Determination of the elemental sulphur content of minerals and ores

A new technique has been developed to determine trace quantities of elemental sulphur in minerals and ores. After separation from the sample by sublimation, the sulphur is determined spectrophotometrically in ethanol. Sulphide, sulphite, sulphate and thiosulphate do not interfere. The effect of the presence of xanthate or dixanthogen is discussed briefly.     

Hydrolysis of thiophosphoryl fluoride

The hydrolysis of thiophosphoryl fluoride has been studied both in acid and alkaline medium. The products are phosphate, fluoride and varying amounts of sulphide, sulphite, thiosulphate and elemental sulphur depending on experimental conditions. The probable mode of formation of the different sulphur species has been explained on the basis of sulphur in a higher oxidation state in the thiophosphoryl fluoride molecule.     

Catalytic-kinetic absorptiostat technique with the indigo carmine—hydrogen peroxide reaction as the indicator reaction

The absorptiostat method previously described is used for the catalytic-kinetic determination of sulphur compounds (sulphide, thioacetamide. thiourea and thiosulphate) in the micromolar range by means of their catalytic action for the indigo carmine—hydrogen peroxide indicator reaction. The thiosulphate catalyst is activated by iron(III) or aluminium(III); aluminium(III) is deactivated by fluoride. On this basis, iron(III) is determined in the ng range, and aluminium(III) and fluoride in the μg range.     

The titrimetric determination of sulphate,thiosulphate and polythionates in mining effluents

A titrimetric procedure is described for the determination of various forms of sulphur (sulphate, sulphite, thiosulphate, dithionate, tri- and tetrathionates after conversion to sulphate) in mining effluents. Metal ions are removed, after an oxidizing step, by a cationexchange resin, and the sulphate is precipitated with a known excess of 0.01 M barium chloride at pH 3.5. The excess of barium is back-titrated with standard 0.01 M ethylenediaminetetraacetic acid (EDTA) solution to a o-cresolphthalein complexone end-point at pH 11.0. The results obtained are in good agreement with those obtained by lengthy gravimetric procedures. Indirectly, dithionate can be determined, and sulphate and oxidizable thio salts such as thiosulphate and di-, tri-, and tetrathionates can be distinguished.     

Determination of some sulphur compounds with N-bromoimides

Two stable oxidants, N-bromophthalimide and N-bromosaccharin are proposed as reagents for the visual and potentiometric titrimetric of thioureas, isothiocyanates, xanthates, dithiocarbamates, thiols, sulphur, thiosulphate, thiocyanate and thiocarbonate. The results are precise within 0.1-0.3%.     

The iodometric determination of dithionite, thiosulphate and sulphite in the presence of alkali and/or cyanide

The analysis of mixtures of dithionite, thiosulphate and sulphite in the presence of cyanide and/or in alkaline solution has been investigated. The effects of such constituents as sulphur, acetonitrile, hexafluoroarsenate, and bromide in alkaline solution were also examined. Satisfactory results were obtained by using low-temperature, oxygen-free, alkaline solutions, containing excess of alkali, at pH > 12.     

New iodometric methods for the microdetermination of arsenic in organic compounds

New methods are described for the iodometric microdetermination of arsenic in organic compounds after wet digestion or oxygen flask combustion. After evaporation of the arsenic solution to dryness and dissolution of the residue in water, acetone is added and the solution is treated with iodide-iodate and the iodine liberated (by the interfering acids and the first dissociation step of arsenic acid) is reduced with thiosulphate. The KH(2)AsO(4) left is then reacted with zinc sulphate in presence of excess of KI and KIO(3). Acetone is added and the liberated iodine is titrated with thiosulphate. This titration corresponds to the second and third dissociation steps of arsenic acid and is used to calculate the arsenic content of the compound. When arsenicals not containing sulphur are decomposed by the oxygen flask method, the arsenic acid solution obtained is reacted directly with zinc sulphate in presence of KI and KIO(3) and the iodine released is titrated with thiosulphate. In this case, the titration corresponds to all three dissociation steps of arsenic acid. The average recoveries obtained by the two methods are 99.5 and 99.9%, respectively.     

