The separation of W(V) from HCl-KSCN medium on polyurethane foam sorbents for its spectrophotometric determination in steels and silicates

A simple procedure for selective sorption of tungsten is described. The method involves reduction of W(VI) to W(V) with tin(II) chloride (2%, w/v) at 8-9M hydrochloric acid, formation of the W(V)-SCN complex with 0.2M KSCN and its sorption on polyurethane foam within 20 min. The sorbed complex is then eluted with acidified acetone (1 ml of 1M hydrochloric acid and 8 ml of acetone) followed by addition of 1 ml of 0.1M KSCN to the eluent. The method has been applied to the spectrophotometric determination of tungsten in steels and silicates by measuring the absorbance of the eluted solution at 400 nm. Beer's law is obeyed for the range 0.1-12 mug W/ml. Other elements, e.g., Co(III) (50 mug/ml), Cu(II) (10 mug/ml), Ti(IV) (20 mug/ml), V(V) (10 mug/ml) and Mo(VI) (0.5 mug/ml) have no effect on the method. Interference of copper, up to 100 mug/ml has been eliminated by masking with thiourea and that due to molybdenum by prior separation with thioglycollic acid on PUF. The method has been verified with standard samples.     

Spectrophotometric determination of vanadium in biological materials with N-benzylbenzohydroxamic acid

A spectrophotometric method for the determination of vanadium in biological materials with N-benzylbenzohydroxamic acid is proposed. The method is highly selective for vanadium and is free from rigid control of reaction conditions. No separation of iron prior to the determination of vanadium is necessary. Cu(II), Co(II), Ni, Mn(II), Cr(III), Ce(IV), Zr, Mo(VI), Ca, Sr, Ba, UO(2)(II) and many others metal ions do not interfere. Fairly large quantities of Ti(IV) and W(VI) are tolerated.     

Novel spectrophotometric method for the determination of molybdenum in a PVA medium.

A novel spectrophotometric method for the determination of trace molybdenum in the presence of a large amount of tungsten was developed. This proposed method was based on the formation of a green charge-transfer polyoxometalate, molybdo-11-tungstophosphate-3,3',5,5'-tetramethylbenzidine-N-propanesulfonic, which was solubilized and stabilized in a PVA medium; the wavelength of the maximum absorption was at 660 nm. Beer's law was obeyed in the Mo concentration range of 0.04-1.6 microg ml(-1). The molar absorptivity was 1.35 x 10(4) l mol(-1) cm(-1). The developed method avoided the interference of W(VI), and was conveniently applied to analyses of some tungsten ores containing Mo(VI) with satisfactory results.     

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.     

Applications analytiques des oxocarbones-II: composition des complexes tungstiques des ions bromanilate et chloranilate: dosage spectrophotometrique du tungstene(VI)

The complexes formed from tungsten(VI) and chloranilate (C(2-)) and bromanilate (B(2-)) have been studied in aqueous solution and as solids, by ultraviolet, visible and infrared spectroscopy. At pH 3-4, the complexes have the composition ligand:tungsten = 2. At pH < 2, only the 1:1 complexes are found. The two reagents allow the spectrophotometric determination of W(VI) (lambda, = 335 nm for H(2)C and 340 nm for H(2)B) in 1.4M HClO(4), at concentrations of about 1 mg/l. The conditional stability constants of the two 1:1 complexes in this medium have been calculated. The tungsten complexes are more stable than the corresponding molybdenum complexes, and the complexes of B(2-) are more stable than the complexes of C(2-) [with W(VI) and Mo(VI)]. It is shown that this result is due to the difference between the pK(1), values of the acids H(2)B and H(2)C. The infrared spectra of the complexes of B(2-) and C(2-) with Mo(VI) and W(VI) are discussed in order to define the interaction between the metal ions and the ligands.     

Synthesis and analytical properties of 3,4-dihydroxybenzaldehyde guanylhydrazone (3,4-DBGH)

Synthesis and analytical properties of 3,4-dihydroxy-benzaldehyde guanylhydrazone are described. The reagent was tested with 43 cations but only Co(II), Fe(II), Fe(III), Mo(VI), W(VI) and V(V) gave colored complexes. Spectral characteristics of the reagent are presented. Procedure for a selective a determination of Co(II), a sensitive determination of Fe(III) and determination of Mo(VI), W(VI) and V(V) in presence of large amounts of Fe(III) are reported. The method was applied for the determination (a) of Co(II) in presence of other cations at excess (b) of Fe(III) in a city drinking water sample without preconcentration and (c) of Mo(VI) in a standard steel sample.     

