The certification of the iodine content of two spiked skim milk powders

Summary The Certification of the Iodine Content of Two Spiked Skim Milk Powders The certification of the iodine content in the BCR certified reference materials 150 and 151 is described. In particular the methods and their results are presented. The certified values are based on the results of 8–10 laboratories, of which each applied a different analyical technique.     

Development of porous and dispersed CRM

Porous and finely dispersed certified reference materials (CRM) were certified using the gas adsorption method. The special certification procedure for IUPAC isotherm classification types I, II, and IV is presented for meso- and macroporous materials with special emphasis on specific surface area, specific pore volume and pore width according to standards DIN 66 131, 66 134, and 66 135. Four CRMs (SiO₂, α-Al₂O₃, two transition aluminas) with a macro- and mesopore range are presented. Certification was made on the basis of BCR guidelines in connection with interlaboratory tests (altogether 38 participating laboratories, 44 various gas adsorption apparatus). Received: 25 April 1997 / Revised: 22 August 1997 / Accepted: 28 August 1997     

Recent developments in the field of environmental reference materials at the JRC Ispra

The production of reference materials for environmental analysis started in the Joint Research Centre at Ispra/Italy in 1972 with the objective of later certification by the BCR, but for obvious budget reasons only a fraction of the total production achieved at Ispra ever reached certification level, although all materials were produced according to the severe quality requirements requested for certified reference materials. Therefore, the materials not destinated to certification are in growing demand as inter-laboratory test materials and as laboratory reference materials, for internal quality control, e.g., by control charts. The history of reference material production within the Joint Research Centre is briefly reviewed and the latest additions described. New developments such as micro-scale reference materials intended for analytical methods requiring sample intakes at milligram or sub-milligram level and therefor not finding supply on the reference material market, and "wet" environmental reference materials, which meet more precisely the "real-world" environmental analysis conditions, are presented and the state-of-the-art discussed.     

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     

Development of clenbuterol reference materials: lyophilized bovine eye samples free of clenbuterol (CRM 673) and containing clenbuterol (CRM 674)

The certification by inter-laboratory testing of two candidate reference materials (RMs) for the mass concentration of the anabolic agent clenbuterol in bovine eye material is described: RM 674 with ca 10 microg clenbuterol per kg of eye matrix and RM 673 clenbuterol-free eye matrix as the negative control (<0.50 microg kg(-1)). Both candidate RMs were certified by eleven EU laboratories, and sixty-six accepted replicate measurements were included in the "Certification Study". The precision of the measurement process was assessed by calculation of the standard variation determined within each laboratory during the certification step. The study was performed according to the "Guidelines for the production and certification of BCR reference materials" and to "ISO guide 31, 33, and 35". The certified clenbuterol mass concentration for clenbuterol-free eye material CRM 673 (calculated on the basis of clenbuterol as the free base) was <0.50 microg kg(-1). The corresponding concentration for clenbuterol-containing eye material CRM 674 was 9.42 +/- 0.88 microg kg(-1). These certified values are very close to the desired target concentration of <0.5 microg kg(-1) and ca 10 microg kg(-1). This study has demonstrated that successful certification of clenbuterol-containing and clenbuterol-free bovine eye materials is possible.     

Use of an excess variance approach for the certification of reference materials by interlaboratory comparison

In the nuclear field, the accuracy and comparability of analytical results are crucial to insure correct accountancy, good process control and safe operational conditions. All of these require reliable measurements based on reference materials whose certified values must be obtained by robust metrological approaches according to the requirements of ISO guides 34 and 35. The data processing of the characterization step is one of the key steps of a reference material production process. Among several methods, the use of interlaboratory comparison results for reference material certification is very common. The DerSimonian and Laird excess variance approach, described and implemented in this paper, is a simple and efficient method for the data processing of interlaboratory comparison results for reference material certification. By taking into account not only the laboratory uncertainties but also the spread of the individual results into the calculation of the weighted mean, this approach minimizes the risk to get biased certified values in the case where one or several laboratories either underestimate their measurement uncertainties or do not identify all measurement biases. This statistical method has been applied to a new CETAMA plutonium reference material certified by interlaboratory comparison and has been compared to the classical weighted mean approach described in ISO Guide 35. This paper shows the benefits of using an “excess variance” approach for the certification of reference material by interlaboratory comparison.     

Statistical estimation of the influence of mineralization methods on the results of heavy metals determination in cereals by the DPASV method

Summary The Community Bureau of Reference (BCR) has undertaken the development of a range of reference materials designed to meet the principal needs for food analysis and measurement. This work falls within the scope of a general collaborative programme designed to improve measurement accuracy and comparability within Europe.The development of well characterised food reference materials frequently poses serious difficulties, not only with respect to stability and homogeneity, but also for accurate certification. A pre-requisite for accurate certification is a high level of agreement between the collaborating laboratories, preferably when employing methods based on different principles.Especially for trace organic analysis, it is necessary to carry-out preliminary intercomparisons of candidate certification methods in order to identify and eliminate the major sources of error. This process is greatly facilitated if the critical steps such as recovery, clean-up and final determination can be studied separately. The paper describes this approach by reference to three milk-powders which were recently certified for their aflatoxin M₁ content and presents results for bovine muscle, bovine liver and pig kidney CRMs recently certified for toxic and nutritional element.     

