The consequences of the mutual recognition of measurement standards for international metrology

After stressing the importance in the modern world of accurate and reproducible measurements, the actions taken by the Bureau International des Poids et Mesures to set up, together with the regional metrology organizations, a series of key comparisons are described. They are the technical foundation of a mutual recognition of national measurement standards arrangement prepared in conjunction with the National Metrology Institutes (NMIs). This arrangement also includes the recognition of calibration and measurement certificates issued by these institutes. Then, the consequences of this arrangement for trade are described. The case of chemical analysis is illustrated by the application of the Kyoto protocol on the reduction of greenhouse gases. But the global workload to be taken up by the International Committee of Weights and Measures, its Consultative Committee for Amount of Substance and the NMIs is huge.     

The meaning of measurement in metrology

The latest version of the International Vocabulary of Metrology gives a meaning of measurement restricted to quantities that can be represented by numerical values and placed in an ordinal sequence. This restrictive definition fits poorly with both the colloquial and the wider scientific understanding of measurement. This paper suggests an extension to the metrological definition of measurement, based on the measurement classification scheme of Stevens, to incorporate non-numerical and nominal measurements. The more inclusive definition and the classification scheme offers insights into the utility, metrological traceability, and limitations of measurements and uncertainty treatments, and enables clarification of other measurement-related definitions.     

Development of metrology for pH measurement in Thailand

It has not been long that metrology is well accepted as an important part in analytical chemistry since it helps the chemists to receive the best measurement and accurate results with traceability. The National Institute of Metrology Thailand (NIMT), which is a public agency under the supervision of the Ministry of Science and Technology, not only focuses on physical standards but also provides and maintains standards in chemical field. pH measurement is one of the most widely used in the laboratories including industries and medical area in Thailand. The chemical laboratory starts working on the project with the objective of disseminating an accurate result in routine pH measurement. In 2002, the laboratory provided a service in calibration of pH meter and organized the first local interlaboratory comparison program (NIMT–C-ILC-1: pH buffer) in pH measurement. There were three buffer solution samples in the range of acid, neutral, and base. A total of 44 laboratories participated in this program. The NIMT chemical laboratory also participated in the proficiency testing program that was conducted by PSB Corporation Testing Group in Singapore. In 2003, NIMT started research in preparation of secondary buffers by using highly accurate pH meters with glass electrode systems. The laboratory produced three secondary buffers, which were pH 4.01, 6.86, and 9.18 with uncertainty 0.020 pH at 25°C. The competence of the laboratory was shown by the measurement results of the pilot study (APMP.QM-P06), which was organized by the APMP electrochemical analysis working group (EAWG/TCQM) in 2005. The title of this study was “pH determination of two phosphate buffers by Harned cell method and glass electrode method”. NIMT aims to achieve for establishment of the primary method for pH measurement in the near future. Presented at -- “BERM-10” -- April 2006, Charleston, SC, USA     

Comparability and recognition of chemical measurement results – an international goal

As a consequence of the globalisation of trade and industry and other human activities, reliability of and confidence in measurement results is increasingly required, also in the field of chemical analysis, so that measurements made in one country will be accepted in other countries without the necessity to repeat them. The prerequisite for confidence is comparability on the basis of known uncertainties which in turn are based on traceability to recognised references. Traceability structures for chemical measurements are required which, by providing calibration means traceable to national standards, allow uncertainty statements to be made at field level, thus establishing comparability. Such traceability structures are now being developed in all industrialised countries. To ensure international comparability, mutual recognition of the national activities in metrology in chemistry is required in addition. The Mutual Recognition Agreement (MRA) for national measurement standards and calibration certificates issued by national metrology institutes, which is currently under way within the framework of the Metre Convention, aimes at providing the necessary international confidence for all kinds of measurements. The field of chemical analysis is included in the international metrological infrastructure through the new Consultative Committee for Amount of Substance (CCQM). Carefully selected key comparison measurements, which cover the most important areas where traceability is required, and which are carried out by national metrology institutes in cooperation with other national institutes entrusted with the provision of part of the national references for chemical measurements, form the basis for declarations of equivalence under the MRA. The results of the first key comparisons and studies carried out so far clearly show that the group of laboratories involved in the key comparisons is capable of establishing the international references (key comparison reference values) for chemical measurements with sufficient accuracy, also in complicated matrices.     

