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Organisationseinheit der BAM
A candidate material for the use as primary standard for silver determination was characterized with respect to total purity. Except the radioactive elements and He, all possible impurities were considered. Based on glow discharge mass spectrometry, inductively coupled plasma-mass spectrometry and carrier gas hot extraction measurements, the demonstrated total purity and its standard uncertainty is w(Ag) = (99.999 52 ± 0.000 11) %. The purity value and its uncertainty is dominated by the contributions from the measurements of the nonmetallic impurities, namely S, N, C and O.
During its 25 years of existence, the Inorganic Analysis Working Group of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM IAWG) has achieved much in establishing comparability of measurement results. Impressive work has been done on comparison exercises related to real-world problems in fields such as ecology, food, or health. In more recent attempts, measurements and comparisons were focused on calibration solutions which are the basis of most inorganic chemical measurements. This contribution deals with the question of how to achieve full and transparent SI traceability for the values carried by such solutions. Within this framework, the use of classical primary methods (CPMs) is compared to the use of a primary difference method (PDM). PDM is a method with a dual character, namely a metrological method with a primary character, based on the bundling of many measurement methods for individual impurities, which lead to materials with certified content of the main component. As in classical methods, where small corrections for interferences are accepted, in PDM, many small corrections are bundled. In contrast to classical methods, the PDM is universally applicable to all elements in principle. Both approaches can be used to certify the purity (expressed as mass fraction of the main element) of a high-purity material. This is where the metrological need of National Metrology Institutes (NMIs) for analytical methods meet the challenges of analytical methods. In terms of methods, glow discharge mass spectrometry (GMDS) with sufficient uncertainties for sufficiently small impurity contents is particularly noteworthy for the certification of primary transfer standards (PTS), and isotope dilution mass spectrometry (IDMS), which particularly benefits from PTS (back-spikes) with small uncertainties, is particularly noteworthy for the application. The corresponding relative uncertainty which can be achieved using the PDM is very low (< 10−4). Acting as PTS, they represent the link between the material aspect of the primary calibration solutions and the immaterial world of the International System of Units (SI). The underlying concepts are discussed, the current status of implementation is summarised, and a roadmap of the necessary future activities in inorganic analytical chemistry is sketched. It has to be noted that smaller measurement uncertainties of the purity of high-purity materials not only have a positive effect on chemical measurements, but also trigger new developments and findings in other disciplines such as thermometry or materials science.
The special importance of the analysis of non-metals in high purity metals, which will serve as national standards for elemental analysis in Germany, is illustrated for oxygen and nitrogen. The typical range of the mass fraction of oxygen and nitrogen in these materials is below 10.MU.g/g, often close to 1.MU.g/g. The two methods applied at BAM for these measurements are classical carrier gas hot extraction (HE) and carrier gas hot extraction after activation with photons (PAA-HE). The approach, the methods and their advantages and limitations are discussed. Comparative results from the measurement of oxygen and nitrogen in Cu, Fe, Ga, Pb, Sn and W are presented. (author abst.)
The degree of equivalence within the participating national metrology institutes for the measurement results of the mass fractions of the analytes Cr, Cu, Fe, Mn and Zn in an aluminium alloy was assessed. This interlaboratory comité consultatif pour la quantité de matière key comparison (CCQM-K42) was organised as an activity of the Inorganic Analytical Working Group of CCQM. In total seven laboratories participated, six of them for all analytes. Measurands were the mass fractions of the analytes in a range of 0.05 and 0.2%. As an outcome the consistency of the results for all elements investigated was acceptable, hence satisfactory comparability was established. An aluminium based certified reference material—undisclosed to the analysts which one it was—was used as test sample. For the purpose of this study homogeneity was tested at BAM. Each laboratory was free to choose any analytical method they wanted to use for the analysis. Consequently various methods of measurement were employed: instrumental neutron activation analysis, X-ray fluorescence spectrometry (XRF) using fused cast-bead method combined with reconstitution technique, inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry. Metrological traceability of the measurement results to the SI unit had to be demonstrated. Therefore, methods such as spark OES or XRF (without fused cast-bead technique)—both of them being most important methods for the analysis of metals and alloys in industrial laboratories—could not be used in the frame of the key comparison.
