Availability of CRMs

Information about CRMs is available from a number of sources. Many suppliers provide a database on their website. The recognized producers of CRMs in Europe are IRMM, LGC, and BAM. Information about CRMs produced by them, called European Reference Materials (ERMs). can be found on the ERM website (www. erm-crm.org). The ERMs are divided into six different categories (groups)  

Eigure 4.2 shows the percentage of CRMs in the various categories. 

a Polish producer of CRMs for inorganic trace analysis has issued ten CRMs (Table 4.5). Details of these CRMs can be found on the producer s website, www.ichtj.waw.pl 

The leading CRM producers in the world are NIST, the National Research Council of Canada (NRCC), and the International Atomic Energy Agency (IAEA). Information about CRMs produced by NIST can be found at the NIST website, www.nist.gov/srm/index.cfm 

IAEA currently specializes in the production of certified RM for radioactive isotope content, but also offers CRM for inorganic trace analysis, organic analysis, and determination of stable isotopes. Information can be foimd via the IAEA homepage, www.iaea.org, or directly from nucleus.iaea.org/rpst/Reference Products/ReferenceMaterials/index.htm 

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Quality control of laboratories depends on the availability of CRMs, round-robin studies, intercomparisons and proficiency tests between methods and between laboratories. Of special importance is a full knowledge of the complex analytical process and the painstaking pursuit of the true value by defining all sources of errors and the application of an adequate error source budget. The application of Poisson and Bayesian statistics could have some advantage. 

Reference measurement methods, maintained appropriately by reference laboratories. Most measurements belong to this group, because there are still limited the availability of CRM and Reference System applicable to chemical and materials property measurements. These measurements should be carried out by laboratories that have competence in maintaining measurement methods supported by a series of measurements with demonstrable traceability to SI. 

However, due to the lack of availability of CRMs, many field laboratories make use of commercially available chemical substances, which are not normally accompanied by a certificate having enough information in accordance with ISO Guide 31. 

The availability of CRMs and MRTC type CRMs of CENAM depends on the number of RM producers and CENAM s own capacity not only in calibration and mea-... 

Similarly, more immunological laboratory methods are needed for detection of these tree nuts, with interlaboratory studies performed to demonstrate both their fitness for a purpose and any unwanted interferences. The studies should have a common approach, because without the availability of CRMs, universally available calibrants are required for standardization of the kits. Better quantitative methods are required as much for... 

The values of para positions, are thus available from pX measurements of benzoic acids. One cannot so easily extend the correlation to ortho groups, however, because steric effects are superimposed on the electronic effects under study. Table 10-1 presents a list3 of crm and ap values. Note that the groups considered as electron-withdrawing relative to H have positive <7 values, and vice versa. Thus, we have a(p-CF ) — +0.54 and cr(/n-CHi) = —0.069. 

A remarkable level of activity can be seen in China. The National Research Center for CRM (NRCCRM) was founded in 1980 and the certification and accreditation program for CBW RMs started in 1983 by co-operation with many Chinese Institutions. In 1993 around 60 RMs and CRMs were available (Chai Chifang 1993) and in 1999 the availability of about 1000 CRMs was reported, around 30 of them clinical, 100 environmental, 200 geological, and 300 metallic matrix materials (Rong and Min 1999). 

Currently available CRMs for MeHg There are a number of CRMs for total mercury in biological, sediment, and water samples (International Atomic Energy Agency and... 

It is clear that the available RMs certified for trace element species are not sufficient to cover present needs. As it is quite unlikely that producers of CRMs will ever be able to meet all demands, users are encouraged to produce their own RMs to guar-... 

This Section describes one of the first successful attempts, by a multi national project team funded by the European Commission s DC XII, to produce and certify a microbiological CRM that is both fit for purpose and meets the requirements of the ISO Guides. The first results are two bacterial strains, Enterococcus faecium (CRM 506) and Salmonella typhimurium (CRM 507) (fanning et al. 1995). Both are available as part of the EU BCR range of CRMs. 

