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Core capability tables list the skills and experiences, which at least partially are needed to successfully carry out a specific analytical task within the IAWG. The required skills and experiences, so-called core capabilities (CC), are identified for each analytical procedure. The summarized CC tables are listed in the appendix of each report on the corresponding key comparison or pilot study. These CC tables enable us to demonstrate that we have the analytical procedure we claim under control by means of other Key Comparison, which do not exactly meet the claimed calibration and measurement capability. This is especially important for: a) fields where no Key Comparison is available, b) Revision of CMC claims or c) when a participation in a Key Comparison was not possible.
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.
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.
High purity materials can serve as a realisation of the Système International d’Unitès (SI) unit amount of substance for the specific element. Solutions prepared from such high purity materials using gravimetric preparation and the concept of molar mass are used as calibration solutions in many fields of analytical chemistry. Calibration solutions prepared this way provide the traceability to the SI and are the metrological basis in elemental analysis.
The preparation and characterization of such primary pure substances, representing the realisation of the SI unit amount of substance, is undertaken only by a small number of National Metrology Institutes (NMI) and Designated Institutes (DI).
Many other NMIs and DIs, however, prepare elemental calibration solutions as calibrants for their measurement services, such as the certification of matrix Reference Materials or the provision of reference values for Proficiency Testing schemes. The elemental calibration solutions used for this purpose are not a direct service to customers, such as preparing secondary calibration solutions, but provide the source of traceability for the other services. Hence, it is necessary for the NMI or DI to obtain data on the purity of the pure metals or other materials used to prepare the solutions with measurement uncertainties meeting the needs of the above described services. This is commonly undertaken as a “fit for purpose” assessment, appropriate for the uncertainty requirement of the service provided to customers.
As a consequence, total purity measurements are a long-term strategy of CCQM-IAWG. Several studies were conducted (CCQM-P107, CCQM-K72 and CCQM-P149) on the measurement of the purity of zinc. From these studies, several conclusions can be drawn for the purity assessment of a pure (metallic) element. These conclusions will be put together in this document in order to assist all NMIs/DIs in performing a purity assessment, whenever needed.
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.
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 %.
This presentation gives a short overview of isotope ratio measurements being carried out in the past few years at BAM in different fields such as plant metabolism, food web structures and archaeology. The corresponding isotope reference materials which have been certified at BAM in parallel are presented as well. Additionally an outlook is being provided on future iRM projects.
Multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) has evolved significantly since its introduction in 1992. The second and third generation instruments now allow isotope ratio measurements at unprecedented precisions, 0.001 % or better. However, precision alone is not enough for producing accurate and reliable isotope ratio measurements. Metrological considerations such as the selection of suitable calibration strategies, proper assessment of instrumental biases, and the estimation of overall measurement uncertainty remain critical to the measurement process. Properly assessed, measurement uncertainty then provides the interval within which a result can be considered both accurate and precise.
All mass spectrometric measurements are affected by instrumental mass discrimination and produce isotope ratios that are biased relative to their “true” ratio. To produce accurate and traceable isotope ratio measurements, it is imperative that certified isotope reference materials (iCRMs) be used for calibration and validation purposes. iCRMs reporting absolute isotope ratios are an analyst’s first choice, particularly when its uncertainty is sufficient for the intended use. However, when smaller uncertainties are required to resolve subtle differences between samples, delta-scale measurements become important. Here, the difference between an isotope ratio measured in a sample and in an internationally accepted isotope reference material (iRM) is determined. This deviation can be positive or negative relative to the iRM, is called a delta value, and is often expressed in per mil units.
This presentation will highlight the potential for MC-ICP-MS to produce isotope ratio measurements with minimal uncertainties by examining three applications involving Mg isotopes: 1) the certification of a set of iCRMs for their absolute isotope ratio using a gravimetric isotope mixture approach; 2) the comparison of these iCRMs with currently accepted Mg delta-scale reference materials through intercalibration, and 3) the determination of isotope fractionation exponents for geochemical applications.