Reference materials Development

NIST methods and Reference Materials Development of reference methods and reference materials for the determination of hormones in human serum... 

The clinical reference materials developed for the validation of the performance of photometric systems... 

For each analyte, mean concentrations and their 95% confidence interval were evaluated for each method employed, because differences among the results obtained by the individual methods were significant. The assigned concentration values were estabhshed based on the interpretation of data respecting the methods of preparation and measurement (taking into account the contribution of a statistical as well as a systematic nature). Accordingly, the mean values assigned for different methods of measurement for five selected analytes from the synthetic sera reference materials developed are presented in Table 2. 

Ferrites have become a reference material developments associated with other new magnetic materials, such as the extra-hard rare-earth inter-metallics (Buschow, 1990), or the extra-soft amorphous ribbons (Boll Hilzinger, 1983) are often assessed by comparison with ferrites. 

Tung, M. S. and Sung, P Calcium Phosphate Type Reference Material Development, Preparation, and Characterization, Characterization and Performance of Calcium Phosphate Coatings for Implants, ASTM STP 1196, E. Horowitz and J. E. Pair, Eds., ASTM International, West Conshohocken, PA, 1994, pp. 99-110. 

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. 

It is known that the reliability of analytical information obtained depends particularly on the range of reference materials (RM) used. The most of RMs developed by the Institute of Geochemistry, SB RAS are included in the State Register of certified types of National Certified Reference Materials of Russian Federation. The reference materials are routinely analyzed for the stability and their life durations are timely prolonged. Developed RMs (27 samples) characterize mainly mineral substances. 

Laser based mass spectrometric methods, such as laser ionization (LIMS) and laser ablation in combination with inductively coupled plasma mass spectrometry (LA-ICP-MS) are powerful analytical techniques for survey analysis of solid substances. To realize the analytical performances methods for the direct trace analysis of synthetic and natural crystals modification of a traditional analytical technique was necessary and suitable standard reference materials (SRM) were required. Recent developments allowed extending the range of analytical applications of LIMS and LA-ICP-MS will be presented and discussed. For example ... 

Because of the complex nature of the discharge conditions, GD-OES is a comparative analytical method and standard reference materials must be used to establish a unique relationship between the measured line intensities and the elemental concentration. In quantitative bulk analysis, which has been developed to very high standards, calibration is performed with a set of calibration samples of composition similar to the unknown samples. Normally, a major element is used as reference and the internal standard method is applied. This approach is not generally applicable in depth-profile analysis, because the different layers encountered in a depth profile of ten comprise widely different types of material which means that a common reference element is not available. 

Standardization. Standardization in analytical chemistry, in which standards are used to relate the instrument signal to compound concentration, is the critical function for determining the relative concentrations of species In a wide variety of matrices. Environmental Standard Reference Materials (SRM s) have been developed for various polynuclear aromatic hydrocarbons (PAH s). Information on SRM s can be obtained from the Office of Standard Reference Materials, National Bureau of Standards, Gaithersburg, MD 20899. Summarized in Table VII, these SRM s range from "pure compounds" in aqueous and organic solvents to "natural" matrices such as shale oil and urban and diesel particulate materials. 

TLC Analysis. Samples were examined by TLC using standard procedures. Rf values were determined and compared with those of authentic reference materials. Radioactive components were located by scanning (Vanguard Instrument Corp., North Haven, Conn., Model 885) or by autoradiography (Eastman Kodak, Rochester, N. Y., type AA film). The relative Rf value of DCDD on silica gel plates (Brinkmann Instruments, Inc., Westbury, N. Y., type For,4) when developed with n-hexane dioxane acetic acid, 90 10 4, V/V/V, was 0.90. The observed impurity had a relative Rf value of 0.40. On Brinkmann alumina plates, developed with n-hexane, DCDD had a relative Rf of 0.32. Neither system separated the chlorinated dibenzodioxin isomers. 

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. 

In 1901, the U.S. National Bureau of Standards (NBS) - now the National Institute of Standards and Technology (NIST) - was founded because of the increasing demand for various kinds of standards in the rapidly developing engineering industries. The early history of the NBS reference material program started in 1905 with a cooperative effort within the iron and steel industry whereby industrial analysts helped characterize the individual reference materials. Cooperation with NBS was recognized as a mark of achievement for the laboratory, so this effort served a dual purpose. It both helped the laboratory develop its measurement skills and also helped NIST understand the meastuement problems associated with a given matrix. 

Finally some additional milestones in organization, research and development of RMs need to be mentioned. The large increase in the number of reference materials being produced led in 1975 to the formation of an ISO Council Committee on Reference Materials (ISO-REMCO) charged with the establishment of international guidelines on principles of certification, methods of use, needs, availability and nomenclature (Klich 1999), see also Sections 1.2 and 1.3. 

After the verification of homogeneity and stability, the characterization of material can take place. Frequently, this step is named certification rather than characterization, which is wrong in view of the discussion about homogeneity and stability and their impact on the reference material. The certification of our reference material is more than the characterization of the material. Flowever, for most people working on the development of measurement methods, the characterization is the most interesting part of the project. This probably explains the huge amount of literature available. 

Lee H-B and Chau ASY (1987) Analytical reference materials Part VII. development and certification of a sediment reference material for total polychlorinated biphenyls. Analyst 112 37-40. Meinke WW (1971) Standard reference materials for clinical measurements. Anal Chem 43(6) 28A-47A. 

Wagstaffe PJ (1984) Development of food-oriented reference materials by the Community Bureau of Reference (BCR) In Wolf WR, ed. Biological Reference Materials, pp 63-78. Wiley Sons. 

Ihnat M (1988b) Criteria for the development ofbiological reference materials. Fresenius Z Anal Chem 332 568-572. 

Ihnat M (1994) Development of a new series of agricultural/food reference materials for analytical quality control of elemental determinations. J AOAC Inti 77 1605-1627. 

Moens L, Verreft P, Boonen S, Vanhaecke F and Dams R (1995) Solid sampling electrothermal vaporization for sample introduction in inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. Spectrochim Acta 508 463-475. Mooijman KA, In t Veld PH, Hoekstra JA, Heisterkamp SH, Havelaar AH, Notermans SHW, Roberts D, Griepink B, Maier E (1992) Development of Microbiological Reference Materials. European Commission Report EUR 14375 EN, Community Bureau of Reference, Brussels. 

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