Accreditation and Quality Assurance (v.14, #11)

IMEKO TC8 workshop on traceability by Carlo Ferrero (579-580).

Measurement uncertainty and metrological traceability are closely connected and interdependent. The former plays a role in assessing the latter, the latter almost invariably contributes to the former as an input component to the uncertainty associated with the measurand. The paper discusses these issues, in connection with the different methods of measurement, direct and indirect.
Keywords: Measurement uncertainty; Metrological traceability; Calibration

Comparison of calibration curves using the L p norm by Luca Callegaro; Francesca Pennecchi; Pier Giorgio Spazzini (587-592).
Interlaboratory comparisons are a fundamental task in order to provide measurements with traceability. The simplest possible scenario implies that a single traveling standard of a quantity is measured at various laboratories. A more complex scenario arises when the laboratories measure a large set of standard values pertaining to a given physical quantity or when the traveling standard is not a realization of the quantity of interest but a measuring instrument. In the last case, it might be convenient to globally compare the calibration curves provided by the laboratories. We will introduce a distance between two generic analytical curves based on the Least Power L p norm of their difference. The properties of such distance will be presented, with particular attention to its dependence on the parameter p.
Keywords: Interlaboratory comparison; Calibration curve; Least Power norm; Distance

Metrological traceability is not always a straight line by Marc Priel; Soraya Amarouche; Paola Fisicaro (593-599).
The two most important concepts in metrology are certainly “traceability to standards” and “measurement uncertainty evaluation”. So far the questions related to these concepts have been reasonably solved in the metrology of “classical quantities”, but for the introduction of metrological concepts in new fields, such as chemistry and biology, a lot of problems remain and must be solved in order to support international arrangements. In this presentation, the authors want to develop the strategy implemented at Laboratoire national de métrologie et d’essais (LNE) in metrology in chemistry and biology. The strategy is based on: (1) pure solutions for calibration of analytical instruments, (2) use of certified reference materials (matrix reference materials), and (3) participation to proficiency testing schemes. Examples will be presented in organic and inorganic chemistry. For laboratory medicine, proficiency testing providers play an important role in the organization of External Quality Assessment Schemes. For the time being, the reference value or the assigned value of the comparison is calculated with the results obtained by the participants. This assigned value is not often traceable to SI units. One of the methods suggested by LNE is to ensure the metrological traceability to SI units of the assigned value for the more critical quantities carried on analytes by implementing the Joint committee for traceability in laboratory medicine reference methods.
Keywords: Traceability in chemical measurements; Certified reference materials; Proficiency testing schemes; Metrological traceability

Metrological traceability chain for PCBs: I.N.Ri.M. activity by Michela Sega; Elena Amico di Meane; Francesca Rolle (601-605).
Metrology in chemistry has its own features, which distinguish it from classical metrology: due to the lack of primary methods applicable in routine measurements, metrological traceability of measurement results can be achieved by using in a proper way suitable certified reference materials (CRMs), which can assure a direct relation to a reference. This article deals with the activity of the Italian National Institute of Metrological Research (Istituto Nazionale di Ricerca Metrologica—I.N.Ri.M.) on the analysis of various polychlorinated biphenyls congeners in organic solution by means of gas-chromatography coupled with mass spectrometry. The metrological traceability approach in the quantification step is pursued via calibration solutions prepared by gravimetrically diluting a CRM. The uncertainty for the calibration solutions was evaluated taking into account all the relevant contributions.
Keywords: Metrological traceability; Polychlorinated biphenyls; Measurement uncertainty; Traceability chain

Metrological traceability in gas analysis at I.N.Ri.M: gravimetric primary gas mixtures by Elena Amico di Meane; Margherita Plassa; Francesca Rolle; Michela Sega (607-611).
Metrologically traceable measurements are needed, in environmental monitoring, to provide meaningful information on the pollution level and the possibility to have suitable reference standards is crucial to this purpose to calibrate instruments. The Italian National Institute of Metrological Research (I.N.Ri.M.), as a primary metrological institute, realizes and maintains primary standards for the basic and derived units of the International System of Units (SI). In this framework and regarding gas analysis, in the last few years I.N.Ri.M. has started a research line on the preparation of primary reference mixtures (PRMs) by the gravimetric method that led to plan and build a facility for evacuating and filling cylinders and a device for high precision weighing. In the present work the developments in such field at I.N.Ri.M. are reported to underline the relevance, in the atmospheric pollutants monitoring, of performing accurate and reliable measurements and having reference standards fit for the calibration of the analytical instrumentation.
Keywords: Gravimetric method; Primary reference gas mixtures; Atmospheric pollutants monitoring; Metrological traceability; Gas analysis

Traceability of absorbed dose in photon radiation therapy: from primary standard to patient treatment by Loïc de Carlan; Didier Baltès; Jean-Marc Bordy; Josiane Daures; Frank Delaunay; Aimé Ostrowsky; Soizic Sorel (613-618).
The relevant standard quantity for radiation therapy is the absorbed dose to water. This quantity refers to the amount of energy locally absorbed in a small volume of water divided by the mass of this volume. The aim of this paper is to present a short overview on the establishment of traceability to national standards of absorbed doses delivered to patients in radiation therapy. The approach used at LNE-LNHB, the French national metrology laboratory for ionizing radiation, to determine the reference value of absorbed dose to water is presented and the chain of traceability from the reference value to the treatment of the patient is described.
Keywords: Radiation therapy; Traceability; Graphite calorimeter; Fricke dosemeter; Ionization chamber; Linear accelerator

Tunisian traceability system by Saloua Ghedamsi (619-621).
The concept of metrology first appeared in Tunisia towards 1909. At the end of the 1990s, bodies for evaluating conformity of measurement at different levels have been instituted to meet calibration and testing needs of the national industry. These bodies were divided into three categories: Class A where we find mainly the Central Laboratory for Analysis and Testing LCAE and the National Defence Laboratory DEFNAT; these two laboratories are in charge of the technological upgrading of the other bodies of Class B which, in turn, would transfer their knowledge to the industries, the latter constituting Class C. Nowadays, the accreditation of Tunisian laboratories at the international level by recognized reference foreign bodies and participation in the European proficiency network enabled the national laboratories of Tunisia to establish the degree of equivalence between their measurement results and those of other foreign laboratories.
Keywords: Metrology in Tunisia; Technological upgrading; Accreditation; Proficiency network

Do we need to consider metrological meanings of different measurement uncertainty estimations? by Manuel Alvarez-Prieto; Juan Jiménez-Chacón; Álvaro Montero-Curbelo (623-634).
Along the years, several approaches for measurement uncertainty estimation have been suggested. Emphasis has been put on the general metrological interpretation of measurement uncertainty, but not on its different meanings when it is associated to given conditions of measurement where analytical work is performed and errors are originated. Three different definitions for uncertainty are proposed for reproducibility and intermediate precision conditions of measurement. These definitions inherit features from the VIM 3 definition of measurement uncertainty. It is argued that if a high performance laboratory keeps errors under control with proper validation and quality assurance programs, measurement uncertainty from intermediate precision condition of measurement is justified as a suitable estimation of its capability to attribute values to a measurand. Alternatively, a laboratory that does not keep errors under control should use uncertainty from reproducibility condition of measurement as the cost of its imperfections. Selection of information sources for measurement uncertainty estimation should be in harmony with its metrological meaning.
Keywords: Uncertainty; Condition of measurement; Metrological meanings; Validation; Intra and interlaboratory studies

Report of the 32nd meeting of ISO/REMCO by Hendrik Emons; Ales Fajgelj; John P. Hammond; Stéphane Sauvage (639-642).