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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 3 (1974), S. 137-142 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Description / Table of Contents: An automatic device for preparing samples for X-ray fluorescence analysis is described. Based on a fusion technique with the proper flux, it produces glass buttons which can lbe directly analysed with the spectrometer.The apparatus consists essntially of two high frequency furnaces which are used for fusing the samples and casting the beads, respectively. The corresponding vessels, i.e. crucible and mould, and made of a special platinum + gold + rhodium alloy. The automatic preparation sequence lasts eight minutes.The preparation reproducibility which can be achieved with this device is illustrated by an application to the analysis of high grade iron ores dissolved in sodium tetraborate. The standard deviation obtained for iron is 0.15% at a 60% iron level.
    Notes: Description d'un appareil automatique de préparation des échantillons pour l'analyse par fluorescence de rayons X, La technique est basée sur la mise en soluation solide de l'échantillon en uve de l'obtention d'une perle directement analysable.L'appreil est composé de deux fours HF, I'un pourla fusion, I'autre pour la coulée Les récipients de fusion et de coulée sont en alliage platine+ or+ rhodium. La seéquence automatique de préparation dure huit minutes.Une application á I'anlyse de minerais de fer reches par miscen solution dens le tétraborate de sodium illustre les reproductibilités de préparation que I'on peut atteindre avec ce matériel (écart type de reproductibiliteé égal á 0,15% de Fe au niveau de 60%).
    Additional Material: 3 Ill.
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  • 2
    Publication Date: 2021-04-07
    Description: The accurate interpretation of Si isotope signatures in natural systems requires knowledge of the equilibrium isotope fractionation between Si-bearing solids and the dominant Si-bearing aqueous species. Aqueous silicon speciation is dominated by silicic acid (H4SiO4o) in most natural aqueous fluids at pH 〈 8.5, but forms H3SiO4−, H2SiO42−, and polymeric Si species in more alkaline fluids. In this study isotope exchange experiments were performed at bulk chemical equilibrium between amorphous silica (SiO2∙0.32 H2O) and inorganic aqueous fluids at pH ranging from 5.8 to 9.9 at 25° and 75 °C with experiments running as long as 375 days. The three-isotope method was used to quantify the equilibrium Si isotope fractionation, Δeq30Si, between amorphous silica and aqueous Si; at pH ∼ 6 this equilibrium fractionation factor was found to be 0.45 ± 0.2‰ at 25 °C, and 0.07 ± 0.6‰ at 75 °C. At more basic pH (〉9), equilibrium Si isotope fractionation factors between solid and aqueous solution are higher, at 1.63 ± 0.23‰ at 25 °C, and 1.06 ± 0.13‰ at 75 °C. Taking account of the distribution of the aqueous Si species, equilibrium Si isotope fractionation factors between H3SiO4− and H4SiO4o of −2.34 ± 0.13‰ and −2.21 ± 0.05‰ at 25 and 75 °C, respectively, were determined. The distinct equilibrium isotope fractionation factors of H3SiO4− and H4SiO4o, and its variation with temperature can be used to establish paleo-pH and temperature proxies. The application of the three-isotope method also provides insight into the rates of isotopic exchange. For the solid grain size used (∼20 nm), these rates match closely the measured bulk dissolution rates for amorphous silica for most of the isotope exchange process, suggesting the dominant and rate controlling isotope exchange mechanism in the experiments is detachment and reattachment of material at the amorphous silica surface.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 3
    Publication Date: 2020-02-12
    Description: This paper contains the results of an extensive isotopic study of United States Geological Survey GSD-1G and MPI-DING reference glasses. Thirteen different laboratories were involved using high-precision bulk (TIMS, MC-ICP-MS) and microanalytical (LA-MC-ICP-MS, LA-ICP-MS) techniques. Detailed studies were performed to demonstrate the large-scale and small-scale homogeneity of the reference glasses. Together with previously published isotopic data from ten other laboratories, preliminary reference and information values as well as their uncertainties at the 95% confidence level were determined for H, O, Li, B, Si, Ca, Sr, Nd, Hf, Pb, Th and U isotopes using the recommendations of the International Association of Geoanalysts for certification of reference materials. Our results indicate that GSD-1G and the MPI-DING glasses are suitable reference materials for microanalytical and bulk analytical purposes.