Anionic interferences with copper ion-selective electrodes chloride and bromide interferences

The effect ofhalide ions on copper ion-selective electrodes is connected with complexation and redox reactions, with the formation of amorphous sulphur, which by blocking the surface causes instability of potential response. It may be eliminated by addition of sodium thiosulphate solution. The electrode behaviour has been explained on the basis of the diffusion model. An equation is proposed for linearization of the calibration curve. The parameters of the semiempirical model which describes the electrode behaviour agree well with the physical meaning presented by the diffusion model. The treatment given enables analytical measurements of copper concentration to be made even in the presence of significant concentrations of chloride or bromide.     

Bestimmung von Thiosulfat in schwefelhaltigen Mineralw?ssern

Zusammenfassung Zur quantitativen Ermittlung kleinster Thiosulfatmengen in schwefelhaltigen Mineralwässern wurden zwei Methoden ausgearbeitet, die auf der Methylenblau-Ausbleichung und auf der Verzögerung der Methylenblau-Bildung von Sulfid mit Dimethyl-p-phenylendiamin durch Thiosulfat beruhen. Mit diesen Verfahren können noch 0,1 bzw. 0,01 mg/l S₂O₃ ^2– bestimmt werden.

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Summary Two methods have been worked out for the quantitative determination of very small concentrations of thiosulphate ion in mineral waters containing sulphur. The first method is based on the bleaching of methylene blue solution and the second one uses the retarding effect of thiosulphate on the methylen blue reaction between sulphide and dimethyl-p-phenylenediamine. 0.1 and 0.01 ppm of S₂O₃ ^2– resp., can be determined by these methods.

     

Gradient chromatographic elution of sulphur anions

The distribution coefficient of sulphide, sulphite, sulphate and thiosulphate anions between different concentrations of aqueous alkali metal chloride solutions and the anion exchanger Dowex 1X8 is studied. The obtained distribution deportment of these anions is explained in the light of water-water, anion-cation and ion-ion interactions as well as the different tendencies of the alkali ions to hydration. Based on the separation factors encountered between adjacent anions, a chromatographic method is adopted for isolation of the sulphur anions by gradient elution. This method is further compared with the chromatographic procedures so far reported for separation of the investigated anions.     

Iodometric microdetermination of sulphur in organic compounds by an amplification reaction

A new method is described for the iodometric microdetermination of sulphur in organic compounds, using a 12-fold amplification reaction after oxygen-flask combustion. The method is based on reaction of the resulting sulphuric add with an excess of saturated barium bromate solution. The unreacted barium bromate is precipitated by addition of acetone, filtered off, redissolved in hot water and after addition of an excess of iodide and acid, the iodine liberated is titrated with thiosulphate. The method is simple, rapid, highly accurate, and of wide application in the microanalysis of organosulphur compounds containing other common acid-forming elements.     

Determination of thiosulphate in the presence of dithionite and sulphite

To determine thiosulphate in the presence of dithionite and sulphite, iodine dissolved in potassium bromide solution is used to oxidize thiosulphate to tetrathionate, and dithionite and sulphite to sulphate. The tetrathionate generated from the thiosulphate is then oxidized with potassium bromate-potassium bromide solution in the presence of hydrochloric acid. The bromine consumption of the tetrathionate is measured by titration of the excess of bromine with sodium thiosulphate after the addition of potassium iodide. For each equivalent of iodine used to determine thiosulphate by the Wollak method, fourteen equivalents of bromine are used to determine thiosulphate by this method.     

Spectrophotometric determination of thiocyanate via coprecipitation and thermal decomposition of copper(I) thiocyanate

A method for determination of thiocyanate (6–100 μg described. It is based on the coprecipitation of copper(I) thiocyanate with copper(I) iodide, followed by decomposition of copper(I) thiocyanate in air at 450°C. The decomposition products are CuS, CuO, SO₂, CO₂ and N₂. Released sulphur dioxide is absorbed in sodium tetrachloromercurate(II) solution, and determined spectrophotometrically with bleached p-rosaniline. The method is unaffected by the presence of halides, sulphide, sulphite and thiosulphate.     

A micro and ultramicro test for sulphur dioxide

Summary A very sensitive reaction for sulphur dioxide is proposed for use on the micro and ultramicro scales. Interference by cyanide, sulphide, and thiosulphate can be prevented. Sulphite can be distinguished from bisulphite.

