Rapid titrimetric methods for the determination of vanadium and molybdenum in mixtures

Summary A rapid and accurate method has been developed for the volumetric determination of molybdenum(VI) and vanadium(V) in mixtures, using cerium(IV) sulphate. In this procedure the sample solution is reduced in a mercury reductor (to give Mo^V and V^IV) and an aliquot of the reduced solution is titrated with Ce^IV solution using either ferroin, N-phenyl anthranilic acid, or barium diphenylamine sulphate as indicator. This titration gives the amount of molybdenum present, as V^IV does not interfere under the conditions applied. Another aliquot of the reduced solution is titrated with Ce^IV solution and rhodamine 6 G as indicator (observing the quenching of the fluorescence). This titration corresponds to the sum of molybdenum and vanadium. The vanadium content can be calculated by difference.

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Zusammenfassung Zur schnellen und genauen volumetrischen Bestimmung von Molybdän(VI) und Vanadium(V) in Mischungen wird Cer(IV)-sulfat als Reagens verwendet. Die Probelösung wird im Quecksilberreduktor reduziert (wobei Mo^V und V^IV gebildet werden) und ein aliquoter Teil der reduzierten Lösung wird mit Ce^IV-Lösung titriert, wobei Ferroin, N-Phenylanthranilsäure oder Bariumdiphenylaminsulfonat als Indicator dient. Aus dieser Titration erhält man den Molybdängehalt, da V^IV unter den angewendeten Bedingungen nicht stört. Ein weiterer Teil der reduzierten Lösung wird mit Ce^IV-Lösung gegen Rhodamin 6 G titriert (Endpunkt durch Fluorescenzlöschung), woraus man die Summe Mo + V erhält. Der Vanadiumgehalt ergibt sich aus der Differenz.

     

Flow-injection spectrophotometric determination of molybdenum and vanadium with carminic acid in the presence of cetyltrimethylammonium bromide

The color-forming reactions of molybdenum(VI) and vanadium(IV) with carminic acid (CA) in the presence of cetyltrimethylammonium bromide (CTAB) were used in the flow-injection determination of these metals. The micellar medium enhances the spectrophotometric features of the Mo(VI)-CA and V(IV)-CA binary complexes, and the higher solubility of these complexes when the CTAB concentration is above critical micelle concentration permits the easy application of flow-injection systems. Under the optimum conditions, linear calibration graphs were obtained from 0.76 to 28.8 g/ml for molybdenum and from 0.30 to 9.1 g/ml for vanadium. The detection limits were 0.33 and 0.16 g/ml for molybdenum and vanadium, respectively. The selectivity of the method was investigated and the procedure was successfully applied to the determination of molybdenum in steels and pharmaceuticals and of vanadium in petroleum products.     

Modifications of spectrophotometric methods for total phosphorus determination in meat samples

Spectrophotometric determination of total phosphorus in meat samples was modified using the molybdenum blue reaction with the following reducing agents: ascorbic acid (AA), hydrazine sulphate (HS), and mixture of hydroquinone and hydrazine sulphate (HHS). Proposed methods were validated by evaluation of statistical parameters such as: linearity, sensitivity, limits of detection (DL) and quantification (QL), precision, and accuracy, against the standard and malachite green (MG) modified procedures and by applying food certified materials. The values of within-day and between-days precision in meat samples for all tested reducing agents were better than 3.4 % and 4.2 %, respectively. The recoveries for CRMs analyses were between 92 % and 102.3 %. Obtained results suggest usefulness of the hydroquinone and hydrazine sulphate mixture in the determination of phosphorus ions.     

The spectrophotometric determination of vanadium in rocks

Vanadium in rock samples is determined, after alkaline fusion of the sample, by means of its catalytic action on the oxidation of aniline to aniline black by hydrogen peroxide. If necessary, chromium can be easily extracted to prevent interference. The sensitive procedure was applied to standard granite Gi and diabase Wi, and to the C.A.A.S. syenite i ; values of 16, 263 and 86 p.p.m., respectively, were obtained.     

