Proficency Testing Scheme — Details

The FIRMS PT Scheme consistsconsists of one round of analyses per year, of two different materials. These materials are tested for homogeneity prior to shipping. Participants are given approximately 6 weeks between material distribution and the deadline for result submission. Results should be submitted as 10 replicate analyses for each isotope ratio for each material with a “nominated” laboratory result consisting of the mean of these replicates together with an indication of the uncertainty in this value (at a minimum the standard deviation of the replicates).

While material selection is controlled by the FIRMS Steering Group, the PT results are collated by LGC PT. LGC PT's scope of accreditation includes the FIRMS PT scheme.

In providing the PT, LGC PT acts as a sub-contractor. However, as a PT provider accredited to ISO/IEC 17043, LGC PT is responsible for the quality of PTs which are part of the FIRMS scheme. To be clear, FIRMS is not accredited for the provision of PTs, LGC PT is.


Results are presented in reports: an anonymised “main” report as well as tailored “individual” reports for each laboratory. Laboratory performance is assessed via z-scores with scores of <2 being satisfactory, between 2 and 3 being questionable and over 3 being unsatisfactory.

The interpretation of results relies on the ‘standard deviation for proficiency assessment’ (SDPA), which is used to assess participant performance for the measurement of each measurand. These are currently 1.5 for H, 0.15 for C and N, and 0.25 for O.

Click here to download LGC's Terms and Conditions (PDF)

Read the FIRMS Scheme Description. (PDF format)


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