Use of long-chain alkylamines for preconcentration and determination of traces of molybdenum, tungsten and rhenium by atomic-absorption spectroscopy-II: molybdenum in soils, sediments and natural waters

Molybdenum is extracted as the thiocyanate complex with the quaternary long-chain aliphatic amine Aliquat 336 in chloroform, followed by evaporation of the solvent, dissolution in MIBK, and atomic-absorption spectroscopy. The method is simple, rapid and sensitive, with few interference problems for the determination of the Mo content of soils and sediments in the range 0.1-1.0 ppm with a relative standard deviation better than 5% when 1-g samples are used. Quantitative extraction from large volumes of aqueous solution has also been confirmed, allowing the determination of Mo in natural waters in the ppM range.     

Use of long chain alkylamines for preconcentration and determination of traces of molybdenum, tungsten and rhenium by atomic-absorption spectroscopy--III. Tungsten in geological samples

Tungsten is determined by atomic-absorption spectroscopy after its reduction to the W(V)-thiocyanate complex with tin metal and extraction with Alamine 336 into chloroform. Atomic absorbance is measured on a final MIBK solution after evaporation of the chloroform and redissolution of the residue in MIBK. Interference effects are shown to be negligible for diverse cations and anions, including Fe, Cu, Cr, Co, Mo, Al and Bi. Analysis of geological samples with an exceptionally wide range of W content from 2.8 ppm to 10% is achieved with relative standard deviations better than 5%.     

Spectrophotometric determination of rhenium in the presence of molybdenum and tungsten

Summary Rhenium(VII) can be separated on a column of Al₂O₃ from a 500-fold excess of Mo(VI) and W(VI) and a 250-fold excess of Cr(III), Mn(II), Ni(II), Co(II), and Fe(III) by elution with 0.1M Nad. For photometric determination, rhenium(VII) is reduced with Sn(II), extracted as the thiocyanate complex into isopropyl ether, and measured at 430 nm. The sensitivity is 0.04 g/ml, if 10-mm cells are used. The interferences were examined statistically and found to be negligible.

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Zusammenfassung Rhenium(VII) läßt sich von einem 500fachen Überschuß an Mo(VI) und W(VI) sowie von einem 250fachen Überschuß an Cr(III), Mn(II), Ni(II), Co(II) und Fe(III) mit Hilfe einer Aluminiumoxidsäule trennen und daraus mit 0,1-m Kochsalz eluieren. Für die photometrische Bestimmung wird Rhenium(VII) mit Sn(II) reduziert, dann als Rhodanidkomplex mit Isopropyläther extrahiert und bei 430 nm gemessen. Bei Verwendung von 10-mm-Küvetten beträgt die Empfindlichkeit 0,04 g Re/ml. Störungen wurden statistisch geprüft und als unbeachtlich erkannt.

     

Separation of rhenium, tungsten and molybdenum by thin-layer chromatography

Re(VII), W(VI) and Mo(VI) can be separated by thin-layer chromatography on silica gel. The best results are obtained with methanol-3M HC1 (7:3) and methanol-1M NH₄NO₃-3 M NH₃ (14:5:1). Dithiol is used as detection reagent.     

Determination of traces of molybdenum and tungsten by extraction and polarography of their salicoylhydroxamates

Molybdenum and tungsten salicoylhydroxamates have been extracted into methyl isobutyl ketone or a mixture of chloroform and isobutyl alcohol from 1.5M hydrochloric acid and subjected to DC and derivative pulse polarography (DPP) after addition of methanolic lithium chloride solution, phosphoric acid and water in defined proportions. Molybdenum gives two DC waves with E(1 2 ) at -125 and -525 mV and a sharp DPP peak at -75 mV, whereas tungsten shows a single DC wave at -840 mV and a DPP peak at -850 mV. The two metals can be determined down to the sub-ppm level.     

