Analytische Chemie
Filtern
Dokumenttyp
- Zeitschriftenartikel (42)
- Vortrag (32)
- Posterpräsentation (7)
- Sonstiges (1)
- Forschungsdatensatz (1)
Schlagworte
- Traceability (28)
- Metrology (22)
- Absolute isotope ratio (18)
- Uncertainty (15)
- Isotope ratio (12)
- Delta value (7)
- Cement (6)
- Copper (6)
- Isotope reference material (6)
- Measurement uncertainty (6)
Organisationseinheit der BAM
- 1.1 Anorganische Spurenanalytik (83) (entfernen)
Eingeladener Vortrag
- nein (32)
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 %.
For the first time, an international comparison was conducted on the determination of the purity of a high purity element. Participants were free to choose any analytical approach appropriate for their institute’s applications and services. The material tested was a high purity zinc, which had earlier been assessed for homogeneity and previously used in CCQM-K72 for the determination of six defined metallic impurities. Either a direct metal assay of the Zn mass fraction was undertaken by EDTA titrimetry, or an indirect approach was used wherein all impurities, or at least the major ones, were determined and their sum subtracted from ideal purity of 100 %, or 1 kg/kg. Impurity assessment techniques included glow discharge mass spectrometry, inductively coupled plasma mass spectrometry and carrier gas hot extraction/combustion analysis. Up to 91 elemental impurities covering metals, non-metals and semi-metals/metalloids were quantified. Due to the lack of internal experience or experimental capabilities, some participants contracted external laboratories for specific analytical tasks, mainly for the analysis of non-metals. The reported purity, expressed as zinc mass fraction in the high purity zinc material, showed excellent agreement for all participants, with a relative standard deviation of 0.011 %. The calculated reference value, w(Zn) = 0.999 873 kg/kg, was assigned an asymmetric combined uncertainty of + 0.000025 kg/kg and – 0.000028 kg/kg. Comparability amongst participating metrology institutes is thus demonstrated for the purity determination of high purity metals which have no particular difficulties with their decomposition / dissolution process when solution-based analytical methods are used, or which do not have specific difficulties when direct analysis approaches are used. Nevertheless, further development is required in terms of uncertainty assessment, quantification of non-metals and the determination of purity of less pure elements and/or for those elements suffering difficulties with the decomposition process.
Previously applied methods for the quantification of sulphur in copper and other pure metals revealed a lack of SI-traceability and additionally showed inconsistent results, when different methods were compared.
Therefore, a reference procedure is required which allows SI-traceable values accompanied by a Sound uncertainty budget. In this study a procedure was developed for the quantification of total sulphur in copper at low concentration levels using inductively coupled plasma-isotope dilution mass spectrometry (ICP-IDMS). The major part of the copper matrix was separated by adding ammonia which forms a complex with the copper while releasing the sulphur followed by chromatographic separation using a weak cation resin. After that the sulphur fraction was further purified by chromatographic means using first an anion exchange method and second a chelating resin. The developed procedure shows high performance, especially concerning high efficiency in matrix removal (>99.999%) while keeping the recovery of sulphur above 80%. Procedure blanks are in the order of 3–53 ng resulting in LOD and LOQ values of 0.2 mg g1 and 0.54 mg g1, respectively. The procedure is sufficient to facilitate value assignment of the total sulphur mass fraction in reference materials. Additionally, relative measurement uncertainties were calculated to be below 1% and the measurement results were traceable to the SI. The procedure reported in this study is a new reference procedure for sulphur measurement in copper, being fit for two major purposes, certification of reference materials and assignment of reference values for inter-laboratory comparison.