Determination of tin in ores, iron, steel and non-ferrous alloys by atomic-absorption spectrophotometry after separation by extraction as the iodide

A simple and moderately rapid method for determining 0.001% or more of tin in ores, concentrates and tailings, iron, steel and copper-, zinc-, aluminium-, titanium- and zirconium-base alloys is described. After sample decomposition, tin is separated from the matrix elements, except arsenic, by toluene extraction of its iodide from a 3M sulphuric acid-1.5M potassium iodide medium containing tartaric and ascorbic acids. It is finally back-extracted into a nitric-sulphuric acid solution containing hydrochloric acid to prevent the formation of an insoluble tin-arsenic compound and the resultant solution is evaporated to dryness. Tin is subsequently determined by atomic-absorption spectrophotometry in a nitrous oxide-acetylene flame, at 235.4 nm in a 10% hydrochloric-0.5% tartaric acid medium containing 250 mug of potassium per ml. Co-extracted arsenic does not interfere. Results obtained by this method are compared with those obtained spectrophotometrically with gallein after the separation of tin by iodide extraction.     

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.     

Determination of selenium in ores, concentrates and related materials by graphite-furnace atomic-absorption spectrometry after separation by extraction of the 4-nitro-o-phenylenediamine complex

A method for determining approximately 0.01 mug/g or more of selenium in ores, concentrates, rocks, soils, sediments and related materials is described. After sample decomposition selenium is reduced to selenium(IV) by heating in 4M hydrochloric acid and separated from the matrix elements by toluene extraction of its 5-nitropiazselenol complex from approximately 4.2M hydrochloric acid. After the extract has been washed with 2% nitric acid to remove residual iron, copper and chloride, the selenium in the extract is oxidized to selenium(VI) with 20% bromine solution in cyclohexane and stripped into water. This solution is evaporated to dryness in the presence of nickel, and selenium is ultimately determined in a 2% v/v nitric acid medium by graphite-furnace atomic-absorption spectrometry at 196.0 nm with the nickel functioning as matrix modifier. Common ions, including large amounts of iron, copper and lead, do not interfere. More than 1 mg of vanadium(V) and 0.25 mg each of platinum(IV), palladium(II), and gold(III) causes high results for selenium, and more than 1 mg of tungsten(VI) and 2 mg of molybdenum(VI) causes low results. Interference from chromium(VI) is eliminated by reducing it to chromium(III) with hydroxylamine hydrochloride before the formation of the selenium complex.     

Determination of bismuth in ores, concentrates and non-ferrous alloys by atomic-absorption spectrophotometry after separation by diethyldithiocarbamate extraction or iron collection

Two simple, reliable and moderately rapid atomic-absorption methods for determining trace and minor amounts of bismuth in copper, nickel, molybdenum, lead and zinc concentrates and ores, and in non-ferrous alloys, are described. These methods involve the separation of bismuth from matrix elements either by chloroform extraction of its diethyldithiocarbamate (DDTC) complex, at pH 11.5–12.0, from a sodium hydroxide medium containing citric acid, tartaric acid, EDTA and potassium cyanide as complexing agents, or by co-precipitation with hydrous ferric oxide from an ammoniacal medium. Bismuth is ultimately determined, at 223.1 nm after evaporation of the extract to dryness in the presence of nitric and petchloric acids and dissolution of the salts in 20% v/v hydrochloric acid, or by dissolution of the hydrous oxide precipitate with the same acid solution, respectively. Results obtained by both methods are compared with those obtained spectrophotometrically by the iodide method after the separation of bismuth by DDTC and xanthate extractions.     

Spectrophotometric determination of tantalum in ores and mill products with brilliant green after separation by methyl isobutyl ketone extraction of tantalum fluoride

A method for determining ~ 0.001% or more of tantalum in ores and mill products is described. After fusion of the sample with sodium carbonate, the cooled melt is dissolved in dilute sulphuric-hydrofluoric acid mixture and tantalum is separated from niobium and other matrix elements by methyl isobutyl ketone extraction of its fluoride from 1M hydrofluoric acid-0.5M sulphuric acid. The extract is washed with a hydrofluoric-sulphuric acid solution of the same composition to remove co-extracted niobium, and tantalum is stripped with dilute hydrogen peroxide. This solution is acidified with sulphuric and hydrofluoric acids and evaporated to dryness, and the residue is dissolved in oxalic-hydrofluoric acid solution. Tantalum is ultimately determined spectrophotometrically after extraction of the blue hexafluorotantalate-Brilliant Green ion-association complex into benzene from a 0.05M sulphuric acid-0.5M hydrofluoric acid-0.2M oxalic acid medium. The apparent molar absorptivity of the complex is 1.19 x 10(4) l.mole(-1).mm(-1) at 640 nm, the wavelength of maximum absorption. Common ions, including iron, aluminium, manganese, zirconium, titanium, molybdenum, tungsten, vanadium, tin, arsenic and antimony, do not interfere. Results obtained by this method are compared with those obtained by an X-ray fluorescence method.     

