Internal laboratory reference materials

An outline laboratory QA procedure would need to include the following. In addition to the use of freshly made synthetic calibration standards, in-house standards, internationally recognized reference materials, and method blanks, as described above, it should include ... 

In order to cope with the lack of CRMs for endogenous species, the practice of laboratory internal QC materials is developing. A Laboratory Reference Material (LRM) was prepared from Brazil nuts (Bertholletia excelsa) for QC of the selenomethionine determinations. The concentration of selenomethionine was 79.9 p,g g-1. The homogeneity and stability of this candidate CRM passed the relevant tests recommended by the Measurement and Testing Programme [97],... 

The role and use of reference materials are in principle well known, in particular for Certified Reference Materials (CRMs) used as calibration materials or matrix materials representing - as far as possible - real matrices used for the verification of the measurement process, or (not certified) laboratory reference materials (LRMs also known as quality control (QC) materials) used, for example, in interlaboratory studies or in the maintenance of internal quality control (control charts). Examples of reference materials relevant to WFD monitoring (water, sediment and biota) are described in the literature (Quevauviller, 1994 Quevauviller and Maier, 1999). 

Every analytical laboratory should have its own reference materials for internal quality assurance, and such materials should conform to the same standards of appropriateness, homogeneity and long term stability as are required for certified reference materials (see section "preparation of reference materials). In practice, however, most analytical laboratories do not use their own "in-house" reference materials for internal quality assurance but rather rely on internationally available reference materials. In the opinion of the present author, this is undesirable since much larger amounts are required for internal quality assurance than for externai quality assurance, and thereby the available stocks of expensively prepared certified reference materials will be consumed much too quickly. 

For corrections of instrument-related errors, an internal standard reference material such as silicon and LaB6 should be used. The development of parallel beam geometry, not only for synchrotron sources but also for laboratory X-ray sources, eliminates the effects of transparency, flat specimens, and displacement errors. On the other hand, the internal standard material is applicable for quantitative analysis of coexisting material in the sample by means of multiphase analysis by the Rietveld method. 

Perhaps the greatest problem in trace analysis is assurance of the accuracy of the results (i.e., the avoidance of systematic errors). Systematic sources of error are possible in every step of an analytical process. The most reliable method for detecting systematic errors is continuous and comprehensive quality assurance, particularly by occasional analysis of (certified) standard reference materials. Strictly speaking, an analytical method cannot be calibrated if suitable (i.e., representative) standard reference materials adequately representing the matrix of the expected test samples are not available. However, internal laboratoiy reference materials can then usually be prepared, whose matrix largely resembles the matrix of the test portions expected. If problems occur in the preparation of such reference samples, the standard addition method (SAM) can be applied, in which internal laboratory standards are added stepwise to the test sample (analyte and matrix)... 

MnO, P2O5 were also measured for some samples. The measured X-ray intensities were corrected for matrix effects, absorption, and secondary fluorescence by the Bence-Albee correction program. Results were internally calibrated against international standards, and a laboratory reference material (hornblende) was repeatedly measured to insure consistency between analytical sessions. The results for each point analysis were normalized to total 99.00% (allowing 1 % for water and trace elements) and then the average calculated for each sample (Table 2). 

Standard reference materials provide a necessary but insufficient means for achieving accuracy and measurement compatibiUty on a national or international scale. Good test methods, good laboratory practices, well-qualified personnel, and proper intralaboratory and intedaboratory quaUty assurance procedures ate equally important. A systems approach to measurement compatibiUty is ikustrated in Figure 2. The function of each level is to transfer accuracy to the level below and to help provide traceabiUty to the level above. Thus traversing the hierarchy from bottom to top increases accuracy at the expense of measurement efficiency. 

The primary purposes for which reference materials are employed are encompassed within the laboratory Quality Assurance Procedures. Quality assurance comprises a number of management responsibilities which focus on how the laboratory is organized, how it deals with situations, how it interacts with users, together with analytical responsibilities re internal quality control and external quality assessment (Sargent 1995 Burnett 1996). Ideally each component follows a documented protocol and written records of all activities are maintained. 

McQueen MJ, Roberts HR, Siest G (1995) Reference materials and reference measurement systems in laboratory medicine - a major international meeting organized by the International Federation of Clinical Chemistry (IFCC), Geneva, October 5-7, 1994. Europ J Clin Chem Clin Biochem 33 977-999. 

In his survey of the use of CRMs in food related publications on the subject of trace elements for the years 1990-1996, Jorhem (1998) checked 82 papers published in five international journals. He found that in 42 papers there was no mention of CRM results and assumed that no CRMs were used. He wrote Since the importance of incorporating CRMs in the AQA-activities today is well recognized, it is surprising that firstly so many laboratories still do not use CRMs and secondly that scientific journals accept papers describing analytical results without the use of reference materials, as part of the verification of the analytical results . 

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). 

