Coulometric determination of neptunium

A coulometric titration method with controlled current and amperometric end-point detection with two indicator electrodes was worked out to determine neptunium in solutions which were obtained while treating the spent nuclear fuel. This method allows to determine in presence of 1000-fold quantities and more of Pu, Ce, Cr, Fe, Mn, 1000-fold quantities and more of U. The error of determination is 0.2% for pure Np solutions and increases up to some precent in presence of large amounts of impurity.     

Coulometric trace determination of chloride

1-2000 nmole of chloride was determined by coulometric titration with silver ions. The error was 0.1-5 %, depending on sample size. Chloride in water could be determined down to 0.01 ppm. The titrations were made in 75% acetic acid, 25% water. The displacement of the electrode potential on dilution of the solvent with water was determined. Two alternative procedures to compensate the end-point displacement are described. The titration times were 2-4 min for pretitration of the solvent and 2-4 min for titration of the sample. In some cases another 4 min were required for equilibrium to be reached. Various solvent compositions were used in order to find the optimum conditions.     

Coulometric determination of serum iron

The iron in 500 μl of serum is determined by a coulometric titration developed for ferroin. The titration step is preceded by chloroform extraction from a protein-free filtrate of serum iron as ferroin perchlorate. Evaporation of chloroform in the presence of an acetate buffer of pH 4.6 causes the ferroin perchlorate to back-extract into the aqueous layer. The ferroin is introduced into a titration cell and titrated with electrogenerated cerium(IV), a modified amperometric end-point detection system being used.     

Coulometric determination of nickel and cobalt

A method has been developed for the successive determinations of nickel and cobalt by controlled potential coulomctric analysis with a. mercury cathode, using an aqueous pyridine electrolyte, Quantitles of the metals from about 10 to l00 mg per 100 ml are determinable with an average error of ±0.5 mg. Because this controlled potential electrolysis technique produces a clean separation of nickel and cobalt it can be used for preparing nickel-free cobalt compounds and cobalt-free nickel compounds.     

Coulometric determination of dissolved oxygen in water

The oxygen content of air-saturated distilled water has been determined at between 10 and 40 degrees by using a controlled-potential coulometric method based on an earlier published method for the iodometric determination of nitrite. The maximum error for the determinations was +/- 0.3% over the whole range, and the time of analysis about 3 min. An equation is given for the solubility in the measured range, and some thermodynamic functions are calculated.     

Coulometric determination of carbonates in rock samples

Summary A commercially available carbon analyser based on the coulometric alkalimetric titration was adapted for the determination of carbonates in rocks and minerals. Wet decomposition of samples with concentrated phosphoric acid is used. The developed procedure enables the selective determination of carbonates in a broad concentration range in samples containing non-carbonate carbon, sulphides, fluorides, borates and low contents of chlorides.

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Coulometrische Bestimmung von Carbonat in Gesteinsproben

Zusammenfassung Ein handelsüblicher Kohlenstoffanalysator, der auf der coulometrisch-alkalimetrischen Titration beruht, wurde für die Carbonatbestimmung in Gesteinen und Mineralien angepaßt. Der Naßaufschluß der Proben erfolgte mit konz. Phosphorsäure. Das Verfahren gestattet eine selektive Carbonatbestimmung in verschiedenartigen Proben, die Nichtcarbonat-Kohlenstoff, Sulfid, Fluorid, Borat sowie kleinere Mengen Chlorid enthalten.

The author wants to express his thanks to Dr. Z. ulcek CSc. and Mr. M. Huka for valuable advices and discussions during the experimental work.     

Coulometric determination of microamounts of hydrogen in metal

Hydrogen in metal was extracted into a carrier gas (argon) by heating at about 1100 degrees , and oxidized to water with copper(II) oxide. The water was converted into ammonia with sodium amide at 80 degrees . The ammonia was then titrated with electrolytically generated hypobromite ion. The blank value of single determination could be reduced to less than 1 mug of water. Hydrogen in stainless steels, tantalum metal and pure tin metal could be determined satisfactorily, and some results were compared with those obtained by the ordinary vacuum extraction method.     

