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.     

Simultaneous determination of titanium and molybdenum in steel samples using derivative spectrophotometry in neutral micellar medium

A simple, selective and sensitive spectrophotometric method has been developed for the individual and simultaneous determination of Ti(IV) and Mo(VI) using resacetophenone p-hydroxybenzoylhydrazone (RAPHBH) in presence of Triton X-100, without any prior separation. Beer's law is obeyed between 0.13-1.2 microg mL-1 and 0.18-1.90 microg mL-1 concentration of Ti(IV) and Mo(VI) at 455 nm and 405 nm, respectively. The molar absorptivity and Sandell's sensitivity of the coloured complexes at pH 3.0 are 3.1x10(4) L mol-1 cm-1, 4.2x10(4) L mol-1 cm-1, and 1.6 ng cm-2, 2.3 ng cm-2 for Ti(IV) and Mo(VI), respectively. The stoichiometry of the complexes were found to be 1:2 and 1:1 (metal:ligand) for Ti(IV) and Mo(VI), respectively. These metal ions interfere with the determination of each other in zero-order spectrophotometry. The first derivative spectra of these complexes permitted a simultaneous determination of Ti(IV) and Mo(VI) at zero crossing wavelengths of 500.0 nm and 455.0 nm, respectively. The effect of foreign ions in the determination of Ti(IV) and Mo(VI) were investigated. The proposed method has been successfully applied for the determination of titanium and molybdenum in standard alloy steel, mineral and soil samples.     

Determination of vanadium in ore samples by atomic-absorption spectrophotometry

An atomic-absorption method is described for the determination of vanadium in ores. With a nitrous oxide-acetylene flame and 200 ppm of Al(3+) added to the sample, a sensitivity of 0.2 ppm for 1% absorption can be obtained. Iron above 0.015M interferes but can be extracted into isopropyl ether from 8M hydrochloric acid; the hydrochloric add itself then interferes and must be removed by evaporation.     

Determination of vanadium,molybdenum and tungsten in chloralkali electrolysis brines by x-ray fluorescence spectrometry

The levels of vanadium, molybdenum and tungsten are critical in chloralkali electrolysis brines because these elements catalyze the hydrogen-producing side-reaction. Preconcentration by chelation with 8-quinolinol and subsequent adsorption on activated carbon, can be combined with energy- or wavelength-dispersive x-ray fluorescence. Under optimized conditions, the detection limits are in the μg 1^-1 range, and below the critical levels. Up to 100 /smg l^-1, reliable results are obtained for V, Mo and W. The coefficient of variation is typically 15% in the 25–100 μg l^-1 range.     

Determination of trace molybdenum in vegetable and food samples by spectrophotometry with p-carboxyphenylfluorone

A new highly sensitive and selective chromogenic reagent, p-carboxyphenylfluorone (p-CPF), was studied for spectrophotometric determination of trace molybdenum. In 0.36 mol L(-1)phosphoric acid medium, p-CPF reacts with molybdenum(VI) to form a 1:3 red complex, which has a sensitive absorption peak at 531 nm. Under optimal conditions, the reaction of molybdenum(VI) with p-CPF completed rapidly and absorbance remains almost constant for at least 24 h. Molybdenum(VI) obeyed Beer's law in the range 0-2.0 microg mL(-1); the apparent molar absorption coefficient, Sandell's sensitivity and the limit of detection were found to be 1.03 x 10(5) L mol(-1) cm(-1), 1.028 ng cm(-2)and 0.73 ng mL(-1) respectively; the effect of various foreign ions were examined in detail. It was found that most coexisting ions can be tolerated in considerable amounts, especially 800 mg of Mn(II), 200 mg of Mg(II), Fe(II), Co(III), Ni(II) and Cd(II), 50 mg of Ca(II) and Al(III), 25 mg of Cu(II) and Fe(III), 10 mg of Hg (II), La(III), Bi(III), Pb(II) and Zn(II) don't interfere with the determination of molybdenum(VI). The proposed method is very simple, sensitive and selective, it has been applied to determine molybdenum in vegetable and food samples with a very high precision and accuracy. Moreover, the synthesis of the reagent and the conditions of the colour reaction were also studied in detail.     