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Zusammenfassung Eine sehr empfindliche Reaktion zum Nachweis von Schwefeldioxid im Mikro- und Ultramikromaßstab wurde vorgeschlagen. Störungen durch Cyanid, Sulfid und Thiosulfat lassen sich vermeiden. Sulfit kann von Hydrogensulfit unterschieden werden.

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Résumé On propose une réaction très sensible pour la recherche de l'anhydride sulfureux à l'échelle micro et ultramicro. On peut éviter l'interférence avec les cyanures, les sulfures et les thiosulfates. On peut distinguer les sulfites des bisulfites.

     

7,7,8,8-tetracyanoquinodimethane chemiluminescence sensitized by Rhodamine B on surfactant bilayer membrane assemblies for determination of sulphide by a flow-injection method

A new chemiluminescence system is described for selective determination of sulphide by a flow-injection method. The weak light emitted from the reaction between 7,7,8,8-tetracyanoquinodimethane and sulphide is efficiently sensitized by Rhodamine B in alkaline solution containing dioctadecyldimethylammonium chloride bilayer membrane aggregates and acetonitrile. The limit of determination is 0.05 ng (injection of 30 mul of 5 x 10(-8)M sulphide), the linear range is two orders of magnitude, the sampling rate is 240/hr, and the relative standard deviation is 3.0% for 0.3 ng of sulphide. Manganese(II), the strongest enhancing species after sulphide ion, provides a signal 1.1% of that for sulphide ion. Manganese(II), iron(II), and species forming precipitates with sulphide ion interfere, but other sulphur anions such as sulphite, sulphate, thiosulphate, and thiocyanate do not.     

The determination of selenium(IV) by thermometric enthalpy titration with thiosulphate

Selenimn(IV) can be titrated in the range 0.2–6 mg with thiosulphate; relative standard deviations are 1.2–0.54%. Experimental conditions were manipulated to use the endothermic enthalpy of dilution and disproportionation of thiosulphate to advantage in improving end-point precision. Common anions do not interfere; interferences from copper(II), iron(III), lead(II) and mercury(II) can be minimized by masking.     

Spectrophotometric study of the formaldehyde-leuco-methylene blue reaction

The sensitivity of the reaction between foimaldchyde and Icuco-mcthyleno blue has been found to be increased in the presence of ethyl alcohol, acetone, dicthyl ketone and methyl ethyl ketone. Acetone has been found to be most effective. Sensitisers increase the absorption maximum and stabilise it, while the rate of development of methylene blue colour is slowed down.Sensitivity also depends upon the content of thiosulphate used to prepare the Icuco-base; a smaller amount of thiosulphate increases greater sensitivity.     

Flow-injection determination of some sulphur anions via the catalyzed iodine-azide reaction

Investigations of the catalysis by sulphide, thiosulphate and thiourea of the iodineazide reaction under flow-injection conditions showed that the reaction was complete within 15 s, 30 s and 2 min, respectively. Determination of 0–1.0×10^?3 M sulphide, 0–8.0×10^?4 M thiosulphate and 0–1.0×10^?3 M thiourea is possible under optimized flow conditions. Catalysis by thiocyanate did not occur under these conditions so that thiosulphate could be determined in the presence of thiocyanate.     

Thiosulphate in the Wollak procedure-analysis and kinetics in acidic formaldehyde medium

The Wollak procedure for the determination of the sum of dithionite and thiosulphate has been investigated. Analytical data and a kinetic study confirm that thiosulphate reacts with formaldehyde under acidic conditions. Both pH and CH(2)O concentration affect the results and satisfactory analysis can be performed only if the pH of the initial sample-formaldehyde mixture remains high enough.     

Titrimetric determination of thiocyanate and thiosulphate ions by oxidation with iodine in alkaline solution

Thiocyanate (2.7-90 mug) and thiosulphate (4.5-90 mug) ions are oxidized by iodine in alkaline media to sulphate ions. After acidification, the excess of iodine is extracted into chloroform, and the iodide ions formed in the redox reaction subjected to an amplification reaction. Either a titrimetric or a spectrophotometric finish may be used. Each thiocyanate and thiosulphate ion results in the ultimate production of 19 and 24 iodine molecules, respectively.