Calibration of two commercially available glow discharge double focusing mass spectrometers, the VG 9000 and Element GD, is described using synthetic pin standards pressed from solution doped copper and zinc matrices. A special pressing die was developed for this purpose and optimal results were obtained with the highest possible pressures, i.e., 95 kN·cm- 2. This calibration approach permits the determination of trace element mass fractions down to µg·kg- 1 with small uncertainties and additionally provides traceability of the GD-MS results in the most direct manner to the SI (International System of Units). Results were validated by concurrent measurements of a number of compact copper and zinc certified reference materials. The impact of the sample pin cross-section (circular or square) was investigated with the use of a new pin-sample holder system for the Element GD. The pin-sample holder was designed by the manufacturer for pin-samples having circular cross-section; however, samples with square pin cross-section were also shown to provide acceptable results. Relative Sensitivity Factors for some 50 analytes in copper (VG 9000, Element GD) and zinc matrices (VG 9000) are presented. The field of applicability of GD-MS may be considerably extended via analysis of pin geometry samples based on their ease of preparation, especially with respect to the accuracy and traceability of the results and the enhanced number of analytes which can be reliably calibrated using such samples.
Determining the influence of impurities on the fixed-point emperatures
of the ITS-90 requires the completion of several tasks. In this paper, the Progress made at Physikalisch-Technische Bundesanstalt (PTB) and BAMFederal Institute for Materials Research and Testing is presented and remaining questions are discussed.
The projected characterization procedure at PTB, which is based on the established SIE method (sum of the individual estimates), using a new indium fixed-point cell is described as an example. This procedure includes an SI-traceable chemical Analysis of the material in the fixed-point cell with sufficiently low uncertainties, the individual experimental determination of the influence of the quantified impurities on the fixed-point temperature, and the establishment of direct links to the phase-transition temperatures of the national standard and of an assumed material of ideal purity.
A characteristic difference to the common practice is the chemical analysis of the fixed-point metal being done after determining the cells freezing temperature. This allows for the detection and consideration of contamination and purification effects due to the filling process, or due to the contact with the carbon crucible and other parts of the fixed-point cell. A chemical analysis of an indium fixed-point was carried out by BAM with relative measurement uncertainties below 30 % which have not been previously achieved. The results provide evidence for the precipitation of some impurities,
which is apparently inconsistent with the corresponding binary phase diagrams, but was explained in a recent publication. Implications for the use of the SIE method shall be described briefly at the end.
The hollow cathode (HC) effect was investigated in non-cooled 15 mm deep drilled flat metallic analytical samples that were easy to prepare. The deep cavity used ("complete HC" in contrast to "recessed HC" with 2-3 mm deep cavity) intensified the HC effect notably and therefore distinctly improved the detection power of the common GD-OES with planar cathodes. A signal enhancement of up to a factor of 150, not reported earlier, in comparison with flat conventional samples was achieved. A better separation of the analytical lines from spectral interferences was observed when the HC assembly was applied. Additionally, an effect of strongly enhanced intensities of atomic lines and somewhat decreased intensities of ionic lines was detected in the case of HC in comparison to usual planar cathodes. The investigations were carried out with samples of copper, steel and zinc matrices using both the same and individually optimised glow discharge (GD) electrical parameters.
Detection and monitoring of volatile elements released during the preparation of ultra high purity zinc by vacuum distillation (VD) is reported using online quadrupole gas source mass spectrometry (QMS). The theoretically calculated vapour pressures (pv) for the volatile impurity elements using Dushman constants and the practically observed mass spectra were found to be consistent (S. Dushman and J. M. Lafferty, Scienific Foundations of Vacuum Technique, 2nd ed., Wiley, New York, 1962). This is the first time that the potential ability of an online mass spectrometer was used for monitoring and understanding the process mechanism during the purification of metals (Zn) using VD. We here also illustrate our findings with the results from high resolution glow discharge mass spectrometer (HR-GDMS) analysis before and after the purification of Zn.
Mass spectrometric detection can play a prominent role in the assessment of different reactions occurring at varied temperatures in a milled ZnO/Al mixture. This is the first time that online mass spectrometric information was used as a tool for monitoring and understanding the chemical reduction process mechanism. We have observed four different types of reaction taking place: (1) distillation of Zn metal, (2) reduction of ZnO by activated Al, (3) melting of Al and finally (4) reduction of ZnO by inactivated Al. The experimental conditions and results observed by QMS were supported with literature data and physical measurement data from X-Ray Diffraction (XRD) which gave us an idea about the complex reaction cascade which occurred during the formation of the zinc metal.
In Germany a system of primary amount of substance standards for elemental analysis is being developed, which forms the material´s basis for the National Standards for element determination. The metrological concept and technical approach is briefly described. The objective of traceability in chemistry, in this case for elemental determination, is illustrated on the example of copper.