The deplorable state of the description of the use of certified reference materials in the literature

A detailed survey of 26 scientific journals showed that journal editors and a majority of authors of the reviewed papers seem unconcerned by the importance of correctly reporting their use of certified reference materials (CRMs). Only around 55% of the abstracts surveyed mention the use of CRMs described in these papers. This, however, is of key importance as the abstract of a paper is most widely available in electronic media. Many authors mentioned the use of CRMs in passing, often in incomplete form and without giving any details of the results obtained. Some are confused about the source of the reference material used, as they fail to report the type or the producer of CRMs applied. Others use materials that do not match the samples analyzed or do not see the need to use any CRM, despite the availability of suitable materials. Even in cases where correct data were given for type and producer of the CRMs, frequently the proper use and statistical evaluation are questionable. To improve this situation it is necessary that publishers should give recommendations where and how the use of CRMs should be described.     

Guidance on the contents of accompanying documentation for reference materials (RMs)

The use of reference materials (RMs) is a key activity for the improvement and maintenance of a worldwide coherent measurement system. As detailed in ISO Guide 33, RMs with different characteristics are used in measurement processes, for the purpose of precision control, bias assessment, calibration, assigning values to other materials, and maintaining conventional scales, to name a few. For the establishment of metrological traceability of measurement results to international scales or other measurement standards, proper use of certified reference materials (CRMs) is essential. From the perspective of a reference material producer, the documentation that is provided with an RM is the value-adding component of the material; for the user, the document is critical for the correct implementation and use of the RM in the measurement process. The ISO Committee on Reference Materials (ISO/REMCO) recognised the importance of the documentation that accompanies a reference material as early as 1981 when the first edition of ISO Guide 31 was published. The third edition of the Guide that was published recently considers the appropriate accompanying documentation for all types of reference materials, i.e. CRMs and non-certified RMs.     

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.     

Certified reference materials for the quality control of environmental analysis within the standards,measurements and testing programme (formerly BCR)

A great number of analyses is performed every year, the results of which are used for many purposes, e.g. the quality of goods and food, the status of quality of the environment or the health of patients. The accuracy of these results is a prerequisite for a good interpretation of the data obtained. One of the most powerful tool for achieving quality control of chemical analysis is to use reference materials (RMs) and certified reference materials (CRMs). These materials are necessary for one or more of the following items: method validation (CRMs), monitoring of the state of statistical control (RMs), samples in inter-comparisons (RMs), etc. The requirements and use of RMs and CRMs in chemical analysis are described, with special emphasis on environmental analysis, and some examples of environmental materials currently in production within the Standards, Measurements and Testing Programme (formerly BCR) of the European Commission are given.     

The new ISO Guide 80: Guidance for the in-house preparation of quality control materials (QCMs)

Reference materials (RMs) are widely used in measurement laboratories for a variety of purposes, and it is important to recognise that the material most appropriate for a particular application should be used. Certified reference materials (CRMs) are used for method validation, the calibration of a measurement system and all other aspects of the evaluation of the measurement system where the trueness of the measurement result is required. For other aspects, such as quality control, precision studies, the checking of the variability between operators, where the results are compared relatively, any suitable reference material can be used. ISO/REMCO, the ISO Committee on Reference Materials, has prepared ISO Guide 80, a guidance document for the in-house preparation of quality control materials (QCMs). QCMs are mostly used to monitor the performance of laboratory methods that have already been validated over time to be able to detect change or when a method goes out of statistical control. QCMs are RMs and as such have to be sufficiently homogeneous and stable for the intended use. QCMs are usually prepared in-house by laboratory staff for in-house use only, and therefore, the requirements for “in-house” QCMs are less demanding than those for a CRM. For example, transport issues are not of concern. The quality assessment of QCMs should involve homogeneity and stability assessments, and a limited characterisation of the material to provide an indication of its relevant property values and their variation, prior to use.     

Non-use and misinterpretation of CRMs. Can the situation be improved?

A survey of 82 scientific papers on trace elements in foods found the use of Certified Reference Materials to be less than anticipated. Less than 50% of the papers reported use of CRMs. When used, the evaluation is usually very crude and provides the user with very little information about his analytical performance. This is mainly due to lack of information/communication between the producers of CRMs, the users and those writing guidelines for the use of CRMs. Several specific problems are pointed out and remedies to improve the situation are described.     

Trends in certified reference materials for the speciation of trace elements.

The measurement of the chemical species of elements (instead of the total element concentration) has become an irreversible trend in analytical chemistry. The motivation lies in the fact that the biochemical and geochemical behaviour of an element is governed by its species. Quality assurance of the analytical procedures used for speciation analysis requires the analysis of representative reference materials, certified for the relevant species. Up to now the number of existing certified reference materials for trace element species is very limited. The most important ones are environmental CRMs certified for trialkyltin compounds, methylmercury, Cr(III)/Cr(VI) and food CRMs certified for arsenic species and methylmercury. Major developments are to be expected in CRMs focussed on environmental problems, including waste treatment, on bioavailability of trace elements in food and on bio-monitoring in occupational health and hygiene. It is, however, unlikely that the producers of CRMs will ever be able to cover all needs. Add to this that many, very active species are notoriously unstable and/or short living and require in-situ analysis. This will lead to different analytical developments, such as analyses in-situ, where the classical concept of CRMs may not stand firm anymore.     

