Selected Reference Material

A sewage contaminated calcareous soil was selected from the bank of reference materials of the Environment Institute of the Joint Research Centre of Ispra (Italy) in order to present both the characteristics of a calcareous soil (CaCOs content of 228 g kg ) and with heavy metal content well above the determination limits of the currently used flame atomic absorption spectrometric method. The soil sample was composed of 15.4% sand (2 mm to 50 mm), 9.3% coarse silt (50 to 20 pm), 34.0% fine silt (20 to 2 pm) and 41.3% clay ( 2 pm). 

This material was sieved to 2 mm, homogenized, sterilized and bottled in dark brown bottles for homogeneity and stability studies, which showed that the material was sufficiently homogeneous and stable to be used in an interlaboratory study. 

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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. 

An appropriate calibration of blank experiments has been performed using biological materials free of analytical compounds, such non-fatty milk, thereby making it necessary to certify these values by contrasting to reference materials too. This is commonly found in the case of feedstuffs and pharmaceuticals, while it is less frequent in clinical chemistry, biological fluids, and other materials such as foods. Suitable and selective reference materials are required to simultaneously... 

The standard data are determined experimentally on a series of carefully selected reference materials, which give unrestricted monolayer-multilayer adsorption. If the appropriate standard data are selected for the particular gas-solid system, it is therefore possible to identify the influence of porosity (micropore filling or capillary condensation) on the path of the isotherm. In this manner it is possible to check the validity of the BET-area and in favourable cases to evaluate the total surface area, the internal area and the external area ... 

Prevention and mitigation of the mechanical degradation process involving carbon can be done keeping the carbon activity in liquid sodium low (carbon concentration should be below 20 wppm) and selecting reference materials with low carbon activity with respect to liquid Na such as to prevent material decarburization. For instance, as reported in Ref. [75] the austenitic steel AISI 316 and the ferritic/martensitic steels 9Cr have a low carbon activity and the carbon activity in 2.25Cr-lMo steel can be reduced by adding Nb [20]. 

US National Library of Medicine (NLM) Gopher Gopher to gopher.nlm.nih.gov. The NLM gopher contains information about the library and selected reference materials. It also provides access to Locator, NLM s online catalog system, and to MEDLARS and TOXNET (for those with access codes). 

Sing (see Ref. 207 and earlier papers) developed a modification of the de Boer r-plot idea. The latter rests on the observation of a characteristic isotherm (Section XVII-9), that is, on the conclusion that the adsorption isotherm is independent of the adsorbent in the multilayer region. Sing recognized that there were differences for different adsorbents, and used an appropriate standard isotherm for each system, the standard isotherm being for a nonporous adsorbent of composition similar to that of the porous one being studied. He then defined a quantity = n/nx)s where nx is the amount adsorbed by the nonporous reference material at the selected P/P. The values are used to correct pore radii for multilayer adsorption in much the same manner as with de Boer. Lecloux and Pirard [208] have discussed further the use of standard isotherms. 

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

Conditions of microwave sampling were selected using soil reference materials P-1, SP-1, SP-3, PKP, PDPV (Russia). 

Detailed designs for fume control systems and selection [Pg.1268]

If all of the material is not to be removed as overhead vapors from the still, leave a percentage of a particular compound in the bottoms, then select the particular compound as the reference material b for a determinations. 

The general construction features and materials are quite similar to the lohe type units. For comparison selections, refer to Huff, Patton,Price,Ahraham, and Van Ormer. ... 

This Chapter reviews some selected historical examples of the development, production and use of reference materials (RMs), from the past century up to the present. It is, of necessity, a rather short and incomplete review describing international efforts in this area. From the references given at the end of this Chapter and at the end of Chapter 3, the reader may investigate further into the past. 

The history of reference materials is closely linked with the development of analytical chemistry. In the 19th Century all chemicals were, in comparison with those of today, of poor purity. Thus, for volumetric analysis suitable purified materials as primary standards had to be specified. One of the first examples was the recommendation of As(III) oxide by Gay-Lussac (1824) for this purpose. Somewhat later, Sorensen (1887) proposed criteria for the selection of primary chemical standards. These were further elaborated by Wagner (1903) at the turn of the last century. It is worthwhile mentioning that their criteria were quite similar to those used today. 

Selection of method appropriate for homogeneity and stability testing Design of the characterization of the reference material Sampling... 

There are also RMs which are prepared for a specific application and are used for validation of relevant methods. Cobbaert et al. (1999) made use of Ion Selective Electrode (ISE)-protein-based materials when evaluating a procedure which used an electrode with an enzyme-linked biosensor to determine glucose and lactate in blood. Chance et al. (1999) are involved with the diagnosis of inherited disorders in newborn children and they prepared a series of reference materials consisting of blood spotted onto filter paper and dried, from which amino-acids can be eluted and... 

Tab. 4.7 IAEA radioisotope reference materials selected for upgrade (Fajgelj et al. 1999) Code Matrix Measurands Interest ...

Traceability, however, is such an important concept that it will undoubtedly also be applied in future to radioisotopic reference materials. The IAEA is giving high priority to such work in its own reference material program. Table 4.7 provides details of some existing materials which have been selected for upgrade. 

Quality assurance of radiopharmaceutical preparation and use is obviously a very important topic because of its direct impact on patient diagnosis, treatment and health (see, e.g. Abreu 1996). Reference materials play only a small - but nevertheless important -role in this process, mainly in the area of calibration of radioactivity-measuring instruments. The materials of interest are all pure chemical containing calibrated activities of selected radionuclides used commonly in nuclear medicine (e.g. Co, Ga, I,... 

Ihnat M (1992) Selection and preparation of relevant reference materials for agricultural purposes. In Rossbach M, Schladot JD, Ostapczuk P, eds. Specimen Banking — Environmental Monitoring and Modem Analytical Approaches, pp 57-73. Springer, Berlin. 

Johnson AM, Sampson EJ, Blirup-Jensen S, Svendsen PJ 1996) Recommendations for the selection and use of protocols for assignment of values to reference materials. Europ J Clin Chem Clin Biochem 34 279-285. 

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. 

Tab. 9.1 Selected driving forces that affect extent of reference material usage (arranged by pairs, in order of increasing external forces)...

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