Spectrophotometric determination of bismuth in concentrates and non-ferrous alloys by the iodide method after separations by diethyldithiocarbamate and xanthate extraction

A method for determining 0.0001-1% of bismuth in copper, molybdenum, lead, zinc and nickel sulphide concentrates is described. After sample decomposition, bismuth is separated from matrix and other elements, except lead and thallium(III), by chloroform extraction of its diethyldithiocarbamate complex, pH 11.5-12.0, from a sodium hydroxide medium containing citric acid, tartaric acid, EDTA and potassium cyanide as complexing agents. Following back-extraction of bismuth into 12M hydrochloric acid and reduction of thallium to the univalent state, bismuth is separated from co-extracted lead and thallium by chloroform extraction of its xanthate from a 2.5M hydrochloric acid-tartaric acid-ammonium chloride medium. Bismuth is then determined spectrophotometrically, at 337 or 460 nm, as the iodide. Interference from lead, which is co-extracted in mug-amounts as the xanthate and causes high results at 337 nm, is eliminated by washing the extract with a hydrochloric acid solution of the same composition as the medium used for extraction. The proposed method is also applicable to lead-, tin- and copper-base alloys.     

Photochemical thallimetric oxidations-estimation of formic acid

A simple, rapid and convenient redox method has been developed for the estimation of formic acid. Formic acid is photochemically oxidized with thallium(III) in the presence of bromide as catalyst, and the thallium(I) formed is determined by titration with potassium bromate. The procedure can also be used for the estimation of thallium(III) with formic acid as reductant.     

The accurate determination of thallium by direct titration with edta using methylthymol blue as indicator

After oxidation with bromine, thallium can be determined accurately by titration with EDTA in alkaline tartrate media of pH 7–10 using methylthymol blue as indicator. The end-point in this titration is considerably sharper than that obtained with xylenol orange as indicator in weakly acidic solution, and is considerably less influenced by the presence of bromide, tartrate and acetate. Up to 2.5 g of ammonium or potassium bromide or chloride and up to 5 g of tartrates, acetates, nitrates or sulphates can be tolerated. About 1 mg of thallium in 75 ml can be determined with an error of about 2 μg by spectrophotometric titration. A selective solvent extraction and an anion-exchange procedure are suggested for the separation of Tl(III) from most other titratable elements.     

Dichromate titration of thallium(I)

The formal redox potentials of the thallium(III)-thallium(I) couple in different acids of varying strengths are reported. The minimum concentration of hydrochloric acid required for a direct titration of thallium(I) with potassium dichromate is 5M. Thallium(I) can be titrated directly with the primary standard oxidant, potassium dichromate, at room temperature, with ferroin as indicator, in 6M hydrochloric acid. Atmospheric oxygen must be excluded.     

Determination of ascorbic acid in fruits and pharmaceuticals by titration with thallium(III)

Summary Ascorbic acid has been determined in fruits and pharmaceuticals by titration with thallium (III) sulfate using promethazine or 4-me-thoxychrysoidine as visual indicators or by potentiometry. Interference of cysteine, glutathione and hydrogensulfite is avoided by their masking with acrylonitrile. Use of cysteine or hydrogensulfite is recommended as an antioxidant during the extraction of ascorbic acid from plant materials.

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Bestimmung von Ascorbinsäure in Früchten und Arzneimitteln durch Titration mit Thallium(III)

Zusammenfassung Die potentiometrische Titration von Ascorbinsäure in Früchten und Arzneimitteln mit Thallium(III) läßt sich unter Verwendung von Promethazin oder 4-Methoxychrysoidin als Indikator durchführen. Die Störung durch Cystein, Glutathion und Hydrogensulfit läßt sich durch Maskierung mit Acrylnitril verhindern. Cystein oder Hydrogensulfit dienen als Antioxydantien bei der Extraktion der Ascorbinsäure aus pflanzlichem Material.

