Spectrophotometric determination of molybdenum(VI)

Molybdenum(IV) gives a red colour with ammonium thiocyanate in 5-8M hydrochloric acid medium, the Sandell sensitivity index being 0.018 ppm Mo(VI)/cm(2). Molybdenum(VI) in 4-7M hydrochloric acid medium forms a red complex with ethyl xanthate and ammonium thiocyanate and this can be extracted into acetophenone. Beer's law is obeyed over the range of 1.2-13.8 ppm, and the Sandell indices at 370 and 470 nm are 0.0016 and 0.0068 ppm/cm(2) respectively. The colour is stable for 40 hr. Most cations do not interfere.     

Spectrophotometric determination of antimony with 3,5,7,4'-tetrahydroxyflavone (kaempferol)

A selective spectrophotometric method is described for determination of antimony with kaempferol. Microgram amounts of antimony can be determined by measurements at 420 run in 0.1M hydrochloric acid. The molar absorptivity is 1.09 x 10(4) at 420 nm and the optimum range for accurate determination is 1.9-7.8 ppm of antimony.     

Separation studies of molybdenum(VI) and rhenium(VII) using TPPO as an extractant

A simple, rapid and reproducible method for the extractive separation of molybdenum(VI) and rhenium(VII) is proposed using triphenylphosphine oxide (TPPO) dissolved in toluene as an extractant. The extractions are carried out from the hydrochloric and hydrobromic acid medium. The extraction of molybdenum is quantitative from 2.54-3.10 M hydrochloric acid and from 3.76-3.98 M hydrobromic acid, and that of rhenium is from 6.78-7.91 M hydrochloric acid. The probable nature of the extractable species is established using log distribution ratio-log concentration plots. The method permits mutual separation of molybdenum(VI) and rhenium(VII) and is applicable for the analysis of alloys and pharmaceutical sample. The detection limits for molybdenum(VI) and rhenium(VII) are 0.8 ppm and 4 ppm respectively.     

The stability of gold solutions

The stability of gold solutions was studied over the concentration range of 0.41-258 ppm at acidities ranging from 6M hydrochloric acid to pH 1, the solutions being stored in glass-stoppered borosilicate bottles. The best conditions were found to be 12-258 ppm solutions at pH 0-2, for which the loss of gold was 4% or less over a period of 400 days.     

Determination of platinum in ores by a combined fire-assay and flameless atomic-absorption method

A combined fire-assay and flameless atomic-absorption procedure for the determination of platinum in ores is described. Silver beads obtained by cupellation are dissolved in aqua regia and made up to standard volume with 6M hydrochloric acid, then 50-mul aliquots are injected into a carbon tube. From 0.5 to 5 ppm platinum can be determined with a precision of approximately 5%. The procedure tolerates other platinum metals and gold in the amounts present in the ores analysed.     

Stripping voltammetric determination of traces of technetium with a glassy carbon electrode coated with tri-n-octylphosphine oxide

Technetium(VII) and Tc(IV) are concentrated from 3 M hydrochloric acid media by complexing with tri-n-octylphosphine oxide applied as a thin layer to a glassy carbon electrode. Differential-pulse cathodic stripping voltammetry from 0 V provides a stripping peak for Tc(VII) at ?350 mV (vs. Ag/AgCl). The detection limit after an enrichment time of 10 min is about 1.8×10^?8 M Tc(VII). Technetium(IV) produces a stripping peak near the Tc(VII) peak which can be used for rough estimates of the Tc(VII)/Tc(IV) ratio within limited ranges. Uranium(VI) in equimolar concentrations interferes.     

Separation and spectrophotometric determination of trace quantities of lithium in high-purity beryllium and beryllium oxide

A spectrophotometric method is described for the determination of trace quantities of lithium in beryllium metal and its oxide. Lithium is selectively separated from beryllium by extraction from 1M potassium hydroxide solution into 0.1M dipivaloylmethane in diethyl ether. Fluoride, added before the extraction, successfully masks the beryllium; as little as 3 microg of lithium can be separated from as much as 1 g of beryllium. The lithium is then back-extracted into 0.1M hydrochloric acid and is determined spectrophotometrically with o-(2-hydroxy-3,6-disulpho-1-naphthylazo) benzene arsonic acid, Thoron. In an acetone-water medium Beer's law is obeyed over the range 0.1-1.0 microg ml. The method has been applied successfully to the determination of lithium in concentrations as low as 3 ppm; the relative standard deviation for the determination of 200 ppm is 3%.     

Spectrophotometric determination of molybdenum by extraction of a green molybdenum(v) species

A simple method is described for the rapid spectrophotometric determination of molybdenum in samples containing 1-60% Mo, with satisfactory accuracy. Molybdenum is reduced with excess of hydrazine sulphate in boiling 5.5M hydrochloric acid and extracted with isoamyl acetate from 7M hydrochloric acid. The green colour is measured at 720 nm against a reagent blank. Beer's law is obeyed over the range 0.08-5.4 mg of molybdenum per ml. Interference from iron and copper is removed by adding stannous chloride and thiourea respectively in slight excess. Titanium, vanadium, niobium, chromium, tungsten, nickel, uranium, and antimony do not interfere even in large amounts. Only cobalt interferes seriously.     