Spectrophotometric determination of molybdenum based on charge transfer complex in PVA medium

A very simple, selective and sensitive method was developed for the spectrophotometric determination of Mo in the presence of W. The method was based on the formation of color charge transfer complex, molybdotungstophosphate-3,3',5,5'-tetramethylbezidine anion, which was solubilized and stabilized in PVA medium. Following the recommended procedure, molybdenum could be determined in the linear range of 0.04-2.5 mug ml(-1) and the molar absorptivity was 1.47x10(4) l mol(-1) cm(-1) at 660 nm. The proposed method had been applied to the determination of trace molybdenum in tungsten ore with satisfactory results.     

Kinetic-spectrophotometric determination of molybdenum (VI) and tungsten (VI) in mixtures

A simple kinetic-spectrophotometric method is described for the determination of molybdenum(VI) and tungsten(VI) in mixtures, without prior separation. The method is based on the catalytic effect of molybdenum(VI) and tungsten(VI) on the oxidation of 2,4-diaminophenol dihydrochloride (DAP) by hydrogen peroxide in acidic medium. The reaction was followed spectrophotometrically by measuring the rate of change in absorbance with time at 500 nm. A partial inhibition in the catalytic activity of each catalyst, when the other one is present, at all ratios of Mo(VI) W(VI) mixtures studied was observed. On the other hand, the catalytic activity of tungsten(VI) dropped to zero whilst that of molybdenum(VI) decreased slightly, in the presence of citrate ions. Two sets of experiments were carried out, the first in the absence and the other in the presence of citrate, and the resolution of Mo(VI)/W(VI) mixtures was achieved by solving two simultaneous equations. Various molar ratios of Mo(VI) W(VI), at the 10^–6 M level, from 0.2 1 to 5 1 can be determined with satisfactory precision and accuracy. The selectivity of the method was investigated and the method was applied successfully to the determination of molybdenum and tungsten in each other's presence in steel.     

Synthesis,Crystal Structure of Cis—dioxo—catecholatotungsten（VI） Complex and Its NMR Studies on the Interaction with ATP

Cis-dioxo-catecholatotungsten(VI) complex anion[W^(VI)O2-(OC6H4O)2]^2- was obtained with discrete protonated ethylenediamine (NH2CH2CH2NH3)^ cations by the reaction of tetrabutyl ammonium decatungstate with catechol in the mixed solvent of CH3OH,CH3CN and ethylenediamine,and compared with its molybdenum anaogue [Mo^(V) O2(OC6H4O)2]^3- by crystal structure,UV,EPR,The results of the UV and EPR spectra show that tungsten is less redox active than molybdenum since the molybdenum is reduced from Mo(VI) to Mo(V) but tungsten stays in the original highest oxidized state Mo(VI) when they are crystallized from the solution above.It is worthy to note that [W^(VI)O2(OC6H4O)]^2- shows the same coordination structure as its molybdenum analogue in which the metal center exhibits distorted octahedral coordination geometry with two cis-dioxocatecholate ligands and might have the related coordination structure feature with the cofactor of flavoenzyme because [Mo^(V)O2(OC6H4O)2]^3- presented essentially the same EPR spectra as flavoenzyme.The NMR studies on the interaction of the title complex with ATP reveal that the reduction of W(VI) to W(V) occurs when the title complex is dissolved in D2O and the W(V) is oxidized again when ATP solution is mixed with original solution and the hydrolysis of the catecholato ligand take places at mean time being monitored by ^1H NMR and ^13C NMR spectra.     

Spectrophotometric determination of molybdenum based on charge transfer complexes sensitized by copper(II)

A new high sensitive spectrophotometric determination of trace molybdenum was investigated. The sensitivity of the determination of molybdenum, which based on the color charge transfer complex of molybdotungstophosphate-3,3′,5,5′-tetramethylbenzidine, was greatly enhanced by copper(II) ions in the presence of polyvinyl alcohol. The improved method maintained the features of simplicity, rapidity and selectivity, especially eliminating the interference from tungsten. Under the optimum conditions, Beer's law was obeyed over the range from 2 to 32 ng ml⁻¹ molybdenum with molar absorptivity being 4.92×10⁵ l mol⁻¹ cm⁻¹ at 660 nm. The relative standard deviation was 1.2% under nine determinations for 16 ng ml⁻¹ Mo(VI). The present method had been applied to the determination of trace molybdenum in tungsten ores with satisfactory results.     

