A CRM is a certified reference material, accompanied by a certificate (issued by an authoritative body) that provides the value of one or more specified properties, along with their associated uncertainty and a statement of metrological traceability.

Only materials that are sufficiently homogeneous and stable over time can become CRMs. Indeed, they could be stored for several years without modification of their certified values.

The certified values of a CRM are usually established after an inter-laboratory study: the material to be certified is sent to several qualified laboratories (each using its own method). The results are then compiled to determine the certified values and their associated uncertainty. The CRM certification process is therefore time-consuming and expensive.

SRMs (= standard reference solutions) also exist. They can be used to help validate methods of analysis, or to “spike” a sample with known levels in order to calculate the recovery.

In Europe, the European Reference Materials consortium is the authority that provides new CRMs (http://www.erm-crm.org).
Other bodies exist, such as the NIST (National Institute of Standards and Technology) in the USA.