Certified reference materials

Certified reference materials (CRMs) are 'controls' or standards used to check the quality and metrological traceability of products, to validate analytical measurement methods, or for the calibration of instruments.^[1] A certified reference material is a particular form of measurement standard.

Reference materials are particularly important for analytical chemistry and clinical analysis.^[2] Since most analytical instrumentation is comparative, it requires a sample of known composition (reference material) for accurate calibration. These reference materials are produced under stringent manufacturing procedures and differ from laboratory reagents in their certification and the traceability of the data provided.

Quality management systems involving laboratory accreditation under national and international accreditation/certification standards such as ISO/IEC 17025 require metrological traceability to Certified Reference Materials (where possible) when using reference materials for calibration.^[3]

Whilst Certified Reference Materials are preferred where available,^[3][4] their availability is limited. Reference Materials that do not meet all the criteria for certified reference materials are more widely available: the principal difference is the additional evidence of metrological traceability and statement of measurement uncertainty provided on the certificate for certified reference materials.^[5]

ISO REMCO, the ISO committee responsible for guidance on reference materials within ISO,^[6] defines the following classes of reference material:^[7][8]

Other bodies may define classes of reference material differently. WHO guidelines for biological^{[nb 1]} reference materials ^[9] provide the terms:^{[nb 2]}

Green Tea standard reference

Standard reference peanut butter.

Schematic of a balanced nested design for a CRM homogeneity test. Large bottles show packaged individual CRM units; small vials show subsamples prepared for measurement.