Filtern
Dokumenttyp
- Zeitschriftenartikel (2)
- Vortrag (1)
Sprache
- Englisch (3)
Schlagworte
- Sulfur (2)
- Biodiesel (1)
- Biodiesel fuel (1)
- Blank characterization (1)
- Copper (1)
- Fuel (1)
- GDMS (1)
- Human serum (1)
- ICP-MS (1)
- Isotope dilution mass spectrometry (1)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (1)
The quantification of the sulphur mass fraction in pure copper and copper alloys by GDMS and LA-ICP-MS revealed a lack of traceability mainly due to a lack of suitable certified reference materials for calibrating the instruments. Within this study GDMS and LA-ICP-MS were applied as routine analytical tools to quantify sulphur in copper samples by applying reference materials as calibrators, which were characterized for their sulphur mass fraction by IDMS beforehand. Different external calibration strategies were applied including a matrix cross type calibration. Both techniques with all calibration strategies were validated by using certified reference materials (others than those used for calibration) and good agreement with the reference values was achieved except for the matrix cross type calibration, for which the agreement was slightly worse. All measurement results were accompanied by an uncertainty statement. For GDMS, the relative expanded (k = 2) measurement uncertainty ranged from 3% to 7%, while for LA-ICP-MS it ranged from 11% to 33% when applying matrix-matched calibration in the sulphur mass fraction range between 25 mg kg-1 and 1300 mg kg-1. For cross-type calibration the relative expanded (k = 2) measurement uncertainty need to be increased to at least 12% for GDMS and to at least 54% for LA-ICP-MS to yield metrological compatibility with the reference values. The so obtained measurement results are traceable to the international system of units (SI) via IDMS reference values, which is clearly illustrated by the unbroken chain of calibrations in the metrological traceability scheme.
A new method combining isotope dilution mass spectrometry (IDMS) and standard addition has been developed to determine the mass fractions w of different elements in complex matrices: (a) silicon in aqueous tetramethylammonium hydroxide (TMAH), (b) sulfur in biodiesel fuel, and (c) iron bound to transferrin in human serum. All measurements were carried out using inductively coupled plasma mass spectrometry (ICP–MS). The method requires the gravimetric preparation of several blends (bi)—each consisting of roughly the same masses (mx,i) of the sample solution (x) and my,i of a spike solution (y) plus different masses (mz,i) of a reference solution (z).
Only these masses and the isotope ratios (Rb,i) in the blends and reference and spike solutions have to be measured. The derivation of the underlying equations based on linear regression is presented and compared to a related concept reported by Pagliano and Meija. The uncertainties achievable, e.g., in the case of the Si blank in extremely pure TMAH of urel (w(Si)) = 90% (linear regression method, this work) and urel (w(Si)) = 150% (the method reported by Pagliano and Meija) seem to suggest better applicability of the new method in practical use due to the higher robustness of regression analysis.
The CCQM-K123 key comparison was organized by the Inorganic Analysis Working Group (IAWG) of CCQM to assess and document the capabilities of the national metrology institutes (NMIs) or the designated institutes (DIs) to measure the mass fractions of sodium, calcium, potassium, magnesium phosphorous and sulfur in biodiesel fuel (BDF). The National Metrology Institute of Japan (NMIJ) and National Institute of Standards and Technology (NIST) acted as the coordinating laboratories.
Results were submitted by 11 NMIs and DIs. The participants used different measurement methods, though most of them used inductively coupled plasma-mass spectrometry (ICP-MS), isotope dilution technique with ICP-MS and inductively coupled plasma-optical emission spectrometry (ICP-OES) with microwave acid digestion.
The material was quite challenging and a number of questions were raised at the IAWG meeting. Concerning S, the variation in S results between participants, particularly those using IDMS methods was discussed at the IAWG meeting. BAM, NIST and NMIJ reviewed their experimental conditions, results and/or uncertainty calculations for IDMS. According to the additional evaluation and investigation, the variances between the revised results became smaller than the original one, the revised results were overlapping between IDMS measurements of S content at the k=2 level. It is not possible to calculate a KCRV with values being modified after submission. It was concluded that this KC does not support S measurements.
Accounting for relative expanded uncertainty, comparability of measurement results for each of Na, Ca, K, Mg and P was successfully demonstrated by the participating NMIs or DIs. It is expected that sodium, calcium, potassium, magnesium and phosphorus at mass fractions greater than approximately 0.1 mg/kg, 0.1 mg/kg, 0.05 mg/kg, 0.05 mg/kg and 0.1 mg/kg respectively in biodiesel fuel and similar matrices (fuels and oils etc.) can be determined by each participant using the same technique(s) employed for this key comparison to achieve similar uncertainties mentioned in the present report. Furthermore, the results of this key comparison can be utilized along with the IAWG core capability approach.