Specific method for spectrophotometric determination of molybdenum in soil

A new, simple and specific spectrophotometric method for the determination of Mo in the soil extracts is described. Mo(VI) is reduced to Mo(V) with sodium borohydride and allowed to react with SCN^– ions in the presence of cationic and neutral surfactants e.g. CPC and TX-100 in the acidic aqueous solution. The molar absorptivity of the complex in both the aqueous, and toluene solutions is (2.30) × 10⁴ 1mol^–1 cm^–1 at absorption maximum, 460 nm. The extraction-procedure preconcentrated Mo at least 3-folds. the detection limit is 125ng Mo/g soil. The analytical variables of the method have been optimised and composition of the complex is proposed. None of the tested foreign ion interfered in the determination of Mo up to a large amount. An attempt for the removal of Fe-interference in the determination of Mo in soil extract has been described. The method has been found to be satisfactorily applicable for the determination of Mo in hot water leachates and acid digested soil solutions at lower ppm levels.     

Mixed micellar medium for the spectrophotometric determination of molybdenum in molybdenum/tungsten mixtures

Effects of cetyltrimethylammonium bromide (CTAB) and/or nonylphenoxypolyethoxyethanol (OP) on the absorption spectra of the complexes of molybdenum and tungsten with bromopyrogallol red (BPR) were studied. Based on these effects, a mixture of CTAB and OP was thus selected as a medium for the selective and sensitive determination of Mo in Mo/W binary mixtures. Under the optimum conditions, Beer's law was obeyed over the range 0.06-0.8 mug ml(-1) Mo with molar absorptivity being 1.3x10(5) l mol(-1) cm(-1) and detection limit 0.025 mug ml(-1). For 1.0 mug Mo, at least 20 mug W did not interfere in the determination of Mo with average recovery and relative standard deviation being 99.5% and <2%, respectively. The method developed maintained the features of simplicity and rapidity and, moreover, its selectivity and sensitivity enhanced greatly due to the use of CTAB/OP mixed micellar medium. When coupled with a compatible concentration method, the proposed method could be used for the determination of trace Mo in natural waters.     

Electrothermal atomic-absorption spectrophotometric determination of molybdenum

The sensitivity for determining Mo by ETA-AA is dependent on the heating programme employed when the peak-height method is used, but not when the peak area is used for evaluation of the AA signals. The linear range is greater at lower heating rate. Molybdenum can be directly determined in up to 8% NaCl solution without chemical pretreatment or background correction by making use of the high ashing temperature allowed, at which the matrix NaCl can be totally removed. The minimum recovery is 94.5%. Amounts of alkaline earth metals greater than 4000 times the amount of Mo give scatter signals, but these are time-resolved from the Mo signal. Any small effect on the peak height or area can be compensated for by background correction. The interference of tungsten is significant even at low concentrations (2-5 mug/ml) owing to the formation of stable compounds. Mo is determined in brines and acid digests of phosphate rocks after preconcentration and separation with the APDC-MIBK system, by ETA-AA of the organic extracts with or without mineralization.     

Catalytic-adsorptive stripping voltammetric determination of molybdenum in plant foodstuffs

In acetate buffer solution (pH 3.5) containing oxine and chlorate, ultratrace amounts of molybdenum can be determined after adsorptive accumulation of the Mo(VI)-oxine complex on a hanging mercury drop electrode, coupled with the catalytic effect on the reduction of chlorate. Under optimized conditions, the catalytic-adsorptive stripping voltammetric procedure gives excellent selectivity and an extremely low detection limit of 1.7 pM molybdenum (60 s accumulation). The stripping peak current increases linearly with molybdenum concentration between 10 pM and 5.0 nM. The procedure is applied to determine traces of molybdenum in plant foodstuffs.     

