SI-traceable certification of the IMEP-12 water sample combining contributions from different reference laboratories

In the International Measurement Evaluation Programme (IMEP-12) comparison, a synthetically prepared water sample was offered to the analytical laboratories to perform measurements of As, B, Cd, Cr, Cu, Fe, Mg, Mn, Ni and Pb. The choice of elements to be measured was based on EU legislation, which the comparison was aiming to support. As to the IMEP policy, the laboratories’ results were presented according to the certified/assigned reference values established by several reference laboratories all around the world. The performed certification campaign is described in detail in this paper. Isotope dilution mass spectrometry (IDMS) was applied as a primary method of measurement (PMM), whenever possible, to achieve SI-traceable results. Apart from IDMS for reference measurements of some elements, k _o-neutron activation analysis (k _o-NAA) and external calibration (Ext-Calib) using inductively coupled plasma-mass spectrometry (ICP-MS) were applied. The reference values were characterised as “certified” (for B, Cd, Cr, Cu, Fe, Mg, Ni and Pb) or “assigned” (for As and Mn) according to the IMEP policy. Measurement uncertainty of the certified/assigned reference values was calculated according to the ISO/BIPM guide using the specialised software GUM Workbench.     

Establishment of SI-traceable reference ranges for the content of various elements in the IMEP-9 water sample

 The International Measurement Evaluation Programme (IMEP) attempts to shed light on the current state of the practice in chemical measurements. The main tool, which assists this attempt and also differentiates IMEP from similar projects, is the establishment of SI-traceable reference ranges (where possible) for the elements offered for measurement to the participants for every IMEP round. The Institute for Reference Materials and Measurements (IRMM), as the founder and co-ordinator of IMEP has the responsibility of establishing the SI-traceable reference ranges. This is a large task that requires knowledge, skill and resources. IRMM collaborates with a network of reference laboratories in order to achieve the establishment of SI-traceable reference ranges in a transparent and reliable way. The IMEP reference laboratories must have demonstrated experience and have a proven and successful record in the use of primary methods of measurements (mainly isotope dilution mass spectrometry) and the application of uncertainty evaluation according to ISO/BIPM guidelines. In IMEP-9 "trace elements in water", results from 7 reference laboratories (including IRMM) were combined by IRMM to establish SI-traceable ranges for the 15 elements, which were then offered for measurement to the 200 participants worldwide. This paper does not discuss the individual contribution of the reference laboratories (this could be the subject of individual papers) but describes the procedures and criteria used in order to establish the reference ranges for the IMEP-9 samples by combining the individual contributions. All results submitted to IRMM are included, so as to make this publication as realistic as possible. Received: 31 December 1999 / Accepted: 7 March 2000     

Establishment of SI-traceable reference values for the content of various elements in the IMEP-14 sediment sample

For the first time in the International Measurement Evaluation Programme (IMEP)-14, a sediment sample was offered to analytical laboratories to perform measurements of As, Cd, Cr, Cu, Fe, Pb, Hg, Ni, U and Zn. In line with IMEP policy, the results were presented according to the certified / assigned reference values established by several reference laboratories around the world. The certification campaign is described in detail. Isotope dilution mass spectrometry was applied as a primary method of measurement, whenever possible, to achieve SI-traceable results. For reference measurements of As, Fe, Hg and Zn, k₀-neutron activation analysis and Zeeman atomic absorption spectrometry were applied. The reference values (ranges) were characterised as ”certified” (for Cd, Cr, Pb, Ni and U) or ”assigned” (for As, Cu, Fe, Hg and Zn) according to IMEP policy. The measurement uncertainty of the certified / assured reference values was calculated according to the ISO/BIPM Guide. Received: 7 June 2001-10-27 Accepted: 19 August 2001     

SI-traceable values for cadmium concentration in the water samples of IMEP-6

 The certification measurement for the cadmium concentration in the samples as performed by Isotope Dilution (ID) using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is described in framework of the International Measurement Evaluation Programme (IMEP). By using a primary method of measurement (ID), making up a full uncertainty budget and using a sensitive technique (ICP-MS), reference values traceable to SI can be obtained for this material. The uncertainty budget is performed in accordance with the ISO and EURACHEM guides on uncertainty. A comparison is made with certification results of other experienced laboratories also using primary methods where possible. Received: 8 July 1996/Revised 26 August 1996/Accepted: 1 September 1996     

SI-traceable values for cadmium concentration in the water samples of IMEP-6

 The certification measurement for the cadmium concentration in the samples as performed by Isotope Dilution (ID) using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is described in framework of the International Measurement Evaluation Programme (IMEP). By using a primary method of measurement (ID), making up a full uncertainty budget and using a sensitive technique (ICP-MS), reference values traceable to SI can be obtained for this material. The uncertainty budget is performed in accordance with the ISO and EURACHEM guides on uncertainty. A comparison is made with certification results of other experienced laboratories also using primary methods where possible. Received: 8 July 1996/Revised 26 August 1996/Accepted: 1 September 1996     