Determination of vanadium, molybdenum and tungsten in complex matrix samples by chelation ion chromatography and on-line detection with inductively coupled plasma mass spectrometry

In this work, two kinds of chelating resin, bis(2-aminoethylthio)methylated resin (BAETM) and γ-aminobutyrohydroxamate resin (γ-ABHX) were synthesized. Of these, the former has a hydrophobic skeleton, and the latter a hydrophilic skeleton. The functionalities of each were 0.91 and 2.21 mmol g⁻¹, respectively. The chelating behavior of these resins towards vanadium, molybdenum and tungsten as a function of pH was studied. To perform trace metals analysis in complex matrices, a hyphenated method-chelation ion chromatography (CIC) coupled on-line detection with inductively coupled plasma mass spectrometry (ICP-MS) was developed. With a BAETM resin column (5×0.4 cm i.d.) as the separator, a sample volume of 20 μl, nitric acid (pH 1.5) as the eluent and a flow rate of 1 ml min⁻¹, the detection limits for the determination of vanadium, molybdenum and tungsten were lower than 0.05 ng ml⁻¹and the linear ranges were up to 100 ng ml⁻¹ for each element. By increasing the injected sample volume to 250 μl, the resin concentrator improved the detection limit to 0.01 ng ml⁻¹. For the determination of these elements (5 ng ml⁻¹ for each) spiked in artificial sea water samples, γ-ABHX resin column (3×0.6 cm i.d.) demonstrated well resolved peak separation between the analytes and the matrix elements—calcium and magnesium, by using sodium nitrate (10 ml, 10⁻⁴ M) as the eliminator.     

The determination of vanadium,molybdenum and tungsten by infrared spectroscopy

The infrared spectra of the 8-hydroxyquinolinates of molybdenum, vanadium and tungsten in the region 3–15 μ were investigated. It was found possible to determine the elements quantitatively, singly or in pairs, with an error of about 3%. Molybdenum was determined at 10.80 μ and 10.93 μ, vanadium at 10.50 μ, and tungsten at 10.61 μ or 10.90 μ.     

Determination of cobalt,molybdenum and vanadium in austrian mineral waters by ICP-AES after ion-exchange separation and preconcentration

A method is described for the determination of cobalt, molybdenum and vanadium in mineral water samples by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) after separation of these elements from the matrix by ion exchange. The samples are acidified with concentrated hydrochloric acid (10 ml/l) and the elements are adsorbed as thiocyanate complexes. Elution is performed with a mixture 2M in perchloric acid and 1M in hydrochloric acid and subsequently with 1M hydrochloric acid. After evaporation of the eluates and dissolution of the residue the volume of the measuring solution for ICP-AES is 10 ml. The recoveries for Co, Mo and V at a concentration level of 1 g/1 in mineral waters were approximately 99%. A concentration factor of 100 is achieved by this procedure.     

Chromatographic separation of vanadium, tungsten and molybdenum with a liquid anion-exchanger

In acidic solution only molybdenum(VI), tungsten(VI), vanadium(V), niobium(V) and tantalum(V) form stable, anionic complexes with dilute hydrogen peroxide. This fact has been used in developing an analytical method of separating molybdenum(VI), tungsten(VI) and vanadium(V) from other metal ions and from each other. Preliminary investigations using reversed-phase paper chromatography and solvent extraction led to a reversed-phase column Chromatographic separation technique. These metal-peroxy anions are retained by a column containing a liquid anion-exchanger (General Mills Aliquat 336) in a solid support. Then molybdenum(VI), tungsten(VI) and vanadium(V) are selectively eluted with aqueous solutions containing dilute hydrogen peroxide and varying concentrations of sulphuric acid.     

Ion-exchange separation of vanadium, zirconium, titanium, molybdenum, tungsten and niobium

Schemes for the separation of two or more of the elements vanadium, zirconium and/or titanium, molybdenum and tungsten from each other and from relatively large amounts of niobium have been developed, a strongly basic anion-exchange resin being used. Interference from niobium is avoided by using hydrofluoric acid to elute vanadium, zirconium, titanium and molybdenum. The application of coupled columns to improve the efficiency of separation of multicomponent mixtures is demonstrated. The use of an "interval" equation defining the volume interval between successively eluted solutes is proposed for calculating the column length required for a particular separation. This equation is especially useful for determining the extent to which a column must be lengthened when overlapping occurs because of high column loading.     

极谱法测定化探样品中钨钼的技术改进

针对传统极谱法测定化探样品中钨钼时操作手段繁琐问题加以改进。试样以硫酸-二苯乙醇酸-二苯胍-氯酸钠体系为混合底液,将经过碱熔融后的样品以甲基橙为指示剂,用硫酸(1+1)调酸度后,加入固定比例的混合底液,摇匀,无需定容,放置25~30min后直接测定。采用二次倒数波测定,钨峰电位在-660mV左右,钼峰电位在-30mV左右,钨钼的质量浓度在0.02~1.0μg/mL内呈线性关系,钨检出限为0.5μg/g,钼检出限为0.3μg/g。方法灵敏度高,快捷、简单,适用于大批量化探样品的测定。     

Determination of small amounts of titanium in pure molybdenum,tungsten, vanadium and their oxides after separation on silica gel

A new method for the separation of titanium from molybdenum, tungsten and vanadium is described, based on sorption of the titanium complex with hydrogen peroxide on silica gel under dynamic conditions. The eluted titanium is determined spectrophotometrically with diantipyrylmethane. The method can be applied to the determination of small amounts of titanium in tungsten, molybdenum and vanadium metals and in their oxides.     

