SRM Definitions

Reference Material (RM) - Material, sufficiently homogeneous and stable with respect to one or more specified properties, which has been established to be fit for its intended use in a measurement process.

1. RM is a generic term.
2. Properties can be quantitative or qualitative, e.g. identity of substances or species.
3. Uses may include the calibration of a measurement system, assessment of a measurement procedure, assigning values to other materials, and quality control.
4. A single RM cannot be used for both calibration and validation of results in the same measurement procedure.
5. International Vocabulary of Metrology – Basic and General Concepts and Associated Terms has an analogous definition (VIM - ISO/IEC Guide 99:2007, 5.13), but restricts the term "measurement" to apply to quantitative values and not to qualitative properties. However, Note 3 of ISO/IEC Guide 99:2007, 5.13, specifically includes the concept of qualitative attributes, called "nominal properties".

(ISO Guide 30:2015)

Certified Reference Material (CRM) - Reference material characterized by a metrologically valid procedure for one or more specified properties, accompanied by a certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability.

1. The concept of value includes qualitative attributes such as identity or sequence. Uncertainties for such attributes may be expressed as probabilities.
2. Metrologically valid procedures for the production and certification of reference materials are given in, among others, ISO 17034:2016 and ISO 33405:2024.
3. ISO 33401:2024 gives guidance on the contents of certificates.
4. VIM has an analogous definition (ISO/IEC Guide 99:2007, 5.14).

(ISO Guide 30:2015)

Reference Material Certificate - Document accompanying a certified reference material stating one or more property values and their uncertainties, and confirming that the necessary procedures have been carried out to ensure their validity and traceability (ISO Guide 30:2015).

NIST Standard Reference Material® (SRM) - NIST CRMs that deliver values certified by NIST.  All SRMs deliver at least one certified property value that is:

1. Metrologically traceable to an internationally recognized higher-order reference system, such as the SI, and
2. Deemed by NIST to be suitable for providing unbiased calibration and/or validation of measurement procedures.

SRMs may also deliver non-certified information. The certified and non-certified values are described in separate sections within the SRM’s documentation: a “Certificate” for physical or engineering performance properties and a “Certificate of Analysis ” for specific chemical properties.

SRMs are issued as “SRM x” where “x” is typically a series of digits from 1 to 5999, with an alphabetic or lot number suffix indicating re-issues.

Note: “Standard Reference Material” and “SRM” are trademarks registered to NIST by the United States Patent and Trademark Office.

NIST Reference Material – Reference materials that deliver property values for established measurands that are fit for the materials’ intended uses, including between-method harmonization, within-method precision assessment, and process stability assessment. RMs are issued as “RM 8xxx,” where the “xxx” is a unique series of three digits. These materials and values have historically been described in a “Report of Investigation” rather than a Certificate or Certificate of Analysis. For RMs developed after July 2020, these documents are termed “Reference Material Information Sheets.”

NIST Research Grade Test Material (RGTM) - A material evaluated during the SRM/RM development phase.  RGTMs may be distributed in a NIST-sponsored interlaboratory inter-comparison to determine the fit for purpose of the candidate SRM/RM material.  It is prepared to be homogeneous and stable but typically has not been quantitatively evaluated for all properties of potential interest.

NIST Traceable Reference Material^TM (NTRM^TM) -  A CRM that is certified by NIST in collaboration with a secondary standards producer and have a well-defined metrological traceability linkage to existing SRMs or PSs. This linkage is established via criteria and protocols defined by NIST to meet the needs of the community served. Reference materials producers adhering to these requirements can sell the materials using the "NTRM" Certification Mark (CM). The certified values are described in a “Certificate of Traceability.” The ongoing specialty gas NTRM program (NIST SP 260-126, NIST SP 260-126 Rev 2013) was established in 1992 in partnership with the US Environmental Protection Agency (EPA). A spectrophotometric filter program (NIST SP 260-140) was initiated in the late 1990s and ended in 2005.

NIST Certified Value - A value reported on an SRM certificate or certificate of analysis for which NIST has the highest confidence in its accuracy in that all known or suspected sources of bias have been fully investigated or accounted for by NIST. (NIST SP 260-136).

NIST Non-Certified Value - A best estimate of the true value based on currently available information; however, they do not meet NIST’s criteria for certification (NIST SP 260-136).

Reference, Information, and Indicative Values - From 1987 until July 2020, NIST non-certified values were called “NIST Reference Values” if a potentially incomplete uncertainty estimate was associated with the value. Values without any associated uncertainty were called “NIST Information Values.” Some reference materials from other providers describe non-certified information as “indicative values.” NIST does not use this term.

NIST SRM Certificate or Certificate of Analysis - In accordance with ISO 33401:2024, a NIST SRM certificate is a document containing the name, description, and intended purpose of the material, the NIST logo, the name of NIST as a certifying body, instructions for proper use and storage of the material, certified property value(s) with associated uncertainty(ies), method(s) used to obtain property values, the period of validity, if appropriate, and any other technical information deemed necessary for its proper use. A Certificate is issued for an SRM certified for one or more specific physical or engineering performance properties and may contain NIST reference, information, or both values in addition to certified values. A Certificate of Analysis is issued for an SRM certified for one or more specific chemical properties.

NIST RM Reference Material Information Sheet - Document issued with a NIST RM that contains all the technical information necessary for proper use of the material, the NIST logo, and the name and title of the NIST officer authorized to issue it. There are no NIST certified values provided, and authorship of an information sheet's contents may be by an organization other than NIST.

Status - SRM/RMs can have one the following status values:

NIST Special Publication (SP) 260-136 - Metrological Tools for the Reference Materials and Reference Instruments of the NIST Material Measurement Laboratory.  This publication is available free of charge from: https://doi.org/10.6028/NIST.SP.260-136-2021

NIST Special Publication (SP) 260-126 (1996)- The NIST Traceable Reference Material Program for Gas Standards.  This publication is available free of charge from: https://doi.org/10.6028/NIST.SP.260-126

NIST Special Publication (SP) 260-126 Rev 2013 (2013)- The NIST Traceable Reference Material Program for Gas Standards.  This publication is available free of charge from: https://doi.org/10.6028/NIST.SP.260-126rev2013

NIST Special Publication (SP) 260-140 - Technical Specifications for Certification of Spectrophotometric NTRMs.  This publication is available free of charge from: https://doi.org/10.6028/NIST.SP.260-140