Suppliers of reference materials

In this section, discussion is limited to suppliers of reference materials which are available internationally, i.e. we are concerned here more with external quality assurance than with internal quality assurance. This is not intended to minimize the importance of reference materials for internal quality assurance indeed these are essential for monitoring the precision of the analytical methods and for establishing statistical control, e.g. using control charts. 

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. 

The major suppliers of internationally available biological reference materials are listed in Table 1 and an overview of their products including type and matrix is presented in Table 2. This information is taken from a (revised) survey by Cortes Toro et al. (1990) and from additonal recent information (Trahey, 1992 Chai Chifang, 1993) which also contain further details pertaining to the elemental concentrations and their uncertainties, the unit weight or volume of material supplied, its cost, and the minumum weight of material recommended for analysis. Another revision of the survey by Cortes Toro et al. (1990) is at present in preparation and will appear soon (Parr et al., 1994). 

OVERVIEW OF BIOLOGICAL REFERENCE MATERIALS AND ELEMENTS QUOTED FOR THE SUPPLIERS LISTED IN TABLE 1. 

If the element symbol is underlined, this indicates that a certified or recommended vaiue is available if not underlined, only an information value is available. Because of frequent changes in available and the offer of new materials the reader should consult actual catalogues of suppliers or other information (e.g. Klich and Walker, 1993) 

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Tab. 8.1 Major producers and suppliers of reference materials for inorganic and organic chemical composition quality control. The table lists in alphabetical order the popular names, or abbreviations, which may not be the full official title...

There are no special problems with the reconstitution or handling of these kinds of materials for electrolytes. The concentration of electrolytes is high, and no contamination problems are to be expected. Many commercial suppliers deliver reference materials for electrolytes in serum and urine. 

Measurement of hardness (qv) at room temperature is relatively easy however, it is the hot hardness at the temperature of cutting that is of importance for tool materials. Figure 3 shows the variation of hot (microindentation) hardness of various tool materials measured at different temperatures. The various suppliers of tool materials can be found in References 11—13 and other trade literature. 

Directories come from a variety of sources, and although most typically consist of an alphabetical listing of names and addresses, they often cover a much broader range of topics. Most magazines oriented to the industrial market publish some sort of buyer s guide or directory issue each year for their readers. These are handy reference publications to have, since addresses and phone numbers are items often provided in addition to listing members of organizations, companies involved in niche markets, suppliers of raw materials, suppliers of equipment, and much more. 

This section introduces the behavior and response of both unreinforced and reinforced plastics under loads lasting usually only a few seconds or minutes up to a maximum of fifteen minutes. Such short-term tests are used to define the basic or reference designing and engineering properties of conventional materials. Such properties as tensile strength, compressive strength, flexural strength (the modulus of rupture), shear strength, and associated elastic moduli are often shown on the data sheets provided by suppliers of plastic materials and are in computerized data banks. The influence of such factors as time, temperature, additives and reinforcements, and molecular orientation on the basic behavior of these properties is discussed in turn [1, 2, 10-14, 62-68, 245-87]. 

For guidance on the classification of chemicals by hazard category, refer to Appendix VI-A of the UFC. For additional assistance, the supplier of each material should be consulted. Manufacturers are required to publish Material Safety Data Sheets (MSDS) which may assist in determining the hazardous material classification. 

Some of the intended categories of use of radioisotopic reference material have been reviewed recently by Fajgelj et al. (1999). They include assignment of property values, establishing the traceability of a measurement result, determining the uncertainty of a measurement result, calibration of an apparatus, assessment of a measurement method, use for recovery studies and use for quality control purposes. It should be noted however that, in general, natural matrix reference materials are not recommended for calibration purposes. This should preferably be done with pure chemical forms of the element labelled with the isotope of interest. Calibrated isotopic sources of this kind are available from a number of commercial suppliers and are not the subject of this review. 

Another major supplier of stable isotope reference materials is the Institute for Reference Materials and Measurements (IRMM) in Geel, Belgium. These materials... 

Tab. 6.6 Examples of biological, food, agricultural and related RMs for chemical composition available from, principally, government agency suppliers (Ihnat 1988,1992,1998a International Atomic Energy Agency 1998 Institute for Reference Materials and Measurements 1999 National Oceanic and Atmospheric Administration 1995 Trahey 1998) ...