Spectrophotometric determination of tungsten in ores and steel by chloroform extraction of the tungsten-thiocyanate-diantipyrylmethane complex

A method for determining up to about 6% of tungsten in ores and mill products is described. It is based on the extraction of the yellow tungsten(V)-thiocyanate-diantipyrylmethane ion-association complex into chloroform from a 2.4M sulphuric acid-7.8M hydrochloric acid medium containing ammonium hydrogen fluoride as masking agent for niobium. The molar absorptivity of the complex is 1510 1. mole(-1).mm(-1) at 404 nm, the wavelength of maximum absorption. Moderate amounts of molybdenum and selenium may be present in the sample solution without causing appreciable error in the result. Interference from large amounts is avoided by separating these elements from tungsten by chloroform extraction of their xanthate complexes. Large amounts of copper interfere during the extraction of tungsten because of the precipitation of cuprous thiocyanate. Common ions, including uranium, vanadium, cobalt, titanium, arsenic and tellurium, do not interfere. The proposed method is also applicable to steel.     

Determination of cobalt and zinc in highpurity niobium, tantalum, molybdenum and tungsten metals by atomicabsorption spectrophotometry after separation by extraction

A method for determining 0.0005-0.05% of cobalt and zinc in high-purity niobium, tantalum, molybdenum and tungsten metals by atomic-absorption spectrophotometry is described. After sample dissolution, cobalt and zinc are separated simultaneously from the matrix materials by chloroform extraction of their thiocyanatediantipyrylmethane ion-association complexes, at pH 3.25, from a citric acid medium approximately 1.2M in sodium thiocyanate. Interference from copper is eliminated with thiourea. Large amounts of iron interfere under the recommended conditions, but moderate amounts may be present in the sample solution without causing appreciable error in the results. Phosphorus (as orthophosphate) interferes in the extraction of cobalt from tungsten solutions. Moderate amounts of other impurities do not interfere in the proposed method.     

Spectrophotometric determination of boron in iron and steel with curcumin after separation by 2-ethyl-1,3-hexanediol-chloroform extraction

A simple and reliable method for determining approximately 0.0001% or more of total boron in iron and low- and high-alloy steels is described. After the sample is decomposed at <70 degrees in the presence of hydrogen peroxide and potassium hydrogen fluoride, the insoluble material is filtered off and ultimately fused with sodium carbonate. The cooled melt is dissolved in dilute hydrochloric acid and the solution is combined with the main solution. Fluoride is subsequently complexed with zirconium and boron is separated from iron and other elements by extraction as borate from 1M sulphuric acid medium into chloroform containing 2-ethyl-1,3-hexanediol. Boron, in a 1-ml portion of the extract, is ultimately determined spectrophotometrically at 550 nm in an ethanol medium, after formation of the curcumin rosocyanin complex in a glacial acetic acid-concentrated sulphuric acid medium. Acid-soluble and acid-insoluble boron can also be determined. Common ions, including large amounts of manganese, chromium, vanadium, titanium, molybdenum, tungsten, niobium and tantalum do not interfere.     

Spectrophotometric determination of arsenic in concentrates and copper-base alloys by the molybdenum blue method after separations by iron collection and xanthate extraction

A method for determining 0.0001-1% of arsenic in copper, nickel, molybdenum, lead and zinc concentrates is described. After sample decomposition, arsenic is separated from most of the matrix elements by co-precipitation with hydrous ferric oxide from an ammoniacal medium. Following reprecipitation of arsenic and iron, the precipitate is dissolved in approximately 2 M hydrochloric acid and the solution is evaporated to a small volume to remove water. Arsenic(V) is reduced to the tervalent state with iron(II) and separated from iron, lead and other co-precipitated elements by chloroform extraction of its xanthate from an 11M hydrochloric acid medium. After oxidation of arsenic(III) in the extract to arsenic(V) with bromine-carbon tetrachloride solution, it is back-extracted into water and determined by the molybdenum blue method. Small amounts of iron, copper and molybdenum, which are co-extracted as xanthates, and antimony, which is co-extracted to a slight extent as the chloro-complex under the proposed conditions, do not interfere. The proposed method is also applicable to copper-base alloys.     