Coulometric determination of uranium with a platinum working electrode

Experimental conditions have been established which enable uranium to be determined coulometrically by the reduction of uranium(VI) to uranium(IV) at a platinum working electrode, by controlled-potential or controlled-potential-limit techniques. The procedure has been used successfully as a subsidiary method in the routine determination of uranium in pure uranyl nitrate solutions. The platinum electrode has several important practical advantages over the well established mercury-pool electrode for the coulometric determination of uranium. The consecutive determination of iron(III) and uranium(VI), or plutonium(IV) and uranium(VI) can be carried out with the same working electrode in the same solution and the coulometric oxidation of uranium(IV) to uranium(VT) is practicable. The rate of stirring of the cell liquor is much less critical in the case of the platinum electrode. Two main problems had to be overcome before a practical procedure could be achieved; hydrogen evolution during the uranium(VI)-(IV) reduction had to be eliminated so that 100% current efficiency could be obtained for the desired reaction and electrode-surface poisoning phenomena had to be controlled so that reaction times could be kept reasonably short. It was found that selection of a hydrochloric acid base solution containing a small amount of bismuth(III) enabled hydrogen evolution to be avoided: also electrode-surface poisoning with this base solution was not particularly serious and could be maintained at a satisfactorily low level by occasionally anodizing the electrode in dilute sulphuric acid. Bismuth(III) forms a complex with chloride ions and its presence increases the hydrogen overvoltage at the working electrode: no visible deposit of bismuth metal forms on the electrode during the uranium reduction. Samples containing nitrate can be analysed provided sulphamic acid is added to this hydrochoric acid base solution.     

Coulometric determination of organic substances using electrogenerated dipositive silver

Summary Conditions are described for the efficient generation of silver(II) and the titration of organic compounds by electrogenerated silver(II). An electrolyte of 0.1 M silver nitrate and 5 M nitric acid at –10°C is used, with a gold generating anode and a current density of 1.5–5 mA/cm². A potentiometric (platinum-S.C.E. pair) or biamperometric (platinum electrodes, 200 mV) end point detection is used. For potentiometric detection, the platinum electrode is preconditioned with AgO in nitric or by anodization. The compounds isoniazid, oxalyldihydrazide, hydroquinone, and resorcinol were titrated down to sub-milligram quantities with errors of 1–2%.

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Coulometrische Bestimmung von organischen Substanzen mit Hilfe von elektrolytisch erzeugtem zweiwertigem Silber

Zusammenfassung Der verwendete Elektrolyt besteht aus 0,1 M Silbernitrat in 5 M Salpetersäure bei –10°C. Die Generatoranode besteht aus Gold (Stromdichte 1,5–5 mA/cm²). Die Bestimmung des Endpunkts erfolgt potentiometrisch (Pt/SKE) oder biamperometrisch (Pt-Elektroden, 200 mV). Für die potentiometrische Bestimmung wird die Indicatorelektrode mit einer Lösung von AgO in Salpetersäure oder durch elektrochemische Anodisierung vorbehandelt. Folgende Substanzen wurden bis herab in den sub-Milligramm-Bereich mit Fehlern von 1–2% titriert: Isoniazid, Oxalyldihydrazid, Hydrochinon, Resorcin.

     

Coulometric titration of copper(II) with electro-generated chromium(II)

The current efficiency for the electrogeneration of chromium(II) for use as a coulometric titrant was studied for several supporting electrolytes. With a mercury cathode and a 0.1 M chromic sulfate-0.1 M potassium chloride medium, 0.8 to 2.8 mg of copper (II) in 110 ml of solution can be titrated using potentiometric end-point detection.     

Substoichiometric determination of chromium

The present work deals with the determination of Cr/III/ by means of the substoichiometric isotope dilution method, using PAN, 1-/2-pyridylazo/-2-naphthol as a complexing agent. Chromium forms a 12 complex with PAN. Heating to 90°C for 3 min was necessary for complete complexation. The complex was extracted into chloroform at pH 3.5 /acetate buffer/. Tens of micrograms of chromium could be determined. Effect of diverse metal ions was also studied.     

