Coulometric titration of zinc with ferrocyanide

A method has been developed for the automatic coulometric titration of zinc ion with ferrocyanide ion generated by the reduction of ferricyanide ion at a platinum cathode. The composition of the zinc precipitate was found to depend on the pH. Over the pH range from about 1 to 3 it corresponds exactly to K₂Zn₃[Fe(CN)₆]₂, but at higher pH values the precipitate contains a smaller proportion of ferrocyanide to zinc. At the optimum pH of 2 quantities of zinc from 0.3 to 30 mg in 8o ml were titrated automatically with an average error smaller than ± 1% The ferriferrocyanide couple should be applicable to other coulometric titrations involving both redox and precipitation reactions.     

Coulometric titration of proteins with silver

The sulfhydryl groups of some proteins were studied by a coulometric argentometric titration; disulfide groups in the presence of sulfite were titrated by the same technique. Direct procedures and a technique utilizing excess coulometrically generated silver(I) were used. The latter method enabled small samples (20–1000 μg of protein) to be titrated with a precision of less than 4%. The proteins were generally titrated in both the native state and the denatured state (8 M urea). Bovine serum albumin, α-chymotrypsin, glutathione reductase, human hemoglobin, insulin, β-lactoglobulin, and ovalbumin were examined and the results compared to those of previous workers.     

Coulometric titration with air transported sample

Air transported samples of a mixture containing the analyte and a supporting electrolyte are consecutively propelled into a microconduit system through a titration cell, a coil and a detector cell. Different amounts of electrochemically generated titrant are obtained in the separate samples while they are passing through the titration cell. Various quantities of the titrant are achieved by changing the duration of the titrant generating process that is done by various time for the sample solution staying in the titration cell (different sample movement rate). The titrated sample is then homogenised in the coil and detected in an electrochemical detector cell that supplies necessary data for the analyte determination. The declared method is experimentally verified on coulometric titration of hydrochloric acid (HCl) with electrogenerated sodium hydroxide and a titration of aniline with bromine generated in a bromide solution.     

Coulometric titration of deactivated phenols with bromine

A number of deactivated phenols containing fluorine, chlorine or bromine, formyi, acetyl, carboxyl or nitro groups have been titrated with anodically generated bromine. The reaction was carried out in a water-acetic acid-pyridine medium and the reactivity was controlled by varying the water and pyridine content and the concentration of bromide ion. Hydrogen in all free positions ortho and para to the phenolic hydroxyl group is generally exchanged for bromine, but in certain instances a partial bromination is possible. The method as developed is widely applicable for deactivated phenols. Only certain ortho-substituted phenols could not be quantitatively titrated. The mean relative error for the phenols titrated was ± 1·2%.     

Coulometric titration of antimony with electrogenerated iodine

A method is described for the coulometric titration of tripositive antimony with electrogenerated iodine, in a buffered solution of pH 8. The end-point can be detected either amperometrically, potontiometrically, or (less precisely) visually with starch indicator. Quantities of antimony between 0.06 and 10 mg are titratable with an average error of 0.001 to 0.01 mg.     

Coulometric titration with gas diffusion separation step

Summary Coulometric titration is employed in combination with a gas diffusion step for the quantitative separation and determination of volatile substances. Complete separation is brought about by filling the sample into a closed circulating loop and transporting it repeatedly past a microporous membrane. The combination of membrane separation module with the coulometric cell allows rapid separation and exploitation of the precise absolute determinations obtainable by the coulometric titration method. The high precision and selectivity of the determination and quantitative separation are discussed using ammonia and sulphur dioxide analyses as examples.Part I: Fresenius Z Anal Chem (1989) 332:849–854     

Coulometric titration of bases in acetic acid and acetonitrile media

The working conditions and the results for coulometric titration of milligram amounts of some bases in 0.1M sodium perchlorate in a mixture of acetic acid and acetic anhydride (1:6), are given. Determinations were made both by coulometric back-titration or direct titration at the platinum anode. Back-titration was done in the catholyte, by coulometric titration of the excess of added perchloric acid. The titration end-point was detected photometrically with Crystal Violet as indicator. The direct titration of bases was done at the platinum anode, in the same electrolyte, to which hydroquinone was added as anode depolarizer and as the source of hydrogen ions, Malachite Green being used as indicator. Similarly, bases can be determined in acetonitrile if sodium perchlorate, hydroquinone and Malachite Green are added to the solvent. Errors are below 1 %, and the precision is satisfactory.     