Ultrasound and microwave-assisted extraction of metals from sediment: a comparison with the BCR procedure

In this paper we investigate alternatives to mechanical stirring for the extraction of the mobile fraction of metals from sediment, and analyze whether these techniques can reduce extraction time and improve reproducibility. We compare the quantities of metal extracted from BCR601 and BCR701 certified sediments using ultrasound bath, microwave-assisted extraction and the first step in the certified BCR sequential extraction procedure. Some environmentally important not-certified metals such as As, Mn, Co, Fe and Al have been included in this study. In the case of microwave-assisted extraction, we compare tests in which samples are exposed to constant, low power irradiation with tests using pulsed high power.

In the tests using the ultrasound bath, less metal was extracted than with the other extractive techniques and standard deviations were comparable to those obtained with the BCR procedure; in assays using microwaves at constant power, extraction efficiencies were different for different metals and for different reference materials and, in some cases, standard deviations were higher than those for the reference method. In contrast, tests with microwaves and constant temperature produced encouraging results: R.S.D.s lay in the 2–4% range, both for certified and not-certified metals; these values are very low compared to those for the reference method. Extraction efficiencies for certified metals were close to 100% for Cd, Zn, Cu and Ni and around 80% for Pb and Cr.     

Certification of the mass fractions of Ca,Cu, Cl,I, Fe,K, Mg,P, Pb,N, Na and Zn in skim milk powder

Analyses of milk and milk products are routinely performed by a number of dairy laboratories to control the quality of these products with regard to e.g. nutritional components and potential exposure to toxic elements. In order to improve and control the quality of such analyses the Community Bureau of Reference (BCR) has organized series of certification campaigns to produce reference material of milk certified for a variety of elements and compounds. The increasing demand is such that the stock of some of these materials is now exhausted. Consequently, the BCR decided to produce a new batch of CRM of skim milk powder certified for its contents of Ca, Cu, Cl, I, Fe, K, Mg, P, Pb, N, Na and Zn (CRM 063R). This material was carefully prepared (spray-drying) and its homogeneity and long term stability was verified. This paper presents the certification work performed.     

Certified reference materials for the quality control of fluorine in coal, fly ash and clay

A group of laboratories has worked in various intercomparisons in the frame of the BRC-programme (European Commission) to improve their methods for fluorine determination, especially for coal analysis. These exercises allowed to detect and remove sources of error. Methods were improved to such an extent that the certification of fluorine and chlorine in different materials could be envisaged and the BCR consequently decided to produce coal, fly ash and clay materials certified for their F content. In addition, chlorine was certified in the fly ash CRM.     

Development, production and certification of microbiological reference materials

Since 1986 the National Institute of Public Health and Environmental Protection (RIVM) in the Netherlands has been developing and testing reference materials (RMs) for use in the field of water and food microbiology within the framework of the Measurements and Testing Programme (former BCR) of the European Union. The materials consist of gelatin capsules filled with artificially contaminated spray dried milk. Individual and collaborative studies on stability and homogeneity of the materials are described. The positive results obtained are followed by certification studies on certain reference materials. The results of two certification studies have now satisfactorily been completed, and certified values, related to the methods used, have been given for two certified reference materials (CRMs) containing the bacterial strains Salmonella typhimurium (5 cfp/capsule) and Enterococcus faecium (500 cfp, capsule), respectively. Two other RMs containing Bacillus cereus and Enterobacter cloacae will be certified by the end of 1994.     

Development and certification of reference materials for residues of organochlorine and organophosphorus pesticides in beef fat ACSL CRM 1 and 2

Beef fat samples were prepared and tested as candidate reference materials for organochlorine and organophosphorus pesticides. The CRMs consisted of beef fat spiked with pesticide solutions. One sample (ACSL CRM 1) was prepared containing close to 0.2 mg/kg of each of the organochlorine pesticides dieldrin and heptachlor epoxide. A second sample (ACSL CRM 2) was prepared containing close to 0.8 mg/kg of each of the organophosphorus pesticides diazinon, chlorpyrifos and ethion. The spiking levels and homogeneity of the materials were verified. The coefficients of variation of 5 analyses carried out to test between-jar homogeneity for each reference material were dieldrin, 3.5%; heptachlor epoxide, 1.1%; diazinon, 2.1%; chlorpyrifos, 1.2% and ethion, 3.1%. No instability in any of these compounds was detected over a twelve month period. The candidate reference materials were found to be suitable for certification by interlaboratory testing. The certification process was based on a two-stage nested design described in ISO Guide 35. Analysis of results reported by collaborating laboratories provided an assessment of the homogeneity of the reference materials. The certified values together with their upper and lower 95% confidence limits are: ACSL CRM 1*Dieldrin*0.199 mg/kg **(0.188, **0.210 mg/kg) *Heptachlor epoxide*0.194 mg/kg **(0.176, **0.212 mg/kg) ACSL CRM 2*Diazinon*0.805 mg/kg **(0.755, **0.855 mg/kg) *Chlorpyrifos*0.790 mg/kg **(0.728, **0.852 mg/kg) *Ethion*0.813 mg/kg **(0.746, **0.879 mg/kg). A certificate for each material was prepared according to the guidelines set out in ISO Guide 31. Received: 25 April 1997 / Revised: 19 August 1997 / Accepted: 28 August 1997     

