Analytische Chemie
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Absolute Isotope Ratios
(2018)
Measurement results and scientific models leading to important decisions in forensics, food fraud or climatology are based on isotope ratio data. Molar masses of multi-isotopic elements are as well based on isotope ratio data. Thus, in the case of Si, isotope ratios directly impact the redefinition of the SI base units kilogram and mole. Therefore, new strategies are required leading to new primary isotope reference materials, whose isotope ratios are traceable to the SI. This in turn will ensure the comparability of isotope ratio data and will render the traceability exception requested by the CCQM superfluous. Such new procedures will be developed for the key elements S, Si, Ca, Sr and Nd at relative uncertainty levels of ≤ 0.01 %.
An introduction into absolute isotope ratios is given, with application fields ranging from fundamental science to geochronology and forensics. This is followed by a proposal for developing new calibration approaches for obtaining absolute isotope ratios at unrivaled uncertainty levels. This new developments will set the basis for improvements in all scientific fields.
CCQM-P149 is an attempt to obtain a snapshot on actual procedures the NMIs and DIs within CCQM-IAWG applied to the purity characterization of their “fit for purpose” elemental Standards. This presentation describes how the results of CCQM-P149 may be used to underpin calibration and measurement capabilities being claimed in the BIPM database.
A new method combining isotope dilution mass spectrometry (IDMS) and standard addition has been developed to determine the mass fractions w of different elements in complex matrices: (a) silicon in aqueous tetramethylammonium hydroxide (TMAH), (b) sulfur in biodiesel fuel, and (c) iron bound to transferrin in human serum. All measurements were carried out using inductively coupled plasma mass spectrometry (ICP–MS). The method requires the gravimetric preparation of several blends (bi)—each consisting of roughly the same masses (mx,i) of the sample solution (x) and my,i of a spike solution (y) plus different masses (mz,i) of a reference solution (z).
Only these masses and the isotope ratios (Rb,i) in the blends and reference and spike solutions have to be measured. The derivation of the underlying equations based on linear regression is presented and compared to a related concept reported by Pagliano and Meija. The uncertainties achievable, e.g., in the case of the Si blank in extremely pure TMAH of urel (w(Si)) = 90% (linear regression method, this work) and urel (w(Si)) = 150% (the method reported by Pagliano and Meija) seem to suggest better applicability of the new method in practical use due to the higher robustness of regression analysis.
Detector deadtime
(2023)
Determination of absolute (SI‐traceable) isotope ratios: The use of Gravimetric Isotope Mixtures
(2023)
The presentation is brief overview on how to use gravimetric isotope mixtures to determine SI traceable isotope ratios. There is no mass spectrometer on earth that directly measures isotope ratios. Mass spectrometers will always measure signal intensity ratios instead. The actual problem is that the measured intensity ratios differ more or less from the isotope ratios. The difference can be up to more than 10 % in case of lithium while it‘s below 1 % in case of the heavier elements like lead or uranium. Consequently, the signal intensity ratios are expressed for example in V/V depending on the type of mass spectrometer you are using, while the isotope ratios are expressed in mol/mol. This phenomenon is called Instrumental Isotopic Fractionation (or short IIF) but the more common name is still mass bias (even though this name is not entirely correct). To convert the measured into the isotope ratio usually a simple multiplication with a so-called correction (or short K) factor is done. Therefore, the problem is to determine the K factor. In absence of isotope reference materials the golden route is via gravimetric isotope mixtures, which will be explained within the presentation.
