Intercalibration of Mg Isotope Delta Scales and Realisation of SI Traceability for Mg Isotope Amount Ratios and Isotope Delta Values

Abstract

The continuous improvement of analytical procedures using multi‐collector technologies in ICP‐mass spectrometry has led to an increased demand for isotope standards with improved homogeneity and reduced measurement uncertainty. For magnesium, this has led to a variety of available standards with different quality levels ranging from artefact standards to isotope reference materials certified for absolute isotope ratios. This required an intercalibration of all standards and reference materials, which we present in this interlaboratory comparison study. The materials Cambridge1, DSM3, ERM‐AE143, ERM‐AE144, ERM‐AE145, IRMM‐009 and NIST SRM 980 were cross‐calibrated with expanded measurement uncertainties (95% confidence level) of less than 0.030‰ for the δ25/24Mg values and less than 0.037‰ for the δ26/24Mg values. Thus, comparability of all magnesium isotope delta (δ) measurements based on these standards and reference materials is established. Further, ERM‐AE143 anchors all magnesium δ‐scales to absolute isotope ratios and therefore establishes SI traceability, here traceability to the SI base unit mole. This applies especially to the DSM3 scale, which is proposed to be maintained. With ERM‐AE144 and ERM‐AE145, which are product and educt of a sublimation–condensation process, for the first time a set of isotope reference materials is available with a published value for the apparent triple isotope fractionation exponent θapp, the fractionation relationship ln α(25/24Mg)/ln α(26/24Mg).

The triple-isotope calibration approach: a universal and standard-free calibration approach for obtaining absolute isotope ratios of multi-isotopic elements

“…13 to 16). It depicts the metrological compatibility between both values within the stated expanded uncertainties (k = 2) [13]. For E n values of less than or equal to 1, both values are metrological compatible with each other; in older terms, they agree within their uncertainties.…”

“…When looking at the θ values of these measurements (Table 2), it is obvious that all θ values obtained by MC-ICP-MS measurements overlap (within expanded uncertainties) with the theoretical range of equilibrium and non-equilibrium isotope fractionation, while θ values obtained by MC-TIMS in most cases do not. For TIMS, this might be an indication for massindependent effects, whereby it is more likely that two or more mass-dependent fractionation effects are coupled, which can lead to θ values outside the theoretical range [13]. In the case of MC-ICP-MS, it is a strong indication for IIF, which is dominated by a mass-dependent process.…”

Determination of lithium in human serum by isotope dilution atomic absorption spectrometry

“…Table 1 summarizes the results of the Li quantification by ID-HR-CS-GFAAS. The corresponding uncertainties were calculated according to the Guide to the Expression of CRMs can be evaluated by applying the E n value, which is the difference of two values divided by the expanded uncertainty of this difference [24]. Both values are considered metrologically compatible for E n < 1 and not metrologically compatible for E n > 1.…”

Multicollector Inductively Coupled Plasma–Mass Spectrometry with 1013 Ω Faraday Cup Amplifiers for Ultrasensitive Mg Isotopic Analysis of Cerebrospinal Fluid Microsamples

“…The intercept of the linear relation, providing the δ 26 Mg value for ERM-AE143 relative to DSM3, was in a good agreement with the reported value. 29,30…”