Absolute isotope ratios of carbon dioxide a feasibility study

One way of obtaining isotope ratios, traceable to the International System of Units, is the gravimetric isotope mixtures method. Adapting this method to carbon dioxide is challenging since measuring all twelve isotopologues at once with a gas mass spectrometer is currently not possible. The calculation of the mass bias correction factors is no straightforward task due to the fact that the isotopic equilibrium has to be considered. This publication demonstrates a potential way of adapting this method to carbon dioxide while considering isotope equilibrium. We also show how we prepared binary blends from enriched/depleted carbon dioxide parent gases and how equilibrating the different gases by heating affects the measurements. Furthermore, we reveal mathematical limitations of our approach when the gases are not in isotope equilibrium and which issues occur due to measurement limitations. In a simulation, using authentic data, we asses our approach in terms of achievable uncertainties and discuss further improvements, like using atomic spectroscopy methods

A convenient and economic approach to achieve SI-traceable reference values to be used in drinking-water interlaboratory comparisons

Abstract Metrologically traceable reference values add an essential benefit to interlaboratory comparisons: unlike consensus values, they can be used to establish national and international comparability. Furthermore, the participating laboratories obtain a reliable and unbiased benchmark to check their results for accuracy. Usually, metrologically traceable reference values are obtained by so-called primary methods which demand excessive efforts at great expense. Within the framework of two national drinkingwater interlaboratory comparisons (proficiency testing rounds), a new approach to provide metrologically traceable reference values was applied. It is solely based on existing data which were collected during the comparison itself. Lead (Pb) measurements serve as an example to show how metrologically traceable reference values were derived from the lead amount added during sample preparation and the amount of lead already present in the drinking-water matrix used to prepare these samples. Within this approach, the matrix content is calculated in a way similar to a standard addition experiment. An uncertainty budget for the reference value was set up which describes the link to the corresponding SI units. Isotope dilution mass spectrometry (IDMS) as a primary method was used to validate this approach in the case of cadmium, chromium, copper, lead, and nickel

Amount of substance and the mole in the SI

Abstract Following the revision of the International System of Units (SI), that takes effect on 20 May 2019, the unit mole is defined by using a fixed number of elementary entities. This number is the fixed numerical value of the Avogadro constant, which is the defining constant of the unit mole. This definition was made possible because the determination of the Avogadro constant had reached a level of relative uncertainty that allowed its value to be fixed and, at the same time, safeguard continuity of measurement results before and after the definition. The motivation for the revision of the SI and the mole in particular will be explained and the experimental work that allowed it is summarized

The molar mass of a new enriched silicon crystal: maintaining the realization and dissemination of the kilogram and mole in the new SI

The local distribution of the isotopic composition and molar mass M of a new silicon crystal (Si28-24Pr11) highly enriched in the 28Si isotope is reported, with focus on the experimental methods as well as on the associated uncertainties. The crystal was used in 2018 for the production of two additional silicon spheres for the realization and verification of the Avogadro constant NA using the “X-ray-crystal-density (XRCD) method” which is a primary method for the dissemination of the revised SI units mole and kilogram. 17 subsamples have been investigated (from five different axial and in several radial positions) by isotope ratio mass spectrometry using a multicollector-inductively coupled plasma mass spectrometer (MC-ICP-MS). The average molar mass of the crystal is M = 27.976 933 787(77) g/mol with a relative combined uncertainty uc,rel(M) = 2.7 × 10−9. The mean amount-of-substance fraction of 28Si is x(28Si) = 0.999 993 104 (66) mol/mol indicating that this crystal has the highest enrichment in this isotope which has ever been used for the determination of NA. No local variations in M and x(iSi) (i = 28, 29, and 30) could be identified due to material properties. The results are compared with those from two previous enriched crystals

OCEAN—An EXCEL add-in for 17O correction using a novel approximation

In this publication, an alternative mathematical approach for 17O correction is presented. It is shown comprehensively how the newly developed formulas are derived and what the differences are to the established algorithm recommended by Brand et al. Additionally, two simulations are presented, which demonstrate the performance (in terms of accuracy and precision) of the approach. Part of this work is an EXCEL Add-In, which allows users to perform 17O correction, normalization and uncertainty propagation on their own. This enables the users - who are limited to measure only the masses 44 to 46 - to fully control their data evaluation. • Improved accuracy over a wider range. • Easy use and implementation of the scheme. • Convenient uncertainty calculation in accordance with international standards

Mass Spectrometric Investigation of Silicon Extremely Enriched in ²⁸Si: From ²⁸SiF₄ (Gas Phase IRMS) to ²⁸Si Crystals (MC-ICP-MS)

A new generation of silicon crystals even further enriched in ²⁸Si (<i>x</i>(²⁸Si) > 0.999 98 mol/mol), recently produced by companies and institutes in Russia within the framework of a project initiated by PTB, were investigated with respect to their isotopic composition and molar mass <i>M</i>(Si). A modified isotope dilution mass spectrometric (IDMS) method treating the silicon as the matrix containing a so-called virtual element (VE) existing of the isotopes ²⁹Si and ³⁰Si solely and high resolution multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) were applied in combination. This method succeeds also when examining the new materials holding merely trace amounts of ²⁹Si (<i>x</i>(²⁹Si) ≈ 5 × 10^–6 mol/mol) and ³⁰Si (<i>x</i>(³⁰Si) ≈ 7 × 10^–7 mol/mol) extremely difficult to detect with lowest uncertainty. However, there is a need for validating the enrichment in ²⁸Si already in the precursor material of the final crystals, silicon tetrafluoride (SiF₄) gas prior to crystal production. For that purpose, the isotopic composition of selected SiF₄ samples was determined using a multicollector magnetic sector field gas-phase isotope ratio mass spectrometer. Contaminations of SiF₄ by natural silicon due to storing and during the isotope ratio mass spectrometry (IRMS) measurements were observed and quantified. The respective MC-ICP-MS measurements of the corresponding crystal samples show–in contrast–several advantages compared to gas phase IRMS. <i>M</i>(Si) of the new crystals were determined to some extent with uncertainties <i>u</i>_rel(<i>M</i>) < 1 × 10^–9. This study presents a clear dependence of the uncertainty <i>u</i>_rel(<i>M</i>(Si)) on the degree of enrichment in ²⁸Si. This leads to a reduction of <i>u</i>_rel(<i>M</i>(Si)) during the past decade by almost 3 orders of magnitude and thus further reduces the uncertainty of the Avogadro constant <i>N</i>_A which is one of the preconditions for the redefinition of the SI unit kilogram

Combining Isotope Dilution and Standard Addition—Elemental Analysis in Complex Samples

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