The role of reference materials

In this article the role of reference materials is confined to chemical measurements only. Recognized reference materials are one of the tools to obtain comparability of analytical results. Recognition demands confidence in the reference materials and in the reference material producers. A reference material producer is a technical competent body that is fully responsible for the certified or other property values of the reference material. The "analyte" has to be specified in relation to the selectivity of analytical procedure. The full range of reference materials can be presented as a three-dimensional space of the coordinates: analyte, matrix and application. If reference materials are used for calibration or correction of calibrations they establish the traceability of results of chemical measurements. The traceability is only valid within a stated range of uncertainty. Pure substances can represent the unit of amount of substance. A precondition is the microscale specification of the analyte and the accurate determination of the main component and/or the impurities.     

The role of reference materials in analytical chemistry

The paper demonstrates a concept and possible models for an international infrastructure of chemical measurements by using reference materials.The function of reference materials to establish traceability and means of quality assurance is emphasized.     

The role of reference materials in food analysis

Reliability and accuracy of measurements in food and agricultural materials are essential both for implementation of the legislation concerning public health and consumer protection and for the elimination of disputes arising from trade requirements and technical barriers. In such process the crucial step is represented by the programmes aimed at the quality assurance of analytical data produced by laboratories involved in food analysis. In this framework a major role is played by the proper use of reference materials. This report provides an overview on relevance, availability, use, certification procedures and perspective of reference materials in food analysis. Measurement harmonization procedures are also discussed.     

The role of reference materials in the analytical laboratory

Summary Importance, definition, preparation, characterization, selection and use of reference materials in the analytical laboratory are discussed in general.

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Die Rolle der Referenzmaterialien im analytischen Laboratorium

Zusammenfassung Bedeutung, Definition, Herstellung, Charakterisierung, Auswahl und Verwendung von Referenzmaterialien im analytischen Laboratorium werden allgemein diskutiert.

     

The reference materials syndrome

This paper examines specific cases in the literature where analysts using spectroscopic instrumentation report elemental concentrations that agree with information values reported in reference material certificates that are subsequently found to be incorrect.     

The future demand for geological reference materials

Geological RMs (G-1 and W-1) were introduced in 1951 for the purpose of validating the accuracy of silicate rock analysis by dc arc spectrography. Since then the introduction of an array of other spectrographic methods has greatly enhanced research into geological processes. The range of elements that could be determined was expanded, and the detection limits for measurement was lowered repeatedly through the years. The development and use of reference materials was critically important in supporting this rapid expansion of geological research. Essentially, all RMs are of importance to the geosciences community since G-1 and W-1 have been prepared and distributed by national geological institutions, first by the USGS or the CRPG, rather than by national metrology institutions. These geological institutions are not yet certifying their RMs according to ISO Guides. The International Association of Geoanalysts (IAG) is seeking to meet this higher metrological requirement. Since the inception of the IAG certification program in 2003, five powdered silicate rock materials have been issued to meet the demand with respect to calibration, method validation, traceability, etc. for whole rock major and trace element analysis. The introduction of microanalytical techniques nearly decades ago and the more recent advent of MC-ICP-MS have become new driving forces in geochemical research. The first opened the possibility of performing in situ elemental composition studies at the ??m scale. The second led to the discovery of small isotope composition variations of mass- and non-mass-dependent processes in ??non-traditional?? stable isotopes (e.g., Fe, Cu, Zn, Mo, W, and Hg) through cosmo- and geochemical processes. Coupling the two techniques expands in situ analysis to isotopic studies. These developments have created great demand for (certified) RMs for both isotope ratio and microanalytical measurements for the geochemical community that is not yet being met. Homogeneity at a ??m scale and unmatched matrices of the natural minerals or synthetic doped glasses hamper the progress in certification of RMs for the microanalytical measurement community. A challenge for the production of isotope RMs is to prepare an RM solution with an isotopic composition similar to the natural systems under investigation. Refined cadmium and nickel metals, for example, have fractionated isotopic compositions far above the range observed in natural systems of interest. Yet, the calibration RM cannot fulfill its purpose when the uncertainty of its isotopic composition exceeds that of the unknowns being measured against it. In this regard, the IAG has recently certified a calibration solution for the determination of Os isotopic ratios. It is also working through member organizations, USGS, and MPI for Geochemistry (Mainz) to develop appropriate microanalytical standards. In addition to these current and future challenges, establishing metrological traceability of geological reference materials in the absence of starting points developed by national metrology institutions is a major issue that needs attention in all future certifications.     

