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- Isotope reference materials (4)
- Boron isotope variations (3)
- Boron isotopes (3)
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Analytische Methoden zur Feststellung der Herkunft eines Baustoffes sind bislang kaum entwickelt worden. In Deutschland gibt es eine Reihe von Kalkiagerstätten, die in unterschiedlichen geologischen Formationen Kalk oder Dolomit enthalten. Das unterschiedliche geologische Alter von Kalken sowie die ursprüngliche mineralische Zusammensetzung und die geologische Historie spiegeln sich im 87Sr/88Sr-lsotopenverhältnis weder. Mittels der Thermionen-Massenspektrometrie kann dieses Verhältnis ermittelt und somit zur Herkunftsbestimmung eines Kalkes herangezogen werden.
Isotopic reference materials are essential to enable reliable and comparable isotope data. In the case of boron only a very limited number of such materials is available, thus preventing adequate quality control of measurement results and validation of analytical procedures. To address this situation a unique set of two boron isotope reference materials (ERM-AE102a and -AE104a) and three offset δ11B reference materials (ERM-AE120, -AE121 and -AE122) were produced and certified. The present article describes the production and certification procedure in detail. The isotopic composition of all the materials was adjusted by mixing boron parent solutions enriched in 10B or 11B with a boron parent solution having a natural isotopic composition under full gravimetric control. All parent solutions were analysed for their boron concentration as well as their boron isotopic composition by thermal ionisation mass spectrometry (TIMS) using isotope dilution as the calibration technique. For all five reference materials the isotopic composition obtained on the basis of the gravimetric data agreed very well with the isotopic composition obtained from different TIMS techniques. Stability and homogeneity studies that were performed showed no significant influence on the isotopic composition or on the related uncertainties. The three reference materials ERM-AE120, ERM-AE121 and ERM-AE122 are the first reference materials with natural δ11B values not equal to 0. The certified δ11B values are -20.2 for ERM-AE120, 19.9 for ERM-AE121 and 39.7 for ERM-AE122, each with an expanded uncertainty (k = 2) of 0.6. These materials were produced to cover about three-quarters of the known natural boron isotope variation. The 10B enriched isotope reference materials ERM-AE102a and ERM-AE104a were produced for industrial applications utilising 10B for neutron shielding purposes. The certified 10B isotope abundances are 0.29995 for ERM-AE102a and 0.31488 for ERM-AE104a with expanded uncertainties (k = 2) of 0.00027 and 0.00028, respectively. Together with the formerly certified ERM-AE101 and ERM-AE103 a unique set of four isotope reference materials and three offset δ11B reference materials for boron isotope determination are now available from European Reference Materials.
An analytical artefact is reported here related to differences in instrumental mass fractionation between NIST SRM glasses and natural geological glasses during SIMS boron isotope determinations. The data presented demonstrated an average 3.4 difference between the NIST glasses and natural basaltic to rhyolitic glasses mainly in terms of their sputtering-induced fractionation of boron isotopes. As no matrix effect was found among basaltic to rhyolitic glasses, instrumental mass fractionation of most natural glass samples can be corrected by using appropriate glass reference materials. In order to confirm the existence of the compositionally induced variations in boron SIMS instrumental mass bias, the observed offset in SIMS instrumental mass bias has been independently reproduced in two laboratories and the phenomenon has been found to be stable over a period of more than one year. This study highlights the need for a close match between the chemical composition of the reference material and the samples being investigated.
Nous montrons l'existence d'un artefact analytique reliéà différents fractionnements de masse instrumentaux, observés sur les verres NIST SRM et des verres naturels durant des mesures des isotopes de bore par SIMS. Les données montrent une différence d'environ 3.4 entre les verres NIST et les verres naturels, de composition variant de basaltique à rhyolitique, en termes de fractionnement des isotopes du bore principalement induit par le phénomène de dispersion. Comme aucun effet de matrice n'a été observé entre les verres basaltiques et les verres rhyolitiques, le fractionnement de masse instrumental de la plupart des verres naturels peut être corrigé en utilisant des verres de références appropriés. Dans le but de confirmer l'existence de biais de masse liéà la composition lors de mesure du bore par SIMS, nous avons reproduit indépendamment le décalage observé entre deux laboratoires et ce phénomène s'est révélé stable sur une période de plus d'un an. Cette étude met en lumière le besoin d'ajuster précisément les compositions chimiques des matériaux de référence et des échantillons à analyser.
The strontium isotope composition of food samples has been successfully used to trace the provenance of both herbal and animal agricultural products. Adequately accurate and precise 87Sr/86Sr ratios, however, are key to unravel environmental and anthropogenic strontium contributions of specific growing areas. In a recently published analytical method in Food Chemistry by Choi et al. (2008) a demonstrably inadequate protocol for the determination of 87Sr/86Sr ratios of ginseng is presented. Based on well established geological and analytical fundamentals the 87Sr/86Sr ratios presented by Choi et al. (2008) are too inaccurate and imprecise to be used to trace the origin of the ginseng. Appropriate wet chemical separation techniques and mass spectrometric instrumentation enables the generation of 87Sr/86Sr data with very low expanded uncertainties (<0.05%, k = 2). Those high quality data allow the identification of even small strontium contributions of source reservoirs or physical and anthropogenic processes if diagnostic isotope compositions are present.
In situ secondary ion mass spectrometry (SIMS) analyses of δ7Li, Li/Ca, and Mg/Ca were performed on five synthetic aragonite samples precipitated from seawater at 25°C at different rates. The compositions of δ7Li in bulk aragonites and experimental fluids were measured by multicollector inductively coupled plasmamass spectrometry (MC-ICP-MS). Both techniques yielded similar δ7Li in aragonite when SIMS analyses were corrected to calcium carbonate reference materials. Fractionation factors α7Li/6Li range from 0.9895 to 0.9923, which translates to a fractionation between aragonite and fluid from -10.5‰ to -7.7‰. The within-sample δ7Li range determined by SIMS is up to 27‰, exceeding the difference between bulk δ7Li analyses of different aragonite precipitates. Moreover, the centers of aragonite hemispherical bundles (spherulites) are enriched in Li/Ca and Mg/Ca relative to spherulite fibers by up to factors of 2 and 8, respectively. The Li/Ca and Mg/Ca ratios of spherulite fibers increase with aragonite precipitation rate. These results suggest that precipitation rate is a potentially important consideration when using Li isotopes and elemental ratios in natural carbonates as a proxy for seawater composition and temperature.