A survey of the current state and probable direction of development of research activity internationally within metrology

In a complex field of chemistry, two areas of present and on-going research will be highlighted, namely the traceability of measurement results including measurement uncertainty and the measurement of the Avogadro constant.

Traceability and measurement uncertainty

Traceability, a property of a measurement result that links the result through a chain of calibrations to a national or international standard, is now thought to be central to obtaining comparable results. Thus if measurements are made of the same measurand in different laboratories, they may be compared if each measurement has been made traceable to the same reference (for example a realisation of an SI unit). A major report commissioned by IUPAC on traceability is presently being prepared. 

The problem unique to chemistry is that the unit of the amount of substance, the mole, requires the definition of the entity that is being measured. This means that, unlike other units such as mass, length and time, there are potentially as many standards as there are chemicals for the amount of substance. Therefore the calibration and traceability chain for a chemical measurement is not so easily established.

Reference materials are crucial to this process and their production and characterisation is being researched. Understanding the requirements of measurement uncertainty for laboratory accreditation, and how to determine the uncertainty of a measurement is also the subject of intense debate and research. 

Measurement of the Avogadro constant

A major international effort, including Australian participation, is devoted to making highly pure silicon spheres and then counting the number of silicon atoms within them. The Avogadro constant, the number of entities in one mole of a substance, is presently known to about 1 part in 10⁵. An improvement by a further factor of 100 will allow the kilogram, the last remaining artefact standard, to be redefined in terms of the Avogadro constant. 

Future research developments

It is likely that the future thrust will be to harmonise the different strands of metrology in chemistry to obtain a unified theory of measurement in chemistry and how quality assurance of chemical results may be achieved on an international scale.

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