated DTPA) at particular points on the surface of the semiconductor material ZnSb without separation of antimony. The same titrant can be used for the determination of zinc in the presence of cadmium if the latter is masked with-dithiocarbaminopropionic acid.

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Zusammenfassung Die Coulometrie eignet sich sehr gut für die Ultramikroanalyse, besonders wenn geeignete Maßflüssigkeiten und Methoden zur Endpunktermittlung zur Verfügung stehen. Die Wahl dieser Methoden ist abhängiga) von der erforderlichen Genauigkeit und b) von der Durchführbarkeit mit kleinen Lösungsmengen. Am besten ist jene Methode, die bei Verwendung eines einfachen Mikrogefäßes genaue Resultate liefert; die amperometrische Bestimmung mit zwei metallischen Elektroden entspricht diesen Anforderungen. Die Wahl des Titrationsmittels hängt zum Teil von denselben Kriterien ab wie bei Makrotitrationen, aber für ultramikroanalytische Zwecke sind manche Kriterien (Löslichkeit der Reaktionsprodukte, Reaktionsgeschwindigkeit) besonders wichtig. Komplexone eignen sich für die Titration vieler Kationen; man kann damit durch Ultramikro-Coulometrie 10^–10 bis 10^–7 g Metall in 3–5l Lösung bestimmen. Im allgemeinen ist die Empfindlichkeit der Titration um so größer, je komplizierter das Komplexon gebaut ist. Wenn man z. B. anstelle von ÄDTA Diäthylentriaminpentaacetat (DTPA) verwendet, wird die Nachweisgrenze für Zink um 1–2 Größenordnungen herabgesetzt. Verwendet man geeignete Komplexone und Maskierungsmittel, so lassen sich die Elemente in Gegenwart anderer Elemente bestimmen. Zum Beispiel kann man Zink durch coulometrische Ultramikrotitration mit elektrogeneriertem DTPA an bestimmten Punkten der Oberfläche des Halbleiters ZnSb ohne Abtrennung des Antimons bestimmen. Das gleiche Titrationsmittel kann für die Bestimmung von Zink in Gegenwart von Cadmium dienen, wenn man dieses mit-Dithiocarbaminopropionsäure maskiert.

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Presented at the International Symposium on Microchemical Techniques 1977, Davos, May 1977.     

Cathodic Reduction of Chromium on a Surface of Nickel Modified by Aromatic Carboxylic Acids

Effect of organic compounds (salicylic, acetylsalicylic, and p-nitrobenzoic acids) adsorbed on a nickel surface or introduced into solution on the cathodic reduction of Cr(VI) is studied by measuring voltammetric curves in a wide potential range up to the beginning of electrodeposition of black chromium. If the adsorbate is salicylic or p-nitrobenzoic acid, only the maximum current corresponding to incomplete reduction Cr(VI) Cr(III) increases in cathodic polarization curve (PC). On a surface modified by acetylsalicylic acid, in addition to an increase in the maximum current, all parts of PC shift towards positive potentials. The Cr(VI) reduction on modified surfaces accelerates presumably due to the electron transfer from the cathode surface onto Cr(VI) atoms, accelerated by the formation of bridges with an increased electron conduction.     

Die Hydrolyse des Ga3+-Ions; potentiometrische Untersuchungen in 3m NaClO4 bei 60°C

The hydrolysis of the ion Ga³⁺ has been investigated at 60°C by potentiometric titrations in a sodium perchlorate medium of the constant ionic strength 3 m. Solutions of various total gallium concentrations B were alkalified by means of a coulometric technique. The concentrations h of the free hydrogen ions were measured with the aid of a glass electrode. From the experimental data, Z, the average number of OH bound per Ga was calculated. The mathematical analysis of the curves Z(logh)_B is consistent with the following formulation of the hydrolysis reactions with log*β_l = log k₀ k^l = ?1,7 ? 11,55 l.     

