CCQM-K44 was an activity of the Inorganic Analysis Working Group (IAWG) of CCQM and was coordinated by the Joint Research Centre–Institute for Reference Materials and Measurements (IRMM, Geel, Belgium) of the European Commission (EC). In CCQM-K44 the amount contents of Cd, Cr, Cu, Pb, Hg, Ni and Zn in sewage sludge were the measurands under investigation. Results were reported by six national metrology institutes (NMIs). During the CCQM–IAWG Spring meeting in Paris, April 2006, the approaches to calculate the KCRV as proposed by the coordinating laboratory were discussed and agreed on. The final report was submitted in June 2006. After the final report had been submitted to the CCQM in June 2006 the coordinating laboratory was informed that MIRS/IJS was not a designated institute and therefore could not represent the Slovenian NMI in CCQM-K44. This was contrary to what MIRS confirmed to the coordinating laboratory at the beginning of CCQM-K44. After several discussions between MIRS and the CCQM the coordinating laboratory was asked to amend the final report accordingly. In this revised version of the CCQM-K44 final report the results of MIRS/IJS were taken out of CCQM-K44 and included in the pilot study CCQM-P70, which was organised in parallel to CCQM-K44.

Due to the limited number of participants compared to previous key comparisons the mixture model median (MM-median) of all reported results could not be applied as KCRV for all the measurands. During the CCQM–IAWG Spring meeting in Paris, April 2006, the approaches to calculate the KCRV as proposed by the coordinating laboratory were discussed and first agreed on. As a result the final report and degrees of equivalence were finalised and submitted to the CCQM. Subsequent discussions between the IAWG and the CCQM were held, resulting in a different approach as proposed by the coordinating laboratory. Particularly Maurice Cox from NPL recommended the weighted mean and its standard uncertainty (k = 1) as KCRV independently of the number of participants. The coordinating laboratory agreed to this proposal and amended the final report using the weighted mean KCRV in CCQM-K44 for all measurands.

The reported results of the NMIs fall within a range of ±4% deviation from the KCRVs for Cr and Hg. For Pb and Cu the NMIs reported results within ±9%. For Zn the spread of all laboratories but one is ±2%. For Cd two of the three participating NMIs reported results within ±0.2% from the KCRV. The coordinating laboratory agreed with BAM, CENAM and LNE that due to the observed spread of the results Ni will be reported as inconclusive and no KCRV or degrees of equivalence for Ni will be included in this report.

The methods applied were isotope dilution mass spectrometry (IDMS) using quadrupole inductively coupled plasma-mass spectrometry (ICP-MS) or thermal ionisation mass spectrometry (TIMS), external calibration using atomic absorption spectrometry (AAS).

K₀-neutron activation analysis (k₀-NAA) and x-ray fluorescence (XRF) were also used as analytical techniques.

This final report presents the participants' results in CCQM-K44 for all analytes under investigation. In Annex 1, the results with the KCRV are presented. In Annex 2, the questionnaire data are presented.

The pilot study CCQM-P70 was carried out in parallel to this key comparison for the same measurands in the same sewage sludge material. Participation was meant for IAWG members, who did not immediately want to report results in a key comparison, and invited expert laboratories.

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 (MRA).