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     

人参皂苷Re标准样品的研制

以藏药诃子为原料,研制诃黎勒酸国家标准样品. 诃子经60%乙醇提取,大孔树脂富集,制备液相色谱技术得到诃黎勒酸标准品. 采用高效液相色谱（HPLC）、液相色谱-质谱（LC-MS）和薄层色谱（TLC）等手段进行纯度分析. 采用紫外光谱（UV）、红外光谱（IR）、高分辨质谱（MS）和核磁共振波谱（NMR）技术进行结构确认. 最后进行均匀性、稳定性和联合定值. 结果表明,诃黎勒酸样品均匀性良好,4 ℃储存,24个月内稳定. 联合定值确定诃黎勒酸纯度标准值为99.33%,符合国家标准品的要求. 研制出的诃黎勒酸（GSB 11-3724-2020）国家标准样品,可用于含量测定、检测方法评定、相关产品的检测与质量控制.     

NIES certified reference materials for arsenic speciation

 The National Institute for Environmental Studies (NIES) recently prepared two candidate certified reference materials (CRMs) for arsenicals to meet the growing demand for the quality assurance of arsenic speciation analysis. The NIES candidate CRM No. 14 Brown Alga was prepared from Hijiki seaweed for the certification of inorganic arsenic content, and No. 15 Scallop was prepared from adductor muscle of scallop for the certification of arsenobetaine content. The preparation of the candidate CRMs is briefly described. Cooperative analyses for total arsenic content of the candidate CRMs have been underway. The preliminary speciation analysis at NIES revealed difficulty in establishing suitable conditions for extracting arsenic species from the materials. Chromatograms of arsenic species by a high performance liquid chromatography-inductively coupled plasma mass spectrometric detection system are presented to provide information about arsenic species present in these candidate CRMs.     

Calibration and uncertainty assessment for certified reference gas mixtures

The weighted least squares method to build an analysis function described in ISO 6143, Gas analysis—Comparison methods for determining and checking the composition of calibration gas mixtures, is modified to take into account the typically small number of instrumental readings that are obtained for each primary standard gas mixture used in calibration. The theoretical basis for this modification is explained, and its superior performance is illustrated in a simulation study built around a concrete example, using real data. The corresponding uncertainty assessment is obtained by application of a Monte Carlo method consistent with the guidance in the Supplement 1 to the Guide to the expression of uncertainty in measurement, which avoids the need for two successive applications of the linearizing approximation of the conventional method for uncertainty propagation. The three main steps that NIST currently uses to certify a reference gas mixture (homogeneity study, calibration, and assignment of value and uncertainty assessment), are described and illustrated using data pertaining to an actual standard reference material.     

Uranium isotope dilution mass spectrometry using NBL certified reference materials as spikes

The isotope dilution mass spectrometry method of analysis is used to determine the elemental uranium contents in a wide variety of uranium bearing materials. The method is based on the mass spectrometric analysis of a mixture prepared by diluting the sample to be analyzed with a spike of distinctly different isotopic composition to that of the sample. In this work, a beginning is made to identify suitable candidates among the multitude of certified reference materials (CRMs) available at the New Brunswick Laboratory to supplant the use of ²³³U which remains now as the preferred spike nuclide. The results of the study presented here identify CRM 112-A (of normal isotopic composition) and CRM 115 (depleted uranium composition) as suitable candidates to replace ²³³U as spike material for determining uranium in high enriched uranium materials, and CRM 116 (²³⁵U mass fraction of >90 %) for determining uranium in materials of low enrichment.     

Reference materials and certified reference materials for spectrometry in Romania

Several reference materials (RMs) and certified reference materials (CRMs) are widely used in Romania as measurement standards in different spectrochemical measurements. Among them, single element standard solution certified for their mass concentration play a key role in ensuring the required traceability of results expressed in this measurement unit. A short review of the locally available elemental RMs and CRMs used in atomic spectrometry or in other analytical techniques where aqueous standard solutions are required (usually called RMs or CRMs for spectrometry) is given. The experience of the INM in preparation and certification of such materials is described. Some aspects regarding their use for ensuring the accuracy and for confirmation of the traceability of analytical measurements, especially through calibration and metrological validation of main instrument performances, are discussed.     

Reference materials and certified reference materials for spectrometry in Romania

Several reference materials (RMs) and certified reference materials (CRMs) are widely used in Romania as measurement standards in different spectrochemical measurements. Among them, single element standard solution certified for their mass concentration play a key role in ensuring the required traceability of results expressed in this measurement unit. A short review of the locally available elemental RMs and CRMs used in atomic spectrometry or in other analytical techniques where aqueous standard solutions are required (usually called RMs or CRMs for spectrometry) is given. The experience of the INM in preparation and certification of such materials is described. Some aspects regarding their use for ensuring the accuracy and for confirmation of the traceability of analytical measurements, especially through calibration and metrological validation of main instrument performances, are discussed.     

Accreditation and the need for certified reference materials

The comparability of data from accredited laboratories is not always as good as customers would desire. A number of reasons for this fact are given. Clients of laboratories do not specify methodology, which may lead to the application of systematically different methods or to methodology with improper performance characteristics. Laboratories do not always validate methodology sufficiently which is, however, among others provoked by a lack of reference materials. It is argued that accreditation cannot enforce comparability on itself, but needs to be embedded in a measurement infrastructure. The quality systems which underly accreditation form a basic element. In addition, adequate methods, good laboratory performance studies and certified reference materials are required.     

