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- Chemical analysis (2)
- Carrier gas hot extraction (1)
- Comparability (1)
- Elemental determination (1)
- Fixed points (1)
- ITS-90 (1)
- Impurities (1)
- Inter laboratory comparison (1)
- Metrology (1)
- Metrology in chemistry (1)
- Microwave induced plasma spectrometry (1)
- Non-metal determination (1)
- Phase diagrams (1)
- Primary standards (1)
- Purity assessment (1)
- Thermal effects (1)
- Traceability (1)
- Uncertainty (1)
The International Temperature Scale of 1990 (ITS-90) is based on thermodynamic equilibrium states of ideally pure substances. The largest contribution to the uncertainty budgets of most metallic fixed points is the influence of impurities on the fixed-point temperature. Therefore, a traceable chemical analysis of the remaining impurities with small uncertainty is the basis of further progress. Further requirements are better knowledge of the phase diagrams at very low impurity contents, impurity segregation, and the quantification and correction of thermal effects during a fixed-point realization. In this article, current and future activities at PTB and BAM in order to develop improved metallic fixed-point cells of the ITS-90 are reviewed.
An inter-laboratory study was performed by some National Metrology Institutes in order to take a snap shot of the comparability and the capability of performing purity assessments of high purity materials as needed for providing national standards for elemental determination. The measurand was defined as the value of the sum of the mass fractions of Ag, Al, Cu, Fe, Pb and Zn in the bulk of a high purity nickel material and the interim results for the six individual impurities. Whereas for the analytes Ag, Al, Cu and Fe there was no agreement within the target uncertainty of 30%, agreement could be achieved for Pb and Zn. The discrepancies observed for the individual analytes resulted in a variation of a factor of 8 of the reported values for the impurity of nickel with respect to the six defined metallic analytes. The reference measurements using IDMS and for Al using GD-MS confirmed the lower reported values.
The determination of O, N and H using a microwave induced plasma coupled to carrier gas hot extraction was exploratory investigated. The signal intensities versus time of blanks and calibration materials were recorded. To check for interferences the signal intensities versus wavelength were recorded at the times just before increase and at the maximum of the time dependent analytical signal. O, N and H were investigated at their prominent wavelengths of 777 nm, 174 nm and 486 nm, respectively. Calibration was performed for O, N and H in the ranges of 027 µg, 351000 µg and 343 µg respectively. For concentration values in the middle of the linear part of the investigated calibration interval, a relative precision of 5% at 13 µg, 2% at 74 µg and 0.6% at 23 µg for O, N and H respectively was found. The maximum matrix load to the plasma used was found to be 150 µg min-1. From the signal to noise ratio and the sensitivity obtained, instrumental limits of detection (3s) of 0.01 µg for O, 1 µg for N and 0.1 µg for H were found. Assuming a typical sample mass of 1 g this corresponds to relative LODs of 0.01 µg g-1, 1 µg g-1 and 0.1 µg g-1 for O, N and H respectively.
The application of metrology in chemical analysis is today hampered by psychological and practical barriers. The argumentation is based on the differences in physical and chemical metrology, which arises mainly from the objects of the measurements. The term measurement is discussed in the realm of analytical chemistry with a special focus on the inherent relation between chemical identification and determination as well as the consequent use of the concept of traceability and uncertainty.