Synthetic, spectroscopic, and structural studies on organoimido molybdenum, tungsten, and rhenium phthalocyanines

Unprecedented imido phthalocyaninato complexes of pentavalent refractory metals [PcM(NR)Cl] (M = Mo, W, Re; R = tBu: 1, 3, 6, Mes: 2, 4, 7 or Ts: 5) have been synthesized by reductive cyclotetramerization of phthalonitrile in the presence of appropriate bis(imido) complexes of Mo, W and Re as templates. While d(1) Mo(V) and W(V) species 1-5 show distinctive EPR spectra corresponding to metal centered radicals with hyperfine coupling of two magnetically non-equivalent nitrogen atoms (4 equatorial and 1 axial N), corresponding d(2) Re(V) compounds 6 and 7 are diamagnetic. [PcMo(NtBu)Cl] 1 crystallizes from 1-chloronaphthalene in the tetragonal space group P4/n. The molecular structure reveals, that the metal center is located above the plane of the equatorial N4 and displaced towards the axial π-donor ligand. Due to the thermodynamic trans effect the Mo-Cl bond trans to the imido group is elongated to about 2.600(2) ?.     

The preconcentration, separation and spectrophotometric determination of traces of silicate

A method for the determination of traces of silicate based on the use of a strong base anion exchange in a preconcentration step and a batch-reactive stripping agent technique prior to spectrophotometric determination has been proposed. The reaction of molybdate and silicate in acidic solution to form 12-molybdosilicic acid permits recoveries exceeding 90% in analyzing solutions containing 0.02 to 0.1 μg of silicon/ml.     

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 traces of carbon, nitrogen and oxygen in molybdenum and tungsten

The determination of carbon and nitrogen in molybdenum and of carbon, nitrogen and oxygen in tungsten, is described. The analytical techniques applied were charged-particle activation (carbon, nitrogen and oxygen), photon activation (carbon and oxygen), combustion (carbon) and vacuum-fusion extraction (nitrogen and oxygen). Chemical methods yielded upper limits in the 2-5 mug/g range. Activation analysis yielded 100 and 8 ng/g for carbon in molybdenum and tungsten respectively, 500 and 74 ng/g for nitrogen in molybdenum and tungsten respectively and 70 ng/g for oxygen in tungsten. The results obtained by charged-particle and photon activation agreed satisfactorily.     

The determination of small amounts of long-chain tertiary alkylamines and quarternary ammonium salts

Bromocresol green has been investigated as an alternative to ammonium erdmannate for the absorptiometric determination of small amounts of long-chain alkylamines and quaternary ammonium salts in aqueous solution in a solvent extraction procedure. The molecular absorption coefficient of the reagent at 615 nm is about 3 times that of the erdmannate ion at 353 nm; visual methods of comparison are simplified by the blue colour of the bromocresol green anion The sensitivity of both the bromocresol green and the erdmannate method may be increased by stripping the coloured reagents into a small volume of aqueous solution. Both methods are free of interference from iron, but the present procedure has the disadvantage of a blank which depends both on the pH and on the concentration of excess reagent.     

Simultaneous determination of tungsten and molybdenum in sea water by catalytic current polarography after preconcentration on a resin column

The simultaneous determination of tungsten and molybdenum in sea water is based on preconcentration by column extraction with 7-(1-vinyl-3,3,5,5-tetramethylhexyl)-8-quinolinol (Kelex- 100) resin, and measurement of the polarographic catalytic currents obtained in a solution of chlorate, benzilic acid and 2-methyl-8-quinolinol. When the concentration factor is 50, the detection limits are 2.4 pM for tungsten and 17 pM for molybdenum (for a signal-to-noise ratio of 3). The precision of the determination is ca. 10% for 67 pM tungsten and ca. 5% for 106 nM molybdenum in sea water (n=4). Results for sea water and other natural waters are presented.     

The determination of molybdenum and tungsten in solutions by thin-film X-ray-fluorescence spectrometry

Thin-film X-ray-fluorescence spectrometry was applied to the analysis of solutions containing Mo and W in concentrations ranging from 50 mgl^?1 to 6 gl^?1. The diameter of the sample and its corresponding effect on minimizing errors due to a differential chromatographic effect are discussed. The effect of sample loading was also investigated. The precision of analysis varies from 0.7 to 5.6%, and the limit of detection for Mo is 0.63 μg of element on the filter paper.     

Flame atomic-absorption determination of traces in pure and technical grade selenium

Summary The solubility of selenium dioxide in n-butanol (151 g of SeO₂ in 100 g of n-butanol at 20°C) was used for the extraction separation of large amounts of selenium from accompanying elements. The effect of selenium dioxide on the flame atomic absorption (FAAS) determination of tellurium, antimony, iron, lead, copper, bismuth, silver, nickel, cadmium, manganese, zinc, calcium and magnesium was studied.As a result of the studies a direct method and an extraction method for the FAAS determination of metal traces in technical grade and pure selenium were developed. The limits of determination were calculated. The consistence of both methods was proved by comparing the values of the difference between the trace concentrations (twice as high as the limits of determination) determined by means of the calibration curve and the standard addition.

