Application of CRMs

CRMs play a significant role in quality assurance systems in analytical laboratories, especially in the case of trace analysis. Generally, they are applied in analytical 

A commonly recommended and accepted way of checking accuracy is the analysis of CRMs along with routinely analyzed samples. The RM(s) applied for this purpose should obviously be as similar as possible in both the type of matrix and content of determined element(s). In this case, it can be assumed that the possible systematic errors resulting from matrix effects, spectral interferences, etc. are the same or at least similar in the CRM and in the analyzed samples. The result of measurement of f/m can be then compared with the certified value Aj-ef Cref, where f/m and (/ref expanded uncertainties of the measurement result and certified value, respectively. Good agreement of the result of measurement and the certified value confirms correctness of analysis. Taking into account numerical values, the following condition should be fulfilled [60]  

Normally, CRMs are used for the verification of accuracy, precision, and reliability of the results of analysis carried out in a laboratory (i.e., for checking the quality of its routine work). The CRM is analyzed at specific intervals and the results obtained are used to draw control charts (e.g., Shewhart chart) [63]. This allows visual assessment of the measurement system, the emergence of systematic errors, etc. Application of CRMs for the constmction of control charts is advantagous because of the homogeneity and stability of CRMs, and the ability to assess the accuracy of the results obtained in the laboratory by comparison with the certified value. 

Demonstrating that the analytical method used is accurate is equivalent to showing that the stages of sample preparation (dissolution, extraction etc.), which can break the chain of traceability, do not cause systematic error. The results of the measurements are then traceable to the units in which the certified values are expressed. 

CRMs are also used for calibration of the measurement instmment. For example, pure metals or alloys are used for X-ray fluorescence (XRF) and other spectroscopic methods in industrial laboratories. Because the uncertainty associated with a certified value contributes to the total uncertainty of the measurement, Wref should be as small as possible. Therefore, wherever possible, CRMs used to calibrate instruments should be pure substances or solutions. Matrix CRMs are not recommended for calibration of measuring instruments, because the uncertainty of certified values are generally higher than those of pure substances or solutions. Moreover, using this approach, an analyst is deprived of independent verification of the accuracy of obtained results, which should be the primary function of CRMs. 

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The producers need to establish, in general terms or for specific applications of CRMs, dear instructions for the user on how to establish traceability to the stated reference and (implied in the use of CRMs of national metrology organizations) the SI. But the authors experience is that, as the workload in commercial analytical laboratories increases (as analytical laboratories seek to demonstrate their competence and quality to an increasingly discriminating... 

Quality Assurance/Quality Control Validation of steps and analytical results throughout, by independent or reference method(s), application of CRMs, RMs, contiol materials (internal QC), interlaboratory comparisons, proficiency tests to validate accuracy and precision competent analyst/specialist... 

Over the last seventeen year s the Analytical center at our Institute amassed the actual material on the application of XRF method to the quantitative determination of some major (Mg, Al, P, S, Cl, K, Ti, Mn, Fe) and trace (V, Cr, Co, Ni, Zn, Rb, Sr, Y, Zr, Nb, Mo, Ba, La, Ce, Pb, Th, U) element contents [1, 2]. This paper presents the specific features of developed techniques for the determination of 25 element contents in different types of rocks using new Biaiker Pioneer automated spectrometer connected to Intel Pentium IV. The special features of X-ray fluorescence analysis application to the determination of analyzed elements in various types of rocks are presented. The softwai e of this new X-ray spectrometer allows to choose optimal calibration equations and the coefficients for accounting for line overlaps by Equant program and to make a mathematic processing of the calibration ai ray of CRMs measured by the Loader program. 

The validation of calibration with CRMs is commonly performed by parallel application of independent methods, for details see below. 

Rossbach M, Ostapczuk P, Emons H (1998) Microhomogeneity of candidate reference materials Comparison of solid sampling Zeeman-AAS with INAA. Fresenius J Anal Chem 360 380-383. Rossbach M, Stoeppler M (1987) Use of CRMs as mutual calibration materials and control of synthetic multielement standards as used in INAA. J Radioanal Nud Chem Artides 113 217-223. Sargent M (1995) Development and application of a protocol for quality assurance of trace analysis. Anal Proc 32 71-76. 