热表面电离同位素稀释质谱法测定 IMEP-9

同位素稀释质谱法(IDMS)是微量、痕量元素量值测量的准确方法之一[1,2] .已应用到环保、生化等领域中,在痕量、超痕量化学分析中起着重要的作用[3～5] .欧共体联合研究中心标准物质与测量研究院(EC-JRC-IRMM)从1988年开始专门组织了国际测量评估计划(IMEP).该计划已实施多次,每次都有来自不同国家和地区的200多个实验室参加比对测量.IMEP国际比对样品中无机元素的标准值大都采用 IDMS 方法测得 [6].本实验室应 EC-JRC-IRMM 的邀请参加了 IMEP-9 国际比对标准样品的定值工作.本工作采用 IDMS 对 IMEP-9 天然水样品中的镁进行了测定研究.针对样品中 Mg 含量较低, 试剂、环境等因素的污染,轻质量数元素在质谱分析中磁场不易稳定、分馏效应影响较大等问题进行了大量实验研究,测得数据的不确定度为 0.25%,已被 EC-JRC-IRM M 作为 IMEP-9 国际比对标样的标准值[7]. 1 实验部分 1.1 仪器与试剂 Finnigan-MAT261 热表面电离同位素质谱计;25Mg 浓缩同位素(中国原子能科学研究院);氧化镁:优级纯;盐酸、水:经石英亚沸蒸馏提纯.     

A synopsis of different approaches to the certification of reference materials

Proliferation of Biological and Environmental Reference Materials (RMs), agencies and individuals preparing and characterizing them for a wide variety of inorganic and organic chemical constituents, makes it pertinent to look at the various certification approaches followed. This synopsis presents amalgamated versions of several of the major certification approaches, for natural-matrix RMs, alluding to some of the many factors that significantly affect the conduct and outcome of the analytical characterization exercises.     

IMEP-12: trace elements in water; objective evaluation of the performance of the laboratories when measuring quality parameters prescribed in the European Directive 98/83/EC

The International Measurement Evaluation Programme (IMEP) is an interlaboratory comparison scheme, founded, owned and co-ordinated by the Institute for Reference Materials and Measurements (IRMM) since 1988. IMEP-12, for the fourth time in the series, focused on trace elements in water and it was designed specifically to support European Commission directive 98/83/EC. Reference values for the concentration of ten elements were established with expanded uncertainties according to GUM. In total, 348 laboratories from 46 countries in five continents participated in the comparison and the degree of equivalence between the results of the laboratories and the reference values is presented graphically. Samples from the same batch were distributed to ten laboratories from European Countries, which represented their country in the framework of the EUROMET project 528. Participation in this comparison was offered to the European Co-operation for Accreditation (EA) for participation of accredited laboratories from all over Europe in the framework of the collaboration between IRMM and EA and to laboratories from the EU new member states and acceding countries in the frame of IRMM’s ‘Metrology in Chemistry support program for EU new member states and acceding countries.’     

Trends in the certification of reference materials

The certification of reference materials is still a rapidly developing area. Mostly driven by demands from laboratories, new reference materials are produced, and even new categories of materials are developed, such as genetically modified organism materials or materials for qualitative analysis. Even in more classical areas, such as the certification of chemicals for purity, there are important new insights, in particular in modelling the measurements and the property values. Laboratories are asking increasingly for uncertainty budgets of reference materials that are compatible with the concepts of the Guide to the expression of uncertainty in measurement, thus putting stronger demands to improve not only the quality of the materials, but also of the science and technology behind a certification. Three important issues are highlighted to exemplify these trends: the further interpretation of homogeneity and stability data, the appreciation of asymmetry due to mathematical constraints (relevant for, e.g., purity and trace analysis), and the certification of reference materials for qualitative measurement.Presented at BERM-9—9th International Symposium on Biological and Environmental Reference Materials, 15–19June 2003, Berlin, Germany     

Preparation and certification of JAC river water reference material for trace element analysis

 The Japan Society for Analytical Chemistry has recently issued a river water-certified reference material (CRM) for use in the ultratrace analysis of elements in fresh water. The river water CRM consists of a set of two (natural and spiked) 500-ml samples. The natural water is certified for Pb, Cr, As, Cu, Fe, Mn, Zn, B and Al at their sub-μg/l levels, while the spiked water is intended for use in the regulatory analysis of tap water and fresh water. Key words River water · Trace element analysis · Regulatory analysis · Reference materials     

Preparation of the bovine liver 12-02-01 reference material and the certification of element contents from an interlaboratory comparison

Summary The preparation of the bovine liver 12-02-01 reference material, its stabilization and homogeneity testing is presented. Evaluation of an interlaboratory comparison in which 31 laboratories took part using several analytical methods is described. From the results of the intercomparison, the contents of the elements Cd, Cu, Hg, Mn, Pb, Se, and Zn were certified, while for the elements Br, Co, Fe, K, Mo, Na, and Rb, information values were derived. Non-recommended values for the elements Ag, As, Ca, Cl, Cr, Cs, La, Mg, S, Sb, Sn, Sr, and V were also evaluated.Denoted as CZIM-liver in the report [23]     