Determination of molybdenum by atomic-absorption spectrometry after separation by 5,5'-methylenedisalicylohydroxamic acid extraction and further reaction with thiocyanate and tin (II)

A method is described for the determination of molybdenum down to the microgram level, in samples of soil, steels, fertilizers and pharmaceuticals. After attack with acids, this element is separated from matrix elements by extraction of its 5,5'-methylenedisalicylohydroxamic acid (MEDSHA) complex from 4M hydrochloric acid, into methyl isobutyl ketone. Molybdenum is determined by atomic-absorption spectrometry (AAS), after conversion of the Mo-MEDSHA complex into the MoSCN(-) complex in the organic phase. The detection limit is 0.03 microg/ml, with a relative standard deviation not exceeding 1.5% at a level of 2 microg/ml. The method is highly selective and suffers only from interference by tungsten.     

Determination of molybdenum and tungsten at trace levels in rocks and minerals by solvent extraction and X-ray fluorescence spectrometry

Separation by solvent extraction followed by X-ray fluorescence spectrometry has been used for determination of molybdenum and tungsten in rocks and minerals. Samples are decomposed either by heating with a mixture of hydrofluoric acid and perchloric acid or by fusion with potassium pyrosulphate, followed by extraction of molybdenum and tungsten with N-benzoylphenylhydroxylamine in toluene from 4-5M sulphuric acid medium. The extract is collected on a mass of cellulose powder, which is dried in vacuum, mixed thoroughly and pressed into a disc for XRF measurements. The method is free from all matrix effects and needs no mathematical corrections for interelement effects. The method is suitable for determination of molybdenum and tungsten in geological materials down to ppm levels, with reasonable precision and accuracy.     

Solid-liquid extraction and cation-exchange solid-phase extraction using a mixed-mode polymeric sorbent of Datura and related alkaloids

Tropane alkaloids solid-liquid extraction methods were developed and comprised ambient pressure ones: extraction with hot solvent, extraction at room temperature, on ultrasonic bath as well as pressurised liquid extraction (PLE) techniques. The highest yields of l-hyoscyamine in methanol PLE method (3 x 5 min, 110 degrees C) and scopolamine extracted with 1% tartaric acid in methanol (15 min, 90 degrees C) were determined. A mixed-mode reversed-phase cation-exchange solid-phase extraction (SPE) procedure was optimised for simultaneous recoveries of L-hyoscyamine, scopolamine, scopolamine-N-oxide from plant extracts as well as quaternary alkaloid representative: scopolamine-N-methyl bromide. First three alkaloids were efficiently eluted (recoveries 80-100%) from an Oasis MCX cartridge with methanol-10% ammonia (3:1, v/v) solution, whereas for the quaternary salt tetrahydrofuran-methanol-25% ammonia (6:1:3, v/v) was used with recoveries 52-6%. HPTLC-densitometric assay on silica gel plates was elaborated at 205 nm without derivatization and included: single development (over a distance 9.5 cm) with acetone-methanol-water-25% ammonia (85:5:5:8, v/v) mobile phase for L-hyoscyamine and scopolamine separation, whereas for scopolamine-N-oxide and scopolamine-N-methyl bromide a second development (to a distance 5.5 cm) with acetonitrile-methanol-85% formic acid (120:5:5, v/v) was applied. Newly elaborated RP-HPLC-diode array detection method was performed on Waters XTerra RP-18 column with gradient of acetonitrile in 15 mM ammonia solution and alkaloids were baseline separated within 20 min. Both chromatographic methods were validated and their quantitative results were compared. Good correlation between HPLC and HPTLC quantitative results was measured (correlation coefficients of mean values were 0.92086 and 0.99995 for L-hyoscyamine and scopolamine, respectively). In the RP-HPLC method, which was from 1.5- up to 7-fold more sensitive than HPTLC, limits of detection (LOD) and limits of quantitation (LOQ, in bracket) were (in ng/microl) as follows: 0.25 (0.82) for L-hyoscyamine, 0.29 (0.97) for scopolamine, 0.13 (0.45) for scopolamine-N-oxide and 0.58 (1.91) for scopolamine-N-methyl bromide. By the use of the optimised chromatographic methods, 14 various samples from the leaves and fruits of Datura sp. were screened for L-hyoscyamine and scopolamine contents and the most promising samples were established.     