Determination of small amounts of TBP and DBP in uranyl nitrate solutions

Tri- and dibutylphosphate (TBP and DBP) in concentrated uranyl nitrate solution are determined by a method based on the solvent extraction of zirconium-95. The distribution ratio of zirconium-95 between dilute solutions of TBP and DBP in dodecane and 10M hydrochloric acid and 1Mnitric acid respectively is measured. There is a logarithmic relationship between the distribution ratio and concentration of TBP and DBP, which enables them to be determined rapidly and with an error of +/- 10% over the range 1-100ppm of TBP and 40-600 ppm of DBP. The lower limit is 0.5 ppm for TBP and 10 ppm for DBP.     

Determination of uranium in minerals and rocks

A method is described for the determination of uranium in minerals and rocks by spectrophotometry and fluorimetry. After treatment of the sample with hydrochloric acid, uranium is separated from matrix elements by adsorption on a column of the strongly basic anion-exchange resin Dowex 1 x 8 from an organic solvent system consisting of IBMK, tetrahydrofuran and 12M hydrochloric acid (1:8:1 v v ). Following removal of iron, molybdenum and co-adsorbed elements by washing first with the organic solvent system and then with 6M hydrochloric acid, the uranium is eluted with 1M hydrochloric acid. In the eluate, uranium is determined by means of the spectrophotometric arsenazo III method or fluorimetrically. The suitability of the method for the determination of both trace and larger amounts of uranium was tested by analysing numerous geochemical reference samples with uranium contents in the range 10(-1)-10(4) ppm. In practically all cases very good agreement of results was obtained.     

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.     

Determination of phosphorus traces in platinum alloys by two-phase isotope exchange

The method of ZEMAN and KRATZER for the determination of phosphorus traces by means of two-phase isotope exchange was modified for the determination of phosphorus in pure platinum or pure platinum alloys. It was found that Pt, Rh, Ag, and As do not interfere with the determination. Among the elements usually present in platinum metal or platinum alloys, only gold interferes. It was removed by extraction from 7M HCl by MIBK and AmOAc. Hydrochloric acid also interferes but it can be removed by evaporation. The analytical procedure is given for the solution obtained by pressure decomposition of the sample (0.5 g) in a steel bomb with PTFE inlay. It is possible to determine >2 ppm P (approximate error −10%). Using a calibration dependence instead of the well known equation for isotope exchange, the content of P in the standard solution labelled with³²P need not be known.     

Substoichiometric isotope dilution analysis of iron in biological materials by the 8-quinolinol-extraction

A highly precise and accurate method for the determination of minor amounts of iron by substoichiometric isotope dilution analysis is described. The constant amount of Fe(III) is substoichiometrically extracted with 2·10⁻⁴M oxine in chloroform from the aqueous phase of pH 9.2–10.0 containing 6·10⁻³M tartrate. The interfering ions such as Mn(II), Co(II), Ni(II), Cu(II), and Zn(II), can be removed by the preliminary extraction of Fe(III) from 7.5M hydrochloric acid solutions into isopropyl ether. The present method has been applied to the determination of iron in biological standard reference materials, i.e., the NBS Spinach (SRM-1570) and the NIES Pepperbush (SRM No. 1), and the results obtained are 548±9 ppm (NBS certified value: 550±20 ppm) and 193±4 ppm, respectively.     

Anion-exchange separation and spectrophotometric determination of vanadium in silicate rocks

A combined anion-exchange-spectrophotometric method has been developed for the determination of vanadium in silicate rocks. A rock sample weighing about 0.1 g is decomposed with a mixture of sulphuric and hydrofluoric acids and after removal of HF the residue is taken up with dilute sulphuric acid. This solution is adjusted to be 0.05M in sulphuric acid and contain 0.3% hydrogen peroxide, and is passed through a column of Amberlite CG 400 (sulphate form). The sorbed vanadium is eluted with 30 ml of 1M hydrochloric acid. The effluent is evaporated to dryness, made 0.1M in hydrochloric acid and 3% in hydrogen peroxide content, and passed through a column of Amberlite CG 400 (chloride form) to get rid of accompanying thorium and zirconium. Vanadium is stripped by elution with 20 ml of 1M hydrochloric acid and subsequently determined spectrophotometrically with 4-(2-pyridylazo)resorcinol. The detection limit is 0.4 ppm.     

Untersuchungen zur elektrochemischen Simultanbestimmung von Blei und Zin

Zusammenfassung Die invers-voltammetrische Simultanbestimmung von Blei und Zinn ist in 1 M salzsaurem Methanol ohne Lösungswechsel möglich. Die Arbeitsbedingungen werden angegeben. Pb kann neben einem 30–50fachen Sn-Überschuß und Sn neben der 10fachen Pb-Menge bestimmt werden. Tl stört, ist jedoch meist nicht vorhanden oder kann leicht abgetrennt werden.