Coulometric titration of uranium with electrogenerated titanous ion

In a citrate medium of pH 0.5 to 1.5 uranyl ion can be titrated to the +4 state with titanous ion generated by reduction +4 titanium at a mercury cathode. By titrating at 85° equilibrium is quickly established, and the equivalence point is determinable with high precision by the usual potentiometric technique. The method is sufficiently accurate to serve for precise assays of macro amounts of uranium Using a strictly constant generation current, and measuring time to the e.p., the average error of nineteen titrations of 28 to 112 mg quantities of uranium was — 0.02%.     

Coulometric titration of gold with electrogenerated chloro-cuprous ion

A method for the coulometric titration of +3 gold to the metallic state with clectrolytically generated chloro cuprous ion is described Quantities of gold from as little as I mg to 100 mg or more were titrated in a volume of 100 ml with an average error of ± 0.3%.The titration is applicable to the determination of gold in the presence of large amounts of copper, silver, mercury, lead, and most of the elements with which gold commonly is associated. Small amounts of +4 platinium (less than half the amount of gold) are innocuous, but larger quantities of platinum produce a large positive error     

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.     

Coulometric titration of some phenolic steroids with bromine based on thin-layer hydrodynamic biamperometric end-point detection

Four phenolic steroids were titrated coulometrically with bromine in a methanol—water solvent containing hydrochloric acid and sodium bromide. End-point detection was achieved with a twin electrode thin-layer cell placed in a flow loop connected to the titration vessel. Linear-segmented biamperometric titration curves were recorded. Concentrations of 17-β-estradiol were determined in the range from 442 ppb to 8.84 ppm with relative inaccuracies of -1.3% and +2.2%, respectively. Part-per-million solutions of estrone and estriol were titrated with good accuracy and precision. Somewhat poorer precision and accuracy was found for the determination of 17-α-ethynyl estradiol.     

Coulometric titration of thallous ion with electrogenerated ferricyanide ion

Thallous ion can be coulometrically titrated to thallic oxide in strongly alkaline medium by means of ferricyanide ion generated by anodic oxidation of ferrocyanide ion at a platinum anode. The equivalence point may be detected either potentiometrically or amperometrically. With 8 to 20 mg of thallous ion in 125 ml the accuracy and precision are within ± 0.2%.     

Coulometric titration of benzoic and isonicotinic acid derivatives of hydrazides and acylhydrazones

It was found that benzoic acid hydrazides rapidly and quantitatively react with electrogenerated chlorine and bromine under the conditions of galvanostatic coulometry. Benzoic acid hydrazides were determined in model solutions. A good precision (RSD varied from 1 to 6%) allowed coulometry to be applied to the determination of isonicotinic acid hydrazide in isoniazid tablets and isonicotinic acid 3-methoxy-4-hydroxybenzylidenehydrazide in phthivazid tablets.     

Coulometric titration of small amounts of chloride

Summary Coulometric titrations of small amounts of chloride with electrogenerated silver ions in mixed aqueous solvents containing 50 and 90% of ethanol, acetone or acetic acid have been compared. The end-points were detected with zero-current potentiometry, potentiometry with indicator electrode polarized to the end-point potential, potentiometry with two polarized electrodes and amperometry with two polarized electrodes. Best results were obtained in 90% ethanol medium by zero-current potentiometry. At the level of 0.18g of chloride (in 50 ml) the error was approximately 10%. Although the solubility products indicating that the solubility is lowest in 90% acetic acid and 90% acetone media, the response in these media is too slow for practical purposes.