There are a number of CRMs available for this group of elements in semm and urine (see Table 6.3). The most severe problems with the determination of these trace elements are contamination and loss. Therefore, strict protocols are necessary to prevent these problems. Contamination can be prevented by cleaning thoroughly all used utensils, and the use of highly purified chemicals. Loss is mostly due to exchange between the container walls and can be prevented by working at a pFI<2. 

Reported data should achieve a clear, purpose-oriented level of accuracy and precision, especially when data produced by several laboratories often needs to be compared as part of a decision process. It has become accepted by more and more analysts that to overcome differences between national standards and specifications and measurement procedures or to make Total Quality Management (TQM) an achievable reality, freely available and internationally agreed points of reference are needed. Therefore RMs and CRMs must be easily available indeed the availability of reference materials has been described as an issue of strategic importance to the EU (Maier et al. 1997). 

Simply producing reference materials is not enough they have to be used properly. Chapter 7 reviewed the proper use of RMs, but unless RMs and CRMs can be easily obtained and moved from one country to another without delays, duty or unnecessary controls, their use will be inhibited. Likewise, information about the materials that are available, their use, and their application should be freely available if analysts are to make informed decisions about the selection and use of a RM or CRM. It has already been made clear in previous Chapters that the correct choice of reference material for a particular application requires not only information about the RM, which is relatively easily available, but also information about the uses and applications of the reference material. Unfortunately, neither the availability of information about the reference materials and their uses nor their free movement across national borders are at all satisfactory. 

It may be concluded that many authors are convinced that it is sufficient to report the use of CRMs in an incomplete form and without giving any details of results, and not reporting the type and producer of CRMs used. Not infrequently it could be noted that CRMs from one producer were attributed to another, showing that the author(s) and reviewer really do not know from which source the RMs applied originated. Others use materials that do not match the samples analyzed or, even worse, do not see the need to use any CRM despite the availability of suitable and not too expensive materials to check the reliability of their work. From all this it is clear that. 

Comment CRMs NRCC CRMs DOLT-i (dogfish liver) and DORM-i (dogfish muscle) used, but no use of mussel or hair CRMs, despite availability of both. 

The Promochem Group was the first international specialist supplier of certified reference materials (CRMs) and pharmaceutical reference substances used in environmental, medical and trace element analysis. Their experience provides a viewpoint that echoes, reinforces and expands on many of the trends discussed above (Jenks 1997). From the middle of the 1980 s, sales of CRM by Promochem increased between 10 % and 20 % annually, depending on the market sector and application. Since then National and International Metrology Institutes, such as the now privatized U.K. Laboratory of the Government Chemist (LGC), the European and U.S. Pharmacopoeias, the E.U. IRMM and others have recognized that efficient distribution of RMs, backed by available technical support, is as important as production and certification. Thus, they have moved to spread their influence outside their national origins. The Web and e-commerce will continue to grow as major facilitators of better information dissemination and supply of CRMs. 

Provided the sample matrix and analyte concentration are appropriate, matrix Certified Reference Materials (CRMs) can make ideal proficiency testing samples. The assigned value is the certified value given on the certificate accompanying the CRM. The certificate will also give an uncertainty estimate for the certified value, and the use of CRMs allows the traceability of analytical data to be established. However, matrix CRM availability is limited and the materials are often expensive. Hence, Certified Reference Materials are seldom used as PT samples. 

A CRM is an ideal test material for a PT scheme. Unfortunately their high cost and lack of availability of snitable CRMs in the qnantity and concentration range needed limit their nse. Very often a PT scheme has to deal with more or less nnstable samples to meet the laboratories requirements. In this case CRMs are very unlikely to be available. 

X is the mean determined value and n is the number of measurements for which the SD was calculated. If SD data of the certified reference materials are not available, 95% confidence limits may be used as an estimate of CRM SD (see second form of formula for z score) [21]. 

