Rhenium determination

Resolution, analysis complicated by insufficient, 201 of x-rays, 61, 113-115 Response time of multiplier phototube, 57 Rhenium, determination by x-ray emission spectrography, 328 Rhodium, determination by x-ray emission spectrography, 328 Risk, consumer, 215 producer, 215... 

Many catalysts used in chemical synthesis can be treated in the same way, often the nitrous oxide/acetylene flame is used because of the refractory nature of the elements to be determined. Harrington and Bramstedt [56] have determined rhenium in electro-chemical surface catalysts by stripping the coating with molten potassium hydroxide/ potassium nitrate. This melt was extracted with hydrochloric acid, the residue was fused with sodium peroxide for further rhenium determination. Titanium, being the substrate on which the catalyst was coated, was added to the standards, an air/acetylene flame and 343.3 nm were used for the finish. 

Molybdates yield sparingly soluble orange-yellow molybdyl oxinate with oxine solution the pH of the solution should be between the limits 3.3-7.6. The complex differs from other oxinates in being insoluble in organic solvents and in many concentrated inorganic acids. The freshly precipitated compound dissolves only in concentrated sulphuric acid and in hot solutions of caustic alkalis. This determination is of particular interest, as it allows a complete separation of molybdenum from rhenium. 

The rates of ligand exchange of 0.01 M hexahalo-technetium(IV) and hexa-halo-rhenium(IV) complexes were measured in the 8 M solutions of their corresponding acid at 60 °C. The overall exchange rates R were determined as follows ... 

SS). Data for the metals of group VIII and for rhenium in group VIIA are given in Fig. 1, which is divided into three fields separating the metals of the first, second, and third transition series. The specific activity is defined as the activity per unit surface area of metal. Metal surface areas required for the determination of specific activities are derived from measurements... 

MARE [32-38], Neutrino oscillation experiments have proved that neutrinos are massive particles, but cannot determine their absolute mass scale. Therefore, the neutrino mass is still an open question in elementary particle physics. An international collaboration is growing around the project of microcalorimeter arrays for a rhenium experiment (MARE) for directly measuring the neutrino mass with a sensitivity of about 0.2eV/c1 2 4. 

Koide et al. [537] have described a graphite furnace atomic absorption method for the determination of rhenium at picomolar levels in seawater and parts-per-billion levels in marine sediments, based upon the isolation of heptavalent rhenium species upon anion exchange resins. All steps are followed with 186-rhenium as a yield tracer. A crucial part of the procedure is the separation of rhenium from molybdenum, which significantly interferes with the graphite furnace detection when the Mo Re ratio is 2 or greater. The separation is accomplished through an extraction of tetraphenylarsonium perrhenate into chloroform, in which the molybdenum remains in the aqueous phase. 

Structure determinations of secondary metal alkyl complexes are relatively rare, yet they provide an opportunity to assess interactions of the metal with the /3-atoms of the alkyl. The angles (excluding hydrogen) about C(24) all exceed 109°, ranging from 111.7° to 115.1°. There is no evidence for any Re 0 interaction (compare V), this distance exceeding 3 A. Both the /3-carbon, C(25), and its attached hydrogens are over 3 A from rhenium. The hydrogen on the a-carbon, C(24J, is 2.76 A from rhenium. 

In catalyst preparation, one can use this knowledge to determine the relative contributions of various hydroxyl groups before and after application of the active phase onto the support. In this way Sibeijn etal. [31] established that rhenium oxide attached to acidic sites of the alumina support exhibits higher activity for the metathesis of olefins than rhenium oxide on neutral or basic sites. As, however, rhenium species preferentially exchange with basic hydroxyls, one needs to increase the loading above a certain value (6 wt% for an alumina of 200 m2/gram) before the catalyst exhibits appreciable activity [31]. 

In this regard a more significant determination should be obtained from a study of the polyhydride complexes [ReH7(PR3)2], in that (i) if the complex is a classical hydride the rhenium atom would be in its maximum oxidation state (+ 7) and, therefore, could not undergo further oxidation processes (ii) if the complex is a non-classical hydride, the rhenium atom would be in a lower oxidation state and, consequently, could display oxidation processes. 