The need for new isotope reference materials

Isotope reference materials are needed to calibrate and validate analytical procedures used for the determination of isotope amount ratios, procedurally defined isotope ratios or so-called δ values. In contrast to the huge analytical progress in isotope ratio analytics, the production of isotope reference materials has not kept pace with the increasing needs of isotope analysts. Three representative isotope systems are used to explain the technical and non-technical difficulties and drawbacks, on one hand, and to demonstrate what can be achieved at its best, on the other hand. A clear statement is given that new isotope reference materials are needed to obtain traceable and thus comparable data, which is essential for all kinds of isotope research. The range of available isotope reference materials and δ reference materials should be increased and matrix reference materials certified for isotope compositions or δ values, which do not exist yet, should be provided.     

Are certified reference materials a victim of quality systems? The need for working matrix-certified reference materials

The use of natural matrix-certified reference materials by commercial environmental laboratories is increasing rapidly. These materials are now an essential component of the quality systems of most commercial environmental laboratories. The use is increasing faster than existing producers, principally government agencies, can meet. The use of data from well established laboratory proficiency schemes is shown to be one alternative way of producing natural matrix-certified reference materials designed for use as day-to-day within-batch control materials.     

Stability of reference materials

Summary The problem of stability of reference materials is particularly difficult when dealing with complex biological matrices and certification of the content of relatively unstable organic components. This paper considers two aspects of the problem: a) the preparation and packaging of material in a form which gives the greatest likelihood of achieving acceptable stability; b) the design of the measurement studies undertaken to monitor short-term stability for shipment, laboratory handling and long-term storage stability.     

The importance of reference materials in doping-control analysis

Polyamidoamine (PAMAM) dendrimers and water-soluble 3-mercaptopropionic acid (MPA)-capped CdSe quantum dots (QDs) were combined to produce a new gel containing supramolecular complexes of QDs/PAMAM dendrimers. The formation of the QDs/PAMAM supramolecular complexes was confirmed by high resolution electron microscopy and Fourier transform infrared (FTIR) analyses. Molecular dynamics simulations corroborated the structure of the new QDs/PAMAM-based supramolecular compound. Finally, on the basis of the prominent fluorescent properties of the supramolecular complexes, PAMAM dendrimer was functionalized with folic acid to produce a new QDs/PAMAM-folate derivative that showed an efficient and selective performance as a marker for gastric cancer cells.     

The preparation of biological and environmental reference materials

The facilities of the Institute for Reference Materials and Measurements for the preparation of biological and environmental reference materials are discussed under the aspect of satisfying important parameters for the preparation of candidate reference materials. The choice of transformation methods and their possible influences on quality and long-term conservation, the need for automation as well as the importance of quality control are particularly emphasized.     

Availability of reference materials: COMAR the database for certified reference materials

COMAR is the international database for certified reference materials. A new user-friendly web-based version, COMAR², has been developed by BAM and CONET Consulting AG which will be available in December 2002. The advantages of COMAR² are briefly explained.Presented at the International ILAC/IAF Conference on Accreditation in Global Trade, 23-25 September 2002, Berlin, Germany     

Multipurpose biological reference materials

Summary Reference materials to meet multipurpose needs for analysis of both inorganic and organic constituents in biological investigations are not readily available. A human total diet material is being investigated as a reference material for a wide variety of constituents of interest to human nutrition and health. This material shows a stable assay value for the natural levels of a number of vitamins following freeze-drying or radiation sterilization. This is an important feature in producing materials for long term stability as a Reference Material for natural levels of these constituents. An exception is an increase of 34% in assay value of folic acid upon freeze-drying and an 85% increase upon freezedrying followed by radiation sterilization.

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Vielseitig verwendbare biologische Referenzmaterialien

     

The use of reference materials in the finnish industry

Summary A report is given on the results of a survey of the use of reference materials in the chemical industry of Finland. It has been found that there is virtually no production of reference materials in Finland and that most of the materials used are not certified. Mostly, different materials are used which are pharmacopoeia standards with regard to their physical properties. Some companies were found to use more than 100 different reference materials.

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Verwendung von Referenzmaterialien in Finnland

Zusammenfassung Es wird über das Ergebnis einer Umfrage zur Benutzung von Referenzmaterialien in der chemischen Industrie Finnlands berichtet. Es ergab sich, daß in Finnland praktisch keine solchen Substanzen hergestellt werden und die meisten der verwendeten Materialien nicht zertifiziert sind. Meist werden verschiedenartige chemische Substanzen verwendet, die in Bezug auf ihre physikalischen Eigenschaften einem Arzneibuchstandard entsprechen. Einige Firmen benutzen mehr als 100 verschiedene Referenzmaterialien.