Evaluation of results derived from the analysis of certified reference materials - a user-friendly approach based on simplicity

Certified reference materials (CRMs) have now been in regular use for several decades. Their production and certification are regulated by international standards. But, even today there are no agreements on procedures for evaluating results obtained by the users. As a consequence, the way CRM results are treated in the literature leaves a lot to be desired. A statistical evaluation is rarely, if ever, described in published reports. The most common approach is to compare the found mean and/or range with the certified range and then state if the mean falls within the certified range, or if the two ranges overlap. If this happens, the analyst is usually satisfied. In addition, usually no regard is paid to the fact that the certified interval is based on a 95% confidence interval (CI) and the found interval on standard deviation and that this evaluation has little, if any, statistical relevance. Long-term evaluation of a CRM often consists in nothing more than producing a control chart, which relates the found results to the certified mean and CI. This paper is an attempt to improve the situation by providing a set of easy-to-use guidelines for evaluating results from CRMs. During the process we have identified different areas in which there is a need for such guidelines: 1. short-term evaluation of a single, or multiple, determination at one or several specific times; 2. identification of systematic and random errors; 3. evaluation of CRMs when used in a collaborative trial of a method; and 4. long-term evaluation for monitoring an analytical process over extended periods of time. It is important that the guidelines do not require expert competence in statistics from the analyst. Such obstacles would probably render most guidelines unused.     

Certified reference materials as a quality tool in food control: much used—often misused—sometimes abused

Certified reference materials (CRMs) are important tools in the quality control of food analyses. There are, however, many ways in which CRMs can be abused and misused. It can be due to ignorance, as well as to overuse of expensive materials. The major drawback of CRMs is probably that the analyst knows the level of the analyte. The statistical evaluation of CRM results in reports and publications is often limited to a comparison between the found and the certified levels, which yields little, and sometimes erroneous, information. Recoveries based on CRMs often give a picture that is far too bright, with little consideration of uncertainties. The way the use of CRMs is described in most scientific journals is often very crude and shows that CRMs are seldom used to their full capacity. The objective of this paper is to try to summarise the ways in which a CRM can be misused and thereby put into focus how to make better use of such materials. It also gives examples on how to evaluate CRMs, using a procedure that was recently introduced by the Nordic Committee on Food Analysis.     

Trends in certified reference materials for the speciation of trace elements

The measurement of the chemical species of elements (instead of the total element concentration) has become an irreversible trend in analytical chemistry. The motivation lies in the fact that the biochemical and geochemical behaviour of an element is governed by its species. Quality assurance of the analytical procedures used for speciation analysis requires the analysis of representative reference materials, certified for the relevant species. Up to now the number of existing certified reference materials for trace element species is very limited. The most important ones are environmental CRMs certified for trialkyltin compounds, methylmercury, Cr(III)/Cr(VI) and food CRMs certified for arsenic species and methylmercury. Major developments are to be expected in CRMs focussed on environmental problems, including waste treatment, on bioavailability of trace elements in food and on bio-monitoring in occupational health and hygiene. It is, however, unlikely that the producers of CRMs will ever be able to cover all needs. Add to this that many, very active species are notoriously unstable and/or short living and require in-situ analysis. This will lead to different analytical developments, such as analyses in-situ, where the classical concept of CRMs may not stand firm anymore.     

Determination of the minimum sample mass of a solid CRM to be used in chemical analysis

Summary A method for the quantitative determination of the minimum representative sample mass of a solid reference material is described and illustrated. If CRMs are to be used to calibrate microtechniques, the uncertainty which should be assigned to the certified value in that case, can also be evaluated. The method is applied in the preparation and certification of several reference materials with which CBNM was involved.     

First order speciation of As using flow injection hydride generation atomic absorption spectrometry with in-situ trapping of the arsine in a graphite furnace

A simple method is described to distinguish between As species that react with sodium tetrahydroborate (III) to form AsH₃ and the naturally occurring As species that are unreactive. Results for this rudimentary or “first order” speciation scheme are reported for biological tissue, aquatic plant material, urine and natural water samples. Biological tissue and aquatic plant samples were briefly solubilized in a mixture of 50% nitric acid, no sample preparation was required for the urine or natural water samples. Organoarsenic species which do not react with sodium borohydride under acidic conditions such as arsenobetaine, arsenocholine and tetramethylarsenic, are converted to As(V) by on-line photo-oxidation or microwave heating in a mixture of 0.5 M NaOH and 0.05 M K₂S₂O₈. The sample is subsequently acidified, reduced with sodium borohydride and the generated arsine is trapped in a heated graphite furnace prior to atomization. The superior detection limit (0.14 ng) of the trapping technique permits the dilution of most types of samples, minimizing or eliminating interference effects. Without photolysis or microwave heating a combined result for As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) is obtained. Results are reported for the first order speciation of As in a suite of certified reference materials (CRMs) including National Research Council (NRC) biological tissues and natural water samples, Community Bureau of Reference (BCR) aquatic plant materials and the National Institute of Standards and Technology (NIST) SRM 267ON urine sample. The determination of a non-hydride forming As fraction in untreated urine and natural water certified reference materials (CRMs) has revealed a species of As previously undetected in NRC seawater CRMs.     