In discussing these pathways and considering the broad spectrum of analytical chemistry applications in contrast to the limited supply of CRMs, one has to keep in mind that the unbroken chain of comparisons may be hterally demonstrated in only a few instances and that for a long time to come data are accepted by inferred quality, including traceability. 

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. 

The Reference Materials Committee (REMCO) of ISO was established in 1976 and was initially known as REMPA. The aim of this committee is to carry out and encourage a broad international effort for the harmonization and promotion of CRMs and their production and applications. Through the ISO website (Table 8.4), it is easy to access vast amounts of information about the activities of ISO and its various technical committees. 

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. 

Challenges of ICP-AES/MS for polymer/additive analysis are the lack of CRMs. A monograph describes applications of ICP-AES [182]. 

The mechanism summarized in equations (40)—(42) is applicable, with some modifications,92 94 to the CTTM photochemistry of Crm and Rh111 acidoammine complexes. Thus the primary photochemical step is formation of a substitutionally labile reduced metal species and an oxidized ligand radical. In most systems, however, no permanent redox chemistry occurs owing to the facile reoxidation of the metal. The only net photoprocess observed in these cases is substitution of one or more ligands.70 95... 

Methods involve extractions of analytes into organic solvents, as well as treatments with acidic or basic reagents. Solid-phase extraction can be used for removal and pre-concentrations of analytes in aqueous solutions. Applications of low-power focused microwave technology have been investigated as a means of dissolution, and good results have been reported for extractions of organometal-lic compounds of tin and mercury (Schmitt et al., 1996 Szpunar et al., 1996). Analyses of CRMs were used for verification. The time necessary for quantitative isolations of the analytes was greatly reduced, e.g. 24 h to 5 min. In addition, there were reductions in solvent volumes, and improvement in analyte recoveries. Some of the analytical procedures for speciation of particular elements such as mercury, described later in this chapter, include microwave-assisted sample preparation. 

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],... 

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. 

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. 

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. 

In most field analysis in which separation techniques are the main difficulties, the traceability chain could not be accomplished easily by the use of calibration standards of a simple matrix. Consequently, either the validation of analytical methods or calibration by complex matrix reference materials is required. However, unless the process is clearly described with corresponding uncertainty, the validation process becomes a bottleneck for establishing a traceable measurement. Then, in most applications, the role of CRMs of a similar matrix becomes crucial in the quality of measurements. 

Chromium(n). The applications of chromium(n) salts in preparative organic chemistry have been reviewed.69 The kinetics of oxidation of Cr11 to Crm by halogen radical anions, a particularly simple one-electron oxidation scheme, have been determined.70 Hydrated electrons are formed71 during the photochemical oxidation of aqueous chromium(n). 

The plot of Fig. 10 is interesting since it also includes / -substituted thiophenes and permits a test of the applicability of the benzene crm+ constants. 

In recent years several applications of the HC1 proteolysis have been published in the field of Se speciation, for example, as regards Se-enriched lactic acid bacteria [66], mullet and cockles [8], and algae [67], where the technique provided extraction efficiencies of greater than 90 percent and preserved the integrity of the selenoamino acids. The general usefulness of this method of Se speciation is, however, questionable. Sometimes the authors do not state clearly whether phenol - an essential compound for the prevention of oxidation of SeCys - was used or not. In practice, neither phenol nor the short-duration MW-assisted irradiation can prevent the alteration of selenoamino acids [68-71], At the moment, no final conclusion on the applicability of HC1 proteolysis can be drawn, as CRMs certified for SeCys are still unavailable. On the other hand, an Se extraction efficiency of 80-90 percent can be achieved with this method only if either proteins are at least partly separated from the other components of the matrix, for example, separate analysis of fish muscles is carried out [8], or a considerable portion of Se is originally contained in inorganic forms in the sample, as observed by B Hymer and Caruso [1] in the case of Se-enriched food supplements. 

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