    Keywords: 550 - Earth sciences
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  • 4
    Publication Date: 2020-02-12
    Description: A new method was designed and used for determining the half-life of the isotope 10Be. The method is based on (1) accurate 10Be/9Be measurements of 9Be-spiked solutions of a 10Be-rich master solution using multicollector ICP mass spectrometry (MC-ICP-MS) and (2) liquid scintillation counting (LSC) using the CIEMAT/NIST method for determining the activity concentrations of the solutions whose 10Be concentrations were determined by mass spectrometry. Important requirements for the success of this approach (a) was the previous coating of glass ampoules filled for counting experiments with 9Be, thereby reducing the risk of the adsorptive loss of 10Be; (b) the removal of Boron from solutions to be measured by MC-ICP-MS by cation chromatography without the introduction of mass fractionation and (c) the accurate determination of the mass bias of 10Be/9Be measurements by ICP-MS which are always affected by the space-charge effect. The mass bias factor was determined to be 1.1862 ± 0.071 for 10Be/9Be from careful fitting and error propagation of ratios of measured Li, B, Si, Cr, Fe, Cu, Sr, Nd, Hf, Tl and U standard solutions of known composition under the same measurement conditions. Employing this factor, an absolute 10Be/9Be ratio of 1.464 ± 0.014 was determined for a first dilution of the 10Be-rich master solution. This solution is now available as an absolute Be ratio standard in AMS measurements. Finally, a half-life of (1.386 ± 0.016) My (standard uncertainty) was calculated. This value is much more precise than previous estimates and was derived from a fully independent set of experiments. In a parallel, fully independent study using the same master solution, Korschinek et al. [35] have determined a half-life of (1.388 ± 0.018) My. The combined half-life and uncertainty amounts to (1.387 ± 0.012) My. We suggest the use of this value in nuclear studies and in studies that make use of cosmogenic 10Be in environmental and geologic samples.
    Keywords: 550 - Earth sciences
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  • 5
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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  • 6
    Publication Date: 2020-02-12
    Description: A new method for the in situ measurement of stable Si isotope ratio using UV-femtosecond laser ablation connected to a multiplecollector inductively coupled plasma mass spectrometer (MC-ICP-MS) has been established. The use of medium mass resolution mode (with a resolving powerm/Δm=8000) permits to resolve spectral interferences on 28Si, 29Si and 30Si allowing for determination of the 29Si/28Si and 30Si/28Si ratios with high accuracy and precision on wide, interference-free plateaus. A three-isotope plot demonstrated that interferences, if existing, are negligible for Si isotope ratios. The laser spot size is 35 μm and measurements are made using square rasters of 150 μmside length. Different types of elemental Si, Si-oxide and silicate matrices have been analysed by laser ablation using the international standard NBS28 as the bracketing standard. Thus δ29Si and δ30Si have been determined for the silicon isotope standard IRMM-017 (δ30Si±2 S.D.=−1.26±0.24‰; n=89) and BigBatch (δ30Si=−10.55±0.42‰; n=15), as well as San Carlos Olivine (δ30Si=−0.81±0.19‰; n=14), Caltech Rose Quartz (δ30Si=0.10±0.13‰; n=14) sponge needles (Stylocordyla borealis; δ30Si=−2.19±0.32‰; n=14) and JER-diopside glass (δ30Si=0±0.09‰; n=14) samples. The overall repeatability achievable is 0.15‰ (2 S.D.) on δ29Si and 0.24‰ (2 S.D.) on δ30Si. The silicon isotope standard IRMM-018 has also been measured and was confirmed to be heterogeneous. The two isotope ratios follow an equilibrium mass-dependent fractionation law which can be represented as δ30Si=1.93× δ29Si. Published extractions methods have been used to wet-chemically purify Si from the JER-diopside glass. The Si extracted was presented as Si-gel and ablated like a solid. The results show excellent agreement with in situ measurements of this glass that confirms that this technique can be employed to a wide variety of matrices, including Si purified from solution. The new technique presents a viable alternative to solution MC-ICP-MS for bulk measurements and the most precise technique so far for in situ measurement of Si isotope ratios.
    Keywords: 550 - Earth sciences
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  • 7
    Publication Date: 2020-02-12
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  • 8
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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