Certification of major and trace elements in a Leucomonzogranite, GMN-1, using the GeoPT proficiency testing certification protocol

In the past, many geochemical reference materials have been characterised either by the compilation of data published in the research literature, or by relatively informal ‘round-robin’ type of collaborative analysis programme. Neither approach complies with the most recent recommendations in ISO-REMCO Guide 35:2017. In order to develop a more rigorous approach that would lead to the full certification of such materials, Potts et al. (2019) published a certification protocol based on the well established GeoPT proficiency testing programme designed for laboratories that routinely analyse silicate rocks and related materials. In developing this certification protocol, a full assessment of compliance with the most recent version of ISO-REMCO Guide 35 was undertaken.
This protocol has now been applied to the certification of a leucomonzogranite (GMN-1), based on round 51 of the GeoPT programme that included participation by 112 laboratories from 43 countries. This exercise has led to the certification of 9 major and 39 trace elements.
In the development of this protocol, a number of issues remain that are not fully resolved in Guide 35. One is the potential clash between the requirements of proficiency testing in relation to procedures recommended for certification, perhaps the most important being the way in which well characterized consensus values derived from an assessment of data contributed to the proficiency testing programme effectively demonstrate the property of traceability.

Potts P J, Webb P C and Thompson M (2019). The GeoPT proficiency testing programme as a scheme for the certification of geological reference materials. Geostandards and Geoanalytical Research, 43, 409-418, doi: 10.1111/ggr.12261.