Not all reference materials carry the same analytical authority. The distinction between a certified reference material (CRM) and a characterised in-house standard is significant — and frequently misunderstood.
Certified Reference Material (CRM):
– Certified values are established through inter laboratory collaboration, typically involving 15–30+ independent laboratories.
– Uncertainty is expressed as a 95% confidence interval derived from statistical analysis of all participant results.
– Metrological traceability is documented — results are traceable to SI units through defined reference methods.
– Homogeneity and stability are tested and documented.
In-house control sample:
– Values are typically assigned by a single laboratory or a small set of laboratories.
– Uncertainty may not be formally quantified.
– Useful for monitoring internal consistency and precision — not for validating accuracy.
In a well-designed QA/QC program, both types are needed. CRMs anchor the accuracy of the system to an externally verified truth. In-house standards track precision and detect within-laboratory drift.
A CRM inserted at 1 per 20 samples provides ~5% coverage for accuracy monitoring. For high-value or high-risk campaigns, 1 per 10 is preferred — particularly where regulatory reporting depends on the data.
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