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.     

Controlled potential coulometric technique for the determination of thorium

A method based on controlled potential coulometry has been developed for the determination of thorium, using mercury as a working electrode. A known amount of EDTA is titrated coulometrically in the absence and in the presence of thorium. The difference in Coulombs obtained in these two titrations corresponds to the amount of thorium present in the aliquot. 0.5M sodium acetate has been used as a supporting electrolyte. Precision for thorium determination in the range of 4–8 mg is found to be better than ±0.2%.     

A titrimetric method for the sequential determination of thorium and plutonium

A method for the sequential determination of thorium and plutonium has been developed. In the sample solution containing thorium and plutonium, thorium is first determined by complexometric titration with EDTA and then in the same solution plutonium is determined by redox titration employing potentiometry. Prior to the determination of plutonium, EDTA is destroyed by fuming with concentrated HClO₄. Thorium is determined at 10 mg level and plutonium at 1 mg level with precision and accuracy of better than ±0.5%.     

Titration curves in complexometric titrations with the redox system Fe(III)/Fe(II)

Potentiometric titrations of metal ions with EDTA have been carried out with a platinum or graphite electrode and the Fe(III)/Fe(II) redox system. In the absence of oxygen and for pH < 2 the titration curves may be described by an equation similar to that given previously for titrations with silver and mercury electrodes. Titration curves for bismuth and indium, which are more strongly complexed than iron, are asymmetrical and useful for analytical purposes. When the titrated ions are complexed less strongly than iron(III) ions the kinetics of metal complexation have a pronounced effect. The titration curves of thorium and copper, which react more rapidly than iron, are analytically useful. The curves recorded rapidly after titrant additions have a better end-point break than those which correspond to thermodynamic equilibrium. When a metal, e.g., nickel, is weakly bound by EDTA, and reacts more slowly than iron, a very small end-point break or none at all is observed.     

A titrimetric method for the sequential determination of thorium and uranium

A method for the sequential determination of thorium and uranium has been developed. In the sample solution containing thorium and uranium, thorium is first determined by complexometric titration with ethylenediaminetetraacetic acid (EDTA) and then in the same solution uranium is determined by redox titration employing potentiometry. As EDTA interferes in uranium determination giving positive bias, it is destroyed by fuming with HClO₄ prior to the determination of uranium. A precision and accuracy of better than ±0.15% is obtained for thorium at 10mg level and uranium ranging from 5 mg to 20 mg in the aliquot.     

Copper (II) as an Amperometric Indicator: Determination of Thorium

Abstract

It has been demonstrated that copper (II) is an attractive amperometric indicator for the titration of small amounts of thorium in solution. EDTA was used as the titrant. Best results are obtained in the titration when the mole ratio of thorium to copper is high. The method should be applicable to several other metal ions that form more stable EDTA complexes than does copper.     

Amperometric complex-formation titrations of traces of copper

Copper has been determined in the submicrogram range by means of a eomplexometric titration with triethylenetetramine (TRIEN), the end-point being detected by following the anodic wave of the chelating agent at a rotating mercury electrode. The influence of the presence of other metals has been investigated both from the theoretical and the experimental point of view. Because of its higher selectivity TRIEN is preferred to other reagents of the EDTA group. The results show that copper can be determined in the presence of large amounts of most other metals.     

A note on successive complexometric determination of thorium and rare earths

An improved method for successive determination of thorium and rare earths is described. It is based on the EDTA titration of thorium at pH 2 (Xylenol Orange as indicator) followed by addition of acetylacetone-acetone mixture, adjustment of the pH to 5-5.5 with hexamine, and by further EDTA titration of rare earths with the same indicator.     

Studies on metallochromic indicators--II. Zincon and its mercury and zinc complexes as indicators in EDTA titrations

Zincon has been found to be an excellent indicator in the titration of mercury(II) with EDTA at pH 5.5-7. Moreover the mercury(II)-Zincon and zinc-Zincon systems have been found to be suitable indicators in the direct EDTA titrations of Pb(2+), Cd(1+) and Ca(2+). Interference studies of a number of cations and anions have been made. Chloride and bromide can be tolerated in the titration of mercury(II), up to equivalent concentrations.     

Applications,involving the iodide ion: VIII. Direct and indirect determination of mercury(I) and analysis of mixtures. Analysis of chromium(VI)-chromium (III) mixtures. Determination of hypochlorite

Mercury(I), down to 3 ppm, has been accurately determined by direct titration with iodide or by back-titrating excess of iodide with mercury (II) using silver amalgam as the indicator electrode. The direct method and additional volumetric ones were applied to the rapid analysis of various mixtures involving mercury(I) with fair accuracy and precision. Analysis of Cr(VI)-Cr(III) mixtures involved potentiometric back-titration of excess iodide and of excess EDTA separately with mercury(II). Back-titration of excess iodide was successfully applied to the determination of hypochlorite.     