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Coulometrische Titration kleiner Mengen Chlorid

Zusammenfassung Die coulometrische Titration kleiner Mengen Chlorid mit galvanisch gebildeten Silberionen in gemischt-wäßrigen Lösungsmitteln mit 50 bzw. 90% Ethanol, Aceton oder Essigsäure wurde verglichen. Der jeweilige Endpunkt wurde mit Null-Strom-Potentiometrie, potentiometrisch mit einer polarisierten Indikator-Elektrode, potentiometrisch mit zwei polarisierten Elektroden bzw. amperometrisch mit zwei polarisierten Elektroden bestimmt. Die besten Ergebnisse wurden in 90% ethanolischem Medium mit Null-Strom-Potentiometrie erhalten Bei der Bestimmung von 0,18g Chlorid in 50 ml betrug der Fehler etwa 10% Wiewohl die Löslichkeitsprodukte in 90%iger Essigsäure bzw. 90%igem Aceton am kleinsten sind, verläuft die Endpunkteinstellung in diesen Medien für praktische Zwecke zu langsam.

     

Coulometric titration of acids in non-aqueous solvents

Coulometric titrations of mineral acids, sulphonic acids, carboxylic acids, enols, imides and phenols have been carried out in t-butanol or in acetone with electrically generated tetrabutylammonium hydroxide. Either a potentiometric titration or a visual indicator end-point may be used. The amount of acid titrated ranges from 10 to 60 muequiv, and the precision and accuracy of the method are excellent.     

Coulometric titration of iodide and iodine with electrolytically generated hypobromite

Conditions for the quantitative coulometric titration of iodide and iodine with electrolytically generated hypobromite in the presence of borax buffer have been established. Iodide and iodine are oxidized to iodate. The method, with biamperometric indication of the equivalence point, was successfully applied for a wide range of iodide concentrations (6.21–2115μg with reliability intervals of ±0.21–±11μg) and iodine concentrations (24.26–3311μg with reliability intervals of ±0.36–±11.7μg). The determinations are accurate and sensitive even in the presence of large amounts of bromides and chlorides ($\text{Br}{}^{\mathrm{?}}\text{I}{}^{\mathrm{?}}$= 1.2·10⁶ and $\text{C}\text{l}$^?I^?=4.0·10^{3), as well as in the presence of oxidizing agents such as IO₃?, BrO₃? and CrO₄2? ($\text{I}\text{O}$₃?/I₂)=3.2·105, $\text{I}\text{O}$₃?/I₂=3.1·103, $\text{Br}\text{O}$-₃/I₂}=1.1·10⁴ and $\text{Cr}\text{O}$^2-₄/I₂=1.0·10⁴, as was confirmed by statistical tests. The oxidation mechanism under the conditions of coulometric titrations is discussed.     

Coulometric titration of uranium and uranium-vanadium mixtures with +3 titanium

Coulometric titration of + 6 uranium with electrogenerated titanous ion at a platinum cathode in 8F sulfuric acid can be performed accurately in the presence of ferrous ion as a catalyst Ampero-metric end-point detection is employed. The titration is suitable for the precise assay of uranium compounds. Mixtures of +5 vanadium and +6 uranium can be titrated, because the reduction of +5 vanadium occurs at a more oxidizing potential than the reduction of +4 vanadium and +6 uranium. Using amperometric end-point detection, two end-points are observed corresponding to the reduction of +5 vanadium to the +4 state, and to the simultaneous reduction of + 4 vanadium to the +3 state and +6 uranium to the +4 state. Errors are as small as + 0.3%, provided the uraninium/vanadium ratio is between 0.1 and 10.     

Coulometric titration of +2 copper with electrogenerated +2 tin

Using a supporting electrolyte composed of 4 M sodium bromide-0.2 N hydrochloric acid- 0.2 M stannic chloride, and a platinum generator cathode, +2 copper can be titrated accurately to the +1 state with electrogenerated +2 tin. With potentiometric end-point detection, quantities of copper from about 1 to 35 mg in a volume of 90 ml are titratable with an error of ± 0.3%. The titration is applicable in the presence of most of the elements that are commonly associated with Copper.