Determination of titanium in high-purity molybdenum and tungsten metals with diantipyrylmethane after separation by extraction of its cupferron complex

A method for determining 0.0005–0.10% of titanium in high-purity molybdenum and tungsten metals is described. After sample dissolution, titanium is separated from the matrix materials by chloroform extraction of its cupferronate from an alkaline (pH 8) tartrate-EDTA medium, then determined spectrophotometrically with diantipyrylmethane at 390 nm. Interference from manganese during extraction is eliminated with sodium sulphite. Iron, zirconium, thorium, tin, aluminium and antimony are partially extracted under the proposed conditions, but moderate amounts of these elements may be present in the sample solution without causing error in the results. Interference from iron(III) during colour development is eliminated with ascorbic acid. Other impurities in the two high-purity metals described do not interfere in the proposed method.     

Determination of antimony in ores and related materials by continuous hydride-generation atomic-absorption spectrometry after separation by xanthate extraction

A continuous hydride-generation atomic-absorption spectrometric method for determining approximately 0.02 mug/g or more of antimony in ores, concentrates, rocks, soils and sediments is described. The method involves the reduction of antimony(V) to antimony(III) by heating with hypophosphorous acid in a 4.5M hydrochloric acid-tartaric acid medium and its separation by filtration, if necessary, from any elemental arsenic, selenium and tellurium produced during the reduction step. Antimony is subsequently separated from iron, lead, zinc, tin and various other elements by a single cyclohexane extraction of its xanthate complex from approximately 4.5M hydrochloric acid/0.2M sulphuric acid in the presence of ascorbic acid as a reluctant for iron(III). After the extract is washed, if necessary, with 10% hydrochloric acid-2% thiourea solution to remove co-extracted copper, followed by 4.5M hydrochloric acid to remove residual iron and other elements, antimony(III) in the extract is oxidized to antimony(V) with bromine solution in carbon tetrachloride and stripped into dilute sulphuric acid containing tartaric acid. Following the removal of bromine by evaporation of the solution, antimony(V) is reduced to antimony(III) with potassium iodide in approximately 3M hydrochloric acid and finally determined by hydride-generation atomic-absorption spectrometry at 217.8 nm with sodium borohydride as reluctant. Interference from platinum and palladium, which are partly co-extracted as xanthates under the proposed conditions, is eliminated by complexing them with thiosemicarbazide during the iodide reduction step. Interference from gold is avoided by using a 3M hydrochloric acid medium for the hydride-generation step. Under these conditions gold forms a stable iodide complex.     

Determination of tellurium in ores, concentrates and related materials by graphite-furnace atomic-absorption spectrometry after separations by iron collection and xanthate extraction

A method for determining approximately 0.01 mug/g or more of tellurium in ores, concentrates, rocks, soils and sediments is described. After sample decomposition and evaporation of the solution to incipient dryness, tellurium is separated from > 300 mug of copper by co-precipitation with hydrous ferric oxide from an ammoniacal medium and the precipitate is dissolved in 10M hydrochloric acid. Alternatively, for samples containing 300 mug of copper, the salts are dissolved in 10M hydrochloric acid. Tellurium in the resultant solutions is reduced to the quadrivalent state by heating and separated from iron, lead and various other elements by a single cyclohexane extraction of its xanthate complex from approximately 9.5M hydrochloric acid in the presence of thiosemicarbazide as a complexing agent for copper. After washing with 10M hydrochloric acid followed by water to remove residual iron, chloride and soluble salts, tellurium is stripped from the extract with 16M nitric acid and finally determined, in a 2% v/v nitric acid medium, by graphite-furnace atomic-absorption spectrometry at 214.3 nm in the presence of nickel as matrix modifier. Small amounts of gold and palladium, which are partly co-extracted as xanthates if the iron-collection step is omitted, do not interfere. Co-extraction of arsenic is avoided by volatilizing it as the bromide during the decomposition step. The method is directly applicable, without the co-precipitation step, to most rocks, soils and sediments.     