Chemical measurement and the law: metrology and quality issues

To facilitate just and sound decisions legal measurements must be reliable. The aim of this paper is to explore how this is currently achieved and how it might be better done. It considers the different types of legal proceedings, the role of chemical measurement, level of proof, the different types of chemical measurement, measurement units, the role of government, the chemical measurement industry and its control, legal metrology and the development of a measurement system based on metrological principles. It is argued that recent developments provide the basis for a robust support system, that but more needs to be done. It is also argued that the conventional approach to legal metrology has little place in chemical measurement, but that some controls are needed in some areas. In particular, a harmonised approach to international measurement standards is advocated. Received: 29 December 2000 Accepted: 8 January 2001     

Comparison of international standards concerning the capability of detection for analytical methods

The international standard ISO 11843 specifies the experimental conditions for the estimation of critical values of analytical methods referring to the capability of detection. The present paper aimed at a formal comparison of the ISO 11843 standard with the German standard DIN 32645 and the Commission Decision 2002/657/EC of the EU. In this context the particular scope of each standard is discussed based on a numerical example given in the DIN standard. For practitioners a better understanding of the different guidelines based on the same basics, i.e. the statistical theory of hypothesis testing and the probabilities of false positives α and false negatives β, is to be achieved.     

The role of an independent laboratory association in the standards,metrology, quality assurance and accreditation environment

Whilst there can be no doubt as to the benefit that an independent 3rd party conformity assessment accreditation body plays in ensuring the competency of results, personnel and processes, it is often at the expense of an adversarial relationship with the laboratory community it serves. A significant improvement in this relationship can be obtained by the formation and active participation by an independent laboratory association. This paper describes such an organisation, how it was formed, what role and the functions it currently performs and, most importantly, how it interacts with the national accreditation body and the stakeholders who are its members.     

The role of metrology communities under the WTO system: measurement science and conformity assessment procedures

Technical barrier to trade (TBT) has become one of the significant non-tariff measures with the advent of the WTO system in 1995. The key issue in TBT is that technical regulations, standards, and conformity assessment should not be used as barriers to trade. Regarding conformity assessment, the WTO/TBT Agreement recommends members to enter into negotiations for the mutual recognition of results of each other’s conformity assessment, as well as to permit participation of conformity assessment bodies located in other members. In this paper, it will be reviewed why the role of measurement science is important in terms of international effort to eliminate technical barriers to trade particularly in the area of conformity assessment.     

Practical estimation of the uncertainty of analytical measurement standards

Nowadays, a lot of time and resources are used to determine the quality of goods and services. As a consequence, the quality of measurements themselves, e.g., the metrological traceability of the measured quantity values is essential to allow a proper evaluation of the results with regard to specifications and regulatory limits. This requires knowledge of the measurement uncertainties of all quantity values involved in the measurement procedure, including measurement standards. This study shows how the uncertainties due to the preparation, as well as the chemical and compositional stability of a chemical measurement standard, or calibrator, can be estimated. The results show that the relative standard uncertainty of the concentration value of a typical analytical measurement standard runs up to 2.8% after 1 year. Of this, 1.9% originates from the preparation of the measurement standard, while 2.0 and 0.53% originate from the chemical and compositional stability during storage at −20 °C. The monthly preparation of working calibrators stored at 4 °C and used on a weekly basis, results in an additional standard uncertainty of the analyte concentration value of 0.35% per month due to compositional stability. While the preparation procedure is the major contributor to the total measurement uncertainty, the uncertainties introduced by the stability measurements are another important contributor, and therefore, the measurement procedure to evaluate stability is important to minimize the total measurement uncertainty.     

Impact of international standards and initiatives on proficiency testing for medical laboratories

This paper is intended to briefly discuss several recent initiatives regarding External Quality Assessment (or Proficiency Testing) (PT/EQA) for medical laboratories in various parts of the world. While a brief paper cannot be comprehensive for all regions, it is possible to present some new standards and initiatives that are underway or proposed in many countries. Laboratory medicine was one of the first areas of laboratory testing to develop interlaboratory comparisons, and the first area where such comparisons became compulsory. Because of that, the medical field has often been the leader in the availability and use of PT/EQA, and has introduced many innovations that have been adopted in other areas. Perhaps other areas of testing will similarly adopt the developments discussed here, if they have not already done so. There are important developments in the medical area that are also occurring in other fields of testing, such as the growing number of countries that require some form of participation, and the increasing use of the Internet. These developments are important, but are not discussed further in this paper since they are occurring in many fields of testing.

