ISO Best Practices in Reference Material Certification and Use in Geoanalysis

The International Organisation for Standardisation (ISO) has published many guides, or technical standards, of great value to analytical geochemists. Two of particular importance are Guide 33 (Uses of Certified Reference Materials) and Guide 35 (Certification of Reference Materials). Both were first developed in the 1980s and undergo regular review and updating by the Reference Materials Committee (REMCO) that operates within ISO. Recent revisions have focused on adding statistical rigour to both guides. Although this offers significant advantages for use by professional metrologists, there are consequent issues of comprehension by the analytical chemists who in fact have the greatest need of them. A major focus of Guide 35 is the development of reference material uncertainties that are in full compliance with the Guide on Measurement Uncertainty (GUM), jointly issued by ISO, IUPAC and others. Guide 35 details handling of uncertainty due to (1) degradation on the shelf and in transport, (2) sample heterogeneity and (3) inter‐method and inter‐laboratory bias, as well as within‐laboratory repeatability. The International Association of Geoanalysts has developed a protocol for reference material certification that applies Guide 35 to the specific needs of the geoanalytical community. The approach being taken by the IAG in developing GUM‐compliant uncertainties for its certified values is presented. Recommendations made in Guide 33 for how a laboratory should compare its own results with certified values in assessing laboratory accuracy are outlined. Additionally, the subject of misusing reference materials is discussed. The apparent misuse occurs because so few CRMs exist that meet critical measurement needs of geoanalytical laboratories and that also meet the rigorous metrological demands of the latest editions of the ISO Guides. All of the focus of the IAG certification programme has been to undertake certifications that would fill gaps in CRM availability and thus serve to limit this misuse.     

地质标准物质均匀性检验方法评介与探讨

评介了目前中国地质标准物质研制中样品均匀性检验与评价所用方法,包括:检测方法,统计判别模式,结果的定性、定量表达和最小取样量确定等。对照国家相关技术规范、国际标准化组织导则和国际地质分析者协会的地质标准物质定值协议,探讨了我国地质标准物质均匀性检验与评价中的难点及现存问题。     

The Use of Reference Materials: A Tutorial

Any review of the analytical literature shows that, while reference materials are routinely used in laboratories world-wide, not all uses follow ISO Guide 33 (1989), which outlines best practices. Analytical data quality can suffer as a result. This paper reviews the various uses that the geoanalytical community has made of reference materials from a historical perspective, and suggests improvements in practice that would more closely follow ISO Guide 33 recommendations.     

An Interpretation of ISO Guidelines for the Certification of Geological Reference Materials

Recommendations for the certification of reference materials, as published by the International Organisation for Standardisation (ISO), are reviewed and proposals made as to how they can be adapted for the certification of new geological reference materials. Whilst acknowledging the important contribution made by the large number of existing matrix-matched geological reference materials, it is recommended that future characterisation programmes should follow the ISO guidelines for certification, not the least so that laboratories can readily use the resultant samples to establish the traceability of geoanalytical results.     

Developments at ISO/REMCO and its Impact on the Production and Use of Geological Reference Materials

During the past decade the work of ISO/REMCO, the International Organization for Standardization’s Technical Committee on Reference Materials, was dedicated to achieving global harmonisation, and true involvement of the member countries. The first major accomplishment was the clarification of the terminology in the definitions for reference material and certified reference material, which were published as an amendment to ISO Guide 30 in 2008. The next milestone was the recognition that ISO Guide 34 (‘General requirements for the competence of reference material producers’) be used in conjunction with ISO/IEC 17025 for the accreditation of reference material producers. The third edition of ISO Guide 34 published in November 2009, clarifies the acceptable procedures for the certification of reference materials. This paper will discuss the role of ISO/REMCO in formalising the procedures for the accreditation of reference material producers and the evolution of the terms reference material and certified reference material. The paper will conclude with a case study, where a primary method in a single laboratory – one of the recognised acceptable metrologically valid procedures according to ISO Guide 34 – was used for the certification of reference materials. The reference materials are South African Reference Material SARM 2 (Syenite), SARM 3 (Lujavrite) and SARM 4 (Norite) from the suite of six NIMROCs that were originally certified by the Council for Mineral Technology (MINTEK) in South Africa in the 1970s.     

