The terminology problem
Reference material, certified reference material, standard reference material, reference standard — the terms overlap and are often used interchangeably, which makes sourcing harder than it needs to be. The difference between them is documentation depth and formal certification, not chemistry.
Reference material, certified reference material, and standard reference material
A reference material is any stable, homogeneous material characterized for one or more properties — the broadest term. A certified reference material is a reference material accompanied by a certificate stating those property values with their uncertainty and metrological traceability. "Standard Reference Material" is the trademarked name for the certified reference materials issued by the National Institute of Standards and Technology (NIST).
Where a reference standard fits
A reference standard is the practical, lab-facing version of the same idea: a characterized material used as a baseline for identity, purity, and calibration in a specific workflow. Where the SRM label points to formal certification by a national metrology institute, a reference standard points to a material whose certificate documents the measurements your workflow depends on.
Choosing the right term — and the right material
For most in vitro analytical work, the material's certificate matters more than which label it carries. Confirm identity, purity, and content are reported for the exact lot in your hand, and that the documentation names the method that produced each number. That is what makes a material usable as a fixed point, whatever it is called.