     

Impact of international standards and initiatives on proficiency testing for medical laboratories

This paper is intended to briefly discuss several recent initiatives regarding External Quality Assessment (or Proficiency Testing) (PT/EQA) for medical laboratories in various parts of the world. While a brief paper cannot be comprehensive for all regions, it is possible to present some new standards and initiatives that are underway or proposed in many countries. Laboratory medicine was one of the first areas of laboratory testing to develop interlaboratory comparisons, and the first area where such comparisons became compulsory. Because of that, the medical field has often been the leader in the availability and use of PT/EQA, and has introduced many innovations that have been adopted in other areas. Perhaps other areas of testing will similarly adopt the developments discussed here, if they have not already done so. There are important developments in the medical area that are also occurring in other fields of testing, such as the growing number of countries that require some form of participation, and the increasing use of the Internet. These developments are important, but are not discussed further in this paper since they are occurring in many fields of testing.     

The metrology of unstable measurands

 Type A statistical uncertainty in measurements is usually derived from the standard deviation of the measured data. This is correct as long as the measurand is stable over time and has a meaningful constant value. In such a case the average measurement and the standard deviations are meaningful. However, as measurement methods are refined and become more precise, we can observe that a given measurand may be unstable and change with time and the uncertainty in measurement must be redefined. This is specifically true in the metrology of time which can be measured today more precisly than any other measurand. We argue that in such a case the uncertainty in the prediction of the next measurement should be used instead of the uncertainty in measurement. Both uncertainties coincide for a stable measurand. The prediction of the next measurement is achieved by means of predictors. In this paper we describe the application of linear predictors and especially optimum linear predictors to predict in the presence of various types of instability. To illustrate the issues we use clock instabilities and clock metrology as this field is most developed. A measurand can be unstable but still predictable and thus useful. This is well known in the case of white noise about a linear drift for which the optimum predictor is a linear regression. Since the deviations from prediction of optimum prediction are of white noise, we can now use simple statistics to estimate the uncertainty of the optimum or close to optimum prediction. In this paper we present the various optimum or close to optimum linear predictors optimized for different types of instability and estimate the associated prediction uncertainties.     

IMEP in support of the comparability of measurement results across the Romanian chemical metrology infrastructure

On the basis of quantitative chemical measurements many important decisions are made in support of legislation or in industrial processes or social aspects. For this reason it is important to improve the quality of chemical measurement results and thus make them comparable and acceptable everywhere. The measurement quality is important to enable an equivalent implementation of the European Union regulations and directives across an enlarged EU. In this context, the European Commission–Joint Research Centre–Institute for Reference Materials and Measurement (EC-JRC-IRMM) set up a programme to improve the scientific basis for metrology in chemistry (MiC) in EU candidate countries in the framework of EU enlargement. Several activities were initiated, such as training, fellowships, sponsoring of seminars, conferences and participation in interlaboratory comparisons. To disseminate measurement traceability, IRMM provides through its International Measurement Evaluation Programme (IMEP) an interlaboratory tool to enable the benchmarking of laboratory performance. IMEP emphasizes the metrological aspects of measurement results, such as traceability and measurement uncertainty. In this way it has become a publicly available European tool for MiC. The Romanian Bureau of Legal Metrology – National Institute of Metrology (BRML-INM) actively supports the participation of Romanian authorized and field laboratories in IMEP interlaboratory comparisons. This paper describes the interest of Romanian laboratories participating in this programme, the analytical and metrological problems that became relevant during these exercises and some actions for improvement. The results from Romanian laboratories participating in IMEP-12 (water), IMEP-16 (wine), IMEP-17 (human serum) and IMEP-20 (tuna fish) are presented. To conclude, the educational and training activities at national level organized jointly by the Romanian National Institute of Metrology (INM) and IRMM are also mentioned.     

Role of measurement uncertainty in conformity assessment in legal metrology and trade

There is increasing interest in the role of measurement uncertainty in conformity assessment, particularly where measurements are in support of fair trade, health & safety and the environment. A lack of clarity, however, in treating measurement uncertainties and in setting specification limits for compliance may sometimes lead to drastic consequences. Examples concerning conformity assessment, particularly in the measurement of trace quantities (Cd in plastics and antibiotic trace residues in shrimps), are amongst cases identified in the ongoing EU project MetroTrade, which can be significant impediments to international trade. This paper considers the present status of the role of measurement uncertainty in conformity testing, covering both recent work in international standardisation and physical metrology (e.g. OIML recommendations on weighing). One conclusion is that, while much has been achieved, there still exists some work to be done in order to facilitate acceptance of conformity from both customer and supplier and avoid perceived barriers to trade and serious international trade disputes.Presented at the MetroTrade Workshop on Traceability and Measurement Uncertainty in Testing, 30–31 January 2003, Berlin, GermanyAn erratum to this article can be found at     

The latest international recognition of the Hungarian thermal analysis,the Judit Simon ESTAC Award

Journal of Thermal Analysis and Calorimetry -