Alpha-induced coulomb excitation for the determination of vanadium and molybdenum in steels

A simple, rapid and non-destructive method for the determination of vanadium and molybdenum in steels is described. The method uses prompt spectrometry of the gammarays obtained from coulomb excitation with 5 MeV alpha particle beams. Using the 320 KeV gamma-ray, 3.3% precision was obtained for vanadium analysis. The precision for molybdenum was 3.2% and 5.3% using the gamma-rays of 204 and 536 keV, respectively. The extent of interference from other elements is discussed.     

氯酸钾体系催化动力学光度法测定痕量钒(Ⅱ)

研究了在0.1 mol/L H3PO4介质中,活化剂抗坏血酸的作用下,V(Ⅴ)催化KClO3氧化甲基红褪色的指示反应,由此建立了一种测定痕量V(Ⅱ)的催化动力学光度新方法。研究了影响该催化褪色反应的因素。方法的线性范围为0.09～7.0 ng/mL,检出限为2.9×10-2 ng/mL。方法用于实际样品的测定。     

Extractive spectrophotometric determination of molybdenum(V) in molybdenum steels

An extraction spectrophotometric method has been developed for the determination of traces of molybdenum present in molybdenum steels which is based on the extraction of the orange-red molybdenum-thiocyanate-acetonethiosemicarbazone complex into chloroform from hydrochloric acid medium. The complex has an absorption maximum at 472 nm with a molar absorptivity of 1.9 × 10⁴ liters mol⁻¹ cm⁻¹. Beer's law is valid over the concentration range 0.1–9.5 ppm of molybdenum with an optimum concentration range of 0.4–9 ppm. The equilibrium shift method indicates 1:4:2 composition for molybdenumthiocyanate-acetonethiosemicarbazone complex. The effect of acidity, reagent concentrations, temperature, and interferences from various ions are reported.     

Sensitive spectrophotometric methods for the determination of pindolol

Two simple, sensitive and reproducible visible spectrophotometric methods for the determination of Pindolol in amounts as low as 1 g are described. The first method is based on the oxidation of Pindolol by sodium nitrite under acidic conditions and the coupling of the oxidised intermediate withN-1-(naphthyl)ethylenediamine dihydrochloride (NED) to the colored product. The spectrum of the colored solution is strongly dependent on the length of the incubation period at room temperature during oxidation (3 min, _max 620 nm; 10 min or above _max 540 nm). Other couplers [diphenylamine (DPA) or 1-naphthylamine (-NA)] or indole derivatives (indole, tryptophan or isatin) when used instead of NED or Pindolol, respectively, also react to give a colored product with same maximum in each case irrespective of the length of the incubation period during oxidation. The second method is based on the coupling reaction involving Pindolol and 1,2-naphthaquinone-4-sulphonic acid sodium salt to form a coloured product (_max 660 nm). Both the methods have been employed to determine Pindolol content in bulk forms and pharmaceutical preparations.     

Ion-exchange separation and spectrophotometric determination of vanadium in environmental samples

A selective and sensitive method for the extraction and spectrophotometric determination of vanadium(V) in microgram quantities is described. The molar absorptivity of the yellow vanadium(V)-caffeic acid-Aliquat 336 extract is 1.3 x 10(4) 1.mole(-1).cm(-1) at 370nm. The method is compared with the atomic-absorption spectrometric method and applied to the trace determination of vanadium in steel, alloys, a rock and environmental samples.     