In the absence of pKA data for the individual amine protons in these substitutionally labile complexes it is not possible to evaluate k2 and thereby measure precisely the amount by which deprotonation increases the lability of the complex. Even if such data were available it would be difficult, in complexes containing more than one type of amine proton, to be sure whether the two quantities related to the same proton. In spite of this major drawback it is possible to estimate orders of magnitude. The evidence suggests that in Co111 complexes the amido conjugate base can be between 105 and 1013 times more labile than the amine complex from which it was derived.301 The effect is far less marked in equivalent complexes of Crm, Ru111 and Rh111352-353 and, so far, there... 

Analyzing control materials alongside the test samples greatly improves proficiency in mycotoxin analysis. Certified reference materials (CRMs) represent ideal control materials, due to their statement of uncertainty and traceability, and they should be routinely used as much as possible. Unfortunately, as outstanding as the improvements made in the last decade have been, even though the list of CRMs in the area of mycotoxins is rather long, it is still insufficient. A list of the available reference materials in the mycotoxins area is reported in Table 1 the issue has been reviewed by Boenke (27). 

The development and improvement of analytical methodologies for mycotoxins has been greatly improved by the increased availability of matrix matched certified reference materials (CRMs) (Boenke, 1995) (Table 11.6). The type of matrix CRMs and concentration of the specified mycotoxin are based on the natural occurrence pattern of the toxin in specific foods and feeds. The recent availability of suitable CRMs, while being a prerequisite for the implementation of regulations and standards, will also be invaluable in many ways for the validation of new methods, solving trade disputes and for harmonising proficiency schemes. 

Most methods (electron probe microanalysis, micro-Auger, secondary ion mass spectrometry) cannot be considered as really accurate methods except when applied to quite simple systems. Their application relies on the use of CRMs but these are, with very few exceptions, not available. The reason for the lack of CRMs is the absence of any reliable methods of microanalysis. None of the limited range of primary methods is applicable for the analysis of a solid at a microscopical level. The world of microanalysis is badly in need of at least one method which is able to act as a reference for the other techniques and to link RMs or round-robin exercises to the SI units [22],... 

The accuracy of the methods described above for the analysis of biological and food samples has been checked by dilferent approaches. These include recovery test and standard addition, use of independent analytical methods of proven validity, and verification of the method by means of CRMs, the latter two approaches being the most applied. In the specibc case of biological and food samples, a great variety of CRMs, such as those produced by NIST, BCR, NRC, and IAEA, are available. The reliability of the techniques mentioned in this survey has been mainly checked against these CRMs. There is much evidence in the literature that the capabilities of the solubilization sampling technique compare favorably with those of other techniques. 

Another important use of CRMs is for the validation of in-house reference materials. Since CRMs are fairly expensive and perhaps not as specific as necessary for certain analysis, it would be cost-effective to prepare in-house reference materials when possible. By analyzing a specific sample (that is homogenous and available in a reasonably large quantity) along with a similar CRM, traceability of the found value is established to the certified value. Then this in-house material can be used as a complement to the CRM. A recently published procedure describes how to get the most complete information out of CRMs [16]. 

Figure 7.27 shows that only a few participants indicated that they used a tuna bsh CRM for QA. Forty percent of the participants using a CRM for QA, compared to 30 percent not using a CRM, reported Hg results within 5 percent deviation from the certibed reference value. Final conclusions on the measurement performance according to the use of CRMs could be drawn if all results were corrected for recovery. Unfortunately this information was not available. It is planned to get information on recovery correction from IMEP participants in future IMEP ILCs. 

In terms of methodology, the speciation analysis of Hg has reached its maturity. Because of a convenient conversion of Hg species into volatile compounds, GC has been the dominant separation technique prior to Hg speciPc ICP-MS detection [10, 11, 13, 19]. HPLC methods cannot compete in terms of Pgures of merit with GC. HPLC-ICP-MS is, however, a valuable independent analytical technique that allows the formation of artifacts during derivatization in GC to be controlled. Owing to the availability of a number of CRMs, analytical procedures for the analysis of seafood samples were extensively validated and can be applied in routine analysis. 

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