Coulometric determination of sulfur-containing amino acids using halogens as oxidizing titrants

It is found that cysteine and methionine quantitatively react with electrogenerated halogens under the conditions of galvanostatic coulometry. Cysteine reacts with all titrants, and methionine reacts only with chlorine and bromine. The stoichiometric coefficients of reactions between cysteine and halogens are 1:3, 1:3, and 1:1 for chlorine, bromine, and iodine, respectively. These coefficients for methionine reactions with chlorine and bromine are 1:2 and 1:1, respectively. It is shown that cysteine can be selectively determined in its mixtures with methionine by coulometric titration with electrogenerated iodine. It is found that twofold amounts of methionine do not interfere with the determination of cysteine. A procedure is developed for the direct coulometric determination of methionine in tablets with a relative standard deviation of 3–5%.     

Coulometric determination of ascorbic acid with electrogenerated octacyanomolybdate(V)

A coulometric-potentiometric method is described for the estimation of ascorbic acid with octacyanomolybdate(V) generated electrolytically. The accuracy and precision are comparable with those of the other coulometric methods available.     

Coulometric titration with quinquevalent uranium determination of vanadium(v)

Variadium(V) has been determined by reduction with generated uranium(V) with an accuracy of about ± 0.3%. Amounts as small as 15 μg were successfully titrated. The suggested ph range is 1–2.5. Iron(III) is reduced simultaneuosly with vanadium(V).     

Coulometric determination of uranium in perchloric acid medium and its applications

Amorphous samples of a new inorganic ion exchanger, cerium(IV) selenite have been prepared under varying conditions. The material prepared by mixing 0.025M ceric sulfate and 0.025M sodium selenite in the ratio of 11 was studied in detail for its ion-exchange capacity, chemical stability, IR, thermogravimetry and K_d values. Separations of metal ions have been performed on columns of this ion exchanger.     

Rapid separation and determination of chromium

Chromium(III) is oxidized to chromium(VI) at room temperature or by conventional persulphate oxidation. The chromium(VI) is separated from other metal ions by retention on a small anion-exchange column, and then eluted with a perchlorate solution and measured spectrophotometrically with a flow-through cell. The method is rapid, selective and amenable to automation.     

Coulometric determinations

Two methods for performing coulometric determinations have been developed. Either the precise time of duration of the electrolysis is measured or the voltage is controlled. An indicator is necessary for the first method, while the end-point can be determined by the drop of the generator current to the so-called “background current” in the alternate way.The constant current method usually requires amperometric indication, which may give an incorrect end-point when conditions are not completely suitable. Chemical indicators can sometimes be used. The controlled potential method requires, no indicator, but a good coulometer and an instrument for retaining constant voltage are necessary.Coulometric determinations are based on the reactions of the substances to be determined with halogens, using different oxidizing or reducing agents, and with acids or babes.The degree of accuracy obtained using coulometric titrations corresponds to the volumetric analysis results. In addition, however, coulometry may permit an even greater accuracy, when applied under the proper conditions.The major advantage of coulometry consists in the case, with which, within the limits of the reaction, micro-quantities of the reacting substances can be determined.     

Coulometric determination of the moisture content, using modified Fischer reagent with epichlorohydrin

Application of a coulometric method of water titration in the medium of a modified Fischer reagent in which epichlorohydrin is used to shift the equilibrium of sulfur dioxide oxidation by iodine was experimentally substantiated.     

Coulometric determination of total sulfur and reduced inorganic sulfur fractions in environmental samples

Evaluation of the solid-phase partitioning of sulfur is frequently an important analytical component of risk assessments at hazardous waste sites because minerals containing reduced-sulfur can significantly affect the transport and fate of organic and inorganic contaminants in natural environments. We applied selected methods for the determination of total sulfur, acid-volatile sulfide (AVS), chromium-reducible sulfur (CRS), and extractable-sulfate in standard reference materials and sediment samples from a contaminated site. A coulometric titration method is presented and evaluated for total sulfur, AVS, and CRS. This method is especially advantageous for AVS and CRS determinations because hydrogen sulfide gas evolved during chemical extraction is detected and quantitated in-line; consequently, measurement endpoints can be precisely determined without need for setting arbitrary time limits. The coulometric method allows for improved data quality and increased laboratory throughput of samples. Data on sulfur partitioning are presented for four standard reference materials (NIST 1646a, NIST 2780, CCRMP LKSD-1, CCRMP RTS-3) for the purpose of supporting quality control in environmental studies involving the geochemical and biochemical cycling of sulfur.