A rapid method for spectrophotometric determination of molybdenum in alloy steels

Summary A Rapid Method for Spectrophotometric Determination of Molybdenum in Alloy Steels Molybdenum (VI) forms an orange-red coloured mixed-ligand complex with perazine dimalonate and thiocyanate at room temperature (27°) in hydrochloric acid. The complex is soluble in ethanol. It exhibits absorption maximum at 460 nm. Beer's law is valid over the molybdenum concentration range 0.1–14.0,g/ml. Sandell's sensitivity of the reaction is 0.9·10^–3 g Mo/cm² and the molar extinction coefficient is 1.06·10⁴ 1·mol^–1·cm^–1 at 460 nm. The stoichiometry of the complex is (Perazine·H) [MoO(SCN)₄] as shown by Job's method, equilibrium shift method and elemental analyses of the isolated complex. The proposed method has been used for the determination of molybdenum in ores, alloy steels and in synthetic mixtures containing chromium, tungsten, iron, cobalt, nickel and copper.Presented at the 36th Pittsburgh Conference and Exposition on Analytical Chemistry and Applied Spectroscopy, New Orleans, February 25-March 1, 1985.     

Simultaneous spectrophotometric determination of molybdenum and selenium,and of molybdenum and tellurium

A method is reported for the extraction of molybdenum-phenylfluorone by chloroform. The extraction is complete whether perchlorate ions are present or not but the extractions in the presence of perchlorate ions gave a somewhat more sensitive procedure for the spectrophotometric determination of molybdenum in the solvent phase as the molybdenum-phenylfluorone complex.A procedure is reported for the simultaneous determination of molybdenum and selenium, and molybdenum and tellurium. The method involves first the formation and solvent extraction of the molybdenum-phenylfluorone complex by chloroform in the presence of perchlorate ions, followed by determination of selenium in the remaining aqueous phase as selenium-diethyldithiocarbamate complex after solvent extraction with 2-ethyl-1-hexanol in the presence of perchlorate ions. A similar procedure is reported for the simultaneous determination of molybdenum and tellurium except that in the determination of molybdenum, the phenylfluorone complex is extracted by chloroform in the absence of perchlorate ions. Tellurium is determined in the remaining aqueous phase as tellurium-diethyldithiocarbamate complex after solvent extraction by 2-ethyl-1-hexanol solvent extraction in the presence of perchlorate ions.     

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.     

催化动力学光度法测定水中痕量钒

基于在H3PO4介质中, 抗坏血酸作活化剂, 100 ℃沸水浴加热的条件下, 痕量钒V(Ⅴ)催化溴酸钾氧化三溴偶氮氯膦(TB-chorophosphonazo)的褪色反应, 建立了新的测定超痕量钒的催化光度法. 该方法对钒测定范围是0～1.0 ng/mL, 检出限为0.133 ng/mL. 实验考察了影响催化反应速率的各种因素, 确定了最佳的实验条件. 实验测定了反应的动力学参数: 表观活化能Ea'=93.80 kJ/mol, 表观速率常数为k'=1.307×10-3 s-1, 建立了催化反应动力学方程. 方法灵敏度高, 选择性好, 直接用于环境水体中痕量钒的测定.     

The spectrophotometric determination of molybdenum and uranium with quinalizarin

Quinalizarin reacts very sensitively with molybdenum and uranium to form colored chelates having λ_max at 520 and 630 nm, respectively. The molar ratio for both the chelates is 1:1 (metal:reagent). Optimum conditions including the range for adherence to Beer's law, effect of pH on color intensity, effect of excess of the reagent, sensitvity, and interference of the foreign ions has been reported for the photometric determination of these metal ions using quinalizarin, in 50% ethanolic medium and at 30 °C.     

A new spectrophotometric method for the determination of dithianon in commercial formulations and its residues in foodstuffs

A new, simple, and rapid spectrophotometric method for the microdetermination of dithianon, on the basis of its reaction with a dithiocarbamate, is described. The red color, which develops instantaneously when mixing the fungicide with the reagent in acetonitrile, is stable for at least 1 h and is measured at 520 nm. Beer's law is applicable up to 12 micrograms/mL dithianon concentration. The method has been successfully adapted to the analysis of the fungicide in commercial formulations and its residues on grains and apple (fruit and leaves). A photometric titration method for formulation analysis of the fungicide has also been developed.