BCR certified reference materials for reactor neutron dosimetry

A series of reference materials intended for use as activation or fission monitors for neutron fluence rate measurements has been prepared by the Joint Research Centre of the European Commission. Certification has been carried out by expert European laboratories and distribution of the certified reference materials (CRMs) is through the BCR programme of the Commission. The list (18 CRMs) includes materials to cover the complete energy spectrum, and suitable for different irradiation times. Fission monitors are ²³⁸UO₂ or ²³⁷NpO₂ in the form of microspheres. Activation monitors are high purity metals (Ni, Cu, Al, Fe, Nb, Rh, or Ti), certified for interfering trace impurities, or dilute aluminium-based alloys, where aluminium is chosen as a suitable matrix for reducing the neutron self-shielding effect. Newly certified materials are IRMM-530R Al-0.1%Au, replacing the exhausted IRMM-530 material, used as comparator for k ₀-standardization, and three new Al-Co alloys (0.01-1%Co). Two others, in the process of certification are Al-0.1%Ag and Al-2%Sc for thermal and epithermal fluence rate measurements. Other candidate reference materials currently being certified are two uranium-doped glass intended for dosimetry by the fission-track technique.     

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.     

X-ray fluorescence analysis in environmental radiological surveillance using HPGe detectors

X-ray fluorescence (XRF) has been proven to be a valuable tool for determining trace quantities of heavy metals, such as uranium and lead, in different types of samples. The present paper demonstrates the applicability of XRF spectrometry to measure the concentrations of these heavy metals in samples from natural ore and soil. The values of uranium concentrations in rock from the Peña Blanca uranium ore, in Chihuahua, México, were calculated for the purpose of precertifying the rock powders samples. The comparison with other techniques, such as inductively coupled plasma atomic emission spectrometry, atomic absorption spectrometry, alpha spectrometry and electron microscopy, was used to complete the precertification process, so that the sample powders may be used as secondary standards. The source-sample-detector geometry and the incident angle are the most important factors for obtaining low detection limits. The selected system uses a ⁵⁷Co source of about 0.1 mCi to excite the K X-rays from uranium and lead. X-rays were recorded on a CANBERRA HPGe coaxial detector. The comparative results for two incident angles (90° and 180°) performed previously by other authors show that the best geometry is the backscattering geometry. In the present paper, using EGS4 code system with Monte Carlo simulation, it was possible to determine the location and distribution of background produced by the Compton edge in the optimized geometry. This procedure allowed to find the minimum detectable concentration of uranium and lead, which was experimentally calculated using standards. The possibility of performing in vivo measurements rapidly and easily, as well as the factors affecting accuracy and the minimum detectable concentration in several samples are also discussed.     

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     

Reference materials and certified reference materials for water and food microbiology

Summary The concept of Certified Reference Materials (CRMs) for the verification of the accuracy of analytical methods and the traceability of the results to a CRM, is well accepted in chemistry. The use of Reference Materials (RMs) for intra-laboratory quality control schemes or for round-robin and proficiency testing is well established and follows from certain norms (ISO 9000 and EN 45000 series). For microbiology such concepts have not been fully defined and RMs are only rarely used. CRMs do not exist. To fill this gap the Commission of the European Community, through the BCR programme, has launched projects in collaboration with the RIVM (National Institute of Public Health and Environmental Protection) in Bilthoven (NL). Following fundamental considerations and feasibility studies, several intercomparisons have been held using selected laboratories working with food or water microbiology. Various microbiological strains have been subject of studies: Salmonella typhimurium, Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus for food, Escherichia coli, Enterococcus faecium, Enterobacter cloacae and Staphylococcus warneri for water. To produce materials for interlaboratory studies, a set of milk powders was prepared by spray-drying. Separate portions were contaminated with one of the strains mentioned. The materials were then encapsuled in gelatine. It has been demonstrated that if protected in milk powder matrices, bacteria maintain the ability to be revived, but do not multiply. The modes of evaluation of the results for homogeneity and stability differ from those commonly used in chemistry.     

Non-destructive determination of zinc in biological certified reference materials

Non-destructive neutron activation analysis was employed to determine zinc in ten biological standard reference materials from the National Bureau of Standards and the National Research Council of Canada. The use of a 4 h. irradiation at a medium neutron flux allows excellent accuracies, precision and sensitivities to be attained for all the samples analyzed. It is suggested that neutron activation analysis be one of the benchmark methods for the determination of zinc in biological reference materials for concentrations as low as the one part per million level.     

Uncertainty limits for certified values of standard reference materials

Summary Uncertainty limits usually employ the 95% confidence limits and should include allowances for the uncertainty of known sources of systematic errors of the measurements. But in many cases, when an interlaboratory comparison study is used for certification purposes of standard reference materials, only the 95% confidence limits are considered and given as the uncertainty limit. In this work, we shall show the results as the number of mean values (n) reported vary and only the 95% confidence limits are considered, using as an example the intercomparison study on IAEA/SL-3/lake sediment sample. And finally, we shall compare the results if only the 95% confidence limits are considered with those of the standard deviation and propose when n is large that the standard deviation should be employed instead of the 95% confidence limits as the uncertainty limits, if the other systematic and random errors are not included.     

New Japanese certified reference materials for electrolytic conductivity measurements

Accreditation and Quality Assurance - The National Metrology Institute of Japan (NMIJ) has established three certified reference materials (CRMs) in electrolytic conductivity with a primary...