Westwood S.,Coordinating laboratory |
Josephs R.,Coordinating laboratory |
Choteau T.,Coordinating laboratory |
Daireaux A.,Coordinating laboratory |
Wielgosz R.,Coordinating laboratory
Metrologia | Year: 2014
The CCQM-K55 comparison was undertaken by the CCQM Organic Analysis Working Group (OAWG) for National Measurement Institutes (NMIs) and Designated Institutes (DIs) which provide measurement services in organic analysis under the CIPM Mutual Recognition Arrangement (MRA). The BIPM coordinated the final two rounds of the CCQM-P20 pilot study and developed a 'molar mass v. polarity' model to map the analytical space for comparisons in this area. This model provided the criteria for the selection of the measurands for each of the four consecutive rounds respectively CCQM-K55.a, CCQM-K55.b, CCQM-K55.c and CCQM-K55.d that make up the initial CCQM-K55 key comparison. The mass fraction content of valine in the comparison material was assessed by the BIPM to be in excess of 990 mg/g and the homogeneity and stability of the valine and the associated impurity components were determined as being suitable for the purposes of the comparison. the case of amino acids in general and valine in particular, LC-based and qNMR methods appeared to be more consistent and sensitive and less variable than GC methods requiring a preliminary derivatization step. In cases where a participant's mass balance result for valine was not in agreement with the KCRV the likely source of the deviation could be identified.