Technologie-kritische Elemente (TCE) sind unentbehrliche Materialien für High-Tech Produkte wie Smartphones, Notebooks und Monitors. Ihr Bedarf wird voraussichtlich aufgrund des gesellschaftlichen Wandels hin zu einer grünen Ökonomie exponentiell ansteigen. Dieser Wandel wird vor allem auch durch erneuerbare Energien und Elektromobilität geprägt (European Green Deal). Diese Entwicklung in Verbindung mit einer nahezu fehlenden TCE Produktion in Europa setzt den Markt unter Druck und führt zu steigenden Preisen. Die Sicherung des TCE Nachschubs wurde in der gegenwärtigen Gesundheitskrise noch dringender und wurde daher auch zu einem der Hauptthemen des COVID-19 Recovery Plan, der eine Stärkung der europäischen Resilienz und Autonomie zum Ziel hat. Ein nachhaltige Lösung ist das Recycling der Abfall- bzw. Wertstoffe und letztendlich eine Circular Economy. Allerdings ist die Analyse von Abfallströmen schwierig und erfordert geeignete analytische Lösungen, die SI-rückführbare und somit vergleichbare Messergebnisse im gesamten Recyclingprozess ermöglichen. Die dafür erforderlichen, für TCE zertifizierte, Referenzmaterialien und nötige standardisierte Verfahren fehlen bisher nahezu vollständig. In diesem Beitrag werden die analytischen Herausforderungen, wie z.B. die extreme Heterogenität der Materialien, Schwierigkeiten beim Probenaufschluss und das Fehlen von Referenzmaterialien diskutiert. Und es wird das EMPIR-Projekt MetroCycleEU vorgestellt, dessen Ziel es ist Referenz- und Routineverfahren für ausgewählte TCE (Co, Ga, Ge, In, Ta, Nd, Pr, Dy, Gd, La, Au, Pt, Pd, Rh) zu entwickeln und Referenzmaterialien für Platinen, LEDs und Li-Batterien bereitzustellen.
IDMS Training
(2016)
Based on its proven records especially in reference material certification, isotope dilution mass spectrometry (IDMS) is considered as one of the most powerful and most accurate methods for determining amounts of substance. Contrary to other calibration approaches, IDMS does not directly suffer from long-time changes or drifts in instrument sensitivity. Moreover, provided isotopic exchange between the sample and spike is ensured, losses of analyte do not affect the analytical result. Both advantages are based on the fact that IDMS only requires isotope ratio measurements and isotope ratios are largely unaffected by instrumental drift, setup or by matrix, unless an isobaric interference is present.
The Consultative Committee for Amount of Substance (CCQM), the world's highest institution for metrology in chemistry, considers IDMS as the most important “Primary Method of Measurement” for amount determination. The total combined uncertainty, according to ISO and EURACHEM guidelines, can easily be calculated via the IDMS equations. Applying it correctly, IDMS has the potential to be a primary method of measurement yielding SI traceable values in the most direct way with combined uncertainties significantly smaller than obtainable by other methods.
In general it can be stated that IDMS is the most important reference method for elemental and elemental species analysis, offering highest accuracy and precision or smallest measurement uncertainties, when properly applied. Thus IDMS represents by far the best suited reference method for RM characterisation. Due to its universal applicability IDMS offers sufficient potential to follow future needs in analytical chemistry as well as in the RM sector.
This presentation will demonstrate the basic principle of IDMS and will show its Pros and Cons as well as its pitfalls. Possible sources of errors and bias are mentioned and correction models will be discussed. Notice will be given to metrological aspects such as traceability and uncertainty. Differences in the application of thermal ionization mass spectrometry and inductively coupled plasma mass spectrometry are discussed as well as differences between different types of mass spectrometers. This will be illustrated by practical examples from various fields.
IRWG strategy update
(2023)
IRWG strategy update
(2022)
Isotope analysis
(2017)
The variation of isotope ratios is increasingly used to unravell natural and technical questions. In the past the investigation and interpretation of such variations was the field of a limited number of experts. With new upcoming techniques and research topics in the last decades, such as provenance and authenticity of food, the number of published isotope data strongly increased. Instrumental developments such as the enhancement of inductively coupled plasma mass spectrometers (ICPMS) from an instrument for simple quantitative analysis to highly sophisticated isotope ratio machines influenced this process significantly. While in former times only experts in mass spectrometry were able to produce reliable isotope data, nowadays many laboratories, never been in touch with mass spectrometry before, produce isotope data with an ICPMS. Especially for such user isotope reference materials (IRM) are indispensible to enable a reliable method validation. The fast development and the broad availability of ICPMS also lead to an expansion of the classical research areas and new elements are under Investigation.
This presentation shows the basics and principles for isotope ratio determination using ICP-MS. Additionally, it provides three specific examples for isotope Ratio applications: isotope dilution mass spectrometry; provenancing of archaeoligical artifeacts by lead isotope Ratio Analysis and studies on boron uptake in bell pepper plants.