ISO Guide 35:2017 provides, for the first time, an alternative way of characterising certified reference materials using proficiency testing. In this paper, the properties of assigned values derived from the well-established Geo<i>PT</i> proficiency testing scheme are examined. This scheme, designed for laboratories that undertake the routine analysis of silicate rocks and related materials, routinely has over 100 participants contributing results. Following a detailed assessment of the metrological properties of Geo<i>PT</i> assigned values in relation to Guide 35 recommendations, it is demonstrated that these values may be regarded as certified values, provided a number of criteria are met. These criteria include: a demonstration of sufficient homogeneity of the candidate CRM; circulation, when judged to be appropriate of an established matrix-matched CRM for co-analysis in that round; the robust statistical analysis of data sets using Geo<i>PT</i> established-criteria to decide whether assigning a value is justified (based on a minimum of fifteen valid results);an expert group to manage the certification and the maintenance of appropriate records.In summary, the Geo<i>PT</i> proficiency testing scheme, subject to the arrangements summarised above, is considered to be competent for the certification of geological reference materials.
Potts, Philip J. ; Webb, Peter C. and Thompson, Michael (2019). The GeoPT Proficiency Testing Programme as a Scheme for the Certification of Geological Reference Materials. Geostandards and Geoanalytical Research (Early Access).
Potts, Philip J. ; Webb, Peter C. and Thompson, Michael (2019). The GeoPT Proficiency Testing Programme as a Scheme for the Certification of Geological Reference Materials. Geostandards and Geoanalytical Research, 43(3) pp. 409–418.