长江三角洲沉积物标准物质研制

美国、加拿大等国家先后研制了10余个海湾和河口沉积物标准物质,但定值成分较少,大多侧重于有机污染物和放射性核素值。我国于2007年研制了3个黄河三角洲沉积物标准物质,为进一步满足近海地球化学调查及资源勘探的需要,本文按照ISO导则35和国家一级标准物质技术规范,研制了2个长江三角洲沉积物标准物质。按照不同粒径采集两个候选物样品,样品经干燥、球磨至200目,采用电感耦合等离子体质谱和发射光谱法进行均匀性检验,结果表明F实测值小于列表临界值F0.05(24,25)=1.96,样品均匀性良好。在两年时间内采用X射线荧光光谱法进行了4次稳定性检验,未发现统计学意义上的明显变化,样品稳定性良好。由12家有技术权威的实验室共采用13种准确、可靠的分析方法进行协作定值,最终定值元素53项,涵盖了主量、微量及全部稀土元素,其中主量成分含量呈梯度分布,如Al2O3的含量分别为16.42%、11.48%。该系列标准物质定值元素种类多,定值方法准确,能够为河口三角洲地区地质及环境调查的分析测试工作提供可靠的质量保证。     

地球化学与环境样品分析标准物质和GeoReM数据库

在地球化学和环境样品分析中,标准物质发挥着越来越重要的作用。尽管通常要求分析者必须提供量值溯源的测量过程的信息;但大多数论著都未给出标准物质的数据。文章强调标准物质在地球化学分析工作中的重要性,同时将地球化学与环境样品分析标准物质数据库GeoReM介绍给中国的地质分析工作者。GeoReM数据库收录了1880个地球化学和环境样品分析标准物质的定值数据、汇编数据、分析数据及其他相关信息,其中包括156个由中国制备的标准物质的数据。GeoReM数据库还给出了所收录标准物质推荐使用的首选值及其不确定度。尽管这些首选值大多都不是按照国际标准化组织的有关规定而确定的,但是它们的置信度高,因而被广泛应用于仪器校准和分析数据的质量监控。文章还指出要将中国研制的、发表在中文期刊上的标准物质也收录到GeoReM数据库中,这对于促进中国的相关研究,增加国际认可度具有重要意义。     

Information on Geochemical Standard Reference Materials of the CMGA Countries

This article provides information on the standard reference materials prepared in co-operation by the CMEA-countries. Among the standards are materials of technological or geochemical importance - silicates, carbonates, ores, etc. The article briefly mentions the technology of their preparation, homogeneity control, analyses evaluation and certification used for these materials. It surveys the finished and planned SRM's. The last table gives the names of foreign trade companies in the individual CMEA-countries which are entrusted with the sale of the standard reference materials produced in that particular country.     

Fitness-for-Purpose of Reference Material Reference Values in Relation to Traceability of Measurement, as Illustrated by USGS BCR-1, NIST SRM 610 and IAEA NBS28

As in all fields of sample analysis, reference materials play a large role in supporting measurements in the geosciences. While a rather large number of materials are in distribution (> 380), not all are equally effective or fit-for-purpose in supporting laboratory data quality and thereby assuring the desired comparability of measurements between laboratories. Equally important, reference values that are not fit-for-purpose cannot be used effectively to establish traceability links between laboratory measurements and national and international standards. The needed fitness-for-purpose is not achieved for reference values either when more than one reference value has been proposed and a consensus does not exist among users as to which should be used by all, or when reference value uncertainties are too large in comparison to those of routine laboratory measurements. The focus of this review will be, first to outline the current reality, and second to suggest ways in which certifications of RMs can be improved to provide reference values that are universally accepted and more fit-for-purpose in general laboratory use. The discussion will be illustrated largely by current uses of USGS BCR-1, NIST SRM 610 and IAEA NBS28, as these three materials are those for which the largest body of newly published data exists, according to recent bibliographies of the geoanalytical literature published annually in Geostandards Newsletter: The Journal of Geostandards and Geoanalysis.     

Reference Values Following ISO Guidelines for Frequently Requested Rock Reference Materials

We present new reference values for nineteen USGS, GSJ and GIT‐IWG rock reference materials that belong to the most accessed samples of the GeoReM database. The determination of the reference values and their uncertainties at the 95% confidence level follows as closely as possible ISO guidelines and the Certification Protocol of the International Association of Geoanalysts. We used analytical data obtained by the state‐of‐the‐art techniques published mainly in the last 20 years and available in GeoReM. The data are grouped into four categories of different levels of metrological confidence, starting with isotope dilution mass spectrometry as a primary method. Data quality was checked by careful investigation of analytical procedures and by the application of the Horwitz function. As a result, we assign a new and more reliable set of reference values and respective uncertainties for major, minor and a large group of trace elements of the nineteen investigated rock reference materials.     

International Association of Geoanalysts'Protocol for the Certification of Geological and Environmental Reference Materials

This protocol has been developed by the International Association of Geoanalysts to demonstrate procedures for the certification of geological and environmental reference materials to comply to the fullest extent possible with recommendations of the International Organisation for Standardisation (ISO Guide 35). A practical approach is described on the assumption that certifications will be normally be based on collaborative analysis programmes in which participating laboratories are preselected on the basis of performance in a proficiency testing programme or on the basis of other criteria of merit.     

