On matrix reference materials characterised by proficiency test

Abstract

This paper examines the status of a matrix reference material characterised by the consensus of the results from a proficiency test. It is shown that the very existence of a consensus in chemical measurement attests to its validity. Unique biases in individual laboratories are largely averaged out in forming the consensus. All of the variation between laboratories' results (including that resulting from the unique biases) will be encompassed by the standard error of the consensus. Any common bias among the laboratories remains unknowable. The supposed absence of traceability in a consensus can be overcome by obtaining appropriate information from the selected participants. More fundamentally it is shown that, in any event, a traceability chain is indeed broken in many types of chemical measurement, without detriment to the validity of the result. The overall conclusion is that, with carefully considered safeguards, characterisation of matrix reference materials by proficiency testing is appropriate to establish the concentrations of selected analytes.