Grafting on the resin was achieved via a nucleophilic substitution of the benzylic chlorine by the deprotonated OH-linker of 52 (Scheme 29) by using a mixture of KO Bu, 18-crown-6 and CsBr. Determining the nitrogen content of solid phase samples by elemental analyses was accomplished, to verify the functionalization of the polymer. This enables calculation of the degree of functionalization. Usually, an occupancy of more than 20 percent of the theoretical sites was achieved. Saponification of the functionalized Merrifield resin P-52 leads to the monoanionic NJ, 0 functionalized solid phase. Subsequent reaction with [ReBrtCOlsJ afforded the polymer mounted tricarbonyl rhenium complex P-52-Re (Scheme 29). 

The optical emission spectrum of technetium is uniquely characteristic of the element " with a few strong lines relatively widely spaced as in the spectra of manganese, molybdenum and rhenium. Twenty-five lines are observed in the arc and spark spectra between 2200 and 9000 A. Many of these lines are free from ruthenium or rhenium interferences and are therefore useful analytically. Using the resonance lines of Tc-I at 4297.06, 4262.26, 4238.19, and 4031.63 A as little as 0.1 ng of technetium can be reliably determined. 

X1X cm respectively . Beer s law is obeyed up to a concentration of about 10 mol X r less than 1 /ig of technetium can be determined spectrophoto-metrically. This method is particularly advantageous in the simultaneous determination of technetium and rhenium. 

The strong absorptions of the complex technetium (IV) hexahalides (Fig. 10) can also be utilized for spectrophotometric determinations. A sensitive method has been developed using hexachlorotechnetate (IV) When pertechnetate is heated for 50- 0 min in cone, hydrochloric acid, it is reduced to the complex [TcClgp . The absorption curve of [TcClgf in cone. HCl has a maximum at 338 nm where technetium can be determined in the presence of microgram amounts of rhenium or molybdemun. The molar extinction coefficient is said to be 32.000 (after Jorgensen and Schwochau it amounts to 10.600). About 0.1 fig Tc/ml can be determined. Rhenium present in quantities up to 30 ng/ml has almost no influence on the determination of technetium. The error in the determination of the latter in the presence of molybdenum at a weight ratio of 1 1 is 1-2%. 

Pertechnetate forms a blue complex and perrhenate a brownish-yellow complex with K4[Fe(CN) ] in presence of bismuth amalgam. This permits the spectrophotometric determination of both elements in the same solution . The adsorption maxima of the technetium and rhenium complexes are at 680 and 420 nm, respectively. The molar extinction coefficients are 10,800 for technetium and 4,000 for rhenium. Metals forming color or precipitates with K4[Fe(CN) ] must first be removed. 

Suitable conditions for the quantitative polarographic determination of technetium as pertechnetate are given by Miller et al. who propose a 0.1 M KCl solution of pH 10 or a phosphate buffer solution of pH 7. Since in pH 7 buffer the current is directly proportional to the concentration of technetium over the range of 0.1 to 1.1 ppm, this medium has been used for the determination of low concentrations of technetium in solutions of fission products by the standard addition technique. The half-wave potential of the used wave is —0.68 V vs. SCE. The reaction appears to be irreversible (Fig. 13). It has been found that neither rhenium, ruthenium nor other fission products interfere. However, tetraphenyl-arsonium chloride is reduced at a more positive potential than is pertechnetate therefore, (QH5) AsCl, if present, must be separated. 

Hirschmann M. (1991). Thermodynamics of multicomponent olivines and the solution properties of (Ni,Mg,Ee)2Si04 and (Ca,Mg,Fe)2Si04 olivines. Amer. Mineral, 76 1232-1248 Hirt B., Herr W, and Hoffmeister W. (1963). Age determinations by the rhenium-osmium method. In Radioactive Dating, International Atomic Energy Agency, Vienna. 

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