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- Isotope fractionation (3)
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Organisationseinheit der BAM
- 1 Analytische Chemie; Referenzmaterialien (11)
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- 1.6 Anorganische Referenzmaterialien (1)
- 1.7 Organische Spuren- und Lebensmittelanalytik (1)
- 4 Material und Umwelt (1)
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- 6 Materialchemie (1)
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Blei weist in der Natur die vier stabilen Isotope 204Pb, 206Pb, 207Pb und 208Pb auf, mit den entsprechenden Isotopenhäufigkeiten von 1,4%, 24,1 %, 22,1 % und 52,4 %686. Dabei sind 206Pb, 207Pb und 208Pb radiogene Isotope, welche als Endglieder der natürlichen Zerfallsreihen von 238U, 235U und 232Th entstanden sind. 204Pb ist ein sogenanntes primordiales Isotop, welches bereits vor Entstehung der Erde vorhanden war. Aufgrund dieser Prozesse weisen Gesteine, Mineralien und Erze eine charakteristische Bleiisotopenzusammensetzung auf, die von der Ausgangskonzentration an Blei, Thorium und Uran sowie von der seit der Gesteinsgenese vergangenen Zeit abhängt. Diese Eigenschaft bleibt auch während der Bleigewinnung aus dem Erz, meist Galenit, erhalten, auch wenn das Silber vorher durch Kupellation abgetrennt wurde687. Das in Silbererzen enthaltene Blei war ein willkommenes Nebenprodukt der Erzverhüttung und wurde zur Herstellung von Bleiobjekten verwendet. Artefakte, die aus dem so gewonnenen Blei gefertigt wurden, spiegeln daher die Bleiisotopenzusammensetzung der verwendeten Rohmaterialien wider.
Boron isotope fractionation in soil-plant systems and its influence on biogeochemical cycling
(2022)
Boron (B) is an essential mineral nutrient for higher plants. Although B plant nutrition is well studied, the B isotope fractionation at the soil-plant interface, within plant metabolism, and its influence on biogeochemical cycling is not fully understood. Boron concentrations and isotope variations (δ11B) of the dicotyledonous plants of Chenopodium album and Brassica napus and their growing soils along a climatic gradient were analyzed to decipher these unresolved issues of the B behavior. The boron concentrations and δ11B values show an increasing trend from roots to leaves for both plants, while a decreasing trend from flower to shell and to seed for Brassica napus. A large boron isotope fractionation occurs within the plants with median Δ11Bleaf-root ≈ +20‰, which is related to different boron transporters and transportation ways. Formation of borate dimerized rhamnogalacturonan II in cell and B(OH)3 transportation in xylem lead to heavier δ11B values from root to stem and leaf while B(OH)4 transportation in phloem lead to lighter δ11B values from flower to shell and seed. Although samples cover a distinct transect with systematically different climatic conditions, Δδ11B within the individual plant compartments and between the bulk plants and the soil available B do not show any systematic variation.
This suggests that B uptake from the soil into Chenopodium album and Brassica napus occurs without a distinct isotope fractionation at the soil-plant interface (median Δ11Bbulkplant-soil = 0.2‰) and plants are able to regulate boron uptake. Both the observed large B fractionation within plant and low or absent B isotope fractionation at the soil-plant interface may have profound implications for the biological and geological B cycle. If this observed boron behavior also exists in other plants, their litters would be an important source for exporting 11B-rich biological material from continental ecosystems via rivers to the global oceans. This may be helpful for the explanation of ocean B cycle and the increasing δ11B values over the Cenozoic.
For more than 110 years, BAM has been producing reference materials for a wide range of application fields. With the development of new analytical methods and new applications as well as continuously emerging more stringent requirements of laboratory accreditation with regard to quality control and metrological traceability, the demand and requirements for reference materials are increasing. This trend article gives an overview of general developments in the field of reference materials as well as developments in selected fields of application in which BAM is active. This includes inorganic and metal analysis, gas analysis, food and consumer products, and geological samples. In addition to these more traditional fields of application, developments in the areas of optical spectroscopy, particulary fluorescence methods, and nanomaterials are considered.
Assessment of international reference materials for isotope-ratio analysis (IUPAC Technical report)
(2014)
The measurement uncertainty is an indispensable quality criterion of isotope ratio data and sets important limits for the general use and geochemical interpretation of such data. Despite traceability to the International System of Units (SI) or an accepted standard an uncertainty statement allows the direct comparison of isotope data which have been obtained in different laboratories and/or using different procedures. To realise traceability and comparability of isotope data a realistic uncertainty statements should include uncertainty contributions from all influence quantities. In isotope geochemistry, however, often the term uncertainty is used for terms describing the statistical dispersion of measurement results such as precision, repeatability or reproducibility. Because an measurement uncertainty must include all influence quantities even the so-called external precision or reproducibility will underestimate the overall uncertainty. Without uncertainty statement traceability and comparability of measurement results cannot be established. In cases where no uncertainty for isotope ratio data is presented it is highly recommended that at least the measurement results of a quality control sample with known isotope composition are presented which can be used to evaluate the accuracy and roughly estimate uncertainty.
