Final report on CCQM-K87: Mono-elemental calibration solutions

Abstract

The aim of this comparison was to demonstrate the capability of national metrology institutes to measure elemental mass fractions at a level of w(E) ≈ 1 g/kg as found in almost all mono-elemental calibration solutions. These calibration solutions represent an important link in traceability systems in inorganic analysis. Virtually all traceable routine measurements are linked to the SI through these calibration solutions. Every participant was provided with three solutions of each of the three selected elements chromium, cobalt and lead. This comparison was a joint activity of the Inorganic Analysis Working Group (IAWG) and the Electrochemical Analysis Working Group (EAWG) of the CCQM and was piloted by the Physikalisch-Technische Bundesanstalt (PTB, Braunschweig, Germany) with the help of the Bundesanstalt für Materialforschung und -prüfung (BAM, Berlin, Germany), the Centro Nacional de Metrología (CENAM, Querétaro, Mexico) and the National Institute of Standards and Technology (NIST, Gaithersburg, USA).A small majority of participants applied inductively coupled plasma optical emission spectrometry (ICP OES) in combination with a variety of calibration strategies (one-point-calibration, bracketing, calibration curve, each with and without an internal standard). But also IDMS techniques were carried out on quadrupole, high resolution and multicollector ICP-MS machines as well as a TIMS machine. Several participants applied titrimetry. FAAS as well as ICP-MS combined with non-IDMS calibration strategies were used by at least one participant. The key comparison reference values (KCRV) were agreed upon during the IAWG/EAWG meeting in November 2011 held in Sydney as the added element content calculated from the gravimetric sample preparation. Accordingly the degrees of equivalence were calculated. Despite the large variety of methods applied no superior method could be identified. The relative deviation of the median of the participants' results from the gravimetric reference value was equal or smaller than 0.1% (with an average of 0.05%) in the case of all three elements.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The linkup of mono-elemental solutions to the SI using INAA: a measurement procedure and the achievable uncertainty

“…The expanded measurement uncertainty of the linkup must be less than 0.1 % to achieve a calibration measurement of commercial solutions with an expanded uncertainty associated with the mass fraction of 0.3 %. Overall, this procedure demonstrates an unbroken chain of calibrations to link up the measurement results in the field to the SI [3].…”

Preparation and characterization of primary magnesium mixtures for the ab initio calibration of absolute magnesium isotope ratio measurements

“…[38][39][40] The weighing and dissolution of the enriched, puried materials were carried out such that relative expanded uncertainties for the Mg mass fraction between 0.0037% and 0.0050% could be achieved. As a comparison, primary solutions which were used for the CCQM key comparison K87 offer relative expanded uncertainties of z0.1% for elemental mass fractions of 1 g kg, 41 and primary standards used as back-spike in IDMS were commonly produced with relative expanded uncertainties down to 0.02%. 33 In the case of Mg the smallest relative expanded uncertainty being published is 0.018% and relates to the primary solution used for the CCQM key comparison K8.…”

Gravimetric Complexometric Titration Method to Determine Mass Fraction of Ethylenediaminetetraacetic Acid Disodium Salt Dihydrate in Candidate-Certified Reference Materials

“…Under such circumstances, A o r ðPbÞ would be the unique significant uncertainty source with a relative contribution of 98 %. As previously noted by other authors, measuring a more precise value for the atomic weight of lead that applies to the material in use is key to decreasing the impact of this parameter on the uncertainty budget of the final result [12,16].…”

“…The characterization of mono-elemental calibration solutions requires the accurate determination of the mass fraction of the element in the solution (typically around 1000 mg kg À1 ), with a relative standard uncertainty expected to be better than 0.15 % [9]. These requirements can be met by complexometric titration with ethylenediaminetetraacetic acid (EDTA), a classical analytical method introduced more than 70 years ago [10] that is capable of outperforming instrumental techniques such as atomic absorption spectrometry (AAS) and Inductively Coupled Mass Spectrometry (ICP-MS) for this kind of applications [11,12].…”