Presented at Euroanalysis III conference, Dublin, August 20–25, 1978     

The updated IAEA database of natural matrix reference materials

The International Atomic Energy Agency (IAEA) maintains a database of biological and environmental reference materials of natural origin (human and animal tissues, foods, plants, soils, sediments, etc.) for trace elements, radionuclides, stable isotopes, organic contaminants and other related measurands. The purpose is to help analysts to select reference materials for quality assurance purposes that match as closely as possible (i.e., with respect to matrix type and concentrations of the measurands of interest) the real samples that are to be analyzed. Former versions of this database were prepared in co-operation with the United Nations Environment Programme (UNEP), and provided as hardcopies free of charge. The latest version was from 1995. More recently the database has been updated by the IAEA so that it now contains more than 22,500 values (mass fraction or concentration) for 660 different measurands and 1,705 reference materials developed by 56 producers from 22 countries. This paper gives an overview of the structure and content of the database and of the two ways it may be browsed. Emphasis is given to reference materials that are intended to verifying analysis for radioanalytical measurements. The database is soon accessible on-line, cost-free, via the internet.     

Development of mycotoxin reference materials

Summary The analytical difficulties in mycotoxin determination have given rise to the development of mycotoxin reference materials by the European Community Bureau of Reference (BCR) in cooperation with several European Laboratories, among them the National Institute of Public Health and Environmental Protection. The first project undertaken concerned four milk powders certified for their aflatoxin M₁ content (concentrations 0, 0.1, 0.3 and 0.8 g/ kg). Projects that are well-advanced include two peanut meals (aflatoxin B₁ contents 0 and ca. 200 g/kg) and two compounded animal feedingstuffs (aflatoxin B₁ contents 0 and 10 g/kg). Mycotoxin reference materials are also under development for zearalenone in wheat and maize, and for ochratoxin A in wheat.The general approach followed in the development and certification of mycotoxin reference materials (preparation, testing for homogeneity and stability, intercomparisons of methods and certification exercise) will be discussed and exemplified with the help of the completed project on aflatoxin M₁ in milk powder.

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Entwicklung von Mycotoxin-Referenzmaterialien

     

Homogeneity testing of reference materials

 Homogeneity testing is of the highest importance for the certification of reference materials, as it should demonstrate the validity of the certified values and their uncertainties in the analysis of individual units or portions thereof. However, the conclusions drawn from the results of these studies may often be questioned. It is proposed to improve this situation by quantifying the effect of homogeneity studies in terms of their impact on the uncertainty of certified values. Here it should be noted that the between-units variability directly affects the certified uncertainty, whereas the within-unit inhomogeneity only defines the minimum representative test portion. Received: 18 September 1997 · Accepted: 21 November 1997     

Value assignment of nutrient concentrations in five standard reference materials and six reference materials

A number of food-matrix reference materials (RMs) are available from the National Institute of Standards and Technology (NIST) and from Agriculture Canada through NIST. Most of these materials were originally value-assigned for their elemental composition (major, minor, and trace elements), but no additional nutritional information was provided. Two of the materials were certified for selected organic constituents. Ten of these materials (Standard Reference Material [SRM] 1,563 Cholesterol and Fat-Soluble Vitamins in Coconut Oil [Natural and Fortified], SRM 1,566b Oyster Tissue, SRM 1,570a Spinach Leaves, SRM 1,974a Organics in Mussel Tissue (Mytilus edulis), RM 8,415 Whole Egg Powder, RM 8,418 Wheat Gluten, RM 8,432 Corn Starch, RM 8,433 Corn Bran, RM 8,435 Whole Milk Powder, and RM 8,436 Durum Wheat Flour) were recently distributed by NIST to 4 laboratories with expertise in food analysis for the measurement of proximates (solids, fat, protein, etc.), calories, and total dietary fiber, as appropriate. SRM 1846 Infant Formula was distributed as a quality control sample for the proximates and for analysis for individual fatty acids. Two of the materials (Whole Egg Powder and Whole Milk Powder) were distributed in an earlier interlaboratory comparison exercise in which they were analyzed for several vitamins. Value assignment of analyte concentrations in these 11 SRMs and RMs, based on analyses by the collaborating laboratories, is described in this paper. These materials are intended primarily for validation of analytical methods for the measurement of nutrients in foods of similar composition (based on AOAC INTERNATIONAL's fat-protein-carbohydrate triangle). They may also be used as "primary control materials" in the value assignment of in-house control materials of similar composition. The addition of proximate information for 10 existing reference materials means that RMs are now available from NIST with assigned values for proximates in 6 of the 9 sectors of the AOAC triangle. Five of these materials have values assigned for total dietary fiber-the first such information provided for materials available from NIST.