Accurate measurements of stable isotope abundance ratio variations are often reported using artifact based delta-scales, which rely on suitable isotopic reference materials (iRM) for their realization. For example, variations in the 26Mg/24Mg isotope abundance ratio in natural systems are typically reported as delta26Mg values that represents the relative difference between the 26Mg/24Mg ratio measured in a sample relative to its measurement preferably in an iRM. In the past, such delta26Mg measurements were referenced to NIST SRM 980, the initial zero of the delta26Mg scale. With the development of MC-ICPMS, the detection of small but measurable isotopic differences in different chips of SRM 980 became apparent. It was then replaced by a Mg solution (DSM3), the new zero of the delta26Mg scale. A potential replacement iRM for DSM3 has been developed, ERM-AE143. This iRM has also been measured for its absolute isotope amount ratios1,2 making it traceable to the SI.
The results of an delta26Mg intercomparison experiment include the Mg iRMs SRM 980, IRMM-009, ERM-AE143, AE144, AE145 standards DSM3 and Cambridge-1. The intercomparison involved 5 expert laboratories, consisting of 3 national metrological institutes (BAM, NIST, PTB) and 2 scientific research laboratories (GFZ Potsdam, UBremen).
The iRMs were measured relative to AE143 and cover a range of ≈5 ‰ in delta26Mg. IRMM-009 has the lowest delta26Mg value while DSM3 has the highest, spanning a range in values that covers natural Mg isotope variations. The 2SD reproducibilities of the individual values from the different laboratories range from 0.02 to 0.26 ‰. The mean delta26Mg values, calculated from the laboratory means however show 2SD reproducibilities varing between 0.025 and 0.093 ‰. Propagated measurement uncertainties suggest a standard uncertainty of about 0.1‰ for delta26Mg determinations.
1 JAAS, 2015, 31,179; 2JAAS, 2016, 31, 1440
A set of 59 ancient magical artefacts, mainly made of lead, was selected from the collections of the Staatliche Museen zu Berlin in order to unravel their origins. All the selected artefacts have been studied for their Pb isotope compositions, which covered the whole range of the Mediterranean ore deposits. However, the majority (≈86%) were made of lead matching the small compositional range of the Laurion ore deposits. Only eight out of the 59 artefacts were made of recycled lead or lead from other ore deposits.
Additionally, all but two were approximately dated based on their inscriptions. The lead isotopic composition together with information obtained from the inscriptions, the resulting dating, the context of the find and the known history of each item allowed us to gain more detailed information about the origins of these magical artefacts. The Attic provenance of 36 curse tablets was confirmed, whereas for 11 curse tablets previously classified as non-Attic, the provenance was either confirmed and specified (six artefacts) or changed to Attic (five artefacts). Surprisingly, the majority (six out of eight) of the analysed curse tablets from the Egyptian collection showed a lead isotopic composition closely matching that of Laurion.
A Laurion-like lead isotopic composition was also observed for three of the four analysed oracular tablets from Dodona. Together with the dating information, this points to Laurion as the major and dominant lead source in the Aegean, at least during the fourth–third century B.C. The few curse tablets from earlier than the fourth–third century B.C. point to the use of multiple and thus isotopically more variable lead sources compared with the Roman times.
Rationale: Boron (B) is an essential micronutrient in plants and its isotope variations are used to gain insights into plant metabolism, which is important for crop plant cultivation. B isotope variations were used to trace intra‐plant fractionation mechanisms in response to the B concentration in the irrigation water spanning the
range from B depletion to toxic levels.
Methods: A fully validated analytical procedure based on multi‐collector inductively coupled plasma mass spectrometry (MC‐ICP‐MS), sample decomposition and B Matrix separation was applied to study B isotope fractionation. The Validation was accomplished by establishing a complete uncertainty budget and by applying reference materials, yielding expanded measurement uncertainties of 0.8‰ for pure boric acid solutions and ≤1.5‰ for processed samples. With this validated procedure SI traceable B isotope amount ratios were determined in plant reference materials for the first time.
Results: The B isotope compositions of Irrigation water and bell pepper samples suggest passive diffusion of the heavy 11B isotope into the roots during low to high B concentrations while uptake of the light 10B isotope was promoted during B depletion, probably by active processes. A systematic enrichment of the heavy 11B isotope in higher located plant parts was observed (average Δ11Bleaf‐roots = 20.3 ± 2.8‰ (1 SD)), possibly by a facilitated transport of the heavy 11B isotope to growing Meristems by B transporters.
Conclusions: The B isotopes can be used to identify plant metabolism in Response to the B concentration in the irrigation water and during intra‐plant B transfer. The large B isotope fractionation within the plants demonstrates the importance of
biological B cycling for the global B cycle.