Production of CTC-containing porcine reference materials.

The European Commission (EC) established the Standards, Measurements and Testing programme for the preparation of Reference Materials (RMs) as an aid to harmonise testing for veterinary drug residues throughout the European Union (EU). The production of chlortetracycline (CTC)-free and CTC-incurred pig tissues as candidate RMs is described. High performance liquid chromatography (HPLC) with fluorescence detection of CTC and 4-epi-CTC was used for all tissue analyses. A pilot study revealed that incurred CTC residues were stable in pig kidney, liver and muscle lyophilised powders during storage for 10 weeks at -70, -20 and +37 degrees C, obviating the need for addition of a stabiliser (thimerosal). In the main study, 500 vials each of CTC-free and CTC-incurred kidney, liver and muscle were produced. Target concentrations in the CTC-incurred lyophilised tissue powders were 750-1500, 500-1000 and 300-600 micrograms kg-1 for kidney, liver and muscle, respectively. Following lyophilisation, the mean +/- s concentrations of CTC in the incurred positive RMs were 1,315 +/- 56.9, 765 +/- 35.3 and 378 +/- 16.8 micrograms kg-1 for kidney, liver and muscle respectively. Residual moisture in the RMs ranged from 1.6 +/- 0.53% for muscle to 3.0 +/- 0.50% for liver. Between-vial homogeneity for incurred powders was determined for 20 vials of each material, which had been removed at regular intervals during the filling process. Relative standard deviations (RSDs) for kidney, liver and muscle were 4.3, 4.6 and 4.4% respectively, being within the interassay RSD of the method and indicating that mixing was effective. Stability of powders stored at -18, 4, 20 and 37 degrees C was assessed over a period of 79 weeks. No measurable degradation occurred over this time period at any of the storage temperatures. It is concluded that these candidate RMs are homogenous, stable and are suitable for certification.     

Production and certification of environmental reference materials in Romania

Preparation techniques for single-element and multielement standard solutions, with special emphasis on the potential progress in this field are presented. A short review of locally available reference materials is given. Some aspects of the experience accumulated in Romania regarding the various certification approaches of reference materials are presented and the main characteristics of these certified reference materials are listed. Received: 23 May 1997 / Revised: 15 August 1997 / Accepted: 15 August 1997     

New matrix-free reference material for ethene in the form of optical fibres

Reference materials are indispensable in the quality control and quality assurance of analytical measurements. One novel approach to the generation of standard gaseous mixtures of toxic, reactive, volatile, labile, and malodorous substances involves thermal decomposition or rearrangement, under defined temperature conditions, of compounds immobilized, by chemical bonding, on the surface of an appropriate carrier to release specific amounts of a volatile compound. In this technique the type of support used to immobilize the compound is extremely important, because the amount of analyte released depends directly on the choice of material. In this paper we report the novel preparation of a matrix-free ethene standard in the form of glass fibres coated with a thin layer of aluminium, the surface of which is modified by reaction with a specific compound. As a result of thermal decomposition of this compound, gaseous ethene is formed. In this paper we present the results obtained from tests of stability and homogeneity, two properties of crucial importance in the preparation of reference materials, by comparison of a series of results obtained for randomly chosen samples of the reference material. Interlaboratory comparative studies resulted in determination of a reference value for the ethene formed after thermal decomposition of the surface compound ((2.12?±?0.14) ng per fibre).     

Production of certified reference materials for the detection of genetically modified organisms

Certified reference materials (CRMs) are an essenIial tool in the quality assurance of analytical measurements. They are produced, certified, and used in accordance with relevant ISO (International Organization for Standardization) and BCR (Community Bureau of Reference) guidelines. The Institute for Reference Materials and Measurements (IRMM; Geel, Belgium) has produced the first powdery genetically modified organism (GMO) CRMs in cooperation with the Institute for Health and Consumer Protection (Ispra, Italy). Until now, different weight percentages in the range of 0-5% for 4 GMOs in Europe were produced and certified: Bt (Bacillus thuringiensis)-11 and Bt-176 maize, Roundup Ready soybean, and MON810 maize. Bt-11 and Bt-176 maize and Roundup Ready soybean were produced by IRMM on behalf of Fluka Chemie AG (Buchs, Switzerland). Characterization of used base material is the first step in production and is especially important for GMO CRMs. The production of powdery GMO CRMs and methods used for production control are described. Thorough control of homogeneity and stability are essential for certification of reference materials and ensure validity of the certificate for each bottle of a batch throughout a defined shelf-life. Because production of reference materials and their maintenance are very labor- and cost-intensive tasks, the usefulness of new types of GMO CRMs must be estimated carefully.     

Production of malachite green oxalate and leucomalachite green reference materials certified for purity

Malachite green oxalate (MG oxalate) and leucomalachite green (LMG) have been prepared and certified as pure reference materials. The purities of MG oxalate and LMG were assessed by high-performance liquid chromatography–diode array detection (HPLC–DAD), nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), Karl Fischer titration, ashing and thermogravimetric analysis (TGA). MG oxalate was purified by supercritical fluid extraction (SFE). Prior to purification, commercial MG oxalate purity was estimated to be about 90%. The main impurities present in SFE-purified MG oxalate were identified and quantified using HPLC–DAD. The main impurities were found to be monode-MG (monodemethylated MG oxalate synthesis impurity), 4-(dimethylamino)benzophenone (4-DMABP), MG-carbinol and LMG. The homogeneity of both reference materials was also determined. Issues associated with the stability of LMG and MG oxalate in solution forced an extensive study investigating different parameters i.e. solvent, acid, analyte concentration and temperature. MG oxalate (100 μg/mL) was found to be stable in acetonitrile containing 1% v/v glacial acetic acid for at least 155 days and LMG (100 μg/mL) was stable in acetonitrile for at least 133 days. The final purity value for MG oxalate was 94.3 ± 1.4% m/m at the 95% confidence interval (or 67% m/m if MG cation is reported). For LMG, the certified purity was found to be 98.8 ± 0.8% m/m at the 95% confidence interval. Figure Calibration reference materials for malachite green and leucomalachite green, certified for purity, are essential in characterising these key analytes in a fish matrix reference material     

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.     

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     

Organomineral composite materials for drying of gaseous streams

Specific features of the synthesis of the organomineral binding agent, polyvinyl alcohol—silica sol, with high sorption activity were studied. The adsorption properties of the new material towards water were examined under equilibrium and dynamic conditions. The kinetics of water adsorption and granules based on the new material were investigated. The possibility of using the organomineral binder in technology of the preparation of granulated and block adsorbents designed for drying of gaseous streams was evaluated.     

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 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.     

Production of reference material

Summary Carbon has been determined in the certified reference sample Euro CRM Pure Iron 097-1 to 3.98 g C/g (R = 0.15 at P = 95%) by combustion of the sample portion with subsequent indication of the CO₂ by coulometry. A calibration material based on primary sources of carbon was used with a sufficient small interval of uncertainty of the accuracy and an adequate weighing system. The blank could be kept sufficiently small with a fraction of 23% of the total analytical signal. The surface carbon of the 097-1 was determined to approximately 50% of the total carbon. This result of total carbon is considerably lower than the values in the certificate reading up to 20 g/g. This reflects the strong tendency to too high values in the certificates of reference steels with contents of carbon up to 100 g/g. Examples are given.

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Herstellung von Referenzmaterial — Bestimmung von Kohle in Stählen und reinem Eisen im Bereich von 1–100 g/g mit primärer Kalibrierung

     

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     

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 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.

     

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.