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Information for ISO Guide 80

Guidance for in-house Production of Reference Materials for Quality Control (QCMs)

ISO Guide 80 is preparing by WG8 of ISO Reference Materials Committee (REMCO), which is concerned with guidelines for the preparation, certification and use of reference materials (RMs) and certified reference materials (CRMs).The 35th ISO/REMCO meeting will be held on June 19-22 in Austria. An extract of the Introduction and Scope is noted below.

Introduction
Reference materials (RMs) are widely used in measurement laboratories for a variety of purposes. However, it is important to recognize that the material most appropriate for a particular application should be used. Certified reference materials (CRMs) i.e. those which have property values and associated uncertainties assigned by metrologically valid procedures are primarily used for method validation and calibrations providing traceability.

For metrological quality control purposes, such as demonstrating a measurement system is under statistical control, performs as expected and provides reliable results; where the accuracy of the measurement result is not critical, reference materials which are sufficiently homogeneous and stable can be used. For the purposes of this Guide such materials will be termed ‘Quality Control Materials’ (QCM).

While CRMs are produced by established reference materials producers and are commercially available, QCMs are often produced by a laboratory for its own internal use and are often referred to in the laboratory’s quality documentation as well as in the published literature as in-house reference materials, quality control materials, check samples, etc. Frequently QCMs are characterized only for limited scope, e.g. limited number of analytes and for specific laboratory applications.

The rationale for producing quality control materials can be one or a combination of the following factors:

  • to have a RM representing as closely as possible routine samples, suitable for quality control;
  • to have a suitable day-to-day RM to complement a commercially available CRM;
  • where no suitable CRM is available;
  • where the application does not require a material having the full characteristics of a CRM (e.g. traceability and uncertainty).

Where no suitable CRM is available, laboratories may use QCMs to provide an assessment of the repeatability of a measurement result. QCMs should not be used to establish metrological traceability of a measurement result nor for validation purposes.

However, QCMs should always comply with the basic requirements of any reference material i.e. they must be sufficiently homogeneous and stable. The level of inhomogeneity should be less than the expected standard deviation of the measurement process or an established criterion value against which the assessment of laboratory performance or the “normalization” of results is acceptable. The QCM must be stable for a period of time that is at least as long as that during which it is intended to be used.

The production of a QCM is related to that of a CRM and a producer of a QCM may wish to consult ISO Guides 34 and 35 for further guidance and where appropriate, this Guide will refer to relevant parts of these Guides. Finally, this document cannot substitute for “critical thinking, intellectual honesty, and professional skill”. The quality of any QCM depends as much on these factors as on the use of well-established and valid procedures and methods.

The layout and structure of this Guide provides general information on the production of QCMs in the main chapters, with specific case studies in the annex. The case studies are not complete “process manuals” but are included to highlight some of the key considerations when preparing QCMs. It is expected that the in-house QCM producer will have some knowledge of the type of material to be prepared.

Scope
The production of reference materials for metrological quality control is an important activity which provides materials suitable for the day-to-day demonstration that a particular (part of a) measurement system is under statistical control. Such materials do not require characterization by metrologically valid procedures, and can be prepared by ‘in-house’ i.e. by laboratory staff, to fulfill specific quality control requirements.

This Guide outlines the essential characteristics of, and describes the processes by which reference materials for quality control purposes can be produced ‘in-house’.

For the purposes of this Guide, such materials are generically termed ‘QCMs’ and include materials referred to in the open literature as "in-house reference materials", "quality control materials", "check samples”, “set up samples” etc.

The production of quality control materials is similar to the production of reference materials (RMs), as described in ISO Guide 34 and ISO Guide 35. Much of the content of these Guides is equally applicable to the production of QCMs. However, the requirements for ‘in-house’ QCMs are different from those for a CRM. The quality assessment of QCMs should involve homogeneity and stability assessments, and characterization of the material prior to use. Value assignment, establishment of traceability, uncertainty determination and extensive stability testing are not required for this type of reference material and these processes are not described in this Guide.

This document provides the quality criteria that a material must fulfill to be considered fit-for-purpose for demonstrating a measurement system is under statistical control. Uses of such materials, for example setting up a quality control (QC) chart, are adequately covered elsewhere and are not included in this Guide.

This Guide provides some general information on the production of QCMs which is complemented with a number of specific case studies. The case studies are not complete “process manuals” but are included to highlight some of the key considerations when preparing QCMs.

The primary target audience for this Guide is laboratory staff who are required to prepare materials for specific quality control applications. Commercial producers of QCMs, where transportation is a necessary component of the supply chain, are expected to be familiar with and conform to the requirements of ISO Guides 34 and 35.

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