[en] This study is a large project initiated by the French Nuclear Agency, and concerns the development of a new electrolyte system for the separation of lanthanides by isotachophoresis. This new system is based on a leading electrolyte that incorporates 2-hydroxy-2-methylbutyric acid as complexing agent. The optimization of separation conditions (complexing agent concentration, pH, capillary dimensions, injection conditions, and current intensity) performed by experiments on a commercial capillary instrument with contactless conductivity detection, which allows to improve the separation of 13 lanthanides (La to Lu, except Pm and Ho). We have also directly coupled the isotachophoresis to an inductively coupled plasma mass spectrometer to visualize the mono-elementary elution bands and demonstrate the potentiality of the method for isotope ratio measurements. The application to a simulated solution representative of a fraction of fission products present in a MOX spent fuel is presented in this paper to demonstrate the possible application in future on nuclear fuel samples. (authors)

[en] A selective and sensitive method is described for the determination of trace amounts of molybdenum, based on its reaction with thiocyanate and its extraction (into toluene) as an ion-association complex formed with adogen (methyltrioctylammonium chloride). The molar absorptivity is 2.13 x 10⁴l.mole^-1. cm^-1 at lambdasub(max) 467 nm. The method has been applied to molybdenum determination in steels. (author)

[en] A trace amount of molybdenum(VI) can be determined by using its catalytic effect on the oxidation of iodide to iodine by hydrogen peroxide in acidic medium. Addition of ascorbic acid added to the reaction mixture produces the Landolt effect, i.e. the iodine produced by the indicator reaction is reduced immediately by the ascorbic acid. Hence the concentration of iodide begins to decrease once all the ascorbic acid has been consumed. The induction period is measured by monitoring the concentration of iodide ion with an iodide ion-selective electrode. The reciprocal of the induction period varies linearly with the concentration of molybdenum(VI). The most suitable pH and concentrations of hydrogen peroxide and potassium iodide are found to be 1.5, 5 and 10m M, respectively. An appropriate amount of ascorbic acid is added to the reaction mixture according to the concentration of molybdenum(VI) in the sample solution. A calibration graph with good proportionality is obtained for the molybdenum(VI) concentration range from 0.1 to 160 μM. Iron(III), vanadium(IV), zirconium(IV), tungsten(VI), copper(II) and chromium(VI) interfere, but iron(III) and copper(II) can be masked with EDTA. (author)

[en] The extraction of noble metals with n-octylaniline at varying concentrations of different mineral acids was studied, and optimum conditions for their separation from the base metals commonly present in platinum-bearing materials were established. The successful application of the procedure to the analysis of mattes, sludges, and flotation concentrates is shown. The lower limit of determination in such materials is 100 ppm for Pt and Ir, 40 ppm for Ru, and 10 ppm for Pd and Rh. (author)

[en] A method is described for the atomic-absorption determination of beryllium in geological materials, that utilizes electrothermal atomization after a separation by solvent extraction. Samples are decomposed with hydrofluoric acid and nitric acid in Teflon-lined pressure decomposition vessels. Beryllium is isolated by its extraction as beryllium acetylacetonate at pH 8 into xylene and back-extraction in 3M hydrochloric acid. The method has been successfully applied to the determination of beryllium in 14 U.S. Geological Survey standard rocks. Four subsamples from four bottles of each standard sample were analysed in random order. The mean beryllium contents (ppm) are: AGV-1, 1.98; PCC-1, 0.024; MAG-1, 2.84; BHVO-1. 0.90; DTS-1. 0.026; SCo-1, 1.74; SDC-1, 2.52; BCR-1, 1.44; GSP-1, 1.22; SGR-1, 0.86; QLO-1, 1.83; RGM-1, 2.21; STM-1, 8.75; G-2, 2.29. An analysis of variance shows that all the samples may be considered homogeneous at Fsub(0.95) except AGV-1 and DTS-1 which may be considered homogeneous at Fsub(0.99). (author)

[en] The determination of niobium at levels of 0.01% and below is required in certain specifications for stainless-steel welding electrodes, containing 2 to 3% molybdenum and 0.01% titanium. A method has been developed, based on initial extraction of niobium thiocyanate into butyl acetate followed by stripping with fluoride and re-extraction of niobium thiocyanate after masking of the fluoride by addition of boric acid. The absorbance of the extract is measured at 385 nm. Mo, Ti, V and W can be tolerated at 50 times the concentration of Nb. For higher amounts of Mo, corrections can also be applied. Ta should, however, be restricted to ten times the Nb level. Precision and accuracy of the method are satisfactory. The time taken for an individual determination is about an hour. The method is applicable to mild, low-alloy, stainless and niobium-stabilized steels. (author)

[en] A method is described for the direct spectrophotometric determination of micro-amounts of niobium by extraction into a benzene solution of dibenzo-18-crown-6 (L) from 3 M hydrochloric acid containing potassium thiocyanate. The molar absorptivity of the extracted complex is 3.85 +- 0.03 x 10⁴ l.mole^-1.cm^-1 (relative standard deviation 0.8%). Co-ordinatively unsaturated complexes of the type [NbO(SCN)₃]₂L and NbO(SCN)₃L are extracted, along with ion-pairs, especially when small amounts of L are used for extraction. The ion-pair complex [NbOCl₂(SCN)₃][(LK)₂] seems to be the main species formed in the organic phase. (author)

[en] This a report on round-robin tests concerning the determination of nitrogen traces in molybdenum and tungsten, which were carried out by the refractory metals group of the chemistry section of the Gesellschaft Deutscher Metallhutten-und Bergleute. The following methods were used: classical and modified Kjeldahl methods (in particular, a newly developed micro-Kjeldahl method), inert-gas fusion, vacuum fusion and ultrahigh-vacuum diffusion extraction. As the nitrogen values obtained by the first round-robin test exhibited considerable scatter, possible shortcomings of the various Kjeldahl methods, as well as the quantitative nitrogen recovery by the extraction methods, were carefully examined. The second round-robin test then gave the following results: the nitrogen content of the investigated molybdenum sheet was 2ppm, the content of the tungsten sheet 0.5 ppm. Classical Kjeldahl methods are not applicable to the determination of nitrogen contents below 10 ppm. Frequently, detection limits of Kjeldahl methods range considerably above 10 ppm, mainly because of contamination by reagents and/or the laboratory atmosphere. The micro-Kjeldahl method and the hot-extraction and fusion-extraction methods are capable of determining nitrogen contents down to 1 ppm at best. The only method available for nitrogen determinations in metals at sub-ppm levels is by ultrahigh -vacuum diffusion extraction. The good agreement between the nitrogen values obtained for molybdenum by the micro-Kjeldahl method and by the various extraction methods is the most reliable proof of the quantitative nitrogen recovery by the extraction methods. (author)

No abstract available

[en] A new liquid molybdenum(VI)-sensitive electrode with a membrane based on a solution of the molybdenum(VI)-N-benzoyl-N-phenylhydroxylamine chelate is proposed and its electrochemical behaviour and applicability have been critically investigated. The transfer of molybdenum(VI) across the water-organic solvent interface and across the membrane has been studied by use of sodium molybdate labelled with ⁹⁹Mo, and the response mechanism of the electrode is discussed. (author)