Use of Certified Reference Materials

Results can only be accurate and comparable worldwide if they are traceable. By definition, traceability of a measurement is achieved by an unbroken chain of calibrations connecting the measurement process to the fundamental units. In the vast majority of chemical analyses, the chain is broken because in the treatment the sample is physically destroyed by dissolutions, calcinations, etc. With respect to speciation analysis, the chain is even more complex since it involves successive analytical steps. To approach full traceability it is necessary to demonstrate that no loss or contamination has occurred in the course of the sample treatment. 

The only possibility for any laboratory to ensure traceability in a simple manner is to verify the analytical procedure by means of a so-called matrix RM certified in a reliable manner. The laboratory which measures such an RM by its own procedure and finds a value in disagreement with the certified value is warned that its measurement includes an error, of which the source must be identified. Thus, CRMs having well known properties should be used to  

Verify the accuracy of results obtained in a laboratory Monitor the performance of the method (e.g. cusum control charts) Calibrate equipment which requires a calibrant similar to the matrix (e.g. optical emission spectrometry. X-ray fluorescence spectrometry) Demonstrate equivalence between methods 

Detect errors in the application of standardized methods (e.g. ISO, ASTM). 

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ISO Guide 32 (1997) Calibration in analytical chemistry and use of certified reference materials. International Organization for Standardization, Geneva. 

Pauwels J. De Angelis L, Grobecker KH (1991) Solid sampling Zeeman atomic absorption spectrometry in production and use of certified reference materials. Pure Appl Chem 63 1199-1204. 

Quevauviller Ph (1998) Requirements for production and use of certified reference materials for speciation analysis a European Commission perspective. Spectrodiim Acta 536 1261-1279. Quevauviller Ph, and Horvat M (1999) Artifact formation of methylmercury in sediments. Anal Chem, Letter to the Editor 7i i55A-i56A. 

ISO Guide 33 1989) Uses of certified reference materials (under revision). ISO Publications, Casa Postale 56, CH 1211 Geneva 20, Switzerland. 

More attention should be devoted to the quantitative determination of analytes in real-life samples. The accuracy of the determinations and the traceability of the overall analytical process are insufficiently ensured [120,121], As no primary methods are available for the purpose, this necessarily implies the use of certified reference materials. 

ISO Guide 33 (1989) Uses of certified reference materials. Geneva... 

The development and characterization of Certified Reference Materials is an expensive process. Because of this, emphasis on the use of Certified Reference Materials is usually directed more towards the initial validation of a method it is rarely economical to use a reference material for routine quality control although it can be used to calibrate other, cheaper, secondary materials which can be used for routine quality control. 

Sutarno, R. Steger, H.F., 1985.The use of certified reference materials in the verification of analytical data and methods. Talanta, 32, 439-445. 

Those scientists using available reference materials should be encouraged to report such uses explicitly in the scientific literature. A recent article by Jenks and Stoeppler (2001) goes so far as to suggest that scientific publishers should provide explicit recommendations as to how and where in a paper the use of certified reference materials should be described. Proposal and journal article reviewers also need to be encouraged to question the analytical quality control (and ultimate value) of measurements made without the benefit of reference materials. 

Jenks, P.J., and M. Stoeppler. 2001. The deplorable state of the description of the use of certified reference materials in the literature. Fresenius Journal of Analytical Chemistry 370(2/3) 164-169. 

Kasper-Zubillaga, J.J., Carranza-Edwards, A., Morton-Bermea, O. 2008b. Heavy minerals and rare earth elements in coastal and inland dunes of El Vizcaino Desert Baja Califonia Peninsula, Mexico. Marine Georesources and Geotechnology, 26, 172-188. Sutarno, R. Steger, H.F., 1985. The use of certified reference materials in the verification of analytical data and methods. Talanta, 32, 439-445. 

Establishing the traceability of the measurement is one of the most important requirements in ISO/IEC 17025. Measurement traceability ensures that the measurements in different laboratories are comparable in space and time all over the world. Calibration and the use of certified reference material (see chapters 9, 10 and 14) is the central tool in establishing trace-ability. Therefore a laboratory must have programmes and procedures for both. 

In such cases, which are the most commort, there is a need to provide objective evidence that the validation was carried out, using appropriate and approved methodology. The use of Certified Reference Materials or the comparison against a previously validated method is highly recommended in order for a vahdation to be recognized by regulatory or accreditation bodies. 

Use of certified reference materials for this purpose is possible, but actually it is not an appropriate use of the material. It is better and more economical to use in-house materials of adequate homogeneity and stability (see chapter 13). 

There is a lot of discussion about the use of certified reference material in terms of measurement traceabihty. 

There is a large number of certified reference materials available in the market. It is of highest importance to select an appropriate certified reference material for the intended use. There are a number of criteria, which can be used in order to select the appropriate certified reference material. Depending on the measurement problem the importance of each criterion can vary. Experience and continuous use of certified reference material help to make... 

Summarizing this reference material chapter, you must remember that they are very important components for quality assurance in analytical laboratories. Their production is not an easy job, their selection and use requires specific information and careful decisions have to be made and finally the use of certified reference materials cannot replace careful laboratory work. 

Sampling is just the beginning of the analytical process. On the way from sampling to the test report a lot of different requirements for high quality measurements have to be considered. There are external quality assurance requirements on the quality management system (e.g. accreditation, certification, GLP), internal quality assurance tools (e.g. method validation, the use of certified reference material, control charts) and external quality assurance measures (e.g. interlaboratoiy tests). 

In order to make reliable comparisons it is therefore suggested that, in future studies, decomposition methods that are known to release all the fluoride should be used. Use of certified reference materials (CRM) as part of the quality assurance system should be mandatory. In addition, sufficient information to enable proper comparison of data from different studies must be provided. 

Regular use of certified reference materials and/or internal quality control secondary reference materials... 

Laboratories must use calibration standards that are metrological trace-ability to an embodiment of the unit in which they are expressed. This requires use of certified reference materials, usually to make up working standards that calibrate instruments in the laboratory. Implicit is that results will be expressed in common units, and while this is increasingly the case, the example of the Mars Climate Orbiter (chapter 1) should signal those still using versions of imperial units that it might be time to join the rest of the world and use SI units. 

Extraction to gas phase, liquid phase and solid phase can be used in the preparation of SVOC/POM samples. It is essential to estimate the recovery of each extraction step. One method is spiking the sample with known amounts of internal standards similar to the analytes. The problem of this method is that spiked standards may not bind to the matrix in the same way as the analytes. Another method is to find the method with the highest recovery of a number of methods. Probably a combination of the two methods will give the most reliable results. Finally, use of certified reference materials, if available, will be the best way to determine the total recovery. 

It is shown that an Si-traceable result does not necessarily coincide with the median or average of a number of participants results, thus demonstrating that a set of systematic errors from a set of laboratories is not necessarily normally distributed. It is also shown that the use of certified reference materials (CRMs) does not automatically lead to correct results and the same is true when different systems for quality assurance are applied. 

ILAC-G9 (1996) Guidelines for the Selection and Use of Certified Reference Materials... 

For each analytical measurement, it should be possible to relate the result of the measurement back to an appropriate national or international measurement standard through an unbroken chain of comparisons. For measurement of weight, this would be the kilogram standard in Paris, or for amount of substance it should be the SI unit, the mole. If calibrated by an accredited body, the balance is an instrument which can provide measures of weight which are traceable to national measurement standards. Instruments for chemical analysis must be calibrated by the use of certified reference materials, or other suitable reference materials. 

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