分光光度法同时测定多元素的研究 : 以CPA-矩阵法计算混合体系中Mo、W、Ti三元素的含量

本文将CPA-矩阵法用于光度分析中同时对多元素的测定, 确定了在SAF为显色剂、DTMAB为胶束增敏剂的配合体系中以CPA-矩阵法计算Mo、W、Ti三元素含量的各种最佳实验条件, 建立了在该体系中同时测定互相干扰的Mo、W、Ti三元素的分光光度法. 总结了进行多组份测定时选择分析波长的四项原则, 并依此确定了6个测定波长: 510、512、514、516、518、520nm为Mo、W、Ti三元素的测定波长. 依本文建立的方法, 通过对任意含量配比的三元素混合试样进行测定结果极为满意, 方法具有稳定、准确、简便、快速和经济等特点, 便于推广应用.     

Extractive-spectrophotometric determination of molybdenum with 4-unsubstituted-5-pyrazolones

A fairly sensitive and selective method for rapid determination of tracer amounts of molybdenum(V) as mixed-ligand complexes with thiocyanate and 4-unsubstituted-5-pyrazolones is described. The red complexes are extractable into chloroform from 1-5M hydrochloric or perchloric acid or 1-3M sulphuric arid media. The molar absorptivities are in the range 1.72-2.15 x 10(4)l.mole(-1).cm(-1) at 455 nm (lambda(max)). The method has been applied to the estimation of molybdenum in various synthetic and alloy-steel samples. In presence of excess of the reagent, Cu(II), Co(II), Mn(II), Fe(II), Fe(III), Al(III), Cr(III), Cr(VI), Ti(III), Ti(IV), Zr(IV), Hf(IV), V(III), V(IV), V(V), Nb(V), Ta(V), W(VI) and U(VI) do not interfere.     

An improved flow-injection system for spectrophotometric determination of molybdenum and tungsten in tool steels

A flow-injection procedure for simultaneous spectrophotometric determination of tungsten and molybdenum in steel alloys is proposed. The method exploits the catalytic effects of Mo(VI) and W(VI) on the rate of iodide oxidation by hydrogen peroxide under acidic conditions. A novel strategy for ion-exchange separation of the potential interfering species is proposed, and an AG50W-X8 cationic resin mini-column is used. The sample is injected twice, originating two sequential plugs, citrate being added to one of them in order to suppress the W(VI) catalytic activity thus providing the kinetic discrimination.The system handles 70 samples per hour and requires 1.6 mg KI per determination. A linear response is verified up to 10 mg l⁻¹ Mo (or W) in the injectate, and signal additivity is 98-103%. Results are precise (R.S.D. < 0.04) and in agreement with ICP-OES. Running a standard reference material (IPT-50) assessed also accuracy.     

Übergangsmetallchalkogenverbindungen. Spectrophotometric evidence for the existence of MoO3Se2− and WO3Se2− in aqueous solution. Electronic Spectra of the Ions MeOxSe4−x2− (Me = Mo,W)

A spectrophotometric investigation of the reaction between MeO₄^2? (Me?Mo, W) and gaseous H₂Se leading to the identification of the unknown monoselenoanions of molybdenum(VI) and tungsten(VI) is reported. The electronic spectra agree well with the theoretically predicted ones. Further a comparative study of the spectra of different seleno- and thio-anions was made. The first band in the electronic spectra of MoO₃Se^2? and WO₃Se^2? is due to the Se → metal charge transfer transition.     

Spectrophotometric determination of molybdenum with Alizarin Red S in the presence of poly(sulfonylpiperidinylmethylene hydroxide)

The present work describes a selective and rapid method for the determination of molybdenum with Alizarin Red S (ARS) in the presence of a water soluble polymer, poly(sulfonylpiperidinylmethylene hydroxide) (PSPMH). The ARS modified by PSPMH reacts with molybdenum(VI) in the solutions of pH 3.4-4.0 to produce a red complex. The composition of the complex is 1:4:1 mol ratio of Mo(VI): ARS:PSPMH. The complex obeys Beer's law from 0.05 to 5.50 μg ml⁻¹ with an optimum range. The molar absorptivity is 2.1×10⁴ l mol⁻¹ cm⁻¹ at 500 nm. The interference effects of the foreign cations have been examined and it has been determined that only Cu(II), Al(III) and Fe(III) have to be masked by EDTA and tungsten can be tolerated till 4-fold of molybdenum in case of masking by citrate. The method has been applied to the determination of geological samples without solvent extraction or separation steps.     

