INTERNATIONAL STANDARD | ISO GUIDE 35 Fourth edition 2017-08 | ||
Reference materials — Guidance for characterization and assessment of homogeneity and stability Matériaux de référence — Lignes directrices pour la caractérisation et l'évaluation de l'homogénéité et de la stabilité | |||
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This document was prepared by Technical Committee ISO/REMCO, the Reference Materials Committee of ISO.
This fourth edition cancels and replaces the third edition (ISO Guide 35:2006).
The production of reference materials (RMs) is a key activity for the improvement and maintenance of a worldwide coherent measurement system. As detailed in ISO Guide 33[1], RMs with different characteristics are used in measurements, such as calibration, quality control, proficiency testing and method validation, as well as for the assignment of values to other materials. Certified reference materials (CRMs) are also used to confirm or establish metrological traceability to conventional scales, such as the octane number, hardness scales and pH.
To be comparable across borders and over time, measurements need to be traceable to appropriate and stated references. CRMs play a key role in implementing the concept of traceability of measurement results in chemistry, biology and physics among other sciences dealing with substances and materials. Laboratories use these CRMs as readily accessible measurement standards to establish traceability of their measurement results to International Standards. The property values carried by a CRM can be made traceable to the International System of Units (SI) or other internationally agreed references during production. This document explains how approaches can be developed that will lead to well established property values, which are made traceable to appropriate stated references.
For reference material producers (RMPs), there is an International Standard and three ISO Guides that support the production and certification of RMs to ensure that the quality of the RMs meets the requirements of the end users.
ISO 17034 outlines the general requirements to be met by an RMP to demonstrate competence.
ISO Guide 35 provides more specific guidance on technical issues and explains the concepts for processes such as the assessment of homogeneity, stability and characterization for the certification of RMs.
ISO Guide 31[2] describes the contents of certificates for CRMs, and of accompanying documents for other RMs, respectively.
ISO Guide 30[68] contains the terms and definitions related to reference materials.
Alongside developments in RM production approaches, the range of classes of RMs is growing with advances in technology, increasing the need for more widely applicable technical guidance in RM production. In addition, increasing use of ISO/IEC 17025[52] and ISO 15189[71] by laboratories has led to greater demand for clear statements of metrological traceability.
This document provides detailed guidance on a larger range of homogeneity study designs, and describes a wider range of stability management strategies than ISO Guide 35:2006. It also contains specific provisions concerning the establishment of metrological traceability in RM production.
This document explains concepts and provides approaches to the following aspects of the production of reference materials:
the assessment of homogeneity;
the assessment of stability and the management of the risks associated with possible stability issues related to the properties of interest;
the characterization and value assignment of properties of a reference material;
the evaluation of uncertainty for certified values;
the establishment of the metrological traceability of certified property values.
The guidance given supports the implementation of ISO 17034. Other approaches may also be used as long as the requirements of ISO 17034 are fulfilled.
Brief guidance on the need for commutability assessment (6.11) is given in this document, but no technical details are provided. A brief introduction for the characterization of qualitative properties (9.6 to 9.10) is provided together with brief guidance on sampling such materials for homogeneity tests (Clause 7). However, statistical methods for the assessment of the homogeneity and stability of reference materials for qualitative properties are not covered. This document is also not applicable to multivariate quantities, such as spectral data.
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
NOTE The International vocabulary of metrology will hereafter be referred to as the “VIM”. |
For the purposes of this document, the terms and definitions given in ISO Guide 30, ISO/IEC Guide 99, ISO 3534-2, ISO 3534-3 and the following apply. The definitions in ISO Guide 30 take precedence where more than one definition for the same term exists.
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ISO Online browsing platform: available at http://www.iso.org/obp
IEC Electropedia: available at http://www.electropedia.org/
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1 Withdrawn standard.