     

Determination of ascorbic acid with o-iodosobenzoate: analysis of mixtures of ascorbic acid with methionine and cysteine or glutathione

Ascorbic acid has been determined in pure solutions, pharmaceutical preparations, food-stuffs and biological fluids by titration with o-iodosobenzoate, with visual or photometric detection of the end-point, with leuco-2,6-dichlorophenolindophenol plus potassium iodide as indicator. Cysteine and glutathione, which interfere quantitatively, are masked by cyanoethylation; the cyanoethylated product and methionine have been determined with o-iodosobenzoate in the presence of acidified potassium bromide, with Methyl Red as indicator. Procedures are given for the analysis of mixtures of ascorbic acid with sulphur-containing amino-acids.     

Determination of ascorbic acid with ferricyanide

Ascorbic acid can be determined by titration with potassium ferricyanide in sulphuric, phosphoric or hydrochloric acid media. Twelve indicators, including ferroin and some triphenylmethane and thiazine dyes, have been found suitable. The method has been successfully applied to assay of commercial products for vitamin C. Several organic substances likely to be associated with ascorbic acid in preparations and plant tissues do not interfere.     

微分脉冲伏安法测定硫酸锌溶液中铊

研究了微分脉冲伏安法测定复杂硫酸锌溶液体系中的铊。讨论了伏安图的形成、测定底液和pH值的选择。结果表明:在醋酸介质(pH=4.5±0.2)中,加入适量EDTA、聚乙二醇6000和抗坏血酸的测定体系,采用微分脉冲伏安法可直接测定铊。方法检出限为1.0×10-8g/L,千倍浓度的8种阳离子共存或单独存在时均不干扰测定。方法用于湿法炼锌中上清、一段净化后液、二段净化后液、电积新液、电积废液中铊的测定,相对标准偏差RSD分别为1.6%,2.5%,3.3%,8.3%,4.9%,铊加标回收率为98.4%～102.2%。方法灵敏、简单、快速,用来测定湿法炼锌各阶段硫酸锌溶液中的铊,结果满意。     

Flame AAS determination of thallium in soils

The anion-exchange enrichment of TlCl(-)(4) coupled to flame AAS is applied to the determination of the total, pseudo-total (not bound in the silicate matrix) and mobile (plant available) content of thallium in soils. Ascorbic acid is used as a new efficient eluent of thallium. The limit of detection of the method is 0.04,mug/g, the relative standard deviation at the 1 mug/g level is about 3%. The method is rapid and simple.     

Signal-levelling agents for eliminating the interferences of iron,aluminium, barium and calcium in the determination of lead by flame atomic absorption spectrometry

The interferences of iron, aluminium, barium and calcium on the determination of lead by flame atomic absorption spectrometry are discussed; a titration procedure was used. Ascorbic acid, citric acid, EDTA and nitric acid were used successfully for levelling the interfering effects from the cations.     

Oxidations with alkaline permanganate using monovalent thallium for the back titration: Estimation of hydrogen peroxide

Owing to the instability of hydrogen peroxide in alkaline solutions, direct oxidation with KmnO₄ did not yield accurate results.The back titration of KmnO₄ in the presence of IN NaOH and Ba⁺² ions also gave inaccurate results. The reaction could not be checked at the manganate state. However, in the presence of 2N NaOH and telluric acid quantitative data were obtained, which is not the case if telluric acid is absent.Another advantageous method is the oxidation of hydrogen peroxide with excess KmnO₄ in the presence of 1N NaOH and telluric acid, followed by back titrating excess oxidant with monovalent thallium.     

Determination of thallium(III) by use of a mercury reductor

A convenient method has been developed for the determination of thallium(III) by using a mercury reductor. Thallium(III) is reduced to thallium(I) in 0.5–4N hydrochloric or sulphuric acid medium and the determination is completed by oxidative titration with potassium bromate. The method is extended to analysis of thallium(III)-thallium(I) and thallium(III)-iron(III) mixtures.     

A new radiometric titration method based on separation by means of ion exchange

It is shown that the radio-oxidimetric titration of monovalent thallium is possible even in the case when other metal ions are present in thousand-fold excess. Nitrate and copper interfere. Some examples are given of mixtures of thallium with tin, cobalt or iron, in which both ions are determined.     