Natural pyrite as an electrochemical sensor for potentiometric titrations with EDTA, mercury(II) and silver(I)

The results obtained in potentiometric titrations of copper(II), mercury(II) and iron(III) with standard EDTA solutions are presented. The titration of copper(II) at pH values in the range from 8.11 to 10.99 (ammonia buffer) and the titration of mercury(II) and iron(III) at pH values from 3.59 to 5.65 (acetate buffer) were performed. The titration end-point (TEP) was detected with an indicator electrode made from natural crystalline pyrite as an electrochemical sensor. The results obtained in potentiometric titration with the pyrite electrode were compared with those obtained using a platinum electrode (Fe³⁺), a Cu ion selective electrode (Cu²⁺) and a Hg electrode (Hg²⁺). Accurate and reproducible results with good agreement were obtained, but higher potential changes at the TEP were obtained using the pyrite electrode. In the course of the titration the potential was established within less than 1 min, whereas at the TEP it was within about 2–3 min. The potential changes at the TEP were in the range from 60 to 200 mV per 0.1 ml EDTA, according to the stability constant of the complex formed. The highest potential changes, ranging from 160 to 200 mV, were obtained in the titration of iron(III) at pH 3.59. Reverse titration was also performed and accurate and reproducible results were obtained. Moreover, titration of halogenide and thiocyanate with standard mercury(II) solutions, as well as cyanide with silver(I) solution, were performed and accurate and reproducible results were again obtained. Received: 20 February 1998 / Accepted: 19 November 1999     

Amperometry with Two Polarizable Electrodes. Chelometric Determination of Rare Earths

Abstract

The method of determining rare earths by chelometric EDTA titration with biamperometric end-point indication using two stationary platinum electrodes was studied. The convenient pH range for the determination of lanthanum is 5.0 – 8.0, for yttrium 3.5 – 8.0 and for ytterbium 3.0 – 8.0. Rare earths have been determined in the presence of iron and thorium. Iron and thorium can be titrated at pH 1.5 – 2.0 and rare earths of the lanthanum group can be determined by successive titration at pH 5.0. Large amounts of rare earths of the yttrium group interfere with the determination of iron and thorium.     

Amperometric complex-formation titration of traces of alkaline earths

Alkaline earth metals were determined in microgram quantities by complexometric titration with EDTA, EGTA and DTPA. The end-point was detected by following the anodic wave of the chelating agent at the rotating mercury electrode. All the alkaline earths can be titrated at the microgram level with reasonable accuracy, and calcium may be titrated with EGTA in the presence of a 1000-fold excess of magnesium.     

An improved selective determination of mercury(II) by complexometric titration

A simple and accurate method has been developed for selective determination of mercury in alkaline solution. It involves the addition of an excess of EDTA to the mercury solution, titration of unreacted EDTA with a standard zinc solution, and then addition of N-allylthiourea solution at pH ? 9. By heating, the mercury-EDTA chelate is decomposed selectively, mercury sulfide is precipitated, and the EDTA freed is again titrated with standard zinc solution. Eriochrome Black T is used as indicator. Interference of some cations is discussed.     

主成分回归-络合滴定法测定混合金属离子

提出了用络合滴定法测定混合金属离子.以汞膜电极为指示电极,银-氯化银电极为参比电极,以标准EDTA溶液滴定混合金属离子溶液.采集-系列指定电位点处滴定剂的体积,并以主成分回归法处理滴定数据.利用本文方法对铜、锌、铅、钻混合溶液进行了测定,结果满意.     

Complexometric determination of mercury(II) using Congo Red as indicator

Congo Red is suggested as an indicator for the direct titration of mercury(II) ions with EDTA or with potassium thiocyanate. An interference study of a number of cations has been made. The titration with thiocyanate is more advantageous than that with EDTA.     

Complexometric titration of submicromole amounts of thorium(IV) with photometric end-point detection

Summary Thorium(IV) can be determined in the microgram range by photometric titration with EDTA in the presence of an approximately equivalent amount of the indicator Semi-Xylenol Orange at pH 2 (HClO₄). Most other elements do not interfere. Interfering metal ions can be separated from thorium(IV) by electrolysis at a mercury pool cathode.

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Zusammenfassung Mikrogrammengen Thorium(IV) lassen sich durch photometrische Titration mit EDTA in Anwesenheit einer äquivalenten Menge des Indikators Semixylenol-Orange bei pH 2 (HClO₄) bestimmen. Die meisten anderen Metalle stören die Bestimmung nicht. Störende Metallionen können durch elektrolytische Abscheidung an einer Quecksilberkathode von Thorium (IV) abgetrennt werden.

     

Complexometric determination of thorium in ThO2−PuO2

A method based on the complexometric titration of thorium using ethylene diaminetetra-acetic acid (EDTA) as complexant has been developed for the determination of thorium in thorium-plutonium solution without resorting to prior separation of plutonium. Plutonium in the form of Pu(VI) does not affect the thorium determination when present up to 10% in thorium—plutonium solution. For oxidation of plutonium to Pu(VI), HClO₄ or AgO was used. HClO₄ is preferred. The thorium values obtained without prior separation of plutonium are compared with those obtained after separating plutonium by anion exchange technique. A precision of ±0.5% has been obtained for 5–10 mg of thorium in the aliquot.     

The analysis of zirconium-thorium binary alloys

Thorium-zirconium binary alloys are analysed by complexometric procedures. For alloys containing more than 20% thorium or 5% zirconium by weight, the sum of the constituents is obtained by a back titration procedure at pH 2.6–2.8 with bismuth nitrate using xylenol orange as indicator. Thorium is then masked with sulphate and the liberated EDTA is titrated with bismuth at pH 1.2–1.3. For alloys containing less than 20% of thorium, thorium fluoride is precipitated on lanthanum fluoride to effect its separation before titration. For alloys containing less than 5% of zirconium, the zirconium is separated by precipitation with p-bromo-mandelic acid.     

Determination of tho2 in thoriated tungsten wire

Dissolution of a thoriated tungsten wire in a mixture of nitric and hydrofluoric acids followed by a sodium hydroxide separation of tungsten and EDTA titration of the thorium is used as an improved method for the determination of thorium in thoriated tungsten wire