Certification of High Purity Metals as Primary Reference Materials - A Challenge for Multielement Trace Analysis

Abstract

The Bundesanstalt fü r Materialforschung und -prü fung (Federal Institute for Materials Research and Testing) (BAM) is establishing a system of primary reference materials to meet the demands for metrological traceability and to act as national standards in the field of elemental analysis. For all elements of the periodic table -except those that are gases or radioactive -two different kinds of reference materials are being certified. One is for analyte calibration (Type A) and one for problems concerning matrix matching (Type B). These substances are of very high purity and of defined stoichiometry. As far as possible, pure elements and metals rather than pure compounds are used. The certification of both types of material requires most elements of the periodic table to be certified at very low levels using trace element analysis methods. The application of these methods is described and examples of the certification of copper and iron are given.

High Purity Metals as Primary Calibration Materials for Elemental Analysis-Their Importance and Their Certification

“…For further experimental details see. 1) In specific cases two special sample introduction tech- Other methods than ICP MS are shown in Fig. 3, left side.…”

“…For further information see. 1) Because it is extremely difficult to achieve uncertainties of 0.01% by determining the mass fraction of the main component directly by a primary method, we generally applied the indirect "difference method". Therefore it was necessary to determine the contents of all possible impurities (including gases and nonmetals).…”

“…Reagents, sample pretreatment and dissolution using liquid sample methods (mainly ICP mass spectrometry (ICP MS) and atomic absorption spectrometry (AAS)) are described elsewhere. 1) ICP mass spectrometry with laser ablation (LA ICP MS) was calibrated in case of copper analysis with pressed pellets of Cu-powder (m5N; alfa Johnson-Matthey). The pellets had been made from copper powder doped with multi-element standard solutions.…”

“…This was confirmed by investigations with secondary ion mass spectrometry (SIMS). 1,9) In Fig. 4 the original and the doped copper grains are mapped in different magnifications using SEM.…”

“…A stronger ablation from pressed pellets than from solid samples was found by SEM micrographs. 1,9) Additionally a selective evaporating of analytes from the pellets was observed by investigation of analytical signals and by SIMS micrographs of ablated sample areas. That is why analytical comparability of calibration pellets and compact pure copper material is difficult.…”