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**Amount of substance

If we refer to the physical quantities, the notion of metrology in chemistry is quite new. The fact that the BIPM committee dealing specifically with metrology in chemistry, the Comité Consultatif pour la Quantité de Matière (Consultative Committee for Amount of substance (CCQM), has only been created in 1993 is a proof of that. In addition, metrology in chemistry has not yet achieved the same level of development in each of its main fields. More particularly in the organic chemistry field and above all, in the area of biological analyses where the aspect of traceability of measurements and also the definition of the measurand still raise questions for many routine analyses.

The European directives and their national transpositions constitute powerful drivers for the development of metrology references. For instance, the law on air and the rational use of law on energy of 30 December 1996 were the determining factors that structured the studies to be carried out in analytic chemistry in the area of gases. Likewise, the European directive on the ozone precursors (Volatile Organic Compounds, VOCs) of 2002 is underpinning several activities in this area. And also, the European directive of 23 October 2000, that sets the framework for a common policy in the area of water, implies studies to be carried out for developing metrology references in the organic and inorganic chemistry fields alike.

Four sub-fields, corresponding to the traditional disciplines of chemistry are covered by metrology activities: gas, inorganic, organic chemistry and electrochemistry. It should be noted that these subs-divisions become artificial all the more than the fields of application seem more relevant because of the societal stakes in which metrology in chemistry plays a considerable role: consumer protection, environment quality and health for instance.

Metrology in chemistry applied to gases

Historically, this is the most advanced field for the implementation of one continuous metrology chain running from the highest level metrology references up to the users, with the aim of ensuring and demonstrating traceability of the field measurements.

The main activities carried out in this area cover the preparation of reference gas mixtures and their transfer together with the methods for gas analysis. These activities are closely linked, since in this metrology field metrology skills lie primarily on the preparation of reference standards, and chemical analysis turns out to be one tool allowing verifying the quality of the mixtures prepared. However, the development of references in indoor air area is strongly based on the acquisition of analytical skills. Similarly, the determination of the purity of gases used calls for the development of fresh analytic skills.

Main actions implemented by the Laboratoire national de métrologie et d’essais (LNE) :

Installation for preparation of reference gaseous mixtures using dynamic method
Installation for preparation of reference gaseous mixtures using dynamic method

Metrology in inorganic chemistry

In this field of elementary analytic chemistry, there are huge needs in terms of traceability and improvement in the uncertainty reductions, such as commercial elementary standard solutions used by laboratories to calibrate their instruments, for example. Providing reference methods to the analytical laboratories constitutes one major asset for this area. To achieve this purpose, the LNE has been strongly involved in studies and developments concentrating on the improvement of traceability of the anionic standard solutions and the production of certified reference materials (single element solutions). The LNE has also initiated collaboration with Proficiency Testing providers to ensure traceability of the consensus value of one inter-laboratory test.
The reference method in the inorganic field remains the isotope dilution, a primary method with high exactitude, that was implemented with Inductively Coupled Plasma – Mass Spectrometry (ICP- MS). Validation of this method is continuing in order to foster skills in the environmental and food processing areas. The means currently available at the laboratory (Quadrupole ICP/MS with collision cell and high resolution magnetic sector and simple collector) have been reinforced (coupled with liquid chromatography) to enable promoting new developments in the area of elements speciation.

Main actions carried out by the Laboratoire national de métrologie et d'essais :

Development of the isotope dilution

  • Study on the influence of mass bias correction in isotope dilution on the measurement uncertainties.

Speciation by liquid chromatography coupled with ICP/MS

  • Implementation of techniques allowing analysis via isotope dilution of the organometallic compounds and of the different redox forms of metals in environmental and food processing (mercury and selenium) matrixes.

Development of ionic chromatography

  • Evaluation of the exactitude of the commercial anionic solutions (anions concerned: Br-, Cl-, NO3-, SO42-, PO43-)

Development of partnerships with Proficiency Testing providers

  • Supply of reference values and production of certified reference materials.

Mass spectometer with magnetic sector and inductively coupled plasma (ICP/MS)
Mass spectometer with magnetic sector and inductively coupled plasma (ICP/MS)

Organic analytic chemistry

This the most recent field in which the LNE has embarked. Again, in terms of traceability and uncertainty levels needs are important and they cannot be met in their entirety as they involve a very high number of compounds. The LNE has recently strengthened its technical potential through the implementation of a liquid phase chromatography system coupled to tandem mass spectrometry (HPLC-MS-MS). The main objective is the development of primary analysis methods for pesticides in the environmental and food processing matrixes via isotope dilution. These materials that are available for water analysis laboratories allow the calibration of the instruments and validation of the analytic protocols. The LNE has recently launched fresh studies in the biomedical field with the development of primary methods for the analysis of glycated haemoglobin and glucose, that are primary indicators in the treatment of diabetes.

Main actions launched by the Laboratoire national de métrologie et d'essais:

Metrology in organic chemistry via isotope dilution

  • Continuation of the development of new methods via isotope dilution (GC/MS) for the polychlorinated byphenyls (PCBs) and the polycyclic aromatic hydrocarbons (PAHs) in the environmental matrixes ;
  • Analysis of pesticides in water through HPLC/MS-MS ;
  • Analysis of pesticides in the food processing matrixes (cereals, biscuits..) via HPLC/MS-MS ;
  • Reliability of the medical analyses. Demonstration and application to dosage of glucose and glycated haemoglobin.

Liquid phase chromatography coupled to tandem mass spectrometry
Liquid phase chromatography coupled to tandem mass spectrometry

Electrochemistry

Measurement of pH and conductivity are crucial in control of the industrial processes. In order to ensure reliability of the measurements, it is necessary to build a metrology structure in France meant for measurements of pH allowing the connection of the measurement apparatuses for in-situ pH measurement. Regarding conductivity, the studies are designed for meeting the industrial needs whilst offering possibilities for connection in the field of very low conductivity. And since a few years, there has been a very significant increase in the requests for calibration services for conductivity meters coming from manufacturers in various industries. To meet these demands, the LNE has developed two primary benches for conductivity measurements in different ranges.

Main actions initiated by the Laboratoire national de métrologie et d'essais :

Development of references in pH-field

  • Certification of the solid primary materials (pH 7 and 10) ;
  • Construction and validation of secondary benches ;
  • Verification of the commercial standard solutions ;
  • In-situ evaluation of the measuring instruments ;
  • Development of references in specific areas (environment, health).

Development of references in conductivity field

  • Validation of the measuring bench for electric conductivity based on the Jones cell ;
  • Implementation of the Van der Pauw cell in the field of very low conductivities (lower than 10-3 S.m-1)

pH Primary measuring bench
pH Primary measuring bench

Van der Pauw Cell
Van der Pauw Cell