Use of certified reference materials CRMs

Results can only be accurate and comparable worldwide if they are traceable. In the vast majority of chemical analyses, the traceability 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 (Quevauviller et al, 1996a). 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 

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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. 

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. 

Taking into consideration the method of °Sr analysis, the activity equilibrium state between °Sr and its decay product °Y is very important. This state is attained 12 days after the separation of radiostrontium [62]. The reliability of the received results of °Sr determination depends on the minimum detectable activity (MDA) [5]. The MDA should be calculated for each analysis sample. Generally, the separation of °Sr with the use of fuming HNO3, and subsequent co-precipitation of radium, lead, and barium as chromates, is used for the analysis of flora, soil, ash filters, and water samples. The fusion products (e.g., Cs) are removed by co-precipitation of the hydroxides, then transformed into yttrium oxalate, and the activity of °Y measured in a low-level proportional counter. The yield is controlled by measuring the activity of Sr (gamma emitter) added to each sample before analysis as an internal tracer [1, 46]. The accuracy of the analytical results obtained should be verified in a validation process with the use of certified reference materials (CRMs). 

The main goal of every procedure for analytical quality control is to allow data within assigned values of accuracy and precision to be obtained. Analytical quality control is primarily achieved by the use of Certified Reference Materials (CRMs) and participation in intercomparison exercises, though calibration solutions and spiked samples can also be used (43, 63, 64). 

A more serious problem arises when the traceability of the whole analytical process is considered. Complete traceability through to the mole is an excellent ideal but nowhere near achievable at present. Comparability between chemical analyses by use of certified reference materials (CRMs) may be regarded as the initial step in the traceability chain to the mole. Even this relatively small first step is constrained by a number of factors. Some of these are ... 

Quality control includes such procedures as checking for proper identification of samples, checking reagent lot numbers and utilities, etc. Control charts should be maintained for both equipment as well as analytical procedure by measurement of QC samples [16]. These are typical samples of sufficient stability and quantity to be used for analytical purposes over a continued period of time. For routine measurement, the number of QC samples should be at least one of twenty samples for analysis, and for more complicated analytical procedures the number of QC samples occasionally increases to 1 1. For infrequent analytical procedures, e.g., in research, a validation of the method should be performed at all runs, and this should also include the use of certified reference materials (CRM) when suitable ones are available. 

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. 

In analytical practice, they are best recognized by the determination of xtest as a function of the true value xtrue, and thus, by analysis of certified reference materials (CRMs). If such standards are not available the use of an independent analytical method or a balancing study may provide information on systematic errors (Doerffel et al. [1994] Kaiser [1971]). In simple cases, it may be possible, to estimate the parameters a, / , and y, in Eq. (4.5) by eliminating the unknown true value through appropriate variation of the weight of the test portions or standard additions to the test sample. But in the framework of quality assurance, the use of reference materials is indispensable for validation of analytical methods. 

Abstract For ensuring the traceability and uniformity of measurement results, the main objectives of national metrology programmes in chemistry are to calibrate and verify measuring instruments, to evaluate the uncertainty of measurement results and to intercompare the analytical results, etc. The concept of traceability has developed recently in chemical measurements, thus, an attempt to implement the principles of metrological traceability especially by appropriateness calibration using composition certified reference materials (CRMs) is underlined. Interlaboratory comparisons are also a useful response to the need for comparable results. The paper presents some aspects and practices in the field of spec-... 

Sometimes the need for sample digestion can be circumvented. One example is the extraction with HC1. The method is based on hot HC1 and is specifically developed for extraction of Sn from canned fruit and vegetables. It is quite rapid and particularly useful for screening purposes. Another example is solid sampling. This is a technique specifically suited for ET-AAS and therefore not generally applicable. It is useful when homogeneity at the milligram level is of interest, for example, in the production of Certified Reference Materials (CRMs). 

The second facility was used in the case of isotopes of a half-life more than one week. Again there are two groups of elements, namely, Ba, Br, La, Lu, Mo, Rb, Sb, U and W (irradiation time of 25 hr, decay time of 1 week, counting time of 30 min) and Ba, Ce, Co, Cr, Eu, Fe, Hf, Rb, Sb, Sc, Se, Sr, Ta, Th and Zn (irradiation time of 25 hr, decay time of 1 month, counting time of 3 hr). In both cases the neutron flux is 2.6 x lO n cm s with a Cd ratio Rcd = 3. Different y-spectrometric measuring equipments by EG G ORTEC were used. The Certified Reference Materials (CRMs) used for the calibration of the measurement systems were Urban Particulate and laboratory standards, as detailed in Table 14.3. 

Several ISO guidelines address the use of certified reference materials [5,36-38], and certified reference materials from BCR and NIST are available for some trace elements in human body fluids, e.g., the BCR CRM 194-196 for Cd and Pb in whole blood. Due to the relatively high cost and limited availability of the CRMs, these materials can only occasionally be used for the internal quality control. Alternatively, the laboratory may prepare or purchase reference/control materials calibrated against and therefore traceable to CRMs [5]. 

It is important to note that several works, in both environmental and food analysis, compare the extraction performance of the IL-based surfactant with the conventional cationic surfactant CTAB [20, 36, 56, 60, 61]. For example, Pino et al. have reported much better extraction efficiencies of PAHs from marine sediments when using Cj C Im-Br (being quantitative) than when using CTAB under the same extraction conditions [36], Moreover, this application was validated using a certified reference material (CRM). 

Quality assurance considerations lead to the need for appropriate reference materials, and their consistent and effective use to monitor the precision and accuracy of laboratory analyses. In this context, certified reference materials (CRMs), now still largely lacking in the polymer/additive area, play an important role. In previous years, some attempts have been undertaken to prepare some inorganic CRMs (VDA and PERM projects), but this is highly insufficient when we consider that some 60 elements are used in polymer/additive formulations. The lack of CRMs for organic compounds in polymeric matrices is an even more serious handicap. Nagoumey and Madan [122] have demonstrated that intermediate or finished in-house materials can be utilised successfully as QA reference materials. Good QC of polymer/additive formulations as yet has not been achieved. 

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. 

Eight Certified Reference Materials (CRMs) (Table 1) were analyzed, in triplicate random order, for 53 elements by five digestion protocols (Table 2) as shown in the experimental design (Table 3). All final determinations were by ICP-AES and -MS in a single batch using a randomized ordering of the prepared digestions. 

The certified reference material (CRM 450), used for the validation of the method, is real contaminated powdered milk with a certified content in PCB-52, PCB-101, PCB-118, PCB-156, and PCB-180. This material contains approximately 3.9% water and 25% fat. It is used after reconstituting and was supplied by the EC Community Bureau of Reference (BCR). 

Four basic requirements for accurate and precise determination of the amount of fluoride or total fluorine in any type of the sample are (1) the sample has to be appropriately pre-treated so that the required form of fluorine can be determined (2) interfering reactions have to be effectively suppressed (3) the final concentration of fluorine must be above the detection limit of the method and (4) if possible, method should be validated using certified reference material (CRM), or the results of analyses compared to the results obtained by an independent method. 

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