Biochemical studies of current environmental levels of trace elements: Cyclotron production of radiothallium and its use for metabolic investigations on laboratory animals

Carrier-free^201+202Tl have been produced in the cyclotron by (p, xn) reactions on mercury targets and used as a trcer for thallium in metallobiochemistry of heavy metal pollution. The separation of^201+202Tl radioisotopes from Hg involved a solvent extraction method leading to labelled univalent Tl(I) ions. This radioactive solution was used to prepare different^201+202Tl labelled compounds such as inorganic Tl(III) ions and organic dimethylthallium. Quality controls have been applied directly on the different radioactive solutions immediately before their administrations to rats in order to ensure that thallium had the chemical form expected. A summary of the main results concerning different aspects of the metabolic investigations on rats such as absorption, retention, excretion, transplacental transport and influence of the different chemical forms of thallium on its metabolism is also reported.     

The determination of thallium in rocks and biological materials at ng g−1 levels by differential-pulse anodic stripping voltammetry and electrothermal atomic absorption spectrometry

Thallium is volatilized from biological materials and rocks after admixture with silicic acid and cellulose/magnesium chloride, respectively, by combustion in oxygen in a quartz apparatus, and from rocks after admixture with magnesium chloride by fusion at 1250°C in a quartz tube drawn to a capillary at one end and sealed at the other end. The condensed thallium is dissolved in a small volume of acid which is used directly to determine thallium procedure was found to be 1 ng g^?1 (deposition time 10 min). The results are in satisfactory agreement with those obtained by electrothermal atomic absortion spectrometry after extraction.     

Chemical analysis of manganese nodules: Part III. Determination of Thallium,Molybdenum and Vanadium after Anion-Exchange Separation

A method is described for the determination of thallium, molybdenum and vanadium in manganese nodules. After dissolution of the sample in a mixture of perchloric and hydrofluoric acids, thallium and molybdenum are adsorbed on the strongly basic anion-exchange resin Dowex 1 (chloride form) from 6 M hydrochloric acid containing bromine. Molybdenum is eluted with 2 M perchloric acid-1 M hydrochloric acid and determined by a.a.s. with a nitrous oxide—acetylene flame. Thallium is eluted with an aqueous solution of sulphur dioxide and, after evaporation of the eluate, this element is determined by a.a.s. with an air—acetylene flame. The same method is used for the assay of vanadium in the 6 M hydrochloric acid effluent. The method was used successfully for the determination of thallium, molybdenum and vanadium at the ppm level in numerous samples of nodules from the Pacific Ocean and Lake Michigan.     

A new radiometric titration method based on separation by means of ion-exchange

The determination of thallium with potassium chlorate is chosen as an example for the earlier suggested new radio-oxidimetric titration procedure, in which phase separation is achieved by means of a strongly basic anion exchanger in the solution. Concentrations of thallium down to 2·10⁻⁶ M have been determined. Special care has to be taken for concentrations lower than 10⁻⁵ M as UV radiation is a disturbing factor. Other oxidizing agents have also been tested.     

Dichrometric determination of thallium (I)

Summary A dichrometric procedure has now been developed for the direct volumetric titration of thallium(I), to an iodine monochloride end point. The concentration of the hydrochloric acid must be at least 7.5 N at the end point.     

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.     

Thallimetric oxidations-VI Titrimetric and spectrophotometric methods for the determination of phosphite and analysis of binary mixtures of phosphite and oxalate

Titrimetric and spectrophotometric methods have been developed for the estimation of phosphite at mmole and mumole levels, respectively. Thallium(III) is used as an oxidant and the thallium(I) produced is determined either oxidimetrically with potassium bromate or by measurement of the absorbance of thallium(III) at 260 nm in the presence of 0.1 M hydrochloric acid and 1 M perchloric acid. Based on the fact that phosphite and oxalate are oxidized under different conditions, methods are described for the analysis of binary mixtures of phosphite and oxalate. A method is also described for estimation of thallium(III) with phosphite as reluctant, and is applied for analysis of mixtures of thallium(I) and thallium(III).