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Eingeladener Vortrag
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The preparation and analysis of the oxygen mass fraction of three pure copper reference materials (BAM-379/1, BAM-379/2, BAM-379/3) intended for the calibration of spark emission spectrometry are described here. Data of homogeneity testing and round robin certification in collaboration with 12 independent laboratories from metalworking industry and research are reported. Problems with the establishment of traceability in this special case are discussed.
Three methods for direct solid sampling of bulk material namely IR laser ablation, glow discharge and spark OES, were compared with respect to analytical figures of merit obtained for elemental analysis with atomic spectrometry. Matrices investigated were copper, pressed doped copper powder, and magnesium alloys. For the vast majority of analytes, statistical equivalence regarding precision (usually ≤ 5%) and the performance of the calibrations between the compared methods was demonstrated.
The traceabiiity requirements for certification analyses of reference materials are much more stringent than for routine analysis, where certified matrix reference materials (CRM) can be used for calibration and to establish traceabiiity. Although the ISO-Guides related to CRM production and certification are not fully clear concerning calibration, many established CRM-producers do not accept matrix-CRMs for calibration in case of certification analyses, e.g. to avoid circular reasoning. These requirements limit the methods used for certification to those that can be calibrated using Standards of known high purity and stoichiometry or mixtures of such Standards. Powerful solid sampling techniques such as glow discharge mass spectrometry (GD-MS) or spark-optical emission spectrometry (SOES), where usually compact CRMs are used for calibration, seem not be applicable for certification analyses. Especially GD-MS is a powerful tool for trace element determination of solid samples. Beside metallic impurities the use of specific gas mixtures enables also the determination of interesting nonmetallic impurities such as sulfur and phosphorus. Within BAM a calibration approach, was developed which enables to use mixtures of Standards of known high purity and stoichiometry also for GD-MS. Analogue to matrix adaption in solution based techniques, the calibration approach is based on doped pressed powder pellets.
Approach and application on the certification analyses of copper and Steel CRMs are presented.