A number of scientific journals regularly publish papers reviewing the state of the art in the RM business as well as original contributions on certification, inter-laboratory comparisons, and on RM/CRM applications. Table 8.2 lists the most popular and widely cited. The most prolific journals are Fresenius Journal, JAAS, Science of the Total Environment and Water, Air, Soil Pollution, all with around or even more than 50 papers mentioning reference materials from 1998 and 1999. Of these, Fresenius Journal led in 1998, with more than 80 papers. This was partly because it traditionally publishes, so far in six special issues, a series of papers presented at the International Biological and Environmental Reference Materials Symposia (BERM) series. The role and contribution of the BERM series of meetings is reviewed below. 

Over the past decade, a major trend has been the development of the use of proficiency testing (PT) or evaluation materials (Fox 2000). PT materials are a type of reference material, which aid in assessment of analytical laboratory measurement quality. There will be an increased use of such materials as part of laboratory accreditation programs and other new quality assurance efforts, including internal audits. At the same time, a number of providers have used PT schemes to produce a form of RM intended to meet the ever-growing need for RMs required for routine QC use (Jenks 1995,1997). 

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. 

Institut de Recherches de la Siderurgie, France International Organization for Standardization ISO Council Committee on Reference Materials International Union for Pure and Applied Chemistry Laboratory of the Government Chemist, UK, formerly NPL National Bureau of Standards, USA, now NIST National Committee for Clinical Laboratory Standards, USA National Institute for Biological Standards and Control, UK Japanese National Institute for Environmental Studies National Institute of Occup. Health, Oslo, Norway National Institute of Standards and Technology, USA, formerly NBS,... 

It is important that a measurement made in one laboratory by a particular analyst can be repeated by other analysts in the same laboratory or in another laboratory, even where the other laboratory may be in a different country. We aim to ensure that measurements made in different laboratories are comparable. We are all confident that if we measure the length of a piece of wire, mass of a chemical or the time in any laboratory, we will get, very nearly, the same answer, no matter where we are. The reason for this is that there are international standards of length, mass and time. In order to obtain comparable results, the measuring devices need to be calibrated. For instance, balances are calibrated by using a standard mass, which can be traced to the primary mass standard (see also Chapter 5). The primary standard in chemistry is the amount of substance, i.e. the mole. It is not usually possible to trace all of our measurements back to the mole. We generally trace measurements to other SI units, e.g. mass as in 40 mg kg-1 or trace back to reference materials which are themselves traceable to SI units. 

The previous chapters of this book have discussed the many activities which laboratories undertake to help ensure the quality of the analytical results that are produced. There are many aspects of quality assurance and quality control that analysts carry out on a day-to-day basis to help them produce reliable results. Control charts are used to monitor method performance and identify when problems have arisen, and Certified Reference Materials are used to evaluate any bias in the results produced. These activities are sometimes referred to as internal quality control (IQC). In addition to all of these activities, it is extremely useful for laboratories to obtain an independent check of their performance and to be able to compare their performance with that of other laboratories carrying out similar types of analyses. This is achieved by taking part in interlaboratory studies. There are two main types of interlaboratory studies, namely proficiency testing (PT) schemes and collaborative studies (also known as collaborative trials). 

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. 

Natural abundance data are nearly always reported as delta values, 5 in units of per mil ( mil = 1000), written %o. This is a relative measurement made against a laboratory s own reference material, a working standard , calibrated against an international standard. Delta values are calculated from measured isotope ratio as ... 

Internal quality control (IQC) is one of a number of concerted measures that analytical chemists can take to ensure that the data produced in the laboratory are of known quality and uncertainty. In practice this is determined by comparing the results achieved in the laboratory at a given time with a standard. IQC therefore comprises the routine practical procedures that enable the analyst to accept a result or group of results or reject the results and repeat the analysis. IQC is undertaken by the inclusion of particular reference materials, control materials , into the analytical sequence and by duplicate analysis. 

If the ocean sciences are to move forward and adopt the regular use of reference materials, the advantages of using such materials (and the pit-falls of not using them) need to be more broadly disseminated. Proposal and journal article reviewers should question the analytical quality control of measurements made without the benefit of reference materials. Outreach focused on how to use reference materials in the ocean sciences will further increase the awareness of the individual investigators and provide a focus for proper handling and application of a laboratory s internal reference materials. 

Internal standards Used to demonstrate method reproducibility. Reference materials, such as the low permeability markers mannitol and atenolol and the high permeability markers metoprolol and ketoprofen, may be used to compare values between laboratories [3, 50]... 

The second module. Method, involves determining the level of verification and validation to which the user s methodology has been subjected. Verification is the general process used to decide whether a method in question is capable of producing accurate and reliable data. Validation is an experimental process involving external corroboration by other laboratories (internal or external) of methods or the use of reference materials to evaluate the suitability of methodology (1). A menu of choices includes (1) the method has only been verified, (2) the method has been both verified and validated, or (3) the method has been neither verified or validated. 

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