The revised database holds over 23 000 analyte values for 660 measurands and 1670 reference materials produced by 56 different producers, from 22 countries. The database is restricted to natural matrix materials (i.e. made from naturally occurring materials, excluding calibration standards manufactured from pure chemicals). Information has been extracted from the relevant certificates of analysis, information sheets, and other reports provided by the reference material producers. As a general rule, the authors have only included in the compilation reference materials for which a certificate of analysis or similar documentation is on file. Information included in the survey is on values for measurands determined in reference materials, producers, suppliers, the cost of the materials, the unit size supplied, and the recommended minimum weight of material for analysis, if available. The new searchable database has been designed to help analysts to select reference materials for quality assurance purposes that match as closely as possible, with respect to matrix type and concentrations of the measurands of interest and their samples to be analyzed see Table 8.3. 

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 most cases, mass spectra on single compounds were obtained with reference materials provided by commercial suppliers. This is the case for fatty acids, diacids and TAGs (Ribechini et al., 2008a). Nevertheless when the molecules of interest are not commercialy available it may be useful to synthesise and purify them in the laboratory as shown for the esters of beeswax (Gamier et al., 2002). 

Note (4) is very important as it highlights the fact that the reference material used for the method validation cannot be used again when the method is in routine use for calibration purposes. The same type of material can be used, but it needs to come from a different supplier. The same material cannot be used for calibration purposes and then as a quality control material. 

Some reference material producers/suppliers use different names to describe their materials. For example, a Standard Reference Material (SRM) is a certified reference material issued by the National Institute of Standards and Technology (NIST), while European Reference Materials (ERMs) are CRMs produced under a joint collaboration between three European reference materials producers, i.e. BAM (Federal Institute for Materials Research and Testing, Germany), IRMM (European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Belgium) and LGC (UK). 

Medical grade plastics are discussed with reference to biocompatibility and the tests that the end-product manufacturer should perform in order to ensure the safety of the material. Regulatory requirements are described, and tabulated data is presented on mostly European suppliers of medical grade plastics. The data shows that most companies rely onUSP Class VI certificates to demonstrate the suitability of their materials for the medical industry. However, it is argued that most manufacturers of medical devices would benefit more from tests carried out according to ISO 10993. 6 refs. 

At the same time, decisions must be made regarding the producers of these materials. For new reference material needs, identified within agencies such as NIST or NRC-Canada, this entails a decision as to whether to produce the material in-house or to sub-contract the work elsewhere. For externally recognized needs, both a supplier (e.g., either one of the recog-... 

To examine an entire process from beginning to end (raw material suppliers to stability of the final product) as a unit operation. With this frame of reference, the important factors in ihe entire process and their effect on each other can be determined. The use of initial screening experiments on each of the individual steps would identify the important factors to include in the overall design. This is the only practical way to determine how the process is going to react at the high and low set points for each of the important factors in the process while the other important factors are at either their high or low set points. 

To identify other hazardous wastes in shop, the three types of the material safety data sheet (MSDS) provided by the supplier of the product should be reviewed. A plant manager can also find out the hazardous ingredients in the processing chemical and refer to the State Hazardous Waste Regulations or call the State Division of Hazardous Waste. 

As far as the use of the certified reference material is concerned, in an ideal situation the supplier or producer should give advice on the appropriate use to the user. In addition it is essential to obtain information relevant to storage temperature, influence of moisture and influence of contamination. The possibility of dividing the certified reference material into different portions after opening in order to maintain its original properties should always be considered. 

Standard reference materials are available from several suppliers in the UK, a selection of agricultural substances is available from the Laboratory of the Government Chemist, and in the US from the National Institute of Standards and Technology (NIST), where the Standard Reference Materials programme is described at ... 

Standard reference material (SRM) for wavelength accuracy, stray light, resolution check, and photometric accuracy can be purchased from NIST. Certified reference materials (CRMs) which are traceable to NIST and recertification services can be purchased from instrument manufacturers and commercial vendors [12]. The cost of neutral-density filters and prefabricated standard solutions in sealed cuvettes can be substantial. When purchasing performance verification standards from a secondary supplier other than a national standard organizations such as NIST in the United States and National Physical Laboratory (NPL) in the United Kingdom, make sure that the traceability of the standards are available in the certificates. The traceability establishes the relationship of individual results to the national standard through an unbroken chain of comparisons. 

Residue-testing laboratories might also need to review their sample preparation processes and consider modifying or eliminating tissue homogenization prior to residue extraction. Suppliers of proficiency-testing services should also question whether certain drugs are appropriate to include in such studies. For example, liver spiked with sulfaquinoxaline, sulfadiazine, or sulfamerazine is not suitable for preparation of spiked interlaboratory check samples or reference materials. 

The suppliers of rubbers and other raw materials have been releasing technical brochures and bulletins pertaining to the suitability of various rubbers and the rubber chemicals of various kinds and various application details based on their laboratory test data and field trials. These publications are extremely useful resources for understanding rubber technology and its diversified facets. For this reason the addresses of a few references of technical literature considered as valuable sources of information are given in the appendix. 

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