Reference material producer

ISO Guide 34 (1996) Quality system guidehnes for the production of reference materials. (Revised March 1998 as ISO/REMCO document No 464 General requirements for the competence of reference material producers . The revised Guide 34 will appear early 2000.) International Organization for Standardization, Geneva. 

Not all reference materials producers currently employ the various techniques that would characterize materials for microanalytical use. Such techniques include measurement of particle size distribution, particle composition, and the determination of component homogeneity with microanalytical techniques. Nevertheless, some... 

ISO Document N 464 (1998) General requirements for the competence of reference materials producers, revised ISO Guide 34. International Standards Organization, Geneva. 

The revised database holds over 23 000 analyte values for 660 measurands and 1670 reference materials produced by 56 different producers, from 22 countries. The database is restricted to natural matrix materials (i.e. made from naturally occurring materials, excluding calibration standards manufactured from pure chemicals). Information has been extracted from the relevant certificates of analysis, information sheets, and other reports provided by the reference material producers. As a general rule, the authors have only included in the compilation reference materials for which a certificate of analysis or similar documentation is on file. Information included in the survey is on values for measurands determined in reference materials, producers, suppliers, the cost of the materials, the unit size supplied, and the recommended minimum weight of material for analysis, if available. The new searchable database has been designed to help analysts to select reference materials for quality assurance purposes that match as closely as possible, with respect to matrix type and concentrations of the measurands of interest and their samples to be analyzed see Table 8.3. 

As usually viewed by the reference material producers, a fundamental philosophy of certification rests on the concept of independent methodology, which is the application of theoretically and experimentally different measurement techniques and procedures to generate concordant results leading to one reliable assigned value for the property. Such assigned values are thus method-independent. Extractable concentrations are generated by specific procedures and are thus method-dependent, an idea that has to be rationalized with the fundamental method-independent concept in reference material certification work. 

Some reference material producers/suppliers use different names to describe their materials. For example, a Standard Reference Material (SRM) is a certified reference material issued by the National Institute of Standards and Technology (NIST), while European Reference Materials (ERMs) are CRMs produced under a joint collaboration between three European reference materials producers, i.e. BAM (Federal Institute for Materials Research and Testing, Germany), IRMM (European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Belgium) and LGC (UK). 

General Requirements for the Competence of Reference Materials Producers , ISO Guide 34, International Organization for Standardization (ISO), Geneva, Switzerland, 2000. 

Homogeneity. Homogeneity assures that the analysis of all subsamples of the reference material taken for measurement will produce the same analytical result within the stated measurement uncertainty. This is particularly important in the case of certified reference materials. Reference material producers therefore must specify the minimum amount of sample for which homogeneity has been measured and is valid. Finally, the ease of re-homogenizing the material after packaging must be taken into consideration. 

The preparation of a reference material requires substantial planning prior to undertaking a specific project (see Box 5.1). The process begins with the definition of the material to be produced, for example, preparation of a seawater-based reference material containing the nutrient elements N03, P04, and Si(OH)4 at concentration levels appropriate to oceanic samples and certified for these constituents." Such definitions arise either from internal decisions by reference material producers (such as NIST or NRC-Canada) typically in response to perceived needs, or through external pressure on these producers from potential users. (This report, for example, explicitly identifies a number of pressing needs for reference materials for the ocean sciences.)... 

Direct participation of the oceanographic research community will enable collection of matrix-based materials such as natural seawater or sediments in an efficient manner (for example, material collection could be combined with other scheduled research activities). Furthermore, the extensive analytical skills of the oceanographic research community can be harnessed to conduct the necessary testing for homogeneity, stability, and ultimately characterization of the proposed reference materials. At the same time, complete success requires the participation of reference material producers, who bring to the table extensive knowledge and experience in the preparation and stabilization of reference materials, and on occasion access to necessary facilities. 

This collaborative approach to the development of consensus materials could thus result in the eventual certification of those materials, if required. Arrangements could possibly be developed with existing certified reference material or reference material producers to disseminate information and to distribute materials to the oceanographic research community. 

As far as reference materials are concerned, the property values carried by reference materials, should be traceable to other references and in an analogous way the same features which are valid for the analytical laboratories, are also valid for the reference materials producers. 

The presentation gives some definitions that are important to the selection use and production of reference materials and provides doeumentation for further reading and study. There is discussion on the different types of reference materials with some insight into their production process. This is followed by information relevant to selection and use of reference materials with a discussion on the relation between reference materials and traceability, which is very important in the context of this presentation. Finally some internet addresses are given of the major certified reference materials producers. 

ISO Guide 34 2009 General reqirirements for the competence of reference material producers... 

The National Analytical Reference Laboratory, now part of the NMI, was set up by Bernard King and then taken forward by Laurie Bezley. I am fortunate in chairing a committee that scrutinizes pure reference materials produced by the NMI and have worked fruitfully with organic chemists Steven Westwood and Stephen Davis. Thanks, too, to Lindsey MacKay, Adam Crawley, and many colleagues at NMI. 

ISO Guide 34 (1996) Quality system requirements for reference material producers. ISO, Geneva... 

The key elements of a traceability chain, values and links between values, have already been described [4], More complete traceability chains are presented in Fig. 1. The symbols used are b = amount content [5, 6] in amount (mol) per mass (kg) of element (or compound) E in material X. Note that the chain is constituted by values linked by operations called measurements , defined as above. The analyst could attempt the establishment of a complete traceability chain as shown (Fig. 1, left chain), but that would require a huge amount of work, or may not be possible, e.g. because the chain may be broken (in the upper part under chemical operations ). The same reasoning applies to the value carried by a reference material (central chain or right chain in Fig. 1). Every time we use a reference material, two traceability chains are involved as illustrated in Fig. 1 one for the measurement result obtained on the unknown sample (left chain), and one for the value carried by the reference material, (either the central or the right chain). They must, by their very nature, be similar. The first one must be demonstrated by the analyst. The second one must be demonstrated by the reference material producer. They sell the product and therefore must be accountable for the product. 

Alternatively, at point 2 in Fig. 1, the reference material producer could have chosen another traceability route, e.g. a coulometric measurement of the number of atoms of the element under investigation, which would have ended in the product Tt (electric current times time) and hence in amperes and seconds. Ultimately, the end of this traceability chain is then located in the value of the Avogadro constant and the value of the charge of the electron [7],... 

Logically it follows that a traceability chain can equally be stated to the value of a reference measurement obtained by a reference measurement producer on the analyst s sample at point 1 in Fig. 1. This concept has the unknown sample travelling from the analyst to the (reference measurement) producer, rather than having the (reference) material travelling from the (reference material) producer to the analyst. This approach will be developed further on another occasion.)... 

To this effect, in analytical chemistry it has been good practice that the analyst obtains a reference material with a matrix Z, similar - but of course not identical - to the one of the material X which needs to be measured. By performing the same operations on a sample of matrix reference material Z as performed on the sample with matrix X, an estimate can be obtained of the overall correction factor X(aE,Z). The value of the amount content 6(aE,Z)RM cert of the reference material as supplied by the reference material producer is known. The value b(aE,Z)sampie Qbs is observed by the analyst Hence, a correction factor can be calculated X(aE,Z) for losses during digestion and recovery etc. (the chemical operations in Fig. 2) as determined with the help of the reference material. It can be applied to the measurement on the unknown sample. In short, this process can be described by Eq 2 ... 

Establishing the traceability chain of a result of a measurement is too long and too expensive a process for an analyst to carry out the analyst must be able to obtain ASs from reference material producers and/or National Measurement Institutes (NMIs), the values of which can be used as stated references that puts the burden of such a programme (with justifications) on producers and NMIs. 

Reference material producers and NMIs must provide values, which can perform two functions ... 

A traceability structure based on the National Institute of Standards and Technology (NIST)-traceable reference materials produced by commercial suppliers under the supervision of NIST in the United States. 

Abstract In this article the role of reference materials is confined to chemical measurements only. Recognized reference materials are one of the tools to obtain comparability of analytical results. Recognition demands confidence in the reference materials and in the reference material producers. A reference material producer is a technical competent body that is fully responsible for the certified or other property values of the reference material. The analyte has to be specified in relation to the selectivity of analytical procedure. The full range of reference materials can be presented as a three-dimensional space of the coordinates analyte,... 

Historically, there have been several ways of demonstrating metrological linkages of traceability. One of the earliest was for a reference laboratory to calibrate an artifact by measuring it and then provide it, along with certified results, to one or more laboratories so that they could also measure it and then compare their results with those of the reference laboratory. Later, distribution of certified reference materials, produced in lots by reference laboratories, provided an exactly analogous linkage for those kinds of materials amenable to production and certification in lots. 

In the field of environmental analyses, the traceability of results of laboratories is not established on a classic common base where one unique standard pure solution or certified reference material (produced by a NMI for instance) is used by all laboratories as a first basic step for calibration and method validation. Many laboratories ensure the traceability of their results by using commercial solutions or by preparing in-house solutions for the calibration of then instruments. The reliability of these... 

A reference material producer is a technically competent body [organisation or firm, public or private] that is fully responsible for assigning the certified or property values of reference materials it produces and supplies which have been produced in accordance with ISO Guides 31 and 35.)... 

One of the remaining questions concerns the QA of chemical reference materials and the competence of RM producers. Whilst laboratory accreditation normally requires the use of physical measurement standards that have been produced in accredited calibration laboratories, the situation regarding chemical measurement standards is, so far, much less formal. General Requirements for the Competence of Reference Material Producers (3,4) have been available since 1996, but the implementation of accreditation based on these requirements is still in its infancy. There is a need for a more balanced approach to accreditation practice related to measurement standards. For example, should only reference materials produced by accredited producers be used as measurement standards in accredited test laboratories Or, does the whole system of the QA of measurement standards need to be re-examined ... 

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