Determination of molybdenum by atomic-absorption spectrophotometry

A new procedure is described for precise estimation of molybdenum by atomic-absorption spectrophotometry using an airacetylene flame. Phosphoric acid was found to be effective in suppressing interference by Fe(III), Al, Sb(III), Ca, Mg, Pb and Mn(II).     

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.     

Determination of vanadium by atomic absorption spectrophotometry

Methods for the determination of vanadium, in the range 0.5–100 mg/l, by atomic absorption spectroscopy in an oxy-acetylene as well as in a nitrous oxideacetylene flame are presented. For use with oxy-acetylene flames, vanadium is extracted as vanadium cupferrate into a mixture of methyl isobutyl ketone and oleic acid (78:22, v/v) and the organic phase is aspirated to the flame. The sensitivity is 0.7 mg/l of vanadium in the organic phase. For nitrous oxide-acetylene flames, an aqueous solution of vanadium is aspirated directly. The sensitivity is further improved by the use of methyl isobutyl ketone, the addition of Al³⁺ and diethylene glycol diethyl ether. Many potential interferences were examined and methods to overcome those found are given.     

电感耦合等离子体质谱(ICP-MS)法测定地质样品中镉、铬、钨、钽和铌

地质样品成分复杂,各元素物理化学性质差异大,在有盐酸介质存在的的情况下,敞口湿法一次消解容易出现易挥发元素Cd、Cr等测定结果不稳定;敞口湿法一次消解,难溶元素W、Ta、Nb等消解不完全。本文以HNO3—HF—HClO4—H2SO4为消解体系,用电热板湿法重复消解样品,建立起了ICP-MS同时测定地质样品种不同性质Cd、Cr、W、Ta、Nb的样品分析方法。通过优化仪器参数条件,选择带碰撞池He气模式（ked）,以50g/L酒石酸为测定介质,采用三通在线加入103Rh和185Re内标补偿基体效应和信号飘逸,解决了难溶元素W、Ta、Nb结果偏低、易挥发元素Cd、Cr结果精密度较差的问题。该方法用国家一级标准物岩石、土壤、水系沉积物质验证,相对标准偏差(RSD)小于8%,准确度(△lgC)均≤0.05,其测定值与标准值一致,用实际样品进行加标回收试验,回收率在89%～110%之间,方法检出限均小于多目标区域地球化学调查规范（DZ/T 0258—2014）。该方法分析流程较简单,结果准确可靠,可满足测定大批量地质样品中Cd、Cr、W、Ta、Nb元素含量的要求。     

Radioactivation analysis of aluminium,vanadium, copper,molybdenum, zinc and uranium in natural water samples using organic coprecipitants

A method is described for the determination of trace metal ions, V, Al, Cu, Mo Zn, and U, in natural water samples by neutron activation analysis, using organic coprecipitation as a preconcentration method. The preconcentration of trace elements was accomplished by converting the dissolved trace metal ions into the oxine chelates atpH 5.2 and extraction of the chelates witho-phenylphenol which is a liquid above 56 °C and solidifies at room temperature. After cooling the extraction system, the fine particles of the organic phase were collected on a millipore filter and the precipitate was air-dried in a clean environment. The solid extract was wrapped up in a sheet of clean polyethylene and subjected to neutron irradiation in a reactor for less than 10 min at a thermal flux of 2·10¹³ n·cm⁻²·sec⁻¹. γ-Ray spectrometry by a coaxial Ge(Li) detector connected to a 1024-channel PHA was performed on the irradiated sample without further chemical separation, and thus the ppb level concentration of the elements in natural water samples could be determined. The fundamental study of the collection of the trace elements is also described.     

FT-IR and FT-FIR studies of vanadium,molybdenum and tungsten oxides supported on different carriers

In the far IR region at low molybdenum loadings, Mo-SiO₂ catalysts present a pseudomolybdate or a polymolybdate species, while bulk-like MoO₃ appears at loadings close to the geometrical monolayer coverage. W-SiO₂ and V-SiO₂ spectra show bands close to those observed on the corresponding bulk oxides.In the case of TiO₂, Al₂O₃, ZrO₂ supported catalysts, a band is observed near 1000 cm^–1 which is assigned to the Mo=O stretching vibration of coordinatively unsaturated Mo ⁿ⁺ ions showing a stronger interaction with the support than one observed on silica.