Reference Materials and Working Standards

VIM describes a reference material through properties sufficiently homogeneous and stable for a defined use. A working standard is distinguished by routine use in calibration or verification. Both names can describe aspects of the same material. Reference material, working standard.

Documentation for a certified material adds specified values, uncertainties and traceability. Certified material definition.

Establishing an international C-peptide standard included assigning a value to a primary calibrant, transferring it to the candidate material through a chromatographic assay and then comparing its behavior in immunoassays.

Each stage answered a different question. Characterizing the calibrant did not remove the need to evaluate the distributed material. To interpret a similar chain, identify the originating value, the procedure transferring it and the specific preparation to which the final result applies. Establishment study.

In developing a certified human-insulin material, researchers evaluated identity, accompanying components and value assignment through complementary procedures. They also studied homogeneity and stability.

These checks serve different functions: molecular characterization does not show that all units are equivalent, and a homogeneity test does not establish how long they will retain their properties. The findings concern the studied material and conditions; they are not storage instructions for other preparations. Certified insulin material.

The C-peptide standard study examined its commutability with human serum and urine samples. Behavior was appropriate in most laboratories, but there were exceptions.

This result prevents an overly broad conclusion: adopting an international standard does not automatically demonstrate equivalence in every method–sample combination. Evidence for use matters as much as value assignment. The report should retain exceptions rather than summarize them as universal acceptance.

Both studies show documentation extending beyond the analyte's name. To review a working standard, look for its identity, the value used, the comparison supporting it and the preparation to which it applies.

When the material changes, the question is which evidence connects the new preparation with the previous one. An identical label does not document that continuity. Nor should stability observed in another study become an expiry date for a different vial.