Proficency Testing Scheme — Details

The FIRMS PT Scheme consists of two rounds of analyses per year with each round consisting 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 and then reports are prepared (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.


Following the first two years of this scheme, LGC PT has been able to extend their scope of accreditation to ISO17043 to include the FIRMS PT scheme. The previous results have also allowed slight modifications to the interpretation of the results to be implemented for future rounds: For C and N isotope ratios the z-scores are now calculated using a fixed standard deviation of performance assessment (of 0.15 permil) rather than the robust standard deviation arising from the participant data. For H and O there is insufficient data at this time to be able to do the same.

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

Read the FIRMS Scheme Description. (PDF format)


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