Electrical properties and surface orientation of some salicylic acid derivatives at water/air interface

Surface activity, effective dipole moments and orientation of molecules at the interface were determined from surface tension () and surface potential (V), measured on aqueous solutions of salicylic acid, acetylsalicylic acid and salicylaldoxime.Applying the Demchak and Fort formula [1], the components of the effective dipole moments were calculated, which are connected to the reorientation of water molecules, hydrophilic and hydrophobic groups and local dielectric permittivities. From the effective dipole moments the orientation angles of the molecules at the water/air interface were estimated.     

Electrogenerated Chemiluminescence of Lucigenin in Ethanol Solution at a Polycrystalline Gold Electrode

The electrogenerated chemiluminescence (ECL) behavior of lucigenin in ethanol solution at a polycrystalline gold electrode was studied under conventional cyclic voltammetric conditions. Compared with the ECL of lucigenin in aqueous solution, one cathodic ECL peak (ECL‐1 at ?0.98 V versus SCE) with a shoulder (S₁ at ?0.42 V) and three new anodic ECL peaks (ECL‐2 at ?0.53 V, ECL‐3 at 0.20 V, and ECL‐4 at 0.51 V) were observed, respectively, on the curve of ECL intensity versus potential. The effects of initial potential scan direction, the presence of O₂ or N₂, potential scan ranges, supporting electrolyte and the concentration of lucigenin on these ECL peaks were examined. The electrochemistry of lucigenin in ethanol solution was also studied. The emitter of all ECL peaks was identified as N‐methylacridone (NMA) by analyzing the ECL spectra. The mechanism for these ECL peaks is proposed to be due to the reactions of lucigenin and its redox products such as Luc and DBA with dissolved oxygen or O₂ electrogenerated by the dissolved oxygen at different potentials. The formation of new anodic ECL peaks in ethanol solution is due to longer lifetime of superoxide ions and easier electro‐oxidation of DBA in nonaqueous solution, revealing that the solvent plays an important role in the lucigenin ECL reactions.     

Anwendung der coulometrischen Titration in der industriellen Analytik

Zusammenfassung Die bis vor kurzem in der Handhabung und Auswertung eher umständliche coulometrische Titration ist durch den Einsatz von modernen Coulometern (mit digitaler Anzeige in Val) so weit vereinfacht worden, daß sie mit konventionellen Titrationsverfahren konkurrenzfähig geworden ist. Die der coulometrischen Titration eigenen Vorteile werden besprochen, und die Einsatzmöglichkeiten werden anhand einer Reihe von Beispielen aus der organischen und anorganischen Chemie beleuchtet.

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Application of coulometric titration in industrial analysis

Coulometers of recent design (with digital indication in eq.) have simplified coulometric titrations to the point where they compare favourably with conventional titrations. The inherent advantages of coulometry are discussed and applications to organic and inorganic compounds are reported.

     

Narrow span coulometric analysis of neptunium

A narrow span (E _o ±0.1 V) controlled potential coulometric method has been developed for the determination of neptunium in 1M H₂SO₄ with a RSD of 0.2%. The main advantage of this method over the existing coulometric methods is that it can tolerate up to a 5-fold excess of plutonium. The method involves carrying out the electrolysis to about 97% and calculating by an iterative computation the formal electrode potential in situ, which is used to calculate the total amount present in the sample. The method consists in oxidation of all the neptunium to Np (VI) by Ce(IV), destruction of excess Ce(IV) and reduction of Np(VI) to Np(V) by NaNO₂, destruction of excess nitrite by sulfamic acid followed by coulometric titration of Np(V) to Np(VI).     

Coulometric Determination of the Antioxidant Capacity of Tea Extracts Using Electrogenerated Bromine

A coulometric procedure based on the reaction between aqueous extracts of tea with electrogenerated bromine compounds was proposed for the rapid estimation of the antioxidant capacity of different kinds of tea. The antioxidant properties of tea with respect to bromine are mainly due to naturally occurring flavonoids, tannins, and some vitamins. Photometric and coulometric data for black teas exhibit good correlation.