钼-水杨基荧光酮-溴化十六烷基三甲基铵显色反应的研究

在0.2-0.8/Ⅳ的盐酸介质中,钼(Ⅵ)与水杨基荧光酮以及溴化十六烷基三甲基铵,可以形成一红色三元络合物。络合物的最大吸收峰位于530纳米,表观摩尔吸光系数ε₅₃₀=1.40×10⁵。钼的浓度为0-8微克/25毫升时,络合物溶液的吸光度遵守比尔定律。三元络合物的组成经测定Mo:SAF:CTMAB=1:2:2。常见金属离子中,除钛与钨(Ⅵ)以外,均不干扰钼的测定。利用本显色反应,曾对多种合金钢中的钼含量进行了测定,取得了较好的效果。     

Simultaneous determination of molybdenum(VI) and tungsten(VI) and its application in elemental analysis of polyoxometalates

Spectrophotometric determination of molybdenum(VI) and tungsten(VI) with application of Artificial Neural Networks is proposed and it was applied for elemental analysis of solid polyoxometalates. Better results in comparison with previously those achieved by previous published method were demonstrated. MALDI-TOF Mass Spectrometry was tested for possible determination of molecular weight of polyoxometalates utilizing different matrices. Phenomena observed during desorption-ionisation processes are discussed. LDI-TOF MS was found to be suitable for the determination of Mo:W ratio in polyoxometalates as a rapid screening method to follow synthetic procedure.     

Anion-exchange separation and spectrophotometric determination of molybdenum and tungsten in silicate rocks

A combined ion-exchange spectrophotometric method has been developed for the determination of molybdenum and tungsten in silicate rocks. After the decomposition of samples with a mixture of sulphuric, nitric and hydrofluoric acids, traces of molybdenum and tungsten are separated from other elements by anion-exchange in acid sulphate media containing hydrogen peroxide. The adsorbed molybdenum and tungsten can easily be stripped from the column by elution with sodium hydroxide-sodium chloride solution. The adsorption and desorption steps provide selective concentration of molybdenum and tungsten, allowing the simultaneous spectrophotometric determination of the two metals with dithiol. Results on the quantitative determination of molybdenum and tungsten in the U.S. Geological Survey standard samples are included.     

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.     

A rapid spectrophotometric method for the determination of molybdenum in industrial, environmental, biological and soil samples using 5,7-dibromo-8-hydroxyquinoline.

A very simple, ultra-sensitive and highly selective non-extractive spectrophotometric method for the determination of trace amount of molybdenum(VI) using 5,7-dibromo-8-hydroxyquinoline (DBHQ) has been developed. 5,7-Dibromo-8-hydroxyquinoline reacts in a slightly acidic solution (0.05 - 1.0 M H2SO4) with molybdenum(VI) to give a deep greenish-yellow chelate which has an absorption maximum at 401 nm. The reaction is instantaneous and the absorbance remains stable for over 24 h. The average molar absorption coefficient and Sandell's sensitivity were found to be 4.13 x 10(3) L mol(-1) cm(-1) and 7 ng cm(-2) of molybdenum(VI), respectively. Linear calibration graphs were obtained for 0.1 - 50 microg mL(-1) of molybdenum(VI). The stoichiometric composition of the chelate is 1:3 (Mo:DBHQ). A large excess of over 50 cations, anions and some common complexing agents (e.g. EDTA, oxalate, citrate, phosphate, thiourea, SCN-) do not interfere with the determination. The method was successfully used in the determination of molybdenum in several Standard Reference Materials (alloys, steels and waters) as well as in some environmental waters (inland and surface), biological samples (human blood and urine), soil samples, solution containing both molybdenum(V) and molybdenum(VI) and complex synthetic mixtures. The method has high precision and accuracy (S = +/-0.01 for 0.5 microg mL(-1)).