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Investigations on the electrochemical simultaneous determination of lead and tinIII. Simultaneous inverse-voltammetric determination of lead and tin in hydrochloric acid methanolic base solution without change of solutions

Summary The determination is possible in 1 M hydrochloric acid methanol as base solution without solution exchange. Working conditions are reported. Pb can be determined in the presence of an 30 to 50-fold excess of Sn, and Sn in the presence of a 10-fold excess of Pb. Tl interferes, however is either not present in many cases or can easily be separated.

Die vorliegende Arbeit wurde in dankenswerter Weise durch Mittel des Verbandes der Chemischen Industrie und der Deutschen Forschungsgemeinschaft unterstützt.     

Flow analysis of silicate rocks for zirconium

A flow analysis system involving the on-line configuration of an anion-exchange column has been examined to enrich and determine trace concentrations of zirconium of several ppm to hundred ppm levels in silicate rocks and minerals. About 100 mg of sample is decomposed by fusion with a mixture of boric acid and lithium carbonate and taken up with 1M hydrochloric acid to a total of 100 ml. Depending upon the concentration of zirconium, either a 1- or 4-ml aliquot is introduced into an aqueous carrier stream, merged with sulphuric acid and passed through a small volume anion-exchange column. The enriched zirconium is then back eluted with hydrochloric acid, colour-developed with Arsenazo III, and detected spectrophotometrically at 665 nm.     

Determination of traces of cadmium in alloy steels by anodic stripping voltammetry

Concentrations of cadmium of the order of 0.1 ppm in alloy steels containing large concentrations of chromium and nickel (ca. 17 and 13% respectively), about 0.1% of copper and a number of metals at low concentrations, were determined by anodic stripping voltammetry with a hanging mercury-drop electrode in 1M hydrochloric acid. Cadmium was separated on Dowex 50W-X8 cation-exchanger in a medium at pH 1.3 containing excess of EDTA. Mercury-film electrodes cannot be used for this determination, because the peak for cadmium is distorted by evolution of hydrogen on the electrode support. The relative standard deviation of the determination of 0.44 ppm of cadmium in steel is 3.2% and the confidence limits for 95% probability are 0.44 +/- 0.02 ppm. The error in the cadmium recovery does not exceed + 8%.     

Spectrophotometric determination of lead with 1-(2-pyridylazo)-2-naphthol and non-ionic surfactants Application to acetic acid extracts of ceramic enamels

The Pb-PAN system in the presence of non-ionic surfactants (polyoxyethylene nonylphenols) has been studied spectrophotometrically. The optimum conditions for Pb determination are pH 9 (Na(2)B(4)O(7)-HClO(4)), 5% surfactant and measurement at 555 nm. The system obeys the Lambert Beer law over the Pb concentration range 1.3-4.5 ppm; the molar absorptivity is 2.02 x 10(4) l.mole(-1).cm(-1) at 555 nm. The relative standard deviation is 0.9% and the limit of detection 0.12 ppm. Lead can be determined in acetic acid extracts of ceramic enamels by extraction with sodium diethyldithiocarbamate into carbon tetrachloride and stripping with 4M hydrochloric acid to remove interferent species. The results obtained are in agreement with those obtained by a standard AAS method.     

Separation of niobium and tantalum by extraction chromatography with bis(2-ethylhexyl)phosphoric acid

A novel method is developed for the reversed-phase extractive chromatographic separation of niobium and tantalum with bis(2-ethylhexyl)phosphoric acid. Niobium is extracted from 1-10M hydrochloric acid and can be stripped with 3M sulphuric acid containing 2% hydrogen peroxide. Tantalum is extracted from 0.1-2M hydrochloric acid and can be stripped with 0.1M hydrochloric acid containing 2M tartaric acid. It is possible to separate niobium and tantalum, in different ratios, from multicomponent mixtures.     

Determination of vanadium and molybdenum by atomic-absorption spectrophotometry

A method is described for the determination by atomic-absorption spectrophotometry of vanadium and molybdenum, up to the milligram level, in samples of yellow cake, uranium-bearing minerals and geochemical standards. After attack with acids these two elements are separated from each other and from matrix elements by means of anion-exchange in 6M hydrochloric acid on the strongly basic anion-exchange resin Dowex 1, X8 (chloride form). Vanadium is unadsorbed and passes into the effluent while molybdenum is adsorbed on the resin. For the elution of molybdenum a mixed aqueous-organic solvent system consisting of methanol and 6M hydrochloric acid (9: 1 v/v) is used. After evaporation of the 6M hydrochloric acid effluent and of the mixed aqueous-organic eluate vanadium and molybdenum are determined by atomic-absorption spectrophotometry. The method was tested by analysing numerous samples with contents ranging from a few ppm to milligram amounts of vanadium and molybdenum. For comparison, the concentrations of these two elements were determined in a large number of samples by spectrophotometric and titrimetric procedures. In all cases very good agreement of results was obtained.