Determination Of Trace Molybdenum Research Articles

Sensitive determination of trace molybdenum in natural waters using dispersive liquid–liquid microextraction and electrothermal atomic absorption spectrometry

A simple, sensitive and rapid method involving dispersive liquid–liquid microextraction was developed for the determination of molybdenum using electrothermal atomic absorption spectrometry. After injection of a ternary mixture containing trichloroethylene (extractor solvent), ethanol (disperser solvent) and ammonium pyrrolidinedithiocarbamate (chelating reagent), the extraction of molybdenum into the aqueous phase occurs. The quantity of the element in the enriched phase was measured using electrothermal atomic absorption spectrometry. Under optimized conditions (pH 2.5, 2.0 mL of disperser solvent, 50 μL of extraction solvent, 50.0 μL of 0.10% m/v chelating solution and centrifugation at 3000 rpm for 2.5 minutes), the method has a detection limit of 0.013 μg L−1, a quantification limit of 0.044 μg L−1 and an enrichment factor of 75 for a sample volume of 5.0 mL. The certified reference material NIST 2781, Domestic Sludge, was used to assess the accuracy of the method. The proposed procedure was successfully applied to the determination of molybdenum in natural water samples.

A novel method of the separation/preconcentration and determination of trace molybdenum(VI) in water samples using microcrystalline triphenylmethane loaded with salicyl fluorone

It is the first time that triphenylmethane was used as an adsorbent to preconcentrate and separate trace amount of molybdenum in water samples. The effects of different parameters, such as acidity, stirring time and various metal ions, the amounts of triphenylmethane and salicyl fluorine, etc. on the enrichment yield of molybdenum have been studied to optimize the experimental conditions. Under the optimum conditions, molybdenum can be adsorbed on the surface of microcrystalline triphenylmethane loaded with salicyl fluorone by the intermolecular action strength. The possible reaction mechanism for the enrichment of molybdenum was discussed in detail in this paper. Mo(VI) can be completely separated from Pb(II), Co(II), Cu(II), Cr(III), Ni(II), Hg(II), Zn(II), Cd(II), Fe(III) and Al(III) in the solution. The proposed method was successfully applied to the determination of trace amount of molybdenum in various water samples by spectrophotometry after preconcentration using microcrystalline triphenylmethane. The preconcentration factor is from 83 (500 ml water sample was enriched to 6.0 ml) to 166 (1000 ml water sample was enriched to 6.0 ml). The detection limit is 1.3 × 10 −5 mg l −1 and the linearity is maintained in the concentration range 3.8 × 10 −3 to 0.36 mg l −1 with a correlation coefficient of 0.9998. The recoveries are in the range of 93.5–104%. The relative standard deviation is 1.8–2.9%. Analytical results obtained with this novel method are very satisfactory.

Determination of trace molybdenum (VI) by oscillographic potentiometric catalyzing kinetic method of simplex optimization

Under the optimum experimental conditions (i. e., pH=1.6, c KI=10.6 mmol/L, \(c_{H_2 O_2 } \)=5.4 mmol/L, \(c_{C_6 H_8 O_6 } \)=1.30 mmol/L) derived from simplex operations, trace molybdenum(VI) was determined through the agency of its catalytic effect on the reaction of H2O2 with I− in acid medium. The detection limit and linear calibration range of molybdenum were obtained as 0.5×10−6 mol/L and 0.5×10−6∼120×10−6mol/L respectively. This method was applied to the examination of the industrial waste water, and the recovery ratios were found to be in the range of 101% and 107%.

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 Trace Molybdenum in Water Samples by Electrothermal Atomic Absorption Spectrometry after Preconcentration with Miniaturized Coprecipitation

Abstract Miniaturized coprecipitation with hydrous manganese(IV) oxide was studied for the preconcentration of sub μg dm−3 levels of molybdenum in water samples. Manganese(IV) oxide was produced by a reaction of permanganate ion with ethanol in the presence of 0.1 mol dm−3 hydrochloric acid. A nanogram amount of molybdenum in a 10 cm3 sample was quantitatively coprecipitated. The amount of manganese required was 0.1—0.40 mg for a 10 cm3 sample. The precipitate was collected on a 10 μm membrane filter, and then dissolved in 50 mm3 of 5.6 mol dm−3 nitric acid and 75 mm3 of 1% hydrogen peroxide. An 80-fold preconcentration factor was obtained by this procedure. The molybdenum concentration was determined by electrothermal atomic absorption spectrometry using a pyrolytic graphite coated cuvette. The detection limit (3σ) was found to be 8.9 ng dm−3. The proposed method was successfully applied to river water and snow samples.

Spectrophotometric Determination of Trace Amounts of Molybdenum in Steel and Pure Iron with a New Chromogenic Reagent Dimethoxyhydroxyphenylflurone

ABSTRACT A simple method for the direct determination of trace molybdenum in low alloy steel and pure iron with selectivity and sensitivity is reported. In the presence of TritonX-100 and sulphuric-phosphoric acid medium, a new chromogenic reagent dimethoxyhydroxyphenyl-flurone (DMHPF) forms a red complex with molybdenum(VI). The molar absorptivity is obeyed from the range of 0˜ 8 μg/25 ml for molybdenum(VI). Most of metal ions and 35000-fold amounts of iron do not interfere with the determination of molybdenum. The proposed method has been successfully used for the determination of trace amounts of molybdenum in steel and pure iron specimens.

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Catalytic spectrophotometric determination of trace molybdenum in natural- and tap-water samples.

A sensitive and simple catalytic spectrophotometric method for the determination of molybdenum has been developed using the molybdenum-catalyzed oxidation of L-ascorbic acid with hydrogen peroxide in the presence of ο-phenylenediamine to produce quinoxaline derivatives. The absorbance of the solution was measured at 340 nm for the determination of molybdenum after reacting for 5 min at pH 3.2 and 25°C and readjusting the pH of the solution to 1 with hydrochloric acid to stop the reaction. The calibration graph was, linear up to 4 ng/ml of molybdenum. The detection limit was 0.03 ng/ml (0.2 ng). The proposed method was successfully applied to river-, rain- and tap-water samples.

Determination of Trace Molybdenum in Biological Matrices by Neutron Activation Analysis

Based on consecutive extractions using bismuth diethyldithiocarbamate and thallium diethyldithiocarbamate as reagents, molybdenum was selectively and highly enriched from biological matrices, and then subjected to neutron activation analysis. Most of interfering elements, e.g., Na, K, Br, P, Fe, U, etc. were simultaneouly removed and the preconcentrated samples always showed only the r rays from molybdenum after neutron bombardment. Thus, molybdenum in the biological matrices could be accurately determined.

Differential Pulse Polarographic Determination of Trace Molybdenum in Uranium with α-Benzoinoxime Extraction

A method for the determination of trace molybdenum in uranium is described based on its specific catalytic reduction wave in the presence of nitric acid. Molybdenum is separated from uranium by α-benzoin oxime extraction and determined by differential pulse polarography. As lower as 1 ng/ml of Mo(VI) is determinable and 98% of recovery can be obtained at present work.