Speciation of Heavy Metals in Soils and Sediments. An Account of the Improvement and Harmonization of Extraction Techniques Undertaken Under the Auspices of the BCR of the Commission of the European Communities

Abstract

An account is presented of a series of investigations and collaborative studies, initiated by BCR, on current methods of metal speciation by extraction of soils and sediments with chemical reagents. It was established by extensive consultation with European experts that the diverse procedures used could be harmonized into agreed methods. These methods, including both single extractant and sequential extraction procedures were subjected to collaborative, interlaboratory trials and the results, presented briefly here, showed that it was both possible and desirable that reference soils and sediments, characterised by certified values for extractable contents, be prepared. As a consequence of these studies two soils have been prepared and will shortly be the subject of interlaboratory analysis with a view to certification of their EDTA and acetic acid extractable contents of some heavy metals. Following this workshop a feasibility study of the agreed sequential extraction procedure will, it is believed, shortly lead to certification of sediments for contents extractable by a defined sequential extraction procedure.     

Reference materials for PAHs in foodstuffs: Results of the certification exercise of two coconut oil reference materials

This certification exercise was the final stage of a stepwise interlaboratory study approach, organized within the SMT-program of the EC, for the development of certified reference materials (CRMs) for the determination of PAHs in foodstuffs. The certification exercise was carried out by thirteen European laboratories using a variety of extraction and clean-up procedures and different analytical procedures. Two different coconut oil materials were certified for their mass fractions of six selected PAHs. Received: 25 May 1997 / Revised: 5 September 1997 / Accepted: 28 September 1997     

The certified reference materials CRM 142 R light sandy soil, CRM 143 R sewage sludge amended soil and CRM 145 R sewage sludge for quality control in monitoring environmental and soil pollution

The determination of various heavy metals in soils and sludges provides an indication for their degree of contamination. Therefore the reliability of such determinations is of utmost importance. Quality assessment can be performed by using adequate certified reference materials. Because of their success, the present supplies of the BCR CRM 142, CRM 143 and CRM 145 are exhausted. The Measurement and Testing Programme (BCR) of the Commission of the European Communities decided to replace them. After a careful preparation procedure of materials sufficiently similar to the exhausted ones and a homogeneity and stability study, the new materials were certified for a series of trace elements also including their aqua regia soluble fraction. Indicative values for other elements are given as well.     

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.     

Quantification of the expected shelf-life of certified reference materials

Stability testing and -monitoring are of the highest importance for the certification of reference materials. However, in general the results of these measurements are only assessed in a qualitative way, and no effort is made to quantify the period of certification or the shelf-life of the CRM. However, the revised ISO Guide 31 “Contents of Certificates, Certification Reports and Labels of Reference Materials” will most probably contain the explicite obligation to mention an expiry date “for all CRMs where instability has been demonstrated or is considered possible”. Therefore a method is proposed for quantifying the expected shelf-life on the basis of linear regression and determination of the intersection of the lower confidence limit of the certified value with the 95% lower confidence bound of the mean degradation curve. Received: 18 September 1997 / Revised: 26 November 1997 / Accepted: 24 December 1997     

Pesticide analysis in ground water. Statistical evaluation of certification data of a multicomponent reference material

21 laboratories participated in the certification of a multicomponent ampouled reference material containing 24 pesticides. This paper describes the statistical analysis of the unbalanced data set returned by the participants in the certification. The simplest method of certification is achieved when laboratories report all the required data. In practice, however, with complex analytical methods such as multicomponent analyses of organic compounds, laboratories are not able to report all the required data. The response for each determinand in the material has been modelled in a three-factor nested model. For computational comfort the model has been rephrased into a general linear model. The statistical problems with unbalanced data are discussed in relation to ISO 5725 and ISO Guide 35. Tests for homogeneity are exact and uninfluenced by the unbalance in data. Unbalanced data cause dependencies between mean squares above the second lowest level of the model, thus exact hypothesis testing is not possible at higher levels. Approximate tests for variation between rounds and laboratories has been constructed by means of Satterthwaite’s formula [1]. A graphical plot of deviances from certified values has been applied to illustrate laboratory performance. Received: 25 May 1997 / Revised: 6 December 1997 / Accepted: 15 January 1998     

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