Determination of silver in ores, concentrates, zinc process solutions, copper metal and copper-base alloys by atomic-absorption spectrophotometry after separation by extraction of the tribenzylamine-silver bromide complex

A method for determining 0.1 μg/g or more of silver in ores and concentrates and 0.001 μg/ml or more of silver in zinc process solutions is described. Silver is separated from the matrix elements by chloroform extraction of the tribenzylamine—silver bromide ion-association complex from 0.08M potassium bromide—2M sulphuric acid and stripped with 9M hydrobromic acid. This solution is evaporated to dryness and organic material is destroyed with nitric and perchloric acids. Silver is determined by atomic-absorption spectrophotometry in an air—acetylene flame, at 328.1 nm, in a 10% v/v hydrochloric acid—1% v/v diethylenetriamine medium. Cadmium, bismuth and molybdenum are partly co-extracted but do not interfere. The method is also applicable to copper metal and copper-base alloys. Results obtained by this method are compared with those obtained by a fire-assay/atomic-absorption method.     

Determination of tungsten in silicates and natural waters

Coprecipitation with hydrous manganese dioxide is used for the concentration of tungsten from natural waters (including sea water) and from solutions prepared from silicate rocks and sediments by hydrofluoric acid attack. After dissolution of the hydrous manganese dioxide precipitate in acidified sulphur dioxide solution, cation excliange is used to separate tungsten and molybdenum from other coprecipitated elements, hydrogen peroxide being used as eluant. Molybdenum is separated from tungsten by extraction of its dithiol complex from 24 N hydrochloric acid medium containing citric acid and can be determined photometrically. After destruction of citric acid, tungsten is determined photometrically with dithiol. The overall cliemical yield of th analytical process is 94±1%. The standard deviation of the method is ±0.010 μg for sea water (0.116 μg W/l) and ca 0.05 μg/g for siliceous sediments containing 0.5–1.0 μg W/g.     

Separation of molybdenum (VI) by extraction withn-octylaniline from hydrochloric acid medium

n-Octylaniline in bezene was used for the extractive separation of molybdenum (VI) from hydrochloric acid medium. Molybdenum(VI) was extracted quantitatively from 10 ml aqueous solution 1.5M in hydrochloric acid and 10M in lithium chloride into 10 ml of 10%n-octylaninline in benzene. It was stripped from the organic phase with 5% aqueous ammonia solution and estimated spectrophotometrically with thiocyanate at 465 nm. The interference of various ions has been studied in detail and conditions have been established for the determination of molybdenum(VI) in synthetic mixtures and alloy samples.     

Extractive separation of molybdenum as Mo(V) xanthate from Iron, vanadium, Tungsten, copper, uranium and other elements

A simple and selective extraction of molybdenum is described. Tungsten is masked with tartaric acid and molybdenum(VI) is reduced in 2M hydrochloric acid by boiling with hydrazine sulphate. Iron, copper and vanadium are then masked with ascorbic acid, thiourea and potassium hydrogen fluoride respectively. The molybdenum(V) is extracted as its xanthate complex into chloroform, from 1M hydrochloric acid that is 0.4M potassium ethyl xanthate. The complex is decomposed by excess of liquid bromine, and the molybdenum is stripped into alkaline hydrogen peroxide solution. The molybdenum is then determined by standard methods. Large amounts of Cu(II), Mn(II), Fe(III), Ti(IV), Zr, Ce(IV), V(V), Nb, Cr(VI), W(VI), U(VI), Re(VII) and Os(VIII) do not interfere. Several synthetic samples and ferromolybdenum have been rapidly and satisfactorily analysed by the method.     

Determination of aluminium in molybdenum and tungsten metals, iron, steel and ferrous and non-ferrous alloys with pyrocatechol violet

A method for determining 0.001-0.10% of aluminium in molybdenum and tungsten metals is described. After sample dissolution, aluminium is separated from the matrix materials by chloroform extraction of its acetylacetone complex, at pH 6.5, from an ammonium acetate-hydrogen peroxide medium, then back-extracted into 12M hydrochloric add. Following separation of most co-extracted elements, except for beryllium and small amounts of chroinium(III) and copper(II), by a combined ammonium pyrrolidincdithiocarbamate-cupfen-on-chlorofonn extraction, aluminium is determined spectrophotometrically with Pyrocatechol Violet at 578 nm. Chromium interferes during colour development but beryllium, in amounts equivalent to the aluminium concentration, does not cause significant error in the results. Interference from copper(II) is eliminated by reduction with ascorbic acid. The proposed method is also applicable to iron, steel, ferrovanadium, and copper-base alloys after preliminary removal of the matrix elements by a mercury cathode separation.