CIPM MRA COMPARISON REPORTS

The CCQM-K169 key comparison on assay of sodium oxalate was jointly organized by the electrochemical analysis working group (EAWG) and inorganic analysis working group (IAWG) of the CCQM to test the abilities of the national metrology institutes (NMIs) to measure the amount content of reductants in high purity substances as well as assaying high purity salts to be used as primary standards. Reductants have not been measured in comparisons for assay of high purity salts yet. Five NMIs participated in this key comparison. The comparison was initiated by NMIJ (Japan), but it was postponed due to COVID-19 pandemic.

Later, NMIJ had to withdraw from participating and piloting. Finally, VNIIM (Russian Federation) acted as a coordinating laboratory. Participating institutes could use a method of their choice. Constant current coulometry and/or gravimetric titrimetry were used.

The spread of the results is larger than typically observed in key comparisons of high purity salts assays. It may be related to a new analyte (reductants have never been measured in key comparisons before), complicated measurement procedure, a small number of participants, and because at least two laboratories experienced in assaying sodium oxalate did not participate. Nevertheless, four out of five NMIs were in reasonable agreement with the key comparison reference value.

Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.

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).