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     

Uncertainty calculations in the certification of reference materials

To serve as a measurement standard, a (certified) reference material must be stable. For this purpose, the material should undergo stability testing after it has been prepared. This paper looks at the statistical aspects of stability testing. Essentially, these studies can be described with analysis of variance statistics, including variant regression analysis. The latter is used in practice for both trend analysis and for the development of expressions for extrapolations. Extrapolation of stability data is briefly touched upon, as far as the combined standard uncertainty of the reference material is concerned. There are different options to validate the extrapolations made from initial stability studies, and some of them might influence the uncertainty of the reference material and/or the shelf-life. The latter is the more commonly observed consequence of what is called ’stability monitoring’. Received: 6 October 2000 Accepted: 4 December 2000     

Contribution to the certification of B, Cd, Mg, Pb, Rb, Sr, and U in a natural water sample for the International Measurement Evaluation Programme Round 9 (IMEP-9) using ID-ICP-MS

 The present paper describes the contribution of the Institute for Reference Materials and Measurements to the certification of B, Cd, Mg, Pb, Rb, Sr, and U amount contents in a natural water sample, in round 9 of the International Measurement Evaluation Programme (IMEP-9). The analytical procedure to establish the reference values for B, Cd, Mg, Pb, Rb, Sr, and U amount contents was based on isotope dilution inductively coupled plasma-mass spectrometry used as a primary method of measurement. Applying this procedure reference values, traceable to the SI, were obtained for the natural water sample of IMEP-9. For each of the certified amount contents presented here a total uncertainty budget was calculated using the method of propagation of uncertainties according to ISO and EURACHEM guidelines. The measurement procedures, as well as the uncertainty calculations are described for all seven elements mentioned above. In order to keep the whole certification process transparent and so traceable, the preparations of various reagents and materials as well as the sample treatment and blending, the measurements themselves, and finally the data treatment are described in detail. Explanations focus on Pb as a representative example. The total uncertainties (relative) obtained were less than 2% for all investigated elements at amount contents in the pmol/kg up to the high μmol/kg range, corresponding to low μg/kg and mg/kg levels. Received: 21 October 1999 / Accepted: 29 January 2000     

A certified reference material for radionuclides in the water sample from Irish Sea (IAEA-443)

A new certified reference material (CRM) for radionuclides in sea water from the Irish sea (IAEA-443) is described and the results of the certification process are presented. Ten radionuclides (³H, ⁴⁰K, ⁹⁰Sr, ¹³⁷Cs, ²³⁴U, ²³⁵U, ²³⁸U, ²³⁸Pu, ^239+240Pu and ²⁴¹Am) have been certified, and information values on massic activities with 95% confidence intervals are given for four radionuclides (²³⁰Th, ²³²Th, ²³⁹Pu and ²⁴⁰Pu). Results for less frequently reported radionuclides (⁹⁹Tc, ²²⁸Th, ²³⁷Np and ²⁴¹Pu) are also reported. The CRM can be used for quality assurance/quality control of the analysis of radionuclides in water samples, for the development and validation of analytical methods and for training purposes. The material is available in 5 L units from IAEA (http://nucleus.iaea.org/rpst/index.htm).     

International Measurement Evaluation Programme (IMEP); IMEP-14: Picturing the performance of analytical laboratories measuring trace elements in sediment

The International Measurement Evaluation Programme (IMEP) is an interlaboratory comparison scheme founded, owned and co-ordinated by the Institute for Reference Materials and Measurements (IRMM) since 1988. IMEP-14, for the first time in the series, is focusing on trace elements in sediment. Reference values for ten elements stating total concentrations and expanded uncertainties according to GUM were established. In total, 239 laboratories from 43 countries in five continents participated in the comparison, and the degree of equivalence between the results from the laboratories and the reference values is presented graphically. Identical samples were distributed to nine National Measurement Institutes within the frame of the CCQM-P15 pilot study. Participation in the IMEP-14 interlaboratory comparison was offered to laboratories in the EU new member states and acceding countries according to the IRMMs Metrology in Chemistry support programme for EU new member states and acceding countries.This revised version was published online in August 2004 with corrections to text especially to the Discussion section.     

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.     

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     

The contribution of various analytical techniques to the certification of reference materials

Two international intercomparisons on the determination of trace elements in geological-environmental materials as well as two similar intercomparisons with biological materials provided a large amount of data elucidating the relative significance of various analytical techniques in the process of certification. The data have been investigated concerning their frequency of use, agreement of results by various techniques, percentage of outliers and general performance of the methods. Because many laboratories supplied results for both biological materials and both materials of mineral origin, the analysis of data in the form of two-sample charts has also been presented. The significance of an adequate procedure for outlier rejection for the proper assigning of certified values is emphasized and the unique role of neutron activation analysis in the certification process has been demonstrated. The use of highly reliable (definitive) methods for the verification of recommended values has been demonstrated.