Certified reference system

Traceability of measurement results is essential in the establishment of a certified reference material. As stipulated in ISO Guides 30 and 35, a certified reference material can only be certified if there is an uncertainty statement with a traceability statement. Basically, traceability means anchoring. In classical analytical chemistry, that SI system is often the best choice as a reference (= anchoring poinf). However, there is a wide range of parameters either defined by a method or defined by the... 

Jenks P, Boekholt a, Maaskant J, Rucinski R (1998) Are Certified Reference Materials a victim of Quality Systems Fresenius J Anal Chem 360 366-369... 

Jenks PJ (1997) Reference Materials, Their Use, Abuse and Development. Anal Eur 4 22-28. Jenks PJ, Boekhoit AH. Maaskant JFN, and Rucinski RD 1998) Are certified reference materials a victim of quality systems The need for working matrix-certified reference materials. Fresenius J Anal Chem 360 366-369. 

Stoll et al. [142] have described a rapid continuous-flow determination of total inorganic carbon in seawater samples. The method runs on an autoanalyser Traacs 800 spectrophotometric system and is calibrated versus certified reference materials readily available. A typical analysis speed of 45 samples per hour can be reached with an accuracy of 2-3 xM and a precision of 2.5 xM. 

In addition, a system for making sure staff are appropriately qualified and trained for the work that they are doing must be in place. This will enable an auditor to see clearly the demonstrated competence of the staff and how this has been checked. The requirements for all major items of equipment must be listed, to ensure that the equipment in use is suitable for the task, is in working condition and, where necessary, is calibrated. For all of the instrumentation there needs to be a documented schedule for maintenance. Measurements must be traceable, that is, the laboratory must be able to show how the calibration of measurement instruments is traceable to National or International Standards. Where this presents practical problems, as in some chemical measurements for example, interlaboratory comparison and the use of reference materials (and preferably Certified Reference Materials) will be required. 

This confirmation is often provided by an external audit or assessment (u.s.). Quality management systems are often certified for conformation with ISO 9000. Probably the most common term with respect to our topic here is certified reference materiaT (CRM). 

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. 

One way to use a CuSum chart to understand such changes is to plot a regular analysis of a reference material (which does not have to be a certified reference material, rather a material which is the same and stable over time) and note any obvious changes to the system on the chart. The quality assurance manager can then evaluate any effects due to the changes and take... 

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... 

Systems of classification very often follow the application fields, e.g. the catalogues of the Institute for Reference Materials and Measurements (IRMM), the National Institute for Standards and Technology (NIST), Laboratory of the Government Chemist (LGC), etc. or the database for certified reference materials COMAR. In all application fields like food and agriculture, environment, health and safety, industry and services, etc., reference materials are used for ... 

Certified reference materials offer the chance to limit the impact of most of the factors described above. They are certified to the mass fractions of the plant materials (typically seeds) used [16]. This makes these standards fully traceable to SI units. The materials are produced under highly standardized and well-characterized conditions and their homogeneity is confirmed. Every analyst calibrating his/her method using these standards will have an analytical system that is traceable to SI units. 

These biological factors also affect the reference materials. It is easy to envisage that different reference materials, all certified with respect to their mass fractions, could be derived from different cultivars or derived from different tissues (processed fractions) and would differ in their genetic make-up. This would result in different relative amounts of DNA for an identical mass fraction. Due to these biological factors these uncertainties can only be avoided if all producers of certified reference materials establish a system of comparable reference materials, accounting for the underlying biological factors. 

In many instances a selected and agreed reference measurement procedure forms the basis of the definition of the quantity and thereby represents the top of the calibration hierarchy. This is particularly true for establishing reference systems for the catalytic concentrations of enzymes. In 1999 members of the IFCC working group and some enzyme reference laboratories decided to establish new 37 C measurement procedures as IFCC reference procedures on the basis of the existing 30 C IFCC procedures and to certify enzyme reference materials for AFT, AST, GGT, CK, FD and amylase in collaboration with the IRMM. The enzymes having IFCC reference measurement procedures have catalytic concentra-... 

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. 

Analyses are performed in accordance with standardized methods issued under the responsibility of a Technical Committee within the Health Ministry. Usually such measurements rely on a comparison of the measured quantity in the unknown sample with the same quantity in a standard , i.e. an RM, according to a specific measurement equation [6], after calibrating the instrument. Calibration of a photometric system for clinical analyses usually means the set of operations that establish, under specific conditions, the relationship, within a specified range, between values indicated by the instrument and the corresponding values assigned to the RMs at the stated uncertainty. Calibration of the photometer itself implies the calibration of wavelength and absorbance scale by means of proper wavelength and absorbance RMs [5], traceable to national standards. A calibration of the instrument is still needed in concentration units to check the indicated provided value. The measurement result is then verified by application of that method of measurement to a certified reference material (CRM). Both the comparator - a photometric device with narrow or wide bandwidth, and the RMs should thus be validated. 

Abstract This article briefly describes research on the development of primary reference gases and the traceability system of gas measurement at the National Research Center for Certified Reference Materials, China. 

Control samples should have a high degree of similarity to the actual samples analyzed otherwise, one cannot draw reliable conclusions on the measurement system s performance. Control samples must be so homogeneous and stable that individual increments measured at various times will have less variability than the measurement process itself. Quality Control samples are prepared by adding known amounts of analytes to blank specimens. They can be purchased as certified reference material (CRM) or may be prepared in-house. In the latter case, sufficient quantities should be prepared to allow the same samples to be used over a longer period of time. Their stability over time should be proven and their accuracy verified, preferably through interlaboratory tests or by other analysis methods. 

The certified values of the produced standards are linked to the national standards by the Primary Laboratory of the Bureau National de Metrologie . This traceability is achieved through the utilisation of measuring instruments which are periodically calibrated standards provided by the Primary Laboratory. At international level, trace-ability is established for a certain number of radionuclides, with national laboratories with which the Primary Laboratory performs direct comparisons or indirect comparisons through the International Reference System of the Bureau International des Poids et Mesures . An official calibration certificate containing all necessary information is provided with each standard. 

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