New developments in the production and use of CRMs in Romania

 A lot of effort is being made in Romania to meet the present main strategic goal – EU integration. Since the confidence in measurements is of considerable importance in almost every field of activity, the National Institute of Metrology (INM) is involved in improving its calibration and measurement capabilities to provide services in accordance with the latest European Regulation. Within this framework the assurance of the required traceability of all measurements plays a most important role. As reliable analytical measurements depend largely upon reference materials and the assurance of the traceability of amount measurements is still developing in Romania, a new approach regarding the function of Certified Reference Materials (CRMs) may be emphasized. The experience of the INM as well as new developments in Romania in preparation and certification of Reference Materials (RMs) are described. A short review of the locally available RMs and CRMs is given. Some aspects regarding the use of RMs and CRMs, especially for calibration, are discussed for their applicability for analytical measurements. Received: 31 October 2002 Accepted: 24 January 2003 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 M. Buzoianu     

Evaluation of results derived from the analysis of certified reference materials – a user-friendly approach based on simplicity

Certified reference materials (CRMs) have now been in regular use for several decades. Their production and certification are regulated by international standards. But, even today there are no agreements on procedures for evaluating results obtained by the users. As a consequence, the way CRM results are treated in the literature leaves a lot to be desired. A statistical evaluation is rarely, if ever, described in published reports. The most common approach is to compare the found mean and/or range with the certified range and then state if the mean falls within the certified range, or if the two ranges overlap. If this happens, the analyst is usually satisfied. In addition, usually no regard is paid to the fact that the certified interval is based on a 95% confidence interval (CI) and the found interval on standard deviation and that this evaluation has little, if any, statistical relevance. Long-term evaluation of a CRM often consists in nothing more than producing a control chart, which relates the found results to the certified mean and CI. This paper is an attempt to improve the situation by providing a set of easy-to-use guidelines for evaluating results from CRMs. During the process we have identified different areas in which there is a need for such guidelines: 1.?short-term evaluation of a single, or multiple, determination at one or several specific times; 2.?identification of systematic and random errors; 3.?evaluation of CRMs when used in a collaborative trial of a method; and 4.?long-term evaluation for monitoring an analytical process over extended periods of time. It is important that the guidelines do not require expert competence in statistics from the analyst. Such obstacles would probably render most guidelines unused.     

Certified reference materials for the quality control of measurements in environmental monitoring

The monitoring and protection of the environment are based on measurement campaigns which cover long periods of time and large geographical areas. Only accurate analytical results allow valid conclusions to be drawn about a situation and its evolution. The use of certified reference materials (CRMS) permits verification of the accuracy of the measurements. The importance of accuracy and the way CRMs may be used are presented in this review. The production and properties required of a good CRM are discussed. An overview of the types of CRMs in the non-nuclear field, available for the monitoring of the environment, is also given.     

Proper use of certified reference materials?

Certified reference materials (CRMs) are important quality assurance tools in the laboratory. It is, however, not certain they are always used properly. Several guidelines are available on the use of CRMs, but appear to be mostly unknown. The users thus get very little help on the way to proper use. Many of the problems with CRMs are well known, but that does not mean they have disappeared. Better use of CRMs will require the involvement of producers and analytical societies, e.g. the AOAC. Editors of international analytical journals could have a great influence on how CRM results and other QA data are treated in publications.     

Matrix certified reference materials for environmental monitoring from the National Metrology Institute of Japan (NMIJ)

Matrix certified reference materials (CRMs) are playing an increasingly important role in environmental monitoring in Japan. The National Metrology Institute of Japan (NMIJ)/National Institute of Advanced Industrial Science and Technology (AIST) has been developing matrix CRMs for environmental monitoring since 2001, and has issued nine kinds of CRMs as NMIJ CRMs. The development of the CRMs was conducted in NMIJ in cooperation with candidate material producers. The isotope dilution mass spectrometry (IDMS) was principally adopted to give reliable certified values. Meanwhile, two or more analytical methods, whose levels of accuracy were well evaluated, were applied to avoid any possible analytical bias. Two typical certification processes, the certification of river water CRMs for trace element analysis and that of marine sediment CRMs for PCB and organochlorine pesticide analysis, are outlined as examples. Presented at -- “BERM-10” -- April 2006, Charleston, SC, USA.     

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.