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Flammen-Atomabsorptionsbestimmung von Spurengehalten in reinem und technischem Selen

Zusammenfassung Aufgrund der Löslichkeit des SeO₂ in n-Butanol (151 g SeO₂ in 100 g n-Butanol bei 20° C) wurde ein Verfahren zur Extraktionstrennung großer Mengen Selen von Begleitelementen entwickelt. Der Einfluß des SeO₂ auf die Flammen-Atomabsorptionsbestimmung von Tellur, Antimon, Eisen, Blei, Kupfer, Bismut, Silber, Nickel, Cadmium, Mangan, Zink, Calcium und Magnesium wurde untersucht.Als Ergebnis wurde ein Direktverfahren und ein Extraktionsverfahren zur Flammen-Atomabsorptionsbestimmung von Spuren in reinem und technischem Selen berechnet. Die Bestimmungsgrenzen wurden berechnet. Die Anwendbarkeit der Verfahren wurde getestet durch die Bestimmung der Differenz zwischen den Spurenkonzentrationen (doppelt so hoch wie die Bestimmungsgrenzen), die mit Hilfe der Standardaddition bzw. der Kalibrationskurve erhalten wurden.

     

Neutron activation analysis of traces in electrolytic zinc sulphate solutions : Part II. determination of molybdenum and rhenium

A neutron activation analysis has been devised for the determination of traces of molybdenum and rhenium in an electrolytic zinc sulphate solution. The activities due to the daughter ^99mTc and to ¹⁸⁶Re were counted. The chemical separation was performed on an anion-exchange resin. The matrix activities were separated by elution with 0.5 N nitric acid. The separation of technetium and rhenium was performed by an elution with 0.2 N perchloric acid. To avoid errors in the molybdenum determination, the uranium present in the sample was separated before the irradiation.     

The determination of molybdenum and tungsten in sea and surface water

A simple method for the determination of molybdenum and tungsten in sea and surface water is presented. Molybdenum and tungsten are concentrated on activated charcoal by adsorption as the ammonium pyrrolidine dithiocarbamate complex; the optimal pH for adsorption is 1.3. Mo and W are then determined by thermal neutron activation, forming ⁹⁹Mo (T_{$\text{1}\text{2}$} = 66.7 h) and ¹³⁷W (T_{$\text{1}\text{2}$} = 23.8 h), respectively. The ^99mTc daughter of ⁹⁹Mo is measured as soon as the equilibrium between ^99mTc(T_{$\text{1}\text{2}$}= 6 h) and ⁹⁹Mo is established. The detection limits are 0.05 μg Mo l^-1 and 0.05 μg W l^-1 (or 0.001 μg W l^-1 after a simple chemical separation).     

Polarographic determination of traces of zinc in bismuth after preconcentration by solid-liquid extraction

Summary Microgram or Nanogram quantities of zinc are extracted from solid basic bismuth nitrate with 0.07M phosphoric acid –0.12M hydrochloric acid for square-wave polarography. ppm of zinc in high-purity bismuth and bismuth nitrate is determined with excellent precision within 2 to 2.5 hours.

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Zusammenfassung Mikrogramm-oder Nanogramm-Mengen Zink werden aus festem basischem Wismutnitrat mit einer Mischung aus 0,07-m Phosphorsäure und 0,12-m Salzsäure extrahiert und durch Rechteckstufen-Polarographie bestimmt. In hochgereinigtem Wismut und Wismutnitrat lassen sich ppm Zn innerhalb 2 bis 21/2 Stunden mit hervorragender Genauigkeit bestimmen.

     

Separation of rhenium from molybdenum, tungsten, vanadium, platinum metals and other elements by reduction and solvent extraction

Reduction in 1 M H(2)SO(4) with liquid zinc amalgam and extraction with isopentanol from 3M H(2)SO(4), separates rhenium from almost all the interfering elements of importance in rhenium determination. The small amounts of Mo, U, Fe and Ru still accompanying rhenium are removed by the thiocyanate-pentyl acetate or the oxine-chloroform extraction. The method is simple, rapid and of very wide applicability. It is particularly useful in the determination of rhenium in various alloys and tungsten-containing samples.