中国地质标准物质制备技术与方法研究进展

评介了中国地质标准物质研制中技术方法方面的研究进展,包括样品加工技术,粒度检测与表征方法,均匀性检验与评价,最小取样量的确定,稳定性检验及其结果表述,定值方式,分析方法、数据处理及定值条件,不确定度评价与量值溯源保证等。对照国家相关的技术规范、国际标准化组织(ISO)的相关指南和国际地质分析者协会(IAG)关于地质标准物质研制的协议,讨论了目前中国地质标准物质制备技术的现状及未来的发展。     

光石沟晶质铀矿:一种潜在的铀矿物电子探针定量分析标准样品

电子探针定量分析是采用元素A在待测样品中的特征X射线强度与标准样品中元素A特征X射线强度相比较而进行的,要实现未知样品的元素定量分析必须要具有相应的标准样品,目前可用于铀元素分析的电子探针分析标准样品极少,且缺乏与天然矿物成分、结构近似的标准样品。国际和国内已经制定了电子探针标准物质研制的规范(GB/T 4930—2008/ISO14595:2003),按该规范规定的方法研究了产于陕西光石沟铀矿床的晶质铀矿,结果表明:这些晶质铀矿晶形发育好,颗粒大,具备良好的纯度、均匀性和稳定性。随机选择30个颗粒进行均匀性检测,UO₂和PbO在95%的置信区间的平均浓度不确定度分别为0.275%和0.060%,具备非常好的均匀性;该晶质铀矿在电子探针电子束长时间(如360s)轰击下和在自然条件下存放,均具有良好的稳定性;采用五家实验室化学分析定值方法确定了该晶质铀矿的化学成分,并计算了不确定度,主量元素UO₂为(86.80±0.36)%,PbO为(4.80±0.07)%,其他元素也给出了参考值。综合以上研究结果:产于光石沟铀矿床的晶质铀矿满足GB/T 4930—2008关于电子探针定量分析标准样品的各项判据,是一个潜在的适用于铀矿物化学成分电子探针定量分析使用的天然矿物标准样品。     

Application of an Ion-Selective Electrode Method to the Determination of Chloride in 41 International Geochemical Reference Materials

Determinations of trace amounts (with one exception) of chloride are reported for 41 international geochemical reference standards, 12 of which have no previously reported literature values. All determinations were made by the chloride-specific ion-selective electrode method of Aruscavage and Campbell with certain refinements. Chlorine is separated from most other elements in geologic materials by acid-dissolution in a gas diffusion cell, and is subsequently determined as the chloride ion in basic solution. A statistical F-test was applied to 19 of the standards for which three bottles of each were analyzed in triplicate with no failures. All these standards, plus the other 22 for which six analyses were performed on a single bottle, exhibited a relative standard deviation of 1-6% for concentrations of chloride >50 ppm. For most samples chloride values agree well both with available, reported experimental values and with recommended or consensus values.     

Report on the 2007 Recertification of the Certified Reference Materials GAS (Serpentinite) and OShBO (Alkaline Granite)

A report is presented on the recertification of two certified reference materials (CRMs) initially prepared and certified by the Central Geological Laboratory of Mongolia (CGL), namely serpentinite GAS and alkaline granite OShBO. Subsequent work done in collaboration with the International Association of Geoanalysts (IAG) followed the International Organisation for Standardisation (ISO) guidelines for certification (ISO Guide 35, 2006) more closely than had been possible originally. The certification protocol followed was that of the International Association of Geoanalysts (IAG). The recertification added to the number of elements that were certified for OShBO (from 21 to 30), but not for GAS (decreased from 15 to 12) because of the greater analytical difficulties posed by that sample matrix in meeting the more stringent metrological requirements for recertification. Further, the uncertainties for these values were established in accordance with the Guide to Measurement Uncertainty ; individual contributions of heterogeneity and bias are reported as appropriate for each of the certified constituents. Traceability of the certified values was demonstrated to the greatest possible extent, based on concurrent analyses of the matrix-matched existing CRMs, SW and GM, by all participating laboratories. The materials are now available from the CGL for use by laboratories in controlling data quality when analysing materials of similar matrices.     

The GeoPT Proficiency Testing Programme as a Scheme for the Certification of Geological Reference Materials

ISO Guide 35:2017 provides, for the first time, an alternative way of characterising certified reference materials using proficiency testing. In this paper, the properties of assigned values derived from the well‐established GeoPT proficiency testing scheme are examined. This scheme, designed for laboratories that undertake the routine analysis of silicate rocks and related materials, routinely has over 100 participants contributing results. Following a detailed assessment of the metrological properties of GeoPT assigned values in relation to Guide 35 recommendations, it is demonstrated that these values may be regarded as certified values, provided a number of criteria are met. These criteria include the following: a demonstration of sufficient homogeneity of the candidate CRM; circulation, when judged to be appropriate, of an established matrix‐matched CRM for co‐analysis in that round; the robust statistical analysis of data sets using GeoPT established criteria; a decision whether assigning a value is justified (including a requirement of a minimum of fifteen valid results); and an expert group to manage the certification and the maintenance of appropriate records. In summary, the GeoPT proficiency testing scheme, subject to the arrangements summarised above, is considered to be competent for the certification of geological reference materials.     

Production and Certification of Synthetic Selenium Isotopic Reference Materials

Due to intensive research into selenium isotopes in recent years, the increasing requirement for reliable and comparable measurement results has created a strong demand for selenium isotopic certified reference materials (iCRM) that were previously not available. To address this, eleven selenium iCRMs were developed, including ten synthetic iCRMs (GBW 04447–GBW 04456) and one natural iCRM (GBW 04457). The synthetic iCRMs were prepared with ⁷⁶Se, ⁷⁸Se, ⁸⁰Se and ⁸²Se solutions and a natural selenium solution; the natural iCRM was prepared with highly pure selenium material. The property values of isotope ratios in these iCRMs were certified by calibrated mass spectrometry with a collision cell multi‐collector ICP‐MS. The mass discrimination effect of the instrument was corrected with corresponding ⁷⁸Se/⁷⁶Se isotope mixtures and ⁸²Se/⁷⁶Se isotope mixtures, which were gravimetrically prepared with purified, isotopically enriched selenium materials. Homogeneity and stability tests were performed, and no significant influences were found. The uncertainty of the property values of the iCRMs was evaluated according to the Guide to the Expression of Uncertainty in Measurement (GUM) of ISO/BIPM and ISO Guide 35. The δ^82/76Se value of GBW 04457 relative to NIST SRM 3149 was also calculated. These iCRMs are intended for use in calibration of instruments and evaluation of methods for the determination of selenium isotope ratios.     

泛滥平原沉积物标准物质研制

泛滥平原沉积物能代表流域内元素的平均分布规律并具有普遍的适用性,是地球化学填图工作的重要介质。目前国际上尚无泛滥平原沉积物标准物质,国外相似标准物质的研制注重于环境方面,定值成分较少;我国同类的土壤和水系沉积物标准物质受限于不同工作需要,研制目的各不相同,且多数标准物质不足。为满足需求,本文研制了长江流域、赣江流域、汉水流域、淮河流域、黄河流域、海河流域、黑龙江流域共7个泛滥平原沉积物国家一级标准物质(编号为GBW07385～GBW07391)。此系列标准物质采用X射线荧光光谱压片法测试了26种成分,主量成分的RSD小于1%,微量元素的RSD约为2%,所有成分的RSD均小于7%,方差检验的F值均小于临界值F0. 05(24,25)=1. 96,表明样品的均匀性良好。在23个月的考察期内,检验的24种成分未发现统计学意义的明显变化,证明样品的稳定性良好。由全国13家实验室采用不同原理的、可靠的多种分析方法共同完成了73种元素和化合物共511个特性成分的定值测试,除GBW07386和GBW07388的CO2未能赋值外,其余494个特性成分给出了认定值与不确定度,15个特性成分给出了参考值,是我国同类标准物质定值最为齐全的一个系列。该系列标准物质代表了各自流域元素的背景含量,适用于多目标地球化学调查、土地质量地球化学调查等样品的分析质量监控,亦可用作环境、农业等领域相关样品测试的量值和质量监控标准。     

Producing Certified Reference Materials at the Central Geological Laboratory of Mongolia

This paper briefly outlines the production and certification of reference materials at the Central Geological Laboratory (CGL) of Mongolia. The marketing of CRMs produced in Mongolia, as well as problems encountered in internationally recognised certification attempts and some proposed solutions, are discussed. The basic elements of the CGL’s strategy for the development of the CRM sector are to produce high quality CRMs according to the requirements of internationally recognised norms, to consider the market needs, to certify the RMs at the international level and to widely advertise them to the geochemical community. The CGL has already established the basis for the further development of this sector by, for instance, accreditation under ISO/IEC 17025, by modernising its preparation technology, by cooperation with international organisations in the field of CRMs and by permanent participation in the International Association of Geoanalysts’ GeoPT™ proficiency testing programme.