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The CCQM-K88 key comparison was organized by the Inorganic Analysis Working Group of CCQM to test the abilities of the national metrology institutes to measure the mass fraction of lead in lead-free solder containing silver and copper. National Metrology Institute of Japan (NMIJ), National Institute of Metrology of China (NIM) and Korea Research Institute of Standards and Science (KRISS) acted as the coordinating laboratories. The participants used different measurement methods, though most of them used inductively coupled plasma optical emission spectrometry (ICP-OES) or isotope-dilution inductively coupled plasma mass spectrometry (ID-ICP-MS). Accounting for relative expanded uncertainty, comparability of measurement results was successfully demonstrated by the participating NMIs for the measurement of the mass fraction of lead in lead-free solder at the level of 200 mg/kg.
It is expected that metals at mass fractions greater than approximately 100 mg/kg in lead-free solder containing silver and copper can be determined by each participant using the same technique(s) employed for this key comparison to achieve similar uncertainties mentioned in the present report.
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.
The article gives a condensed version of the keynote lecture held at the International Mass Spectrometry Conference 2012 in Kyoto. Starting with some examples for isotope research the key requirements for metrologically valid procedures enabling traceable and comparable isotope data are discussed. Of course multi-collector mass spectrometers are required which offer sufficiently high isotope ratio precision for the intended research work. Following this, corrections for mass fractionation/discrimination, validation of the analytical procedure including chemical sample preparation and complete uncertainty budgets are the most important issues for obtaining a metrologically valid procedure for isotope ratio determination. Only the application of such metrologically valid procedures enables the generation of traceable and comparable isotope data. To realize this suitable isotope and/or δ-reference materials are required, which currently are not sufficiently available for most isotope systems. Boron is given as an example, for which the situation regarding isotope and δ-reference materials is excellent. Boron may therefore serve as prototype for other isotope systems.
So-called spikes are solutions of isotopically enriched elements, which are used in isotope dilution mass spectrometry (IDMS) for the accurate quantification of element concentrations. Based on its proven records, especially in reference material certification 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 largely unaffected by instrumental drift, setup or by matrix, unless an isobaric interference is present.