The use of certified reference materials in the Romanian traceability scheme

 For ensuring the traceability and uniformity of measurement results, the main objectives of national metrology programmes in chemistry are to calibrate and verify measuring instruments, to evaluate the uncertainty of measurement results and to intercompare the analytical results, etc. The concept of traceability has developed recently in chemical measurements, thus, an attempt to implement the principles of metrological traceability especially by appropriateness calibration using composition certified reference materials (CRMs) is underlined. Interlaboratory comparisons are also a useful response to the need for comparable results. The paper presents some aspects and practices in the field of spectrometric measurement regarding the metrological quality of the traceability by calibrating the instruments using suitable and reliable CRMs. The uncertainty of results, as a measure of the reliability that can be placed on them, has been adequately described in different documents and, as a consequence, some examples of evaluating the measurement uncertainty are described. The relationship between uncertainty and traceability, as two fundamental concepts of metrology which are intimately linked, is underlined. Received: 12 November 1999 / Accepted: 10 December 1999     

Preparation and analysis of a reference material for the measurement of oxygen in copper

The preparation and analysis of the oxygen mass fraction of three pure copper reference materials (BAM-379/1, BAM-379/2, BAM-379/3) intended for the calibration of spark emission spectrometry are described here. Data of homogeneity testing and round robin certification in collaboration with 12 independent laboratories from metalworking industry and research are reported. Problems with the establishment of traceability in this special case are discussed. Received: 20 July 2001 Accepted: 13 October 2001     

Accreditation of reference material producers

 The use of reference materials is the most pragmatic means by which the analyst can achieve comparability of data. Reference material producers therefore need to have adequate quality systems in place for ensuring the reliability of their materials. In order to provide guidance to both producers and assessors, ISO Guide 34 has recently been produced detailing the quality system requirements for the production of reference materials. CITAC, REMCO and ILAC are now collaborating in the revision of this guide to produce a free-standing document detailing the general requirements for the competence of reference material producers. This paper discusses some of the more important issues described in these documents. The possible formation of an international register containing details of a reference material producer's quality system status is also discussed.     

Uncertainty calculations in the certification of reference materials 4. Characterisation and certification

The main objective of the certification of a reference material is to determine its property values including their uncertainty. In the previous parts of this series, the basis for the evaluation of measurement uncertainty of the property values has been examined, including the conversion of homogeneity and stability study data into standard uncertainties. In this final part, the determination of the property values and the modelling of the certification process is discussed. It is noted that the characterisation of a reference material can be modelled in some cases using analysis of variance statistics, but a more generally applicable model can be developed based on χ²-fitting. Furthermore, it is concluded that there is an advantage in using absolute standard uncertainties instead of relative ones when modelling the certification process. Received: 14 October 2000 Accepted: 21 January 2001     

How accurate must a reference material be?

 This article deals with reference materials (RMs) used for calibration purposes. For most common spectroscopic and chromatographic methods, RMs which have a relative content uncertainty of up to 3% can be used without considerably increasing the overall measurement uncertainty of the complete procedure. It is vital that the correct amount of the RM is used to ensure the quality of the quantitative chemical analyses. This can only be guaranteed if, in addition to the correct determination of the amount, the stability of the RM in the sales packaging is considered in the quoted uncertainty. For instance when the RM is packed in a container made of polyvinylidene fluoride water losses in hot climates can result in an increase in concentration which cannot be neglected. This is also true for high density polyethylene containers (PE-HD) although to a lesser degree. When mercury solutions of 1000 mg/l to 10 000 mg/l are kept in diluted nitric acid in PE containers, a relevant reduction in amount can be measured despite the water losses. However, the solutions remain stable in glass containers.     

Accreditation system for reference material producers and certified reference materials for iron and steel in Japan

  ISO 9000 series strictly requires traceability to national or international measurement standards. It is becoming more necessary to make clear the concept of traceability of measurement standards with respect to chemical composition and to accredit the reference material producers. In Japan, the accreditation system for reference material producers is considered to satisfy the requirement of ISO Guide 34, ISO 9000 series and ISO/IEC Guide 25, while the producer fulfills the concept of traceability of measurement standards. This paper describes the production of iron and steel reference materials in Japan relating to the international standardization of methods (written standards) and accreditation of reference material producers. Received: 11 October 1996 Accepted: 5 December 1996     

The preparation of a cabbage candidate reference material to be certified for residues of agrochemicals

Summary A new cabbage candidate reference material has been prepared for the determination of residues of agrochemicals. The cabbage was grown with deliberate application of a series of pesticide and herbicide mixtures. After harvest it underwent extensive processing to yield the candidate reference material. In particular the collection of base material, its transformation into powder, the production control and final homogeneity assessment are described. The original bottled material is ready for an intercomparison study during 1992/1993 to establish recommended values for the organic constituents and information values for inorganic constituents.     

Preliminary study to prepare a reference material of styrene metabolites – mandelic acid and phenylglyoxylic acid – in human urine

 A preliminary batch of the reference material was prepared by freeze-drying pooled urine samples obtained from healthy persons occupationally exposed to styrene. Tests for homogeneity and stability were performed by determining urine concentrations of mandelic (MA) and phenylglyoxylic acids (PGA). The urinary MA and PGA concentrations were followed over an 8-month period using high performance liquid chromatography (HPLC). No changes of the concentration values were found. Pure PA and PGA from Merck and Fluka, respectively, were used for traceability purposes, because certified or standard reference materials for MA and PGA do not exist. Control material ClinChek-Urine Control (Recipe) was analysed simultaneously. The mean values of MA and PGA compared well with the means of control samples and fell within the control range. The certified values and their uncertainties were evaluated from the results of interlaboratory comparisons, homogeneity (277.0 ± 7.4 mg L⁻¹ for MA and 148.0 ± 4.7 mg L⁻¹ for FGA) and stability tests. The values are unweighted arithmetical averages of accepted results and their uncertainties are combined uncertainties enlarged by coefficient k=1, evaluated from the standard uncertainties of the interlaboratory comparison, homogeneity and stability tests. Received: 17 September 2002 Accepted: 1 November 2002 Acknowledgement This work was supported by the Internal Grant Agency of Ministry of Health of the Czech Republic (Grant NJ/6784–3). Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia Correspondence to I. Šperlingová     

Development and validation of a methodology for uranium radiochronometry reference material preparation

The paper describes a methodology for a reference material preparation to be used for the determination of the production date (i.e. the time elapsed since the last chemical processing) of uranium materials based on the ²³⁰Th/²³⁴U radiochronometer. The reference material was prepared from highly enriched uranium by a complete separation of thorium decay products, thus zeroing the initial daughter nuclide concentration at known time. The complete elimination of thorium from the starting material was verified by gamma spectrometric measurements and by addition of a ²³²Th tracer to the material and its re-measurement in the final product after the separation. The validation of the methodology was carried out subsequently by comparing the ingrown daughter nuclide ²³⁰Th and the measured ²³⁰Th/²³⁴U ratio after recorded times following the last chemical separation with the calculated values obtained on the basis of their respective half-lives. The prepared reference material can be used as a quality control material for age determination of uranium in nuclear forensics and safeguards as well as for method validation.     

Accreditation and authorization in environmental analysis

 Since 1989 testing laboratories in Europe have had the possibility to confirm their competence in carrying out certain testing procedures by means of accreditation. Over the years an independent European Accreditation system has been developed, which many member states of the European Union have joined. The existing accreditation organizations joined to form the unified organization EA (European Cooperation for Accreditation) in 1997. Members of this organization are, inter alia, one representative of the accreditation authorities of each of the member states. The German accreditation system is different to the European system in that it is split. Here, we differentiate between the sector established by law and that which is not. Both sectors, however, pursue the same goal. Because of this double certification of competence and the resulting multiple reviews, German testing laboratories face a considerably greater load in comparison to their European colleagues. Several authorities are already working on the removal of this split accreditation system. The efforts must, however, be concentrated and brought into line. Efforts by the DAP and DACH for flexible accreditation and the creation of a standardized registration authority for testing laboratories in the field of workplace measures are examples of how the German accreditation system could develop in the future.     

Flexibilization of the scope of accreditation: an important asset for food and water microbiology laboratories

Beltest, the Belgian accreditation body, has investigated flexibilization of the scope of accreditation for chemistry laboratories and food and water microbiology laboratories. This flexibilization, synonymous with test-type accreditation, allows a laboratory to add new test methods or retry previous test methods without having to undergo a new audit by Beltest. It has been used for nearly ten years by German and Swiss accreditation bodies. Flexibilization permits the validation of methods and results, given that the competence of the particular laboratory is already well established. This new concept in microbiology allows client’s needs to be adequately met, and facilitates the quick establishment of a method in several laboratories at once in case of a public health crisis. The first laboratory to participate at this investigation on the flexibilization concept, as a test of the concept, was the Belgian reference laboratory for food microbiology.     

Flow-through coulometry as a calibrationless method in inorganic trace analysis

The possibility of calibration-less determination of trace concentrations of some electrochemically active elements such as Ag, As, Cd, Hg, Pb, etc. by flow-through coulometry is described. The analyte species are collected quantitative-ly from the flowing sample solution on a porous working electrode made of vi- treous carbon particles set at either a constant potential or constant current. The deposit is stripped by a constant current in the next step and the correspond- ing electrical charge is measured and evaluated. The analyte concentration is calculated by making use of the com- bined Faraday’s laws of electrolysis. The method exerts detection limits about 1 μg/l or lower and a linear concentration range over 3 orders of magnitude.     

The NATA scheme for accreditation of certifiers of reference materials

 Certified reference materials are widely used for the calibration of measuring equipment and for the evaluation or validation of measurement procedures. The use of reference materials makes possible the transfer of the values of measured or assigned quantities between testing, analytical and measurement laboratories, both nationally and internationally. There is an increasing number of reference materials producers in other countries, and a demonstration of their scientific and technical competence is now more widely considered to be a basic requirement for ensuring the quality of reference materials. This article outlines recent activities by international bodies and their culmination in a scheme of accreditation of certifiers of reference materials which has been developed by the National Association of Testing Authorities, Australia (NATA).     

Review of European Union requirements: quality standards for food analysis laboratories

 The European Union has prescribed strict quality standards for official food laboratories and the methods of analysis to be used in laboratories when carrying out official food control work. These requirements, which are based on accreditation, participation in proficiency testing schemes and using validated methods of analysis, are described in detail. The similar approach being taken within the Codex Alimentarius Commission is also outlined. The procedures prescribed will ensure that official food control laboratories have in place the measures to ensure that consistently reliable data can be produced. Received: 29 November 1995 Accepted: 8 January 1996     

The synthesis and characterization of pure substance reference materials for forensic, agricultural and drugs-in-sport analysis

 The paper reports work on the synthesis, purification and certification of pure substance (organic) reference materials as conducted within the National Analytical Reference Laboratory (NARL). Areas of interest include illicit drugs, agricultural and veterinary chemicals, and steroids and steroid metabolites and their deuterates. The discussion covers the prioritization of work requirements, procedures for synthesis and production, quality assurance, characterization, homogeneity, storage and stability testing, and certification of materials. Future plans for establishing traceability are also discussed.     

In- and off-laboratory sources of uncertainty in the use of a serum standard reference material as a means of accuracy control in cholesterol determination

 Repeated subsampling or a hierarchical design of experiments combined with an analysis of variance (ANOVA) is demonstrated to be a useful tool in the determination of uncertainty components in amount-of-substance measurements. With the reference material of human serum as investigated here for total cholesterol, besides several in-laboratory sources of uncertainty, a vial-to-vial effect which can be regarded as an off-laboratory source was found to be significant. This knowledge might be essential when the material is used for calibration and for the self-assessment of a laboratory. Received: 29 October 1997 · Accepted: 26 November 1997     

Primary reference materials and traceability chain for gas composition

This article briefly describes research on the development of primary reference gases and the traceability system of gas measurement at the National Research Center for Certified Reference Materials, China.     

The interpretation and use of stability data in the certification of reference materials

 Stability tests are carried out on candidate reference materials in order to ascertain that the certification values continue to be valid a reasonable time after completion of the certification analysis. These tests are also used for recommending storage conditions, as well as the duration of storage before certification values need be rechecked. BCR (Community Bureau of Reference) reference materials do not normally have an expiry date, but rely on stability monitoring throughout the lifetime of the certified material. The 1997 version of the BCR Guidelines for the production and certification of reference materials does, however, take into account the necessity of limiting the validity of a certification, when degradation of the material during storage cannot be ignored. This paper discusses an example of significant degradation taking place between the time of completion of the certification analysis and the issue of a formal certificate. Various options are presented together with an account of their influence on the certified values and their uncertainties. Received: 3 October 1997 · Accepted: 3 November 1997     

Micro Determination of Ammonia by a Kinetic Spectrophotometric Method

 A simple and sensitive kinetic spectrophotometric method is described for the determination of micro amounts of ammonia. The method is based on the inhibiting effect of ammonia on the oxidation rate of aqua ethylenediamine-tetraacetate chromium(III) [Cr(HEDTA)(H₂O)] with N-bromo succinimide (NBS) to yield chromium(VI). The reaction was followed spectrophotometrically by measuring the rate of change in absorbance with time at 365 nm, which is the maximum absorption wavelength of chromium(VI). Using the recommended procedure, ammonia can be determined up to 153 μg ml⁻¹ with a linear calibration graph and a detection limit of 0.09 μg ml⁻¹. The method was successfully applied to the determination of ammonia in waste water samples. Recovery experiments for the analyzed samples were 97–100% with relative standard deviation, Sr (%) of ≤ 2.9% indicating high accuracy and precision of the proposed method. The interference of various cations and anions in the determination of ammonia was investigated. Received March 30, 2001 Revision September 3, 2001     

Collection and preparation of a second generation biological reference material for trace element analysis

The paper describes the collection and preparation of a second generation biological reference material (human blood serum) with trace element levels closely approximating those in real human blood plasma or serum samples.