Certified reference materials certification procedures

Quevauviller Ph, Herzig R. and Muntau H (1996b) Certified reference material of lichen (CRM 482) for the quality control of trace element biomonitoring. Sci Total Environ 187 143-152 Quevauviller Ph, Lachica M., Barahona E, Rauret G, Ure A, Gomez A, and Muntau H (1997) The certification of the EDTA-extractable contents (mass fractions) of Cd, Cr, Ni, Pb, and Zn and of the DTPA-extractable contents (mass fractions) of Cd and Ni in calcareous soil by the extraction procedures given CRM 600. EUR Report 17555 Quevauviller Ph. Maier EA, and Griepink B, eds. (1995) Quality Assurance for Environmental Analysis. Elsevier. Amsterdam. 

Certified Reference Material A reference material characterized by a metrolog-ically valid procedure for one or more specified properties, accompanied by a certificate that states the value of the specified property, its associated uncertainty and a statement of metrological traceability. 

Certified Reference Material Reference material, whose property values are certified by a procedure that establishes its traceability to an accurate realization of the unit in which the property values are expressed, and for which each certified value is accompanied by an uncertainty statement (certificate) at a specified level of confidence. 

The certification procedure for seven trace metals (Ba, Ca, Li, Mg, Mn, Na and Sr) in the certified reference material FEBS-1 (National Research Council Canada, Institute for National Measurement Standards, Ottawa, Canada) based on fish otolith matrix by isotope dilution - ICP-MS in comparison to ICP optical emission spectrometry and X-ray fluorescence analysis, is described by Sturgeon et al4X The isotope dilution technique is also employed for species analysis in biological systems,46 e.g., for the determination of mercury species in tuna material,54 or in aquatic systems using cold vapour ICP-MS.55... 

For a trace element concentration to be certified by NBS, it must be determined by at least two independent methods, the results of which must agree within a small experimental error range of 1% to 10%, depending on the nature of the sample and the concentration level of the element. Such accuracy in determining some trace elements for certification of coal SRM is achieved most easily by NAA with radiochemical separation. Scientists at NBS have extensively tested a neutron activation method that involves a combustion separation procedure on coal as well as on several other matrices to be certified as standard reference materials. The procedures they have thus developed to determine mercury (12), selenium (13), and arsenic, zinc, and cadmium (14) are outlined in a following section on methods for determining specific elements in coal. 

Certified Reference Material (CRM) is a reference material, one or more of whose property values are certified by a technically valid procedure, accompanied by or traceable to a certificate or other documentation that is issued by a certifying body. 

According to this vocabulary, a reference material is a material or substance one or more properties of which are sufficiently well established to be used for the calibration of an apparatus, the assessment of a measurement method, or for assigning values to materials. A certified reference material is a reference material one or more of whose property values are certified by a technically valid procedure, accompanied by or traceable to a certificate or other documentation which is issued by a certifying body. 

A reference material certificate is defined by ISO 31 2000—Guide to the Contents of Certificates and Label of Reference Materials—diS a 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 . For example, this would include information relating to the batch number, a description of the material, the concentration of the material, storage conditions, and expiry date. The content of the certificate is discussed in detail in ISO 31 2000— Guide to the Contents of Certificates and Label of Reference Materials. 

Certified reference materials are intended primarily for calibration and in quality control of analytical techniques. A certified reference material is a reference material, accompanied by a certificate, one or more of whose property values are certified by a procedure that establishes its traceability to an accurate realization of the unit in which the property values are expressed and for which each certified value is accompanied by an uncertainty at a stated level of confidence. They are used to test, validate, and optimize new analytical techniques as well as in quality control of routine laboratory work. Table 3 gives a list of environmental samples that provide certified values of PAH content. These are available from various bodies as certified reference materials. In measuring the concentration of a substance for certification purposes, more than two independent and reliable analytical methods are used. Certified reference materials when used for standardization of analytical methods will make comparisons between PAH data obtained by a variety of workers using... 

The traceability of the result of a measurement is defined as the property of the result whereby it can be related to stated references, usually national (NIST, NRC, etc.) or international (CSA and EU) standards, through an unbroken chain of comparisons all with stated uncertainties, e.g.. Figure 2.1. As applied to an analytical standard, distinct from a measurement of an unknown concentration, this concept implies that the purity of the standard has been determined by a traceable sequence of analytical steps, each with a known uncertainty, that permit comparison with a certified reference material (CRM) (Section 2.2.2) from a recognized supplier. This procedure results in a Certificate of Analysis, discussed in Section 2.2.2 for CRMs and also in Section 9.4.4c with respect to the analytical (reference)... 

In the field of RM certification, NAA represents a major analytical technique. It possesses unique quality assurance and self-verification aspects. Not surprisingly, therefore, NAA has been used to certify NIST standard reference materials [470]. By analogy, NAA has also been instrumental in analysing the EC polymer reference materials within the framework of the PERM project [1]. NAA was also used to validate a TXRF procedure for the determination of additives containing Ti